[time-nuts] Distance between GPS Antenni

[lists at lazygranch.com]

I had my doubts it could be sniffed as well, but it was a topic on usenet and I had all the gear. 

Just as a FYI, you can get portable L-band spectrum analyzers relatively cheaply since they are commonly used in satellite work. If you go on ebay, the avcom PSA-45 goes for $300. They are pulled from an old government project and lived in racks. They are digital since there is no sweep rate that I can see. There are a few persistance options including infinite. 

This is not HP quality. Just cheap and dirty to have a look see. I rebuilt the battery pack on mine for about $50. However, the unit seems to draw on the pack when it is not in use so it tends to be dead in 3 days. If you use it right away, you get the rated operating time. They are daylight readable and very light, basically field instrumentation rather than lab gear. 


------Original Message------
From: Philip Pemberton
To: lists at lazygranch.com
To: Discussion of precise time and frequency measurement
Subject: Re: [time-nuts] Distance between GPS Antenni
Sent: Dec 18, 2011 10:48 AM

On 18/12/11 16:44, lists at lazygranch.com wrote:
> I did manage to see the
> actual GPS signal on the spectrum analyzer with the amplified
> antenna. But like I said, I never sniffed an local oscillator
> leakage.

I doubt you would -- the level of LO -> RF leakage in the mixer should 
be pretty minimal, and the MMIC amplifiers used in most active GPS 
antennas are (as I understand it) essentially a "one way path" for RF. 
The RF BPF will probably do a very good job of killing LO leakage, too.

If tracking down an unlicensed TV using LO leakage is "hard", then 
tracking down a GPS receiver would probably be like trying to find a 
bone needle in a field of haystacks.

-- 
Phil.
lists at philpem.me.uk
http://www.philpem.me.uk/