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Sotabeams DSP cw/SSB filter insertion rf in audio

Joel Trenalone
 

Hello All,
I have been slower adding features to my UBITX V5, and just inserted the Sotabeams Laserbeam CW in the high vol line before the volume pot. I added a .1 uf cap on the output of the filter on the recommendation of a previous post on this site and it wokrs really great on CW. I installed a switch to go between the boards digital CW filter and the wider SSB filter  I have NOT added a complete bypass of the filter, so the filter is always inline either in CW or SSB mode  


But I just transmitted SSB for the first time since filter insertion and now I’m getting my voice feeding through the speaker during transmit. I assume that rf is getting into the speaker amp. 


Anyone have this problem, and any advise on how to solve it?
thanks :),
Joel 
KD6AGW

Dennis Zabawa
 

Did you use shielded cable to and from the filter?  How close is the filter board to the uBITX board?

howard winwood G4GPF
 

I used shielded cable to and from the filter, board situated on left hand side of main board between the main board and the case side. I also used the soyabeans lm386 amp circuit with balanced inputs for final audio to speaker.

Joel Trenalone
 

Thanks Dennis,
the board is on the far left of the ubitx board. It’s not a big case so not much more room. I will replace the audio wire with shielded cables to see if it helps. 


Thanks Howard,
Since you us the Sotabeams lm386 circuit, does that mean you are bypassing the ubitx onboard lm386 portion of the circuit?

Also do you guys have the Sotabeams filter powered all the time, or is it unpowered during transmit?

howard winwood G4GPF
 

oops ! got carried away and forgot to mention it is all powered from the receiver power rail.

Dennis Zabawa
 

I am using the SOTABEAMS Variable filter.  I twisted the ground and power wires together and added a 10nF capacitor to keep the RF gremlins out.

Jack, W8TEE
 

I think their DSP filter is pretty good, too.

Jack, W8TEE

On Thursday, January 9, 2020, 7:45:54 AM EST, Dennis Zabawa <kg4rul@...> wrote:


I am using the SOTABEAMS Variable filter.  I twisted the ground and power wires together and added a 10nF capacitor to keep the RF gremlins out.

--
Jack, W8TEE

Joel Trenalone
 

Thanks for all the input. 

I put the power to the receive rail, so it now the filter is not powered during transmit. So not the RF feedback is gone.


But....I can’t here the CW side tone now. After looking at the schematic, I see that the side tone is injected right before volume high. The filter is inserted between V high and the volume pot, so I assumed that when the filter has no power then the side tone cant make it through to the speaker  


it seems the right thing to keep the filter power off during transmit, so I think I’ll move the filter insertion point to right after R70 and before the side tone injection. 


Does this make sense?
thanks for all the help,
Joel

Skip Davis
 

Yes Joel this makes perfect sense. Because you are leaving it in permanently you could remove R70 (a 10 Ohm resistor) and use its mounting pads as your filter insurance point.

Skip NC9O

Skip Davis
 

Arrr! Spellcheck got me insurance should be insertion.

Skip NC9O

Joel Trenalone
 

Skip,
thanks for the advice, as I was trying to figure out how to insert without scratching up the traces on the board. Great idea :)