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Cobra 19 Ultra III power / modulation indicator

sunbulls

Sr. Member
Apr 25, 2017
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Recently I was presented with a Cobra 19 Ultra III that had a blown final even though the TX scale on the front panel would still show all 4 bars when keyed. ?? After replacing the final I looked for some sort of TX meter adjustment, or typically a pot. The RX side has an S meter adjustment, but nothing for the TX. The TX meter indication on this radio is phony. The schematic also shows no direct or indirect connection to the final stage. This was a first for me. For TX indication, usually a small circuit is coupled with a 5 picofarad or less capacitor to the final stage to control a meter, bulb or LED. Not this cheapie!

I decided it was time add my own indicator. The brightness of the LED also fluctuates with modulation. I was fortunate to find small open area between the channel selector and the squelch knob to mount the LED without removing the bezel. Marking and drilling the hole from the front did the trick. Besides the LED, the basic circuit I used consists of only a few caps, two resistors and one diode. It’s the typical TX meter adjustment circuit found on many Cybernet radios.
Cobra19 Ultra III mod.jpg
 

I am getting close to finishing a “Frankenstein” radio and need to add a “Modulation” indicator circuit to the PLL02 chassis I transplanted into the 23 channel base station chassis I am using. The Base station chassis was originally equipped with an “On Air” indicator and have that handled. Remaining is the “Modulation” indicator.

It seems every time I start to clear the bench to continue this project, I get pulled away to something else. This project has been going on for about 8 months. I am ready to button this one up as there are 3 or 4 other things I want to get done.

Thanks for the inspiration.

73
David
 

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