[time-nuts] Re: Testing a GPS mag mount antenna
Skipp, Several responders have correctly referred to the "noise floor", but I believe that none have said what level that is. And it's not trivial to say so, either, because it is dependent on the extent to which the antenna under test sees the sky and ignores blackbody radiation from the ground. An ideal GPS antenna would see only the sky, but not the ground at all. But none are ideal in this regard unless placed on a large level metallic "ground plane". It may happen that in this era of higher-powered L1 transmitters aboard some of the satellites, their total noise power spectral density might exceed cold sky noise by enough to be obvious on a spectrum analyzer looking at the output of an active GPS antenna. But I've saved the good news for last. The noise PSD of the ground as sensed by a passive antenna is about -114 dBm in 1 MHz BW, or -174 dBm in 1 Hz BW. So here is what I suggest for your antenna functional tests: Mount the antenna under test on the end of an insulating horizontal rod, which can be rotated to make the antenna face either the ground or the sky. Examine the spectrum on a span setting of several MHz, and see if the noise level over a BW of a few MHz is higher with the antenna pointed down than when pointed up. Oh, I forgot to mention: for tests like this the antenna should be supported a few feet above the ground level, so that input noise of the LNA does not get reflected off the ground and back into the antenna to an appreciable extent. It also helps if the ground is very rough, like maybe tall grass. What you may see with the antenna looking at the ground is blackbody radiation from the ground being filtered by the input filter of the LNA- and that filter hump is indicative (but not yet proof) of the antenna's working. When the antenna faces the sky, the ground noise hump should disappear and be replaced by the spectrum of the combined signals from all the GPS satellites above you. This is all provided the cascaded combination of the GPS antenna's LNA and the SA's noise floor is is very quiet. With practical antennas and SA's, this is unlikely to ever yield a rise of more than a very few dB if that much. So, to see this, you should setup the SA so that you get an average power spectrum, meaning using lots of video filtering on an old-fashioned swept analyzer, or trace averaging of many traces on an FFT-type SA. The required averaging time to get good smoothing of the noise levels will be minimized by using as wide a resolution bandwidth as you can, but always less than the BW of the spread-spectrum GPS signals or the antenna's inpuy filter. But you don't want to go too wide, either, for you will lose the frequency resolution that may let you distinguish between the antenna's filter hump shape and that spectrum comprising the GPS signals in view at the time. I'd suggest starting with a BW of around 100 kHz as a fair compromise. For more on this aspect of things, look up "radiometer equation" on the web- we'll make a radio astronomer of you yet :-) BTW, it will likely be needed to add some additional gain between the antenna and the SA's input. Many of the older SA's have really rotten NF, like 30 dB or worse. DanaK8YUM On Fri, Aug 20, 2021 at 4:33 PM Gerhard Hoffmann < g...@hoffmann-hochfrequenz.de> wrote: > > Am 20.08.21 um 22:14 schrieb skipp isaham via time-nuts: > > > > Hello to the Group, > > > > I picked a box of used (removed from commercial radio APRS type > > service) mobile/vehicle GPS Antennas. They are mostly the classic > > square molded, black plastic magnetic mount type, about the size of a > > bar of soap when cut to square (2/3 the size of a large bar of soap). > > The coax length terminates to an SMA connector. > > > > I'd like to use some of these unmarked (obviously also unbranded) > > antennas for a few projects. The initial goal is to first set up a > > system to test (good/bad) the antennas, then determine their operation > > voltage, I suspect them to be 3.x to 5.x Volts. They are probably not > > "new enough" to be the type to operate of 3 or 5 Volts DC. > > > > For testing... I purchased a nice NOS Mini-Circuits bias-Tee. > > > > The intent is to now operate the antenna through the bias-tee, in to > > an analyzer. I would initially start the bias supply off at 3 Vdc, > > while also monitoring current. If I don't receive an adequate/valid > > GPS signal off air, I could increase the bias up to 5 Vdc (rinse/repeat). > > > > Should I be able to "see something" on or around the GPS frequency > > other than what I suspect will be something visual looking like a > > noise/pulse source/signal? > > You won't see anything interesting on the spectrum analyzer. The > signal(s) look like noise, and they are buried in the real noise. > > Deeply! In a real receiver, there are probably just 1 bit ADCs, aka > comparators, and the receiver needs to know the pseudo random > > polynomial that was used to blow up the bandwidth of the 50 baud
