Cobra 2000 Need help lowering dead key.

[RichardHartman]

Hello everyone,

I just picked up a Cobra 2000 GTL. It has been recapped and aligned. It currently has a dead key of 3w. I would like to decrease it as well as the modulation swing for AM and SSB. Can anyone help me with the correct location and procedure to do this?

 

[sp5it]

AM carrier VR10
SSB power VR11
More to read: http://www.cbtricks.com/radios/cobra/2000gtl/index.htm

 

[RichardHartman]

Thank you

 

[loosecannon]

modulation adjustment for AM is VR12. rear right corner of the PC board.
LC

 

[kopcicle]

If that doesn't get the dead key where you want it reducing the value of R196 will get VR10 closer to ground. Much below 1K ohm is pretty useless.

 

[RichardHartman]

Thank you everyone for the assistance. Now that I have that set I have a question regarding the modulation meter. The MOD/SWR meter works in SWR mode and in AM. When I switch to SSB the MOD meter does not move. RF meter is the only one that works when modulating in SSB. Is this normal for the 2000 or should the MOD meter work in SSB operation?

 

[wavrider]

don't believe the meter works in ssb mine doesn't work there

 

[hotrod]

i believe meter only works in am mode

 

[Handy Andy]

It's kinda' been covered here in this thread...

https://www.worldwidedx.com/threads/my-cobra-2000-gtl.252424/page-3#post-711574

To elaborate more, the SWR Meter for MOD - has to see MODULATION on the AM Bias line - the one that goes to the Driver and Final.

In SSB mode, the Driver and Final don't see modulation - they only see pure DC, the "modulation" is from the PreDriver and Mixer linearly amplifying the two IF mixed signals together - your Audio IF and the PLL's IF.

Modulation on the AM bias line only occurs when you use the AM mode and only if the AM regulator is passing MOD.

Review the thread linked above - see if it helps you understand the meter wiring - and how the audio side of the Modulation meter - is detected.

Hint: It's thru a cap - which Blocks DC, so if you are in SSB mode, your pushing DC to the Driver and Final - so the cap used to tap, and "Sense" blocks it - the meter just sits there becasue there's no modulation to detect on that tap, it's pure DC.