Re: Topband: S21
Same here on 80m from VE5. Good signal, listening for NA only, but copying very, very few. Doug "Think of all the ways you can hurt yourself laughing." -Original Message- Very nice signals from S21 today on topband, peaking 579 here an hour before sunrise, but alas they have bad receive conditions it appears.Heard many calling from EU/Asia and they did not answer. Band has been extremely poor here this season "over the pole" have tried several times with SM7BIC and no joy. we usually have many QSOs by this time of the year. Either my antennas are not working this season, or this is the worst season in some time. At least here in KH6. Putting up more beverages this next week, but as it is now I can sure hear more than I can work, which I take as a good sign that at least the RX is working. 73 Merv K9FD/KH6 _ Topband Reflector _ Topband Reflector
Topband: S21
Very nice signals from S21 today on topband, peaking 579 here an hour before sunrise, but alas they have bad receive conditions it appears.Heard many calling from EU/Asia and they did not answer. Band has been extremely poor here this season "over the pole" have tried several times with SM7BIC and no joy. we usually have many QSOs by this time of the year. Either my antennas are not working this season, or this is the worst season in some time. At least here in KH6. Putting up more beverages this next week, but as it is now I can sure hear more than I can work, which I take as a good sign that at least the RX is working. 73 Merv K9FD/KH6 _ Topband Reflector
Re: Topband: S21 impedance measurements
On Sat, Jul 14, 2012 at 9:28 PM, Richard (Rick) Karlquist < rich...@karlquist.com> wrote: > > > On 7/14/2012 2:15 PM, George Dubovsky wrote: > >> All, >> >> I guess it's time for me to put up my "common mode choke" test technique >> for all to shoot at. I have a HP 4815A Vector Z meter, a N2PK VNA, and a >> HP 8753C VNA. I have all the probe adapters for the Z meter, and I have >> been bitten by the small amount of stray C that you just can't eliminate >> (but you should be able to calculate out). I have finally decided that >> my standard test is based on the following: >> >> I made up a board out of .062 FR-4 that is approximately 6" across (and >> about 4" wide). I cut three 50 Ohm microstrip lines full width across >> the 6" dimension. I soldered an N connector on each end (6 connectors >> > > SINCE YOU ASKED, there are a number of unresolved issues here from > a strict metrological viewpoint: > > 1. Your fixture is not an enclosed box. A defined Faraday cage is > recommended. The results might be affected by lead dress or whether > the test bench is conductive or not. Any fixture imposes an arbitrary > and finite spacing between the DUT and the ground plane. In general, > the measured impedance will depend on this. There is no "correct" > answer. > Agreed. In all cases, I placed the unit under test on a wood workbench. In addition, after I had decided on the final balun design for each band, and packaged it in its final pvc enclosure, I attached it to a short section of 2' aluminum tubing to simulate mounting on the yagi boom > > 2. The N connectors should be male and female and you should use > a 2 port type N calibration kit. > Agreed. The 2 females is a luxury I allowed myself at HF, but it is a known source of inaccuracy. > > 3. You used the common short cut of a through cal instead of a > full 2 port cal. This means that you are not calibrating out source > and load mismatch. A common short cut to fix this is to put pads > around the DUT. This can work fairly well. > I always used either 6 dB or 10 dB pads on both ports (right at the test fixture) for these tests. > > The designer of the network analyzer can recognize that the through cal > shortcut is popular and accomodate the user by going to a lot of > trouble to provide well matched ports. Or not. It turns out that > getting well matched ports translates into massive padding. This > has the disadvantage of loss of dynamic range. Then there is the > question of allowing the user to turn the internal padding on and > off. What if he turns it off and then proceeds to do a through > cal anyway? There is no simple answer to this discussion. > > If the environment seen by the DUT in the test fixture is not > the same as it sees in the application, then the measurement > is just an approximation. > I did attempt to simulate mounting on the boom in my testing, including all of the mechanical hardware that would be involved. > > It is entirely possible that you will get results accurate enough > for ham radio since you are working at HF. But the technique > would not be deemed completely rigorous by metrologists. > Ahh, what do I care about the weather... oh, metrologists ;-) I do appreciate your comments, Rick, and I respect your professional credentials. My goal going in to this exercise was to provide a family of CM chokes that would not screw up my YO-optimized yagis and, after measuring some commercial stuff in the junk box, I concluded that I could do better. 73, geo - n4ua ___ UR RST IS ... ... ..9 QSB QSB - hw? BK
