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Cobra 29LTD Chrome VFO windup...

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.
 
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.
 
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
 
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
 
Pretty sure a resistor is added in series with the electrolytic also. In the video posted by Mikesradiorepair on youtube; he's able to key and unkey the radio fairly quick. I believe the resistor is what decides how long it takes for the channel to slide to center frequency. Also, it takes just as long as it takes to slide to center frequency as it does too receive. This mod also quickly changes receive for a short time after you unkey; which should be the capacitor bleeding off.
No it's more to do with the value of the capacitor that effects the length of the frequency offset. The resistor is more for bleed off after you unkey. That way you don't have to wait for the cap to discharge before you can key again and actually get your effect
 

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