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Cobra 29LTD Chrome VFO windup...

350GA

Member
Oct 14, 2018
35
18
18
33
It's very simple for the Cobra 29. Attach the positive leg of a 47uf electrolytic cap (for quick windup) or a 100uf electrolytic cap (longer windup) to the banded end of D18. Attach the negative leg to the can adjacent to D18. A switch can be installed in series with the negative leg if needed.

The radio will need to be realigned for correct TX "resting" frequency. Attach a frequency counter and key the radio for about 5 seconds to allow the TX frequency to "level out". Then adjust the TX frequency while keeping the radio keyed.

Just remember that this mod will only be heard in the heterodyne on the receiving end when you key up with another station. It will not be heard on your end or if there is no one else keying with you at the same time. You can however hear the windup on a SSB radio set to LSB if you want to hear how slow or fast your windup speed is.
 

Easy money

Member
Jun 22, 2019
4
1
13
42
The way nomad mentioned is how I was doing it on the 29. For the 148/2000 chassis put the positive leg of the cap on the wiper of vr5 and the neg lead to board ground.

No need for a resistor. The cap will bleed off within a second or two in rx mode and once charged in tx it will have no effect
on the rest of the circuit.

I've heard about someone modifying the software for a Flex radio to do this. I haven't figured that one out yet.
 

nomadradio

Analog Retentive
Apr 3, 2005
5,434
7,903
573
Louisville, KY
www.nomadradio.com
Anyone installed this on a Uniden Washington?

Sure would be annoying if it did this in sideband modes. For that matter sideband is pretty annoying to use unless the clarifier keeps the transmit and receiver frequency each 'locked' together.

Might want to have a way to switch it off for sideband, and back on for AM.

Only place I've seen this mod is in AM-only models. The front-panel clarifier knob never gets connected to the transmit side in this kind of CB.

And if you only used your Washington on AM, it wouldn't matter if this messed up sideband modes.

73
 

nomadradio

Analog Retentive
Apr 3, 2005
5,434
7,903
573
Louisville, KY
www.nomadradio.com
If I'm remembering correctly, there is no "fine tune" or "delta tune" on this model.

And that's the circuit feature that is being hijacked to accomplish this mod.

A radio that doesn't have that knob will be an uphill struggle to design and install to get the key-down windup.

And the wider the frequency up/down range is on that knob, the wider the windup will be on transmit.

73
 

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