Re: [time-nuts] Safely getting the electrical length of a connected antenna feedline
Because Velocity Factor determines the time it takes a EM wave to traverse the cable it ALSO shortens the wavelength by the same amount relative to free space this is why coaxial cables can be used as delay lines and why when cutting resonant sections of coaxial cable the Velocity Factor must be known Content by Scott Typos by Siri > On Aug 11, 2016, at 2:56 PM, Bob Stewart wrote: > > Why is velocity factor an issue? Aren't we only interested in the electrical > time from one end of the coax to the other? > Bob > - > AE6RV.com > > GFS GPSDO list: > groups.yahoo.com/neo/groups/GFS-GPSDOs/info > > From: Didier Juges > To: Bob Albert ; Discussion of precise time and frequency > measurement > Sent: Thursday, August 11, 2016 1:20 PM > Subject: Re: [time-nuts] Safely getting the electrical length of a connected > antenna feedline > > I used the PPS from a Thunderbolt (fast rise lime, low rep frequency, was > handy) and a digital storage scope and a couple of resistors to make a > reflectometer based on this experiment: > > www.ko4bb.com/getsimple/index.php?I'd=coax-cable-impedance-matching > > You can very clearly see a 50 ohm/75 ohm mismatch. > > The biggest variable will be the velocity factor. > > Didier KO4BB > > > ___ > time-nuts mailing list -- time-nuts@febo.com > To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts > and follow the instructions there. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Safely getting the electrical length of a connected antenna feedline
Good point! It is only an issue when you try to calibrate/correlate to the physical length. Didier On August 11, 2016 1:56:09 PM CDT, Bob Stewart wrote: >Why is velocity factor an issue? Aren't we only interested in the >electrical time from one end of the coax to the other? >Bob > - >AE6RV.com > >GFS GPSDO list: >groups.yahoo.com/neo/groups/GFS-GPSDOs/info > > From: Didier Juges >To: Bob Albert ; Discussion of precise time and >frequency measurement > Sent: Thursday, August 11, 2016 1:20 PM >Subject: Re: [time-nuts] Safely getting the electrical length of a >connected antenna feedline > >I used the PPS from a Thunderbolt (fast rise lime, low rep frequency, >was handy) and a digital storage scope and a couple of resistors to >make a reflectometer based on this experiment: > >www.ko4bb.com/getsimple/index.php?I'd=coax-cable-impedance-matching > >You can very clearly see a 50 ohm/75 ohm mismatch. > >The biggest variable will be the velocity factor. > >Didier KO4BB > > >___ >time-nuts mailing list -- time-nuts@febo.com >To unsubscribe, go to >https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts >and follow the instructions there. -- Sent from my Moto-X wireless tracker while I do other things. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Safely getting the electrical length of a connected, antenna feedline
"The biggest variable will be the velocity factor." If you determine the length electrically, you will already have the electricallength. If you need the physical length, then multiply electrical length times the inverse of the velocity factor. -- Joe Leikhim Leikhim and Associates Communications Consultants Oviedo, Florida jleik...@leikhim.com 407-982-0446 WWW.LEIKHIM.COM ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Safely getting the electrical length of a connected antenna feedline
Why is velocity factor an issue? Aren't we only interested in the electrical time from one end of the coax to the other? Bob - AE6RV.com GFS GPSDO list: groups.yahoo.com/neo/groups/GFS-GPSDOs/info From: Didier Juges To: Bob Albert ; Discussion of precise time and frequency measurement Sent: Thursday, August 11, 2016 1:20 PM Subject: Re: [time-nuts] Safely getting the electrical length of a connected antenna feedline I used the PPS from a Thunderbolt (fast rise lime, low rep frequency, was handy) and a digital storage scope and a couple of resistors to make a reflectometer based on this experiment: www.ko4bb.com/getsimple/index.php?I'd=coax-cable-impedance-matching You can very clearly see a 50 ohm/75 ohm mismatch. The biggest variable will be the velocity factor. Didier KO4BB ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Safely getting the electrical length of a connected antenna feedline
I used the PPS from a Thunderbolt (fast rise lime, low rep frequency, was handy) and a digital storage scope and a couple of resistors to make a reflectometer based on this experiment: www.ko4bb.com/getsimple/index.php?I'd=coax-cable-impedance-matching You can very clearly see a 50 ohm/75 ohm mismatch. The biggest variable will be the velocity factor. Didier KO4BB On August 8, 2016 2:18:02 PM CDT, Bob Albert via time-nuts wrote: >I host a group called something like HF Antennas. There I posted a >link to an article on how to measure coaxial cable. The easiest way is >with a spectrum analyzer and a tracking generator. >You connect the generator to the analyzer through a Tee that goes to >the unknown coax. You will see a group of peaks and nulls over the >spectrum. The spacing is a half wave of the cable. The match needs to >not be good to see the nulls best, and you will need to know the >propagation constant of the cable. Chances are, the match won't be >good over the entire range so you are okay with that. Propagation >constant of most coaxial cable runs around 66%. >You can also use a TDR setup but you'll have to make one, with a pulser >and a 'scope. I downloaded a circuit for a pulser that uses one IC. I >have the parts but haven't built it yet, as I am stalled by the problem >of connecting to a 14 pin SMD part. The IC uses one part as an >oscillator and the other 5 in parallel to drive 50 Ohms. Again, you >use a Tee and measure the time for a reflection, bearing in mind that >the trip is two ways over the same cable and the time shown will be >double the time for the calculation. >Bob > > >On Monday, August 8, 2016 12:00 PM, Bob Stewart wrote: > > >Earlier this year, with some help, I pulled the dish off of an old >DishTV antenna on the roof and put a 5V bullet antenna on the mast. I >also pulled a new cable through by attaching it to the old one. The >problem is that I was not able to measure the new cable. So, the >question is, without going back on the roof in this heat, how can I >measure the electrical length of the line I pulled? > >I was thinking of using my 8640B signal generator and sending some RF >back up the line to get a quarter wavelength at the null. But that >assumes a lot, including that the other end is open at 3MHz, or >whatever the frequency works out to be, as well as that the high >voltage on the antenna end won't be high enough to blow the LNA. > >So, how much RF I can safely send up the line? I've got an 8558B >spectrum analyzer, but it's not on the bench, and it would be easier to >use my scope, which sadly is a 70s vintage Tek 455. Do I put this all >together with a lead from the generator to a tee at the measuring >device and tune for a null? My experience at getting precise >measurements on anything longer than a few inches is effectively none, >but I'd guess that I want less than 0.5V at the LNA during this test. >Oh, and I do have an 8444A tracking generator that can output -10 dbm >as well as a 10 db attenuator within easy access. That could get a >quick spot on the null point. > >Most importantly, of course is the question of whether this will even >work. > >Bob - >AE6RV - >AE6RV.com > >GFS GPSDO list: >groups.yahoo.com/neo/groups/GFS-GPSDOs/info >___ >time-nuts mailing list -- time-nuts@febo.com >To unsubscribe, go to >https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts >and follow the instructions there. > > > >___ >time-nuts mailing list -- time-nuts@febo.com >To unsubscribe, go to >https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts >and follow the instructions there. -- Sent from my Moto-X wireless tracker while I do other things. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Safely getting the electrical length of a connected antenna feedline