Re: Topband: S21 impedance measurements
On 7/14/2012 2:15 PM, George Dubovsky wrote: > All, > > I guess it's time for me to put up my "common mode choke" test technique > for all to shoot at. I have a HP 4815A Vector Z meter, a N2PK VNA, and a > HP 8753C VNA. I have all the probe adapters for the Z meter, and I have > been bitten by the small amount of stray C that you just can't eliminate > (but you should be able to calculate out). I have finally decided that > my standard test is based on the following: > > I made up a board out of .062 FR-4 that is approximately 6" across (and > about 4" wide). I cut three 50 Ohm microstrip lines full width across > the 6" dimension. I soldered an N connector on each end (6 connectors SINCE YOU ASKED, there are a number of unresolved issues here from a strict metrological viewpoint: 1. Your fixture is not an enclosed box. A defined Faraday cage is recommended. The results might be affected by lead dress or whether the test bench is conductive or not. Any fixture imposes an arbitrary and finite spacing between the DUT and the ground plane. In general, the measured impedance will depend on this. There is no "correct" answer. 2. The N connectors should be male and female and you should use a 2 port type N calibration kit. 3. You used the common short cut of a through cal instead of a full 2 port cal. This means that you are not calibrating out source and load mismatch. A common short cut to fix this is to put pads around the DUT. This can work fairly well. The designer of the network analyzer can recognize that the through cal shortcut is popular and accomodate the user by going to a lot of trouble to provide well matched ports. Or not. It turns out that getting well matched ports translates into massive padding. This has the disadvantage of loss of dynamic range. Then there is the question of allowing the user to turn the internal padding on and off. What if he turns it off and then proceeds to do a through cal anyway? There is no simple answer to this discussion. If the environment seen by the DUT in the test fixture is not the same as it sees in the application, then the measurement is just an approximation. It is entirely possible that you will get results accurate enough for ham radio since you are working at HF. But the technique would not be deemed completely rigorous by metrologists. Rick N6RK ___ UR RST IS ... ... ..9 QSB QSB - hw? BK
Re: Topband: S21 impedance measurements
All, I guess it's time for me to put up my "common mode choke" test technique for all to shoot at. I have a HP 4815A Vector Z meter, a N2PK VNA, and a HP 8753C VNA. I have all the probe adapters for the Z meter, and I have been bitten by the small amount of stray C that you just can't eliminate (but you should be able to calculate out). I have finally decided that my standard test is based on the following: I made up a board out of .062 FR-4 that is approximately 6" across (and about 4" wide). I cut three 50 Ohm microstrip lines full width across the 6" dimension. I soldered an N connector on each end (6 connectors total). So now I have 3 equal-length 50 Ohm runs spaced about an inch apart. One run I left alone, and that's my THRU calibration path. The second run got a 0.1 inch (or so) gap cut in the middle; I soldered various chip resistors across this gap (in series with the run), and I use this for reference purposes. The third run is almost completely removed except for about 1/2" pad right at each N connector. I soldered a 2" or so piece of wire with an alligator clip to each pad, so that the tips of the alligator clips can be just clipped together in the middle of the board ( making a thru circuit). Now the way I use this is: I calibrate S21 with a 6 or 10 dB pad on each end of the THRU run. Then I move the pads to the run with the resistor gap, and I collect a family of S21 curves with different resistors soldered in the gap - I chose 1k, 2.2k, 3.3k and 4.7k. I only have to do this once. Then, I move the attenuators to the third run with the alligator clips. I clip these on the CM choke I'm evaluating, measure S21, and compare the resulting plot to the previously-taken family of resistor plots and try to make a determination of where the measured choke falls, "resistance" wise. I have been busy over the last few months making chokes for 3 pairs of yagis - I'm putting up 4/4 on 20, 5/5 on 15 and 5/5 on 10 this summer - so I have been taking a *LOT* of data. I am convinced that I can tell if a choke is better on 15 than on 20, for instance, and I'm convinced that I can tell if this number of turns on this many cores is better than the last one I tried. I am not so convinced that I can put an absolute number on the choking resistance of the units that I'm evaluating. I am pretty sure