Improving receive

[Rwb]

A local guy has been running a Quad 6 for about a month now, probably the best he has ever sounded. He has had a 2950, Galaxy 86v, and a Magnum S-45 HP. We talk mostly SSB, he loves it.

they might sound good but as i said controls are in not so good layout. if i cant run controls with ease i dont like it, but thats my opinion

 

[Shadetree Mechanic]

Disclaimer first.

I've never messed with one of these radios, but i wonder if someone would be willing to try an experiment for me in an attempt to help this issue.

(this would do nothing for a narrow receiver issue if that's the actual problem)

Turn the radio on in AM mode with nothing connected to the antenna jack.
turn the volume up to a normal listening level or just higher than that. Squelch down and RF gain all the way up.

how does it sound?
does it sound like there is a lot of hiss coming through the speaker?
like white noise?

if so, adjust T1 slightly just until the receiver quiets down.

now check sensitivity with your sig gen.
can you still hear the tone slightly when under 1uV?

if so, try connecting the radio to your antenna again and see if the performance has improved.

if it's not obvious, im wondering if the first RF amp is overloading later stages.
LC

I was able to adjust T1, but the audio quality did not change. Only by turning the RF gain way down and the volume way up, does it sound clean.

Also, I think I found a clue to the AGC. The document I posted earlier on step 2 showed a resistor added between U1D pin 14 and D40. This seems to be the AGC control. I don't know if the document shows three separate modifications or if all three steps are for the same mod.

EDIT: Maybe this was for the S meter fix...

 

[Shadetree Mechanic]

Ok, now I think we are getting somewhere....

The third mod in the document is RX Audio, and the first part is to delete R205 and solider a strap across it. (short) This R205 is on the line labeled "AGC DET" so it appears to be the signal that goes to the AGC Detector, which must be U1C. So shorting the R205 would give the detector a stronger signal to work with, which would cause it to react quicker. I might try to hold a pair of pointy tweezers across it to see.

The rest of the third mod on the last page appears to deal with audio range. I think the audio is fine for a DX machine, so I will leave all that alone.

.

 

[Shadetree Mechanic]

Quick update: I grabbed my wife's best pointy tweezers and tried it. It definitely cuts down on the rx signal level. It was hard to keep my hand steady while waiting for someone to talk, so I went ahead and removed the resistor. I stripped a twist tie and bent the end in the shape of a tiny L and soldered it in, then trimmed it off.

I believe this mod helps, and is definitely worth doing.