You left out the obvious time-nut solution: Calibrate and characterize an ensemble of HP5071A's to correct absolute time at NIST. Transport the ensemble (correcting, if necessary, for general relativisitic effects) to your house. Set the cable delay in your GPS receiver to zero. The delta between your receiver PPS and the HP5071A Ensemble is the time delay in your cable and GPS Antenna - AFTER you account for the time delta between USNO and NIST time (available at http://www.nist.gov/pml/div688/grp50/nistusno.cfm ) Tim N3QE On Mon, Aug 8, 2016 at 2:18 PM, Bob Stewart wrote: > Earlier this year, with some help, I pulled the dish off of an old DishTV > antenna on the roof and put a 5V bullet antenna on the mast. I also pulled > a new cable through by attaching it to the old one. The problem is that I > was not able to measure the new cable. So, the question is, without going > back on the roof in this heat, how can I measure the electrical length of > the line I pulled? > > I was thinking of using my 8640B signal generator and sending some RF back > up the line to get a quarter wavelength at the null. But that assumes a > lot, including that the other end is open at 3MHz, or whatever the > frequency works out to be, as well as that the high voltage on the antenna > end won't be high enough to blow the LNA. > > So, how much RF I can safely send up the line? I've got an 8558B spectrum > analyzer, but it's not on the bench, and it would be easier to use my > scope, which sadly is a 70s vintage Tek 455. Do I put this all together > with a lead from the generator to a tee at the measuring device and tune > for a null? My experience at getting precise measurements on anything > longer than a few inches is effectively none, but I'd guess that I want > less than 0.5V at the LNA during this test. Oh, and I do have an 8444A > tracking generator that can output -10 dbm as well as a 10 db attenuator > within easy access. That could get a quick spot on the null point. > > Most importantly, of course is the question of whether this will even > work. > > Bob - AE6RV -- > --- > AE6RV.com > > GFS GPSDO list: > groups.yahoo.com/neo/groups/GFS-GPSDOs/info > ___ > time-nuts mailing list -- time-nuts@febo.com > To unsubscribe, go to https://www.febo.com/cgi-bin/ > mailman/listinfo/time-nuts > and follow the instructions there. > ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Safely getting the electrical length of a connected antenna feedline
Thanks David. I have ordered some from ebay, very cheap. 5pcs SO/SOP/SOIC/SSOP/TSSOP/MSOP14 to DIP 14 Adapter PCB Board Converter MA | | | | | | | | | | | 5pcs SO/SOP/SOIC/SSOP/TSSOP/MSOP14 to DIP 14 Ad...US $1.32 New other (see details) in Business & Industrial, Electrical & Test Equipment, Electronic Components | | | | View on www.ebay.com | Preview by Yahoo | | | | | On Wednesday, August 10, 2016 11:01 AM, David wrote: These are a little larger than what I was thinking of but were mentioned the other day in funwithtu...@yahoogroups.com and are probable more suitable for most projects anyway: http://qrpme.com/?p=product&id=MEP On Tue, 9 Aug 2016 16:10:38 + (UTC), you wrote: >Yes, a board with the required footprint would be the way to go. Where does >one find that? > > > On Tuesday, August 9, 2016 12:00 AM, David wrote: > > > Richard mentioned the SMD to leaded adapters which work well. > >Another way which is more suitable for Manhattan or dead bug type >construction is to glue or solder down just tiny printed circuit board >which has the SMD footprint and then solder directly to the leads or >extensions to the pads. This does not increase the lead length any >more than necessary and places the ground plane in close proximity for >best RF performance. If you are desperate, you can cut an SMD >footprint out of an existing unused donor board. > >On Tue, 9 Aug 2016 03:37:07 + (UTC), you wrote: > >>Your comments on layout made me think again of how to implement these >>projects. How do you use a 14 pin SMD IC? I could try to connect it with >>flying leads but I'd like something better. Is there some kind of socket for >>these devices? Or a generic board to receive such things? ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Safely getting the electrical length of a connected antenna feedline
These are a little larger than what I was thinking of but were mentioned the other day in funwithtu...@yahoogroups.com and are probable more suitable for most projects anyway: http://qrpme.com/?p=product&id=MEP On Tue, 9 Aug 2016 16:10:38 + (UTC), you wrote: >Yes, a board with the required footprint would be the way to go. Where does >one find that? > > >On Tuesday, August 9, 2016 12:00 AM, David wrote: > > > Richard mentioned the SMD to leaded adapters which work well. > >Another way which is more suitable for Manhattan or dead bug type >construction is to glue or solder down just tiny printed circuit board >which has the SMD footprint and then solder directly to the leads or >extensions to the pads. This does not increase the lead length any >more than necessary and places the ground plane in close proximity for >best RF performance. If you are desperate, you can cut an SMD >footprint out of an existing unused donor board. > >On Tue, 9 Aug 2016 03:37:07 + (UTC), you wrote: > >>Your comments on layout made me think again of how to implement these >>projects. How do you use a 14 pin SMD IC? I could try to connect it with >>flying leads but I'd like something better. Is there some kind of socket for >>these devices? Or a generic board to receive such things? ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Safely getting the electrical length of a connected antenna feedline
Hi: Another option is so Google for a "Breakout board" for the IC you're looking to work with. People like Spark Fun, Seed studio, &Etc make these. It's a board that holds the chip and the needed accessory parts, but needs something else like an Arduino. -- Have Fun, Brooke Clarke http://www.PRC68.com http://www.end2partygovernment.com/2012Issues.html The lesser of evils is still evil. Original Message On Tue, Aug 9, 2016 at 9:10 AM, Bob Albert via time-nuts wrote: Yes, a board with the required footprint would be the way to go. Where does one find that? You can have small PCBs made for $3 each. There are places here in the US that will do PCBs for $3/square inch with a one square inch minimum. basicpcb.com sone of these. It is not hard to design a basic "carrier board" that has just one chip's footprint and maybe a decoupling capacitor and a 0.1" header connector. Many times the chip's data sheet will have an example PCB layout you can borrow that will fit in a one square inch board. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Safely getting the electrical length of a connected antenna feedline