[time-nuts] Re: Testing a GPS mag mount antenna
The first generation GPS were, IIRC, 50 Watts, +17dBW EIRP. The latest one are higher power at up to 200W, or 23dBW EIRP If you go through the link budget calculations, and assume a receiver with a good noise figure, you can show that with a ground station antenna of more than about 36dBi gain you can see the GPS signal above receiver noise.That gain corresponds to a dish of about 4.5 metres diameter at 1575MHz. Bigger than one most radio amateurs are likely to fit in their back garden, although there are a few moonbouncers around the World with dishes that big.Quite a few have 3m dishes. Andy www.g4jnt.com On Fri, 20 Aug 2021 at 22:33, Gerhard Hoffmann wrote: > > Am 20.08.21 um 22:14 schrieb skipp isaham via time-nuts: > > > > Hello to the Group, > > > > I picked a box of used (removed from commercial radio APRS type > > service) mobile/vehicle GPS Antennas. They are mostly the classic > > square molded, black plastic magnetic mount type, about the size of a > > bar of soap when cut to square (2/3 the size of a large bar of soap). > > The coax length terminates to an SMA connector. > > > > I'd like to use some of these unmarked (obviously also unbranded) > > antennas for a few projects. The initial goal is to first set up a > > system to test (good/bad) the antennas, then determine their operation > > voltage, I suspect them to be 3.x to 5.x Volts. They are probably not > > "new enough" to be the type to operate of 3 or 5 Volts DC. > > > > For testing... I purchased a nice NOS Mini-Circuits bias-Tee. > > > > The intent is to now operate the antenna through the bias-tee, in to > > an analyzer. I would initially start the bias supply off at 3 Vdc, > > while also monitoring current. If I don't receive an adequate/valid > > GPS signal off air, I could increase the bias up to 5 Vdc (rinse/repeat). > > > > Should I be able to "see something" on or around the GPS frequency > > other than what I suspect will be something visual looking like a > > noise/pulse source/signal? > > You won't see anything interesting on the spectrum analyzer. The > signal(s) look like noise, and they are buried in the real noise. > > Deeply! In a real receiver, there are probably just 1 bit ADCs, aka > comparators, and the receiver needs to know the pseudo random > > polynomial that was used to blow up the bandwidth of the 50 baud message > to some MHz in order to reverse that effect. > > And you have to know which part of the polynomial is currently used. > This is done by search & correlation tries. Sloppy wording, I know. > > Only when that reversal is done you have a positive signal/noise ratio. > GPS receivers are 95% math, the rest is electronics > > and packaging. > > You may see a noise molehill at the nominal frequencies, but that means > only that the pre-amplifier and maybe some filtering works. > > And there is a hefty preamplifier to make up for 5 meters of El Cheapo > RG-174 coax. The GPS pseudo-noise is only > > 1 promille of that what you see. > > Disclaimer: Last time I was involved in this was with the Plessey > 1010/2010 chip set in a previous life, for GPS/Glonass combined, > > which was new then. > > > Gerhard, DK4XP > > > > > > > I don't yet have a GPS receiver with a signal strength indicator, else > > I could probably not have to send this post. But, I do have access to > > an analyzer, I bought the bias-tee (was reasonable in price) and I'd > > like to test these 30 antennas to see if they work and determine if > > 3.x volts is enough... or 5 volts is required. > > > > Thank you in advance for any replies and comments. > > > > cheers, > > > > skipp > > > > skipp025 at yahoo.com > > ___ > > time-nuts mailing list -- time-nuts@lists.febo.com -- To unsubscribe > > send an email to time-nuts-le...@lists.febo.com > > To unsubscribe, go to and follow the instructions there. > ___ > time-nuts mailing list -- time-nuts@lists.febo.com -- To unsubscribe send > an email to time-nuts-le...@lists.febo.com > To unsubscribe, go to and follow the instructions there. ___ time-nuts mailing list -- time-nuts@lists.febo.com -- To unsubscribe send an email to time-nuts-le...@lists.febo.com To unsubscribe, go to and follow the instructions there.
