Carrier on SSB

[Animal]

Radio Make and Model: Cobra 148 GTL-DX Mk2
PCB Number: 010AA
PLL Number:
Test gear available: Stand Alone Frequency Counter, Digital VOM

Symptoms: I have a full carrier on USB/LSB (drawing 2.5A)

What is working: Everything else seems fine.

What has been tried: Adjusted VR7 which has no effect whatsoever, checked driver & final bias for 50ma, checked VCO offsets.

Did it suddenly happen ?: It was intermittent, but it's continuous now.

Anything else that may be of help?: When listening on another set - the carrier isn't detected on the opposite sideband.

AM & FM work perfectly (drawing approx. 4A on TX)

Any assistance would be much appreciated.

Steve

[zodiac]

Steve,
I've had the same problem with the Grant and 3900.
If you lift the lid (top) of the radio at the back about 1 inch it stops, give it a try and let us know the result.
Dave.

[Animal]

Dave,

You're correct - it stops when I lift the top lid

What's all that about then & how did you sort a permanent fix (other than the end-crust from a loaf of Hovis wedged between lid & chassis!)

Cheers

Steve

[Animal]

It may be worth mentioning that I've changed the driver & final in this radio to 2SC2166 & 2SC1969 respectively (Eleflow)

I had to back-off VR12 ALC as the RF meter was pegging full-scale on ssb with mic gain at 12 O'clock (& TX audio was distorted)

May have no significance but you never know

Steve

[zodiac]

Are you using a power mike as they pick up noises that we can't here.
When testing for carrier on SSB make sure the mike gain is fully anticlockwise.
It's stray RF that's causing the problem and you need to tame it.
One way is to put a short piece of insulated wire from the Emitter of the 2166 to the Emitter of the 1969, that's the earth or O volt track of them both or the left pin of the three looking from the solder side.
Try to keep the wire as taut as it's possible.

Dave.

[Animal]

Dave,

I didn't have a power mic attached.

Mic gain was set fully anticlockwise.

Fitted the jumper wire as you suggested & all is now good thanks

By the way, why would I be getting stray RF with this set?

Steve

[zodiac]

It's not just your set they all have some RF floating about but it doesn't cause any problems normaly.
Anyway, your now Animal the RF tamer.

Dave.

[Animal]

It's not just your set they all have some RF floating about but it doesn't cause any problems normaly.
Anyway, your now Animal the RF tamer.

Dave.

I might be able to tame RF (or even lions with an upturned chair!) but still haven't managed tame the wife's spending

I've started another thread about the audio on the other Cobra Dave if you fancy a butchers?

Hope the back is a little better?

Steve