On Tue, Aug 9, 2016 at 9:10 AM, Bob Albert via time-nuts wrote: > > Yes, a board with the required footprint would be the way to go. Where does > one find that? You can have small PCBs made for $3 each. There are places here in the US that will do PCBs for $3/square inch with a one square inch minimum. basicpcb.com sone of these. It is not hard to design a basic "carrier board" that has just one chip's footprint and maybe a decoupling capacitor and a 0.1" header connector. Many times the chip's data sheet will have an example PCB layout you can borrow that will fit in a one square inch board. -- Chris Albertson Redondo Beach, California ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Safely getting the electrical length of a connected antenna feedline
Yes, a board with the required footprint would be the way to go. Where does one find that? On Tuesday, August 9, 2016 12:00 AM, David wrote: Richard mentioned the SMD to leaded adapters which work well. Another way which is more suitable for Manhattan or dead bug type construction is to glue or solder down just tiny printed circuit board which has the SMD footprint and then solder directly to the leads or extensions to the pads. This does not increase the lead length any more than necessary and places the ground plane in close proximity for best RF performance. If you are desperate, you can cut an SMD footprint out of an existing unused donor board. On Tue, 9 Aug 2016 03:37:07 + (UTC), you wrote: >Your comments on layout made me think again of how to implement these >projects. How do you use a 14 pin SMD IC? I could try to connect it with >flying leads but I'd like something better. Is there some kind of socket for >these devices? Or a generic board to receive such things? > >Bob > >On Monday, August 8, 2016 8:02 PM, David wrote: > > I actually tested various 74120 dual 4-input NAND drivers which >produce the sync output on my B&K function generator to find ones >which would provide the fastest and cleanest pulse. AS (advanced >schottky) and FAST (fast advanced schottky TTL) were the best for me. >Modern inexpensive discrete logic however can do a much better these >days. > >One interesting thing I learned is that the dual 4-input NAND pinout >overlaps the quad 2-input NAND pinout so in a properly designed layout >where only 2 gates are used, either part can be used. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Safely getting the electrical length of a connected antenna feedline
From: Dr. David Kirkby (Kirkby Microwave Ltd) I thought i might be possible to do this with a VNA, and a test antenna located a known distance apart. So I asked in the Keysight forum on 8th Feb 2015 [] Dave ___ Folks, Yes, I've used the DG8SAQ Vector Network Analyser to measure cable lengths and impedance very easily. The procedure is documented on page 458 et.seq. of this help file: http://sdr-kits.net/DG8SAQ/VNWA/VNWA_HELP.pdf The VNWA proven one of the most useful pieces of kit I've bought, and support is superb. http://sdr-kits.net/VNWA3_Description.html Cheers, David -- SatSignal Software - Quality software written to your requirements Web: http://www.satsignal.eu Email: david-tay...@blueyonder.co.uk Twitter: @gm8arv ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Safely getting the electrical length of a connected antenna feedline
If you have *the* active antenna, it is pretty easy to make a little quadrapole circularly polarized antenna out of a couple of pieces of 141 semi-riged coax, and to transmit signal into the active GPS antenna, and measure the signal coming out of the active GPS antenna. If you don't have the actual antenna being used, you could get close by using another of the same type and manufacture. I tested all of my GPS antennas that way for gain, as a way to be sure that they were functioning properly, but there is no reason that you couldn't use a VNA to test them for phase delay, group delay, whatever you desire. You could even modulate your sweep generator with a pulse, detect the pulse with a diode, and measure the delay with your oscilloscope. -Chuck Harris Dr. David Kirkby (Kirkby Microwave Ltd) wrote: > On 8 Aug 2016 21:23, "Bob Camp" wrote: >> >> Hi >> >> An even more significant question: >> >> Is it worth doing? > >> Your antenna and module could easily have delays >> in the 40 ns range. It has no impact on a “frequency” GPSDO. It is one of > a number of static offsets in a time transfer system. >> >> Even the NIST level outfits seem to have issues coming up with a purely > mathematical answer to “what is the offset”. > > I thought i might be possible to do this with a VNA, and a test antenna > located a known distance apart. So I asked in the Keysight forum on 8th Feb > 2015 > > https://community.keysight.com/thread/23082 > > There's a replay by Dr_Joel, who is a VNA guru. Dr. Joel Dunsmore, > suggesting the use of the group delay function. In one sentence he wrote > > "What is the level of delay accuracy you are looking to achieve. With this > method, 1 nsec is reasonable, but if you need 100 psec or 10 psec, then we > will have to be much more careful." > > The thread never got a complete solution, but it might help if other look > at that, and perhaps start another thread on a similar topic, as that one > is very old. However, if you don't have a VNA, I would not bother asking, > as you are not going to get a response (no pun intended), to a non-VNA > question on a VNA forum. > > But IF it was possible to determine the delay through the antenna/filter > within a ns, it would make measurements of coax length useful, whereas as > Bob said, it is pointless unless you know the characteristics of the active > antenna. > > I don't know if there would be a way of generating a pulse and feeding that > into two antenna > > 1) Active one. > > 2) Passive one at the same distance, and same length of cable. > > The pulse should arrive at the same time if the two antennas had equal > delay. But the signal from the active one will arrive later due to the > delay. That might be possible to see on a scope. > > I think assuming that the delay in the active antenna can't be measured is > maybe an assumption that is untrue. You could perhaps do better if you > built your own antenna, and characterized the SAW filter separately. > > Dave > ___ > time-nuts mailing list -- time-nuts@febo.com > To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts > and follow the instructions there. > ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Safely getting the electrical length of a connected antenna feedline
