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Improving receive
- Thread starter jerry S
- Start date
As in poor sensitivity to weak signals? High noise level that covers up weak signals? Poor AGC action that distorts a loud SSB signal? Tendency to overload from a strong nearby signal on another channel that it should reject?
One of the above? All?
73
Shadetree Mechanic
Delaware Base Station 808
I noticed that mine has the AGC SSB distortion. I can turn the RF gain way down and the volume up and it sounds normal. Is there a fix for this?
Shadetree Mechanic
Delaware Base Station 808
Just digging up info, I did not know that this radio has an engineering menu. A while back I told somebody here that it didn't, and I wasn't very nice about it. If I could find where I said it, I would post this there. Now I am humbly eating Crow.
Anyway, I am thinking that there is an adjustment for AGC in the engineering menu?
Anyway, I am thinking that there is an adjustment for AGC in the engineering menu?
Don't forget to write the stock number values down in case you want to return any values back. There is no factory reset in engineering mode.
Shadetree Mechanic
Delaware Base Station 808
Shadetree Mechanic
Delaware Base Station 808
Here is the service manual for the Lincoln 2, might be close enough to the 2+, I don't know. Did not see any clues for the AGC though.
I'm looking forward to seeing how this one turns out. I wanted a lincoln 2 ever since I cleaned up the mod on frmboybuck's lincoln 2+. I really liked it, a lot, but it wasn't mine, so I didn't get to play with it on air before sending it home.
If it can't be resolved in the menu, I think the next step is to analyze what stages are controlled by the ACG, and potentially applying that control to another stage, perhaps a mixer. When signals can range from down in the weeds to tens of millivolts thanks to those 70lb hammers out there now, the AGC needs to have a dynamic range of over 100dB to not distort on those strong signals. Back in the day, I think less was sufficient, but not with those ghost riders and skullcrackers out there
I am no expert, but from my understanding, it takes more than a shunt diode at the input to do that. And since the gain of the various RX stages needs to be limited to around 10 for stability, to get that much dynamic range, the AGC needs to control the gain of multiple stages, not just at the front end. If I get time, I will look at the manual shadetree just posted and see if I can figure out how many stages it actually controls.
Perhaps a mod could be conjured up that adds a little more AGC range ~ although I admit that I am hardly qualified to be the one to figure that out lol! I remember Lou's book mentioning stage gain can be controlled by shifting the bias points of the various stages (among other methods), and often times, raising the bias higher is better than lowering it because gain is reduced in both directions and transistors are more stable nearer saturation, or something like that. Just sharing my limited understanding of how (i think) the AGC works in hopes it steers this thread towards a real solution.
Sorry for my ramblings, I'll be watching this one!! Back on the side...
If it can't be resolved in the menu, I think the next step is to analyze what stages are controlled by the ACG, and potentially applying that control to another stage, perhaps a mixer. When signals can range from down in the weeds to tens of millivolts thanks to those 70lb hammers out there now, the AGC needs to have a dynamic range of over 100dB to not distort on those strong signals. Back in the day, I think less was sufficient, but not with those ghost riders and skullcrackers out there
I am no expert, but from my understanding, it takes more than a shunt diode at the input to do that. And since the gain of the various RX stages needs to be limited to around 10 for stability, to get that much dynamic range, the AGC needs to control the gain of multiple stages, not just at the front end. If I get time, I will look at the manual shadetree just posted and see if I can figure out how many stages it actually controls.
Perhaps a mod could be conjured up that adds a little more AGC range ~ although I admit that I am hardly qualified to be the one to figure that out lol! I remember Lou's book mentioning stage gain can be controlled by shifting the bias points of the various stages (among other methods), and often times, raising the bias higher is better than lowering it because gain is reduced in both directions and transistors are more stable nearer saturation, or something like that. Just sharing my limited understanding of how (i think) the AGC works in hopes it steers this thread towards a real solution.
Sorry for my ramblings, I'll be watching this one!! Back on the side...
Shadetree Mechanic
Delaware Base Station 808
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'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 would say High Noise level that covers up weak signals, But I haven't played with mine in a while and I'm no radio expert either.
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