Poormans 192 Channel Mod - Cobra 142 GTL

[wcsd106]

I'm performing the Poormans 192 Channel Mod from the files section at "the mod yahoo group" on a Cobra 142GTL. There were already existing holes from another less desirable channel mod, so I figured I'd at least put something a little better in it.

I've got the low channels to come in without any problems. I have coverage from 26.165 up to CB Channel 1 with only a few skips.

I can get the upper channels to come in but I have to set the switches and then turn the radio off then back on to get them and they're buggy at best... turn the channel switch and the VCO loses its lock.

Is there any way to broadband the VCO to allow for the greater channel range? I have cut R71 as detailed in the modification file, but I'm still having
troubles.

Crystal is a 11.125, not the 11.3258 but from my reading "the mod" and this modification both work better with the 11.125 anyway.

Thanks

 

[MisterFatty]

Remove R95

 

[wcsd106]

R95 on the 142GTL board is nowhere near the VCO. It is located near TR30 on the other side of the board closer to the regulator.

On the 148s and 2000s R95 is the go-to resistor, but from what I've been reading, R71 serves the same purpose on the 142s

 

[MisterFatty]

Just took the cover off my 142, my mistake it was R71, same thing as 95, just mixed up the chassis. When I put my Mod in the 142, was no way I could get my VCO to lock full range, removed it, and easily does full range with very little loss from end to end...

I

 

[wcsd106]

Well, I managed to get it working so-so... 26.165 to 28.085 is a little much to ask that VCO to cover I guess.

It is now covering most of the channels, a little buggy on the very high channels, but I don't know many people who use those anyway. The lower channels are working well.

I figure this mod gave me more than what the original one had, so I won't complain.

 

[loosecannon]

you can get the 192 channels out of the VCO if you have clipped R71, its just VERY touchy and requires some time and patience.

your VCO coil is L13, and you will be tweaking it ever so slightly in either direction in order to get all the channels to lock in.

do not ever turn it more than 1/8 of a turn at a time, as you can get it really messed up and frustrate yourself. LOL

ok, you are going to be checking your work by keying the mic and making sure that the TX light lights/changes and that the meter moves over normally.

since you say you have the lowest channel already; go to 28.085 and key the mic.
if its intermittent or doesnt TX, then give L13 a VERY slight nudge in one direction or the other.
is it better or worse?
if its worse, then you needed to turn it the other way, so do that.

you should find that a tweak in the right direction is all you need to get the top channels to come in.

once you have a solid TX on the top channel (28.085), go to your lowest freq. (should be 26.175 BTW) and see if you can TX there.

if you can, you're all set! if not, you need to nudge L13 back the other direction until you get the low channel to TX.

by going back and forth through this procedure a few times (sometimes more than a few) you should find that sweet spot that allows you to get all the channels.

if this just doesnt work for you, come back here and tell us exactly what happened when you did it.

one thing you said got me curious. you said that your low channel was 26.165, did you mod the clarifier on this radio?
if so, there is a chance that you tuned it up on the wrong channel because the clarifier mod wasnt done the right way.

do you have a freq counter? is channel 19 27.185?

let us know and we'll go from there.

good luck!
LC

 

[wcsd106]

Hello,

Yes I have a frequency counter. I was mistaken the lowest channel is 26.175... I'd been messing with it soo much that day I had numbers jumbling my brain.

It seems to want to TX on all of those channels, but when I key up on the upper channels, my frequency counter just goes nuts and displays 27.135ish numbers. This does this with the counter filter on or off.