On 8 Aug 2016 21:23, "Bob Camp" wrote: > > Hi > > An even more significant question: > > Is it worth doing? > Your antenna and module could easily have delays > in the 40 ns range. It has no impact on a “frequency” GPSDO. It is one of a number of static offsets in a time transfer system. > > Even the NIST level outfits seem to have issues coming up with a purely mathematical answer to “what is the offset”. I thought i might be possible to do this with a VNA, and a test antenna located a known distance apart. So I asked in the Keysight forum on 8th Feb 2015 https://community.keysight.com/thread/23082 There's a replay by Dr_Joel, who is a VNA guru. Dr. Joel Dunsmore, suggesting the use of the group delay function. In one sentence he wrote "What is the level of delay accuracy you are looking to achieve. With this method, 1 nsec is reasonable, but if you need 100 psec or 10 psec, then we will have to be much more careful." The thread never got a complete solution, but it might help if other look at that, and perhaps start another thread on a similar topic, as that one is very old. However, if you don't have a VNA, I would not bother asking, as you are not going to get a response (no pun intended), to a non-VNA question on a VNA forum. But IF it was possible to determine the delay through the antenna/filter within a ns, it would make measurements of coax length useful, whereas as Bob said, it is pointless unless you know the characteristics of the active antenna. I don't know if there would be a way of generating a pulse and feeding that into two antenna 1) Active one. 2) Passive one at the same distance, and same length of cable. The pulse should arrive at the same time if the two antennas had equal delay. But the signal from the active one will arrive later due to the delay. That might be possible to see on a scope. I think assuming that the delay in the active antenna can't be measured is maybe an assumption that is untrue. You could perhaps do better if you built your own antenna, and characterized the SAW filter separately. Dave ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Safely getting the electrical length of a connected antenna feedline
I doubt it's worth mentioning that a random SMD footprint cut from a larger board and some of the currently available eBay SMD adapter boards may have plated through holes which could short if used to prototype on copper clad board so it's worth paying a little attention to insulating the 'underside' of the boards. On 9 Aug 2016 08:00, "David" wrote: > Richard mentioned the SMD to leaded adapters which work well. > > Another way which is more suitable for Manhattan or dead bug type > construction is to glue or solder down just tiny printed circuit board > which has the SMD footprint and then solder directly to the leads or > extensions to the pads. This does not increase the lead length any > more than necessary and places the ground plane in close proximity for > best RF performance. If you are desperate, you can cut an SMD > footprint out of an existing unused donor board. > > On Tue, 9 Aug 2016 03:37:07 + (UTC), you wrote: > > >Your comments on layout made me think again of how to implement these > projects. How do you use a 14 pin SMD IC? I could try to connect it with > flying leads but I'd like something better. Is there some kind of socket > for these devices? Or a generic board to receive such things? > > > >Bob > > > >On Monday, August 8, 2016 8:02 PM, David wrote: > > > > I actually tested various 74120 dual 4-input NAND drivers which > >produce the sync output on my B&K function generator to find ones > >which would provide the fastest and cleanest pulse. AS (advanced > >schottky) and FAST (fast advanced schottky TTL) were the best for me. > >Modern inexpensive discrete logic however can do a much better these > >days. > > > >One interesting thing I learned is that the dual 4-input NAND pinout > >overlaps the quad 2-input NAND pinout so in a properly designed layout > >where only 2 gates are used, either part can be used. > ___ > time-nuts mailing list -- time-nuts@febo.com > To unsubscribe, go to https://www.febo.com/cgi-bin/ > mailman/listinfo/time-nuts > and follow the instructions there. > ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Safely getting the electrical length of a connected antenna feedline
Richard mentioned the SMD to leaded adapters which work well. Another way which is more suitable for Manhattan or dead bug type construction is to glue or solder down just tiny printed circuit board which has the SMD footprint and then solder directly to the leads or extensions to the pads. This does not increase the lead length any more than necessary and places the ground plane in close proximity for best RF performance. If you are desperate, you can cut an SMD footprint out of an existing unused donor board. On Tue, 9 Aug 2016 03:37:07 + (UTC), you wrote: >Your comments on layout made me think again of how to implement these >projects. How do you use a 14 pin SMD IC? I could try to connect it with >flying leads but I'd like something better. Is there some kind of socket for >these devices? Or a generic board to receive such things? > >Bob > >On Monday, August 8, 2016 8:02 PM, David wrote: > > I actually tested various 74120 dual 4-input NAND drivers which >produce the sync output on my B&K function generator to find ones >which would provide the fastest and cleanest pulse. AS (advanced >schottky) and FAST (fast advanced schottky TTL) were the best for me. >Modern inexpensive discrete logic however can do a much better these >days. > >One interesting thing I learned is that the dual 4-input NAND pinout >overlaps the quad 2-input NAND pinout so in a properly designed layout >where only 2 gates are used, either part can be used. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Safely getting the electrical length of a connected antenna feedline
Thanks for the tip! I found a few at around a buck apiece. Now to do due diligence to see if they will fit my parts. Bob On Monday, August 8, 2016 9:06 PM, Richard W. Solomon wrote: There are a few adapters over on that "auction" site. Do a search on 14 pin smd to 14 pin dip. 73, Dick, W1KSZ -Original Message- From: time-nuts [mailto:time-nuts-boun...@febo.com] On Behalf Of Bob Albert via time-nuts Sent: Monday, August 08, 2016 8:37 PM To: Discussion of precise time and frequency measurement Subject: Re: [time-nuts] Safely getting the electrical length of a connected antenna feedline Your comments on layout made me think again of how to implement these projects. How do you use a 14 pin SMD IC? I could try to connect it with flying leads but I'd like something better. Is there some kind of socket for these devices? Or a generic board to receive such things? Bob On Monday, August 8, 2016 8:02 PM, David wrote: I actually tested various 74120 dual 4-input NAND drivers which produce the sync output on my B&K function generator to find ones which would provide the fastest and cleanest pulse. AS (advanced schottky) and FAST (fast advanced schottky TTL) were the best for me. Modern inexpensive discrete logic however can do a much better these days. One interesting thing I learned is that the dual 4-input NAND pinout overlaps the quad 2-input NAND pinout so in a properly designed layout where only 2 gates are used, either part can be used. On Mon, 08 Aug 2016 16:31:44 -0400, you wrote: >If you have a function generator with a sync output, you can use that >pulse into a T connector with your scope to do a TDR measurement of the >cable. If you have a scrap of the new cable, you can use that to calibrate the >setup. > >Regards, >Tom ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Safely getting the electrical length of a connected antenna feedline