[time-nuts] Re: Testing a GPS mag mount antenna
Am 20.08.21 um 22:14 schrieb skipp isaham via time-nuts: Hello to the Group, I picked a box of used (removed from commercial radio APRS type service) mobile/vehicle GPS Antennas. They are mostly the classic square molded, black plastic magnetic mount type, about the size of a bar of soap when cut to square (2/3 the size of a large bar of soap). The coax length terminates to an SMA connector. I'd like to use some of these unmarked (obviously also unbranded) antennas for a few projects. The initial goal is to first set up a system to test (good/bad) the antennas, then determine their operation voltage, I suspect them to be 3.x to 5.x Volts. They are probably not "new enough" to be the type to operate of 3 or 5 Volts DC. For testing... I purchased a nice NOS Mini-Circuits bias-Tee. The intent is to now operate the antenna through the bias-tee, in to an analyzer. I would initially start the bias supply off at 3 Vdc, while also monitoring current. If I don't receive an adequate/valid GPS signal off air, I could increase the bias up to 5 Vdc (rinse/repeat). Should I be able to "see something" on or around the GPS frequency other than what I suspect will be something visual looking like a noise/pulse source/signal? You won't see anything interesting on the spectrum analyzer. The signal(s) look like noise, and they are buried in the real noise. Deeply! In a real receiver, there are probably just 1 bit ADCs, aka comparators, and the receiver needs to know the pseudo random polynomial that was used to blow up the bandwidth of the 50 baud message to some MHz in order to reverse that effect. And you have to know which part of the polynomial is currently used. This is done by search & correlation tries. Sloppy wording, I know. Only when that reversal is done you have a positive signal/noise ratio. GPS receivers are 95% math, the rest is electronics and packaging. You may see a noise molehill at the nominal frequencies, but that means only that the pre-amplifier and maybe some filtering works. And there is a hefty preamplifier to make up for 5 meters of El Cheapo RG-174 coax. The GPS pseudo-noise is only 1 promille of that what you see. Disclaimer: Last time I was involved in this was with the Plessey 1010/2010 chip set in a previous life, for GPS/Glonass combined, which was new then. Gerhard, DK4XP I don't yet have a GPS receiver with a signal strength indicator, else I could probably not have to send this post. But, I do have access to an analyzer, I bought the bias-tee (was reasonable in price) and I'd like to test these 30 antennas to see if they work and determine if 3.x volts is enough... or 5 volts is required. Thank you in advance for any replies and comments. cheers, skipp skipp025 at yahoo.com ___ time-nuts mailing list -- time-nuts@lists.febo.com -- To unsubscribe send an email to time-nuts-le...@lists.febo.com To unsubscribe, go to and follow the instructions there. ___ time-nuts mailing list -- time-nuts@lists.febo.com -- To unsubscribe send an email to time-nuts-le...@lists.febo.com To unsubscribe, go to and follow the instructions there.
