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 > <time-nuts@lists.febo.com> 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.