You could get a low cost GPS unit and compare the PPS from it to the PPS from your setup with the long cable. Modern GPS receivers are sensitive enough to work with a poor antenna (indoors) and don't cost much. -- These are my opinions. I hate spam. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Safely getting the electrical length of a connected antenna feedline
Gate drivers are pretty zippy when you leave out the capacitive load of a power fet's gate. They are also available in 8 pin dip. On Monday, 8 August 2016, Bob Albert via time-nuts wrote: > Your comments on layout made me think again of how to implement these > projects. How do you use a 14 pin SMD IC? I could try to connect it with > flying leads but I'd like something better. Is there some kind of socket > for these devices? Or a generic board to receive such things? > Bob > > > On Monday, August 8, 2016 8:02 PM, David > wrote: > > > I actually tested various 74120 dual 4-input NAND drivers which > produce the sync output on my B&K function generator to find ones > which would provide the fastest and cleanest pulse. AS (advanced > schottky) and FAST (fast advanced schottky TTL) were the best for me. > Modern inexpensive discrete logic however can do a much better these > days. > > One interesting thing I learned is that the dual 4-input NAND pinout > overlaps the quad 2-input NAND pinout so in a properly designed layout > where only 2 gates are used, either part can be used. > > On Mon, 08 Aug 2016 16:31:44 -0400, you wrote: > > >If you have a function generator with a sync output, you can use that > pulse > >into a T connector with your scope to do a TDR measurement of the cable. > If > >you have a scrap of the new cable, you can use that to calibrate the > setup. > > > >Regards, > >Tom > ___ > time-nuts mailing list -- time-nuts@febo.com > To unsubscribe, go to https://www.febo.com/cgi-bin/ > mailman/listinfo/time-nuts > and follow the instructions there. > > > > ___ > time-nuts mailing list -- time-nuts@febo.com > To unsubscribe, go to https://www.febo.com/cgi-bin/ > mailman/listinfo/time-nuts > and follow the instructions there. > ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Safely getting the electrical length of a connected antenna feedline
There are a few adapters over on that "auction" site. Do a search on 14 pin smd to 14 pin dip. 73, Dick, W1KSZ -Original Message- From: time-nuts [mailto:time-nuts-boun...@febo.com] On Behalf Of Bob Albert via time-nuts Sent: Monday, August 08, 2016 8:37 PM To: Discussion of precise time and frequency measurement Subject: Re: [time-nuts] Safely getting the electrical length of a connected antenna feedline Your comments on layout made me think again of how to implement these projects. How do you use a 14 pin SMD IC? I could try to connect it with flying leads but I'd like something better. Is there some kind of socket for these devices? Or a generic board to receive such things? Bob On Monday, August 8, 2016 8:02 PM, David wrote: I actually tested various 74120 dual 4-input NAND drivers which produce the sync output on my B&K function generator to find ones which would provide the fastest and cleanest pulse. AS (advanced schottky) and FAST (fast advanced schottky TTL) were the best for me. Modern inexpensive discrete logic however can do a much better these days. One interesting thing I learned is that the dual 4-input NAND pinout overlaps the quad 2-input NAND pinout so in a properly designed layout where only 2 gates are used, either part can be used. On Mon, 08 Aug 2016 16:31:44 -0400, you wrote: >If you have a function generator with a sync output, you can use that >pulse into a T connector with your scope to do a TDR measurement of the >cable. If you have a scrap of the new cable, you can use that to calibrate the >setup. > >Regards, >Tom ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Safely getting the electrical length of a connected antenna feedline
Your comments on layout made me think again of how to implement these projects. How do you use a 14 pin SMD IC? I could try to connect it with flying leads but I'd like something better. Is there some kind of socket for these devices? Or a generic board to receive such things? Bob On Monday, August 8, 2016 8:02 PM, David wrote: I actually tested various 74120 dual 4-input NAND drivers which produce the sync output on my B&K function generator to find ones which would provide the fastest and cleanest pulse. AS (advanced schottky) and FAST (fast advanced schottky TTL) were the best for me. Modern inexpensive discrete logic however can do a much better these days. One interesting thing I learned is that the dual 4-input NAND pinout overlaps the quad 2-input NAND pinout so in a properly designed layout where only 2 gates are used, either part can be used. On Mon, 08 Aug 2016 16:31:44 -0400, you wrote: >If you have a function generator with a sync output, you can use that pulse >into a T connector with your scope to do a TDR measurement of the cable. If >you have a scrap of the new cable, you can use that to calibrate the setup. > >Regards, >Tom ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Safely getting the electrical length of a connected antenna feedline
I actually tested various 74120 dual 4-input NAND drivers which produce the sync output on my B&K function generator to find ones which would provide the fastest and cleanest pulse. AS (advanced schottky) and FAST (fast advanced schottky TTL) were the best for me. Modern inexpensive discrete logic however can do a much better these days. One interesting thing I learned is that the dual 4-input NAND pinout overlaps the quad 2-input NAND pinout so in a properly designed layout where only 2 gates are used, either part can be used. On Mon, 08 Aug 2016 16:31:44 -0400, you wrote: >If you have a function generator with a sync output, you can use that pulse >into a T connector with your scope to do a TDR measurement of the cable. If >you have a scrap of the new cable, you can use that to calibrate the setup. > >Regards, >Tom ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Safely getting the electrical length of a connected antenna feedline
