[eagle] Re: 70 cm Receiver Frequency Stability and One More Glitch
bill at hsmicrowave.com
Mon Jul 2 23:36:11 PDT 2007
Yeh after looking at the schematic - I was afraid that might happen but
didn't know what sort of isolation the logic switch would provide.
The 10 MHz circuit I used in the S2 concept downverter shuts down the
Vcc to the internal 10 MHz when it detects the presence of the external
Perhaps John can look at the circuit I used and determine if its useful.
Regards...Bill - N6GHz
Juan Rivera wrote:
> 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
> 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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