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Spectral purity

Hawkeye351

Well-Known Member
Jun 27, 2021
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Got a question for the pros:
(Handy Andy, Nomad, Shockwave, etc...)

This question regards aligning L40, L42, L43 and L44 (most galaxy styles) to eliminate harmonics, spurries, etc...

After you've adjusted all you can on the above cans to eliminate as much mess as possible but still have some spikes, is there another way to rid a signal of spurries that won't come out? Like cap swaps, resistor swaps, etc...or am I pretty much stuck with what spurries I couldn't ALIGN out?

Here are some pics before I did anything and after aligning those 4 cans as much as I could:

Before:
1115221108a~2.jpg
1115221108~2.jpg

After:
1116221918a~2.jpg
1116222036.jpg


Sorry for pics being flipped.

Are there any caps or resistors I could play with to clean it up more?

Radio is a general lee (dual mosfet version). No swing mods, looks to be original finals. Passthrough gets scorching hot within 10 seconds of keying up. I did replace both 1000uf 25v caps with new 3300uf 35v, the 330uf 16v cap next to passthrough to a new 330uf 35v. Replaced L40, 42, 43 and 44 cause someone cracked the cores.

What else can be done to the RF stage to clean up leftover spikes when no further adjustment seems to work?

Using an Agilent E4411b spectrum analyzer set for no atten. at a reference level of -10db down, sweep at 200ms
 

And why do some of these board styles have a 1k ohm resistor strapped across 2 legs of IC9? The bottom parts layout doesn't have that resistor. Is this some sort of broadbanding mod?
 
I think I've figured out the problem.

As many of you know, a General Lee comes factory with a HI/LO power switch. And inside the radio you have 2 adjustments for those power levels, 1 is VR13 for HI Power adjustment and the other VR14 for LO Power adjustment. Well, both adjustments will affect the other in small amounts.

The proper setting for the HI Power adjustment should be set using volts on your volt meter to 5.45v to no more than 5.60v or else the passthrough starts getting hot quicker. The LO setting you can adjust with watts on a watt meter. Remember, they both affect each other, so you may have to go back and forth a few times to get it right.

Well, what someone had done was remove VR14 (LO Power adjustment) and ran 3 wires up to a 10k ohm pot which they mounted thru a drilled hole on the side of the radio. Problem with this is, when you turn that 10k pot all the way up it keys 7w, which is too much key for LO Power adjustment, so I switched the HI/LO gear switch to HI Power and noticed it was keying 15w, wow. So I reset the HI Power adjustment (VR13) to 5.60v which brought the key down to 7.5w swinging 37w. Flipped the HI/LO switch back to LO Power and turned the 10k pot up all the way and now the key is at 4.5w swinging 28w. Why would you put the variable 10k pot on the LO Power adjustment (vr14)? Letting it cool back down now, then I'll check signal again.
 
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I think I've figured out the problem.

As many of you know, a General Lee comes factory with a HI/LO power switch. And inside the radio you have 2 adjustments for those power levels, 1 is VR13 for HI Power adjustment and the other VR14 for LO Power adjustment. Well, both adjustments will affect the other in small amounts.

The proper setting for the HI Power adjustment should be set using volts on your volt meter to 5.45v to no more than 5.60v or else the passthrough starts getting hot quicker. The LO setting you can adjust with watts on a watt meter. Remember, they both affect each other, so you may have to go back and forth a few times to get it right.

Well, what someone had done was remove VR14 (LO Power adjustment) and ran 3 wires up to a 10k ohm pot which they mounted thru a drilled hole on the side of the radio. Problem with this is, when you turn that 10k pot all the way up it keys 7w, which is too much key for LO Power adjustment, so I switched the HI/LO gear switch to HI Power and noticed it was keying 15w, wow. So I reset the HI Power adjustment (VR13) to 5.60v which brought the key down to 7.5w swinging 37w. Flipped the HI/LO switch back to LO Power and turned the 10k pot up all the way and now the key is at 4.5w swinging 28w. Why would you put the variable 10k pot on the LO Power adjustment (vr14)? Letting it cool back down now, then I'll check signal again.
I'm not a pro but reading your findings is interesting.

I've never seen that type of mod but it reminds me one of the drail mods that he adds in his builds.
 
Thank you for popping in Eldorado...

Problem solved:

Passthrough was weakened,
Finals are not matched,
Dead key was too high in both gears,

Reset power to specs, replaced passthrough with an 817, replaced AF with 1012. That cleaned it up even more, not perfect, but all other spikes are well below 50dbm lower than the fundamental. Best it's gonna get.

Driver seems happy with it, and it's not near as nasty, doesn't get nowhere near as hot as it did, plus power ended up being 35w peak.
 
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