Detect GPS Satellites?

[KG9NZ]

I'm wondering if it would be possible to detect GPS satellites using "standard" receiver equipment. Here is what I propose. Take a scanner with 10.7 MHz IF output and tune it to the GPS frequency. Take the IF output and mix it (say, using a SA602 mixer) with the 1023kHz sequence for an overhead satellite (determined using a satellite tracking program). That sequence can be generated using a crystal oscillator, shift register, and a few gates. Connect a SW receiver to the output of the mixer (tuned to 10.7 MHz) and hear the 50Hz data from the satellite. Maybe even decode it using a sound card. I have the equipment necessary to try this. I'm curious as to whether anyone else has tried something similar, as well as your thoughts on whether this is likely to work or not.

Thanks,
Frank

[trixwagen]

Yeah... I think Geordi tried that same trick in Star Trek to disable the Borg navigation system..

[KC0QNB]

WHY?,. just buy a gps receiver and be done with it, you can then do all kind of cool things with your computer/gps combo

[jon_k]

Originally Posted by KC0QNB

WHY?,. just buy a gps receiver and be done with it, you can then do all kind of cool things with your computer/gps combo

Why?

For electronic experimentation and the reward of building something and making it work.

Sounds like a fun project. I don't know enough to do it myself, but if I did, I'd be all over it.

I just know enough to use a 555 timer circuit, pots, and a relay to make a delayed off-timer.

[slicerwizard]

Originally Posted by KG9NZ

I'm wondering if it would be possible to detect GPS satellites using "standard" receiver equipment. Here is what I propose. Take a scanner with 10.7 MHz IF output and tune it to the GPS frequency.

Do you have a scanner that can pick up –160dBw signals?

[KG9NZ]

Originally Posted by slicerwizard

Do you have a scanner that can pick up –160dBw signals?

Thanks for the reply. I have an Icom PCR-1500 which has a sensitivity of 5uV at that frequency. That would be -93dBm. I have a preamp with 22dB gain specified at this frequency. That would give me -125Bbm, or -155dbW. I have a homemade helical antenna that is supposed to have a 10dBi gain. However, I suspect the actual gain is going to be less due to the homemade construction. If it is 5dBi, that would put me right at receiving -160dbW. But yes, I agree it would be very close. Maybe I could use an active GPS antenna instead.

Frank

[slicerwizard]

Originally Posted by KG9NZ

I have an Icom PCR-1500 which has a sensitivity of 5uV at that frequency. That would be -93dBm. I have a preamp with 22dB gain specified at this frequency. That would give me -125Bbm, or -155dbW.

More like -115dBm.

Your preamp can't amplify what it can't hear and I doubt it would hear a GPS signal.

I'd go with an amplified GPS antenna. 28 dB gain seems to be typical for a good one. It still isn't enough to drive your deaf receiver. I guess you could try sticking your preamp between them, but it sounds sketchy.

[frankh]

If you take a look at this it's probably do able, but you may need some more gear. Good luck, and here's the link http://www.rfspace.com/Gallery.html#11

[KG9NZ]

Originally Posted by frankh

If you take a look at this it's probably do able, but you may need some more gear. Good luck, and here's the link http://www.rfspace.com/Gallery.html#11

Thanks. 3 foot dish! That's going to be a bit difficult for me. Especially given that the dish will have a fairly narrow focus, and GPS satellites (unlike geosynchronous) are constantly moving. But maybe I can use an active GPS antenna instead.

Frank

[Cowthief]

Hello.

Buy one of the really old GPS radios, an early sony marine model will work.
This is a radio with an active antenna and preselector inside a radome with an IF around 45 MHz.
At that point it is run into another IF and detected, a single board.
The rest is also single circuits, only in the computation section are the custom IC.
Very simple by todays standards.