Hi:
One of the chirp receivers I worked with was connected to the audio output of a
shortwave receiver.
Since chirp transmitters sweep frequency (typically 2 to 30 MHz) you don't tune in the frequency domain but rather in
the time domain and compare to a GPS based 1 PPS.
This time difference can be easily converted to the distance between the chirp
transmitter and your antenna.
So the delay inside the shortwave receiver needs to be known in order to get accurate timing, in a similar manner to the
subject active GPS antenna.
http://www.prc68.com/I/RCS-5A.shtml <- general chirp stuff
The solution for the chirp receiver was to use a modulated RF signal into the shortwave receiver and compare the output
and input signals.
http://www.prc68.com/I/Chirp.shtml
This could be done for an active GPS antenna by square wave modulating a carrier at the L1 frequency and feeding the
antenna output to a detector.
The input signal level to the antenna will need to be as high as possible without damaging it, and maybe without
saturating the internal amplifier. If the output signal is still too small for the detector to have a useable output
and additional RF amplifier could be inserted after the active antenna bias-T and it's propagation delay subtracted for
the measured value.
PS This is a good application for a Tunnel (back) diode detector because they have very wide video bandwidth (fast rise
times).
http://www.prc68.com/I/Aertech.shtml#TDD
Mail_Attachment --
Have Fun,
Brooke Clarke
http://www.PRC68.com
http://www.end2partygovernment.com/2012Issues.html
http://www.prc68.com/I/DietNutrition.html
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