First, the nulls are sharper than the peaks. What you do is measure the frequency of adjacent nulls and calculate what frequency makes both of those a half wave or multiple thereof. Then you know the number of half waves to the mismatch. It's the distance from the tee to the remote end. It takes a little thought, or you can read the article which presents some formulas to make for less confusion. I guess. The article focuses on shorted or open lines but you can get readings from nearly any line, as long as it's not a flat line. Of course, the closer you are to a good match, the harder it is to make the measurement, which is why I suggest finding a frequency range far from the design of the termination equipment. Your TDR should work also. Bob On Monday, August 8, 2016 1:23 PM, Bob Albert via time-nuts wrote: I host a group called something like HF Antennas. There I posted a link to an article on how to measure coaxial cable. The easiest way is with a spectrum analyzer and a tracking generator. You connect the generator to the analyzer through a Tee that goes to the unknown coax. You will see a group of peaks and nulls over the spectrum. The spacing is a half wave of the cable. The match needs to not be good to see the nulls best, and you will need to know the propagation constant of the cable. Chances are, the match won't be good over the entire range so you are okay with that. Propagation constant of most coaxial cable runs around 66%. You can also use a TDR setup but you'll have to make one, with a pulser and a 'scope. I downloaded a circuit for a pulser that uses one IC. I have the parts but haven't built it yet, as I am stalled by the problem of connecting to a 14 pin SMD part. The IC uses one part as an oscillator and the other 5 in parallel to drive 50 Ohms. Again, you use a Tee and measure the time for a reflection, bearing in mind that the trip is two ways over the same cable and the time shown will be double the time for the calculation. Bob On Monday, August 8, 2016 12:00 PM, Bob Stewart wrote: Earlier this year, with some help, I pulled the dish off of an old DishTV antenna on the roof and put a 5V bullet antenna on the mast. I also pulled a new cable through by attaching it to the old one. The problem is that I was not able to measure the new cable. So, the question is, without going back on the roof in this heat, how can I measure the electrical length of the line I pulled? I was thinking of using my 8640B signal generator and sending some RF back up the line to get a quarter wavelength at the null. But that assumes a lot, including that the other end is open at 3MHz, or whatever the frequency works out to be, as well as that the high voltage on the antenna end won't be high enough to blow the LNA. So, how much RF I can safely send up the line? I've got an 8558B spectrum analyzer, but it's not on the bench, and it would be easier to use my scope, which sadly is a 70s vintage Tek 455. Do I put this all together with a lead from the generator to a tee at the measuring device and tune for a null? My experience at getting precise measurements on anything longer than a few inches is effectively none, but I'd guess that I want less than 0.5V at the LNA during this test. Oh, and I do have an 8444A tracking generator that can output -10 dbm as well as a 10 db attenuator within easy access. That could get a quick spot on the null point. Most importantly, of course is the question of whether this will even work. Bob - AE6RV - AE6RV.com GFS GPSDO list: groups.yahoo.com/neo/groups/GFS-GPSDOs/info ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Safely getting the electrical length of a connected antenna feedline
If you have a function generator with a sync output, you can use that pulse into a T connector with your scope to do a TDR measurement of the cable. If you have a scrap of the new cable, you can use that to calibrate the setup. Regards, Tom - Original Message - From: "Bob Stewart" To: "Discussion of Precise Time and Frequency Measurement" Sent: Monday, August 08, 2016 2:18 PM Subject: [time-nuts] Safely getting the electrical length of a connected antenna feedline Earlier this year, with some help, I pulled the dish off of an old DishTV antenna on the roof and put a 5V bullet antenna on the mast. I also pulled a new cable through by attaching it to the old one. The problem is that I was not able to measure the new cable. So, the question is, without going back on the roof in this heat, how can I measure the electrical length of the line I pulled? I was thinking of using my 8640B signal generator and sending some RF back up the line to get a quarter wavelength at the null. But that assumes a lot, including that the other end is open at 3MHz, or whatever the frequency works out to be, as well as that the high voltage on the antenna end won't be high enough to blow the LNA. So, how much RF I can safely send up the line? I've got an 8558B spectrum analyzer, but it's not on the bench, and it would be easier to use my scope, which sadly is a 70s vintage Tek 455. Do I put this all together with a lead from the generator to a tee at the measuring device and tune for a null? My experience at getting precise measurements on anything longer than a few inches is effectively none, but I'd guess that I want less than 0.5V at the LNA during this test. Oh, and I do have an 8444A tracking generator that can output -10 dbm as well as a 10 db attenuator within easy access. That could get a quick spot on the null point. Most importantly, of course is the question of whether this will even work. Bob - AE6RV - AE6RV.com GFS GPSDO list: groups.yahoo.com/neo/groups/GFS-GPSDOs/info ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Safely getting the electrical length of a connected antenna feedline
Hi Bob, Correct me if I'm wrong, but for timing purposes, I think that what I want is the electrical length in nanoseconds, not the physical length. I hadn't considered the fact that the distance between peaks would give me a halfwave. But, that's a halfwave of what, exactly? Is it the distance from the far end to the tee, or to the generator or to the measurement device (SA/scope/meter)? And since nanoseconds are important, is it actually to some point within the measuring device? Or, since it's only nanoseconds, maybe the last few inches inside the scope aren't that important? It's starting to sound like what I really want to do the final measurement with is my old Voltohmyst with the RF probe at the tee if I really want to be accurate. That would be using the 8640 and tuning for either null or peak, whichever is sharper. As far as a TDR is concerned, I think that the 1PPS output from my GPSDO should be sufficient. In this case, I think I'd send the 1PPS to a tee at the start input on my 5370 and lock start and stop together with the phase switches opposite for start and stop. For this test, I could actually control the length of time the 1PPS is high so that it doesn't spoil the measurement. But, once again, will I see any sort of spike on the other end with a 3.3V 1PPS pulse? Bob - AE6RV.com GFS GPSDO list: groups.yahoo.com/neo/groups/GFS-GPSDOs/info From: Bob Albert To: Bob Stewart ; Discussion of Precise Time and Frequency Measurement ; Discussion of precise time and frequency measurement Sent: Monday, August 8, 2016 2:18 PM Subject: Re: [time-nuts] Safely getting the electrical length of a connected antenna feedline I host a group called something like HF Antennas. There I posted a link to an article on how to measure coaxial cable. The easiest way is with a spectrum analyzer and a tracking generator. You connect the generator to the analyzer through a Tee that goes to the unknown coax. You will see a group of peaks and nulls over the spectrum. The spacing is a half wave of the cable. The match needs to not be good to see the nulls best, and you will need to know the propagation constant of the cable. Chances are, the match won't be good over the entire range so you are okay with that. Propagation constant of most coaxial cable runs around 66%. You can also use a TDR setup but you'll have to make one, with a pulser and a 'scope. I downloaded a circuit for a pulser that uses one IC. I have the parts but haven't built it yet, as