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

Jim Sanford wb4gcs at amsat.org
Tue Jul 3 15:26:50 PDT 2007


Bill:
As I understand the functionality you have in the S2 receiver in this 
regard, I LIKE it.

Thanks & 73,
Jim
wb4tgcs at amsat.org


Bill Ress wrote:

>Hi Juan,
>
>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 
>10 MHz.
>
>Perhaps John can look at the circuit I used and determine if its useful.
>
>Regards...Bill - N6GHz
>
>Juan Rivera wrote:
>  
>
>>All,
>>
>>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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>
>  
>
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