[eagle] 70 cm Receiver Frequency Stability and One More Glitch

Juan Rivera juan-rivera at sbcglobal.net
Mon Jul 2 22:51:03 PDT 2007



Here's a plot of frequency drift in the 70 cm Receiver - first on internal
reference, then on external reference:



The first part of the plot is with the receiver and the signal generator set
to 435.500000 MHz on internal reference.  You can see the slow steady drift
upwards of about 15 Hz over a period of about 5 minutes.  Then I
reinitialized the receiver for the external reference.  It locked right up
and the output was exactly 10.700000 MHz where it stayed.


The most important thing I noticed is not on this graph.  With internal
reference selected, but while feeding 10 MHz into the external reference
input, (as it might be configured in flight) the two reference signals are
beating together.  It wasn't until I started listening to the output of the
receiver by patching it into a distribution amplifier so I can feed my
counter, the SDR-IQ, the TS-2000, and the HP 8566B all at once that I
noticed it.  The result is that the input signal is FM modulated by the beat
between the two reference oscillators.  I also noticed some unexplained
jumps in frequency that I have not yet been able to capture.  I'll dig into
this again when I have more time.


73, Juan



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