I am stalled by the problem of connecting to a 14 pin SMD part. The IC uses one part as an oscillator and the other 5 in parallel to drive 50 Ohms. Again, you use a Tee and measure the time for a reflection, bearing in mind that the trip is two ways over the same cable and the time shown will be double the time for the calculation. Bob On Monday, August 8, 2016 12:00 PM, Bob Stewart wrote: Earlier this year, with some help, I pulled the dish off of an old DishTV antenna on the roof and put a 5V bullet antenna on the mast. I also pulled a new cable through by attaching it to the old one. The problem is that I was not able to measure the new cable. So, the question is, without going back on the roof in this heat, how can I measure the electrical length of the line I pulled? I was thinking of using my 8640B signal generator and sending some RF back up the line to get a quarter wavelength at the null. But that assumes a lot, including that the other end is open at 3MHz, or whatever the frequency works out to be, as well as that the high voltage on the antenna end won't be high enough to blow the LNA. So, how much RF I can safely send up the line? I've got an 8558B spectrum analyzer, but it's not on the bench, and it would be easier to use my scope, which sadly is a 70s vintage Tek 455. Do I put this all together with a lead from the generator to a tee at the measuring device and tune for a null? My experience at getting precise measurements on anything longer than a few inches is effectively none, but I'd guess that I want less than 0.5V at the LNA during this test. Oh, and I do have an 8444A tracking generator that can output -10 dbm as well as a 10 db attenuator within easy access. That could get a quick spot on the null point. Most importantly, of course is the question of whether this will even work. Bob - AE6RV - AE6RV.com GFS GPSDO list: groups.yahoo.com/neo/groups/GFS-GPSDOs/info ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there. ___ time-nuts m
Re: [time-nuts] Safely getting the electrical length of a connected antenna feedline
Hi Bob, I believe I know the delay for the antenna and Ublox specifies the delay in the receiver. I can't guess within 20ft of the physical length of the antenna. But, this is time-nuts, so yeah I want to be able to work this out. And besides... I figured out how to output an accurate 1PPS with my unit. So, it's no longer just a frequency standard. Briefly: I take advantage of the fact that the sawtooth on the Ublox units is less 22ns wide (about +/- 10.5ns according to my data). I send the 1PPS from the receiver through a 30ns delay line to trigger a d-flop in a 7474, which arms the other d-flop in the 7474. The 30ns delay ensures that the 1PPS output of the Ublox, including the sawtooth, is always within the dead time between the pulses from the OCXO. So, the next 10MHz pulse triggers the other d-flop which goes through a 125 gate to the 1PPS output. 1/16th of a second later (a convenient time for me), the PIC resets the two d-flops and so it goes. So, yeah, that's 100ns late, but the Ublox has a userDelay field, which I set to 100ns. That moves the PPS back to the proper time. Yes, there is a delay of the 10MHz through the d-flop and the gate, but that's knowable. And there's about a 5ns difference bet ween the 1PPS output and the 10MHz output. So, given that the delays are all knowable, I think it's usable as a timing unit now; given the limitations of a GPSDO for that purpose. Any discussion about this method of getting a 1PPS should probably be in a new thread. I'd be happy to link to a schematic if wanted. Bob - AE6RV.com GFS GPSDO list: groups.yahoo.com/neo/groups/GFS-GPSDOs/info From: Bob Camp To: Bob Stewart ; Discussion of precise time and frequency measurement Sent: Monday, August 8, 2016 3:14 PM Subject: Re: [time-nuts] Safely getting the electrical length of a connected antenna feedline Hi An even more significant question: Is it worth doing? More or less: Do you know the delay numbers for your antenna? Do you know the delay numbers for your GPS module? How close can you *guess* the length of the cable? Knowing absolutely nothing at all about your setup, I’ll guess the cable is 50 feet long. Maybe I’m off by 20 or 30 feet. Call that +/-40 to 60 ns. I’d hope you can guess closer than that. Your antenna and module could easily have delays in the 40 ns range. It has no impact on a “frequency” GPSDO. It is one of a number of static offsets in a time transfer system. Even the NIST level outfits seem to have issues coming up with a purely mathematical answer to “what is the offset”. The standard answer is to bring in a calibrated receiver and see how it all measures out. None of that is to say you should *not* work out the line length. It’s just to say that there is only so much value to the measurement. Bob > On Aug 8, 2016, at 2:18 PM, Bob Stewart wrote: > > Earlier this year, with some help, I pulled the dish off of an old DishTV > antenna on the roof and put a 5V bullet antenna on the mast. I also pulled a > new cable through by attaching it to the old one. The problem is that I was > not able to measure the new cable. So, the question is, without going back > on the roof in this heat, how can I measure the electrical length of the line > I pulled? > > I was thinking of using my 8640B signal generator and sending some RF back up > the line to get a quarter wavelength at the null. But that assumes a lot, > including that the other end is open at 3MHz, or whatever the frequency works > out to be, as well as that the high voltage on the antenna end won't be high > enough to blow the LNA. > > So, how much RF I can safely send up the line? I've got an 8558B spectrum > analyzer, but it's not on the bench, and it would be easier to use my scope, > which sadly is a 70s vintage Tek 455. Do I put this all together with a lead > from the generator to a tee at the measuring device and tune for a null? My > experience at getting precise measurements on anything longer than a few > inches is effectively none, but I'd guess that I want less than 0.5V at the > LNA during this test. Oh, and I do have an 8444A tracking generator that can > output -10 dbm as well as a 10 db attenuator within easy access. That could > get a quick spot on the null point. > > Most importantly, of course is the question of whether this will even work. > > Bob - AE6RV - > AE6RV.com > > GFS GPSDO list: > groups.yahoo.com/neo/groups/GFS-GPSDOs/info > ___ > time-nuts mailing list -- time-nuts@febo.com > To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts &g
Re: [time-nuts] Safely getting the electrical length of a connected antenna feedline