[time-nuts] Re: Testing a GPS mag mount antenna
Hi The GPS signals are spread spectrum transmissions. If you look for them with a normal spectrum analyzer they are 10’s of db’s below the noise floor. Yes, that’s a bit weird, but it does work. Your gizmos may or may not include a preamp. First thing I’d do is take a look at current into the device vs supply voltage over at least the 3 to 5V range. They should pull 10ma or more. If they have a preamp (and it has reasonable gain), you should see the noise from the preamp come up as the power comes on. As an example, a 20 db preamp should give you about a 20 db “noise hump” on an analyzer that can see down to the noise floor. Have fun !!! Bob > On Aug 20, 2021, at 4:14 PM, skipp isaham via time-nuts > wrote: > > > Hello to the Group, > > I picked a box of used (removed from commercial radio APRS type service) > mobile/vehicle GPS Antennas. They are mostly the classic square molded, black > plastic magnetic mount type, about the size of a bar of soap when cut to > square (2/3 the size of a large bar of soap). The coax length terminates to > an SMA connector. > > I'd like to use some of these unmarked (obviously also unbranded) antennas > for a few projects. The initial goal is to first set up a system to test > (good/bad) the antennas, then determine their operation voltage, I suspect > them to be 3.x to 5.x Volts. They are probably not "new enough" to be the > type to operate of 3 or 5 Volts DC. > > For testing... I purchased a nice NOS Mini-Circuits bias-Tee. > > The intent is to now operate the antenna through the bias-tee, in to an > analyzer. I would initially start the bias supply off at 3 Vdc, while also > monitoring current. If I don't receive an adequate/valid GPS signal off air, > I could increase the bias up to 5 Vdc (rinse/repeat). > > Should I be able to "see something" on or around the GPS frequency other than > what I suspect will be something visual looking like a noise/pulse > source/signal? > > I don't yet have a GPS receiver with a signal strength indicator, else I > could probably not have to send this post. But, I do have access to an > analyzer, I bought the bias-tee (was reasonable in price) and I'd like to > test these 30 antennas to see if they work and determine if 3.x volts is > enough... or 5 volts is required. > > Thank you in advance for any replies and comments. > > cheers, > > skipp > > skipp025 at yahoo.com > ___ > time-nuts mailing list -- time-nuts@lists.febo.com -- To unsubscribe send an > email to time-nuts-le...@lists.febo.com > To unsubscribe, go to and follow the instructions there. ___ time-nuts mailing list -- time-nuts@lists.febo.com -- To unsubscribe send an email to time-nuts-le...@lists.febo.com To unsubscribe, go to and follow the instructions there.
[time-nuts] Testing a GPS mag mount antenna
Hello to the Group, I picked a box of used (removed from commercial radio APRS type service) mobile/vehicle GPS Antennas. They are mostly the classic square molded, black plastic magnetic mount type, about the size of a bar of soap when cut to square (2/3 the size of a large bar of soap). The coax length terminates to an SMA connector. I'd like to use some of these unmarked (obviously also unbranded) antennas for a few projects. The initial goal is to first set up a system to test (good/bad) the antennas, then determine their operation voltage, I suspect them to be 3.x to 5.x Volts. They are probably not "new enough" to be the type to operate of 3 or 5 Volts DC. For testing... I purchased a nice NOS Mini-Circuits bias-Tee. The intent is to now operate the antenna through the bias-tee, in to an analyzer. I would initially start the bias supply off at 3 Vdc, while also monitoring current. If I don't receive an adequate/valid GPS signal off air, I could increase the bias up to 5 Vdc (rinse/repeat). Should I be able to "see something" on or around the GPS frequency other than what I suspect will be something visual looking like a noise/pulse source/signal? I don't yet have a GPS receiver with a signal strength indicator, else I could probably not have to send this post. But, I do have access to an analyzer, I bought the bias-tee (was reasonable in price) and I'd like to test these 30 antennas to see if they work and determine if 3.x volts is enough... or 5 volts is required. Thank you in advance for any replies and comments. cheers, skipp skipp025 at yahoo.com ___ time-nuts mailing list -- time-nuts@lists.febo.com -- To unsubscribe send an email to time-nuts-le...@lists.febo.com To unsubscribe, go to and follow the instructions there.
