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 <[email protected]> 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 -- [email protected] -- To unsubscribe > > send an email to [email protected] > > To unsubscribe, go to and follow the instructions there. > _______________________________________________ > time-nuts mailing list -- [email protected] -- To unsubscribe send > an email to [email protected] > To unsubscribe, go to and follow the instructions there. _______________________________________________ time-nuts mailing list -- [email protected] -- To unsubscribe send an email to [email protected] To unsubscribe, go to and follow the instructions there.
