Re: a simple spur fix

MadRadioModder
 

I wondered about the cross-talk in the Si5351.  There have been a number of papers written on it being problematic… to the point of suggesting using only one channel of the Si5351 but multiple parts if you need more frequencies.  Channel separation in some cases is only in the 30ish dB range…

 

 

From: BITX20@groups.io [mailto:BITX20@groups.io] On Behalf Of Ashhar Farhan
Sent: Friday, November 9, 2018 9:35 AM
To: bitx20@groups.io
Subject: [BITX20] a simple spur fix

 

so, there is one spur fix that is now consistently working for me.

among rhe solutions, i was looking for one that would be easy to apply.

first, the distortion in the 45 mhz amp is creating harmonic distortion. so a 0.3uh in series with a 10 pf is used across TP13 (output of the 45 MHz IF amp going to the front end mixer). 8 turns on T30-6 gives you 300nh.

second, there is a cross talk inside the Si5351 where the 12 mhz from the bfo leaks into the local oscillator. A 5uh in series with a 47 pf across C202 of the LPF will suppress it. 35 turns on T30-6 gives you 5uh.

- f

 


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