[time-nuts] Re: Isotemp OCXO question
The chip will still work. Its just a AM receiver and you get the AM timecode bits out. It has no value as some sort of reference without removing the BPSK signal that NIST put on. Lots of posts on that stuff back in 2012-2015. Good luck. Paul WB8TSL On Thu, Aug 19, 2021 at 9:09 PM Robert DiRosario wrote: > I have a MAS6180C AM receiver chip, on a board with a few other parts to > complete the receiver. I did not make the board, it came from > Universal-Solder Electronics in Canada. The date on the chip datasheet > is 2014 and on the receiver board 2016, so after NIST messed up WWVB in > 2012. > > Robert > > > On 08/19/2021 07:23 PM, Bob kb8tq wrote: > > Hi > > > > It’s a good bet that whatever the spec on that Isotemp OCXO, it’s way > better in terms > > of temperature and aging then the DS3231. Is it still on frequency > (however many years > > later …..) who knows …. > > > > Many of the “time oriented” WWVB devices stopped working when they put > in the new > > modulation scheme. It’s a pretty good bet that this applies to the > device you have. > > > > Bob > > > >> On Aug 19, 2021, at 6:55 PM, Robert DiRosario > wrote: > >> > >> I got a Trak Systems "Time Code Translator" from ebay. It's a 1U box > with large LEDs for DOY and H/M/S that translates IRIG-A to NASA-36 time > code. I plan on using the case for my WWVB clock. > >> > >> Unexpectedly it has an Isotemp OCXO in it, model OCXO59-11-2, frequency > marked as 1.000 MHz The Isotemp website is more or less dead, it has no > information on it. Does anyone have any information on this model, like > how accurate it is? It has only three wires, which I assume are power, > ground and output, with no EFC input. > >> > >> One thing that I'm sill note sure about is what to do when the receiver > is not receiving WWVB. I was thinking of using something like the DS3231 > RTC module. If this OCXO is better, I may use it. > >> > >> Thanks > >> > >> Robert > >> ___ > >> time-nuts mailing list -- time-nuts@lists.febo.com -- To unsubscribe > send an email to time-nuts-le...@lists.febo.com > >> To unsubscribe, go to and follow the instructions there. > > ___ > > time-nuts mailing list -- time-nuts@lists.febo.com -- To unsubscribe > send an email to time-nuts-le...@lists.febo.com > > To unsubscribe, go to and follow the instructions there. > ___ > time-nuts mailing list -- time-nuts@lists.febo.com -- To unsubscribe send > an email to time-nuts-le...@lists.febo.com > To unsubscribe, go to and follow the instructions there. ___ time-nuts mailing list -- time-nuts@lists.febo.com -- To unsubscribe send an email to time-nuts-le...@lists.febo.com To unsubscribe, go to and follow the instructions there.
[time-nuts] Re: Isotemp OCXO question
Hi OCXO59 package. Likely the 11th OEM version in that package done in 2002. Specs could be just about anything. Like pretty much all oscillator companies, they would build to the OEM’s custom spec. A few OEM’s want their name on the part ( Trimble, Efratom and Symmetericom come to mind ) most seem to be ok with the OCXO manufacturer’s name being on it. Bob > On Aug 19, 2021, at 10:12 PM, Robert DiRosario wrote: > > This is just a little "fun" project. I"m sure any of my GPS receivers will > be more accurate by several orders of magnitude. > > So does anyone know how to "decode" the Isotemp model numbers, assuming there > is some pattern to them? > > Robert > > > On 08/19/2021 09:19 PM, Bob kb8tq wrote: >> Hi >> >> The issue you run into is that the fancy devices tried to derive information >> from >> the phase of the WWVB signal. With an “AM only” receiver accuracy in the 10’s >> (or 100’s … yikes ….) of ms was pretty common. With a phase oriented >> approach, >> you could get into the 100’s of us. Indeed there is a lot of fine print >> involved with >> any WWVB claims. >> >> The change over did not impact the typical WWVB watch or an AM based >> receiver. >> It very much messed up any of the fancy timing stuff. >> >> Bob >> >>> On Aug 19, 2021, at 9:09 PM, Robert DiRosario wrote: >>> >>> I have a MAS6180C AM receiver chip, on a board with a few other parts to >>> complete the receiver. I did not make the board, it came