Hi An even more significant question: Is it worth doing? More or less: Do you know the delay numbers for your antenna? Do you know the delay numbers for your GPS module? How close can you *guess* the length of the cable? Knowing absolutely nothing at all about your setup, I’ll guess the cable is 50 feet long. Maybe I’m off by 20 or 30 feet. Call that +/-40 to 60 ns. I’d hope you can guess closer than that. Your antenna and module could easily have delays in the 40 ns range. It has no impact on a “frequency” GPSDO. It is one of a number of static offsets in a time transfer system. Even the NIST level outfits seem to have issues coming up with a purely mathematical answer to “what is the offset”. The standard answer is to bring in a calibrated receiver and see how it all measures out. None of that is to say you should *not* work out the line length. It’s just to say that there is only so much value to the measurement. Bob > On Aug 8, 2016, at 2:18 PM, Bob Stewart wrote: > > Earlier this year, with some help, I pulled the dish off of an old DishTV > antenna on the roof and put a 5V bullet antenna on the mast. I also pulled a > new cable through by attaching it to the old one. The problem is that I was > not able to measure the new cable. So, the question is, without going back > on the roof in this heat, how can I measure the electrical length of the line > I pulled? > > I was thinking of using my 8640B signal generator and sending some RF back up > the line to get a quarter wavelength at the null. But that assumes a lot, > including that the other end is open at 3MHz, or whatever the frequency works > out to be, as well as that the high voltage on the antenna end won't be high > enough to blow the LNA. > > So, how much RF I can safely send up the line? I've got an 8558B spectrum > analyzer, but it's not on the bench, and it would be easier to use my scope, > which sadly is a 70s vintage Tek 455. Do I put this all together with a lead > from the generator to a tee at the measuring device and tune for a null? My > experience at getting precise measurements on anything longer than a few > inches is effectively none, but I'd guess that I want less than 0.5V at the > LNA during this test. Oh, and I do have an 8444A tracking generator that can > output -10 dbm as well as a 10 db attenuator within easy access. That could > get a quick spot on the null point. > > Most importantly, of course is the question of whether this will even work. > > Bob - AE6RV - > AE6RV.com > > GFS GPSDO list: > groups.yahoo.com/neo/groups/GFS-GPSDOs/info > ___ > time-nuts mailing list -- time-nuts@febo.com > To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts > and follow the instructions there. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Safely getting the electrical length of a connected antenna feedline
I host a group called something like HF Antennas. There I posted a link to an article on how to measure coaxial cable. The easiest way is with a spectrum analyzer and a tracking generator. You connect the generator to the analyzer through a Tee that goes to the unknown coax. You will see a group of peaks and nulls over the spectrum. The spacing is a half wave of the cable. The match needs to not be good to see the nulls best, and you will need to know the propagation constant of the cable. Chances are, the match won't be good over the entire range so you are okay with that. Propagation constant of most coaxial cable runs around 66%. You can also use a TDR setup but you'll have to make one, with a pulser and a 'scope. I downloaded a circuit for a pulser that uses one IC. I have the parts but haven't built it yet, as I am stalled by the problem of connecting to a 14 pin SMD part. The IC uses one part as an oscillator and the other 5 in parallel to drive 50 Ohms. Again, you use a Tee and measure the time for a reflection, bearing in mind that the trip is two ways over the same cable and the time shown will be double the time for the calculation. Bob On Monday, August 8, 2016 12:00 PM, Bob Stewart wrote: Earlier this year, with some help, I pulled the dish off of an old DishTV antenna on the roof and put a 5V bullet antenna on the mast. I also pulled a new cable through by attaching it to the old one. The problem is that I was not able to measure the new cable. So, the question is, without going back on the roof in this heat, how can I measure the electrical length of the line I pulled? I was thinking of using my 8640B signal generator and sending some RF back up the line to get a quarter wavelength at the null. But that assumes a lot, including that the other end is open at 3MHz, or whatever the frequency works out to be, as well as that the high voltage on the antenna end won't be high enough to blow the LNA. So, how much RF I can safely send up the line? I've got an 8558B spectrum analyzer, but it's not on the bench, and it would be easier to use my scope, which sadly is a 70s vintage Tek 455. Do I put this all together with a lead from the generator to a tee at the measuring device and tune for a null? My experience at getting precise measurements on anything longer than a few inches is effectively none, but I'd guess that I want less than 0.5V at the LNA during this test. Oh, and I do have an 8444A tracking generator that can output -10 dbm as well as a 10 db attenuator within easy access. That could get a quick spot on the null point. Most importantly, of course is the question of whether this will even work. Bob - AE6RV - AE6RV.com GFS GPSDO list: groups.yahoo.com/neo/groups/GFS-GPSDOs/info ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Safely getting the electrical length of a connected antenna feedline
b...@evoria.net said: > Earlier this year, with some help, I pulled the dish off of an old DishTV > antenna on the roof and put a 5V bullet antenna on the mast. I also pulled > a new cable through by attaching it to the old one. The problem is that I > was not able to measure the new cable. So, the question is, without going > back on the roof in this heat, how can I measure the electrical length of > the line I pulled? Can you measure the old cable? -- These are my opinions. I hate spam. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
[time-nuts] Safely getting the electrical length of a connected antenna feedline
Earlier this year, with some help, I pulled the dish off of an old DishTV antenna on the roof and put a 5V bullet antenna on the mast. I also pulled a new cable through by attaching it to the old one. The problem is that I was not able to measure the new cable. So, the question is, without going back on the roof in this heat, how can I measure the electrical length of the line I pulled? I was thinking of using my 8640B signal generator and sending some RF back up the line to get a quarter wavelength at the null. But that assumes a lot, including that the other end is open at 3MHz, or whatever the frequency works out to be, as well as that the high voltage on the antenna end won't be high enough to blow the LNA. So, how much RF I can safely send up the line? I've got an 8558B spectrum analyzer, but it's not on the bench, and it would be easier to use my scope, which sadly is a 70s vintage Tek 455. Do I put this all together with a lead from the generator to a tee at the measuring device and tune for a null? My experience at getting precise measurements on anything longer than a few inches is effectively none, but I'd guess that I want less than 0.5V at the LNA during this test. Oh, and I do have an 8444A tracking generator that can output -10 dbm as well as a 10 db attenuator within easy access. That could get a quick spot on the null point. Most importantly, of course is the question of whether this will even work. Bob - AE6RV - AE6RV.com GFS GPSDO list: groups.yahoo.com/neo/groups/GFS-GPSDOs/info ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.