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kit-projects.com AGC Question - Missing C3?

jsternmd
 

I installed the AGC board and found that the audio was dramatically reduced and quite tinny compared to pre-installation.  I'm trying to find out where the problem may be and while checking out the solder points for cold joints, etc or bad SMD component, I noticed that C3 is missing from the board.  It is shown on the picture in the manual but on board the pads have a solder bump bot missing capacitor.  I believe C3 is acting as an emitter bypass capacitor so if missing couldnt that be the cause of cutting out below audio frequency??   I am tempted to just solder in the 470pF in the schematic but wanted to check with experts here first.

Jerry NY2KW  

Gerry Kavanagh
 

Cap missing on my board also, and the audio levels are likewise lower than before I fitted the board...



/ Gerry

jsternmd
 

what version UBitx?  Mine is v5.  I know that there is a different install of the Vol-H wire for UBitx v4.

 

C3 is left out due to its ability to cause oscillation.
What version of ubitx do you have? V4 has a slightly different install to solve low audio.
--
David

 N8DAH
Kit-Projects.com

Shop is open!

 

Looking at the picture you have not tried to adjust the RF gain pot. This must be adjusted for proper audio levels.
--
David

 N8DAH
Kit-Projects.com

Shop is open!

Don, ND6T
 

Looking at the picture it appears that you have not attached the switch. Without a discharge path from the common (S meter, AGC voltage) to ground then C6 will remain charged and the attenuating transistors will be actively reducing your signal. IMHO.
Sorry about not catching this thread earlier, Jerry. I was replying to the emails.
73,
Don

Gerry Kavanagh
 

No, at the time the picture was taken, the switch had not been installed, and the RF gain has not been tweaked.
I had to get a new battery for my signal source so I can properly calibrate the RF gain.
Hopefully willl get the chance to do this later today.
/ Gerry

jsternmd
 

I hae adjusted the pot, I wonder if the pot is defective?  It acts like a trimmer going around with out stops, so I only peaked it for audio volume.

 

Jerry

 

From: BITX20@groups.io [mailto:BITX20@groups.io] On Behalf Of N8DAH
Sent: Monday, July 1, 2019 8:23 AM
To: BITX20@groups.io
Subject: Re: [BITX20] kit-projects.com AGC Question - Missing C3?

 

Looking at the picture you have not tried to adjust the RF gain pot. This must be adjusted for proper audio levels.

 

Jerry,

 That is possible they are very touchy, we have been looking for a better option. You can remove it and add a jumper if it becomes unruly.
--
David

 N8DAH
Kit-Projects.com

Shop is open!

Gerry Kavanagh
 

Tweaked the RF control and now it seems pretty loud.
Will try calibrating for S-meter later so I will have an idea of sensitivity. I have a signal gen that will do 1uV - 50uV in a couple of steps.
/ Gerry

Ted
 

"Looking at the picture it appears that you have not attached the switch. Without a discharge path from the common (S meter, AGC voltage) to ground then C6 will remain charged and the attenuating transistors will be actively reducing your signal. IMHO.
Sorry about not catching this thread earlier, Jerry. I was replying to the emails.
73,
Don"

So if I'm not using the s-meter output of this AGC board, should I ground that tab or use a specific level of resistance rather than leave it open?



73,
Ted

KE2GKB
 

As long as you have wired up the switch per our diagrams you are good! The switch in the off position has the pad grounded. And fast and slow have different resistances. So if your not using the S-Meter just leave it floating as its already handled via the switch :)

73

-- Tim Keller - KE2GKB https://shop.kit-projects.com