the units I'm winding up with are pretty darned good, compared to some relative measurements I have made on some commercial stuff. I know I get the same results with the N2PK and the 8753C. 6 dB pads are good enough - the data is identical with 10 dB pads. But, I also consistently get lower measurements with the Z-meter; for instance, if I conclude that a particular choke has approximately 3k choking impedance based on VNA measurements, I would probably get 1.5k or so with the Z-meter. (Again, it may be the strays in the test fixture thing). The VNA technique has practical appeal to me and,as observed by W8JI (I think), we often don't and can't know the CM Z in the circuit we're choking. So I have concluded that, since this technique is stable and repeatable, it's what I'm going to hang my hat on. Comments, please? 73, geo - n4ua On Sat, Jul 14, 2012 at 3:56 PM, Richard (Rick) Karlquist < rich...@karlquist.com> wrote: > > > On 7/14/2012 11:14 AM, pfizenmayer wrote: > > > Which leads me to ask - what is wrong with measuring the attenuation > with a > > two port VNA with the choke simply in series between port 1 and port 2 > ?(of > > course calibrating out any cables if used) This is basically a "VI" > > measurement and seems to me to give valid measure of the atteuation if > the > > > Hank K7HP > > I have been doing this for over 30 years, and have taught many > others to do it. However, what is "wrong" with the technique > is that network analyzers are only specified in terms of an > insertable coaxial DUT with defined 50 ohm reference planes. > It is up to the user to fixture his actual DUT to look like > this. The fixturing problem is the "final frontier" of > measurement science. The experts don't always agree on what > is the "correct" fixturing modality. Having said that, it > is still plenty useful for ham radio. > > A minor issue is that the user has to be able to convert > between the complex variables of S21 and Z. This doesn't > seem to be built in to any NA's that I have seen. Sometimes, > you can do user math and add the capability. > > The dual of this technique is useful for very low impedance > DUT's. In this case, you shunt the through line with the DUT. > Watch out for ground loops. > > Rick N6RK > > ___ > UR RST IS ... ... ..9 QSB QSB - hw? BK > ___ UR RST IS ... ... ..9 QSB QSB - hw? BK
Re: Topband: S21 impedance measurements
On 7/14/2012 11:14 AM, pfizenmayer wrote: > Which leads me to ask - what is wrong with measuring the attenuation with a > two port VNA with the choke simply in series between port 1 and port 2 ?(of > course calibrating out any cables if used) This is basically a "VI" > measurement and seems to me to give valid measure of the atteuation if the If one wishes to look at this as a simple voltage divider, then the end of the souce cable should be terminated in 50 Ohms, assuming that the unknown impedance is substantially higher. If there is a capacitance from the choke to the ground (true most of the time), then the problem is not so simple anymore, and the circuit should be considered to have a PI (ot T) topology, and be measured accordingly. And if the choke length is an appreciable part of the wavelength (also true most of the time), then the problem becomes even more complex... In both cases it becomes impossible to uniquely define the "choke impedance". Fortunately enough, the perfectly adequate choking action may still exist, regardless of the impossibility to characterize it uniquely. That is, choke operation becomes dependent on surrounding circuits. 73, Sinisa YT1NT, VE3EA ___ UR RST IS ... ... ..9 QSB QSB - hw? BK
Re: Topband: S21 impedance measurements
On 7/14/2012 11:14 AM, pfizenmayer wrote: > Which leads me to ask - what is wrong with measuring the attenuation with a > two port VNA with the choke simply in series between port 1 and port 2 ?(of > course calibrating out any cables if used) This is basically a "VI" > measurement and seems to me to give valid measure of the atteuation if the > Hank K7HP I have been doing this for over 30 years, and have taught many others to do it. However, what is "wrong" with the technique is that network analyzers are only specified in terms of an insertable coaxial DUT with defined 50 ohm reference planes. It is up to the user to fixture his actual DUT to look like this. The fixturing problem is the "final frontier" of measurement science. The experts don't always agree on what is the "correct" fixturing modality. Having said that, it is still plenty useful for ham radio. A minor issue is that the user has to be able to convert between the complex variables of S21 and Z. This doesn't seem to be built in to any NA's that I have seen. Sometimes, you can do user math and add the capability. The dual of this technique is useful for very low impedance DUT's. In this case, you shunt the through line with the DUT. Watch out for ground loops. Rick N6RK ___ UR RST IS ... ... ..9 QSB QSB - hw? BK