from >>> Universal-Solder Electronics in Canada. The date on the chip datasheet is >>> 2014 and on the receiver board 2016, so after NIST messed up WWVB in 2012. >>> >>> Robert >>> >>> >>> On 08/19/2021 07:23 PM, Bob kb8tq wrote: Hi It’s a good bet that whatever the spec on that Isotemp OCXO, it’s way better in terms of temperature and aging then the DS3231. Is it still on frequency (however many years later …..) who knows …. Many of the “time oriented” WWVB devices stopped working when they put in the new modulation scheme. It’s a pretty good bet that this applies to the device you have. Bob > On Aug 19, 2021, at 6:55 PM, Robert DiRosario wrote: > > I got a Trak Systems "Time Code Translator" from ebay. It's a 1U box > with large LEDs for DOY and H/M/S that translates IRIG-A to NASA-36 time > code. I plan on using the case for my WWVB clock. > > Unexpectedly it has an Isotemp OCXO in it, model OCXO59-11-2, frequency > marked as 1.000 MHz The Isotemp website is more or less dead, it has no > information on it. Does anyone have any information on this model, like > how accurate it is? It has only three wires, which I assume are power, > ground and output, with no EFC input. > > One thing that I'm sill note sure about is what to do when the receiver > is not receiving WWVB. I was thinking of using something like the DS3231 > RTC module. If this OCXO is better, I may use it. > > Thanks > > Robert > ___ > time-nuts mailing list -- time-nuts@lists.febo.com -- To unsubscribe send > an email to time-nuts-le...@lists.febo.com > To unsubscribe, go to and follow the instructions there. ___ time-nuts mailing list -- time-nuts@lists.febo.com -- To unsubscribe send an email to time-nuts-le...@lists.febo.com To unsubscribe, go to and follow the instructions there. >>> ___ >>> time-nuts mailing list -- time-nuts@lists.febo.com -- To unsubscribe send >>> an email to time-nuts-le...@lists.febo.com >>> To unsubscribe, go to and follow the instructions there. >> ___ >> time-nuts mailing list -- time-nuts@lists.febo.com -- To unsubscribe send an >> email to time-nuts-le...@lists.febo.com >> To unsubscribe, go to and follow the instructions there. > ___ > time-nuts mailing list -- time-nuts@lists.febo.com -- To unsubscribe send an > email to time-nuts-le...@lists.febo.com > To unsubscribe, go to and follow the instructions there. ___ time-nuts mailing list -- time-nuts@lists.febo.com -- To unsubscribe send an email to time-nuts-le...@lists.febo.com To unsubscribe, go to and follow the instructions there.
[time-nuts] Re: Isotemp OCXO question
Internet Archive to the rescue! https://web.archive.org/web/19990506093727/http://www.isotemp.com/ocxo59.htm According to that page, the OCXO59 series is available in 5 MHz to 50 MHz... So a 1MHz version may have been an OEM version. >From a later archive of their site, here's a PDF datasheet for a 50 MHz OCXO59 series oscillator which includes a drawing for the 59 series with a pinout: http://www.isotemp.com/wp-content/uploads/2011/06/Legacy59-21.pdf On Thu, Aug 19, 2021 at 3:56 PM Robert DiRosario wrote: > I got a Trak Systems "Time Code Translator" from ebay. It's a 1U box > with large LEDs for DOY and H/M/S that translates IRIG-A to NASA-36 time > code. I plan on using the case for my WWVB clock. > > Unexpectedly it has an Isotemp OCXO in it, model OCXO59-11-2, frequency > marked as 1.000 MHz The Isotemp website is more or less dead, it has no > information on it. Does anyone have any information on this model, like > how accurate it is? It has only three wires, which I assume are power, > ground and output, with no EFC input. > > One thing that I'm sill note sure about is what to do when the receiver > is not receiving WWVB. I was thinking of using something like the > DS3231 RTC module. If this OCXO is better, I may use it. > > Thanks > > Robert > ___ > time-nuts mailing list -- time-nuts@lists.febo.com -- To unsubscribe send > an email to time-nuts-le...@lists.febo.com > To unsubscribe, go to and follow the instructions there. > ___ time-nuts mailing list -- time-nuts@lists.febo.com -- To unsubscribe send an email to time-nuts-le...@lists.febo.com To unsubscribe, go to and follow the instructions there.
