Cobra 148 GTL

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Min
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Cobra 148 GTL

Post by Min » Friday 14th Dec 2007, 20:47

Hi, how do I go about tunning the frequency for AM/SSB. I have just installed a frequency mod into it and would like to tune it up now.
I dont have a scope, but I do have a frequency counter, digital voltmeter, multimeter, power/swr meter and all the proper plastic tunning screwdrivers.
The radio is a Cobra 148 GTL, PC-412AD. It has the MB8719pll and the clarifier is locked (no slide).

On Am it is on frequency, but it does tend to change a little and I would like to make it stable.
EG ch 40=27.4050 and will change to 27.4051 then back to 27.4050. It will do this consistantly. Does this really matter???
As for SSB, I`ve got no clue on how to even test to see if its on frequency besides having another radio that is on frequency.

Any help and ideas will be greatly appreciated.

edited- I have just attached a picture of the radio and frequency counter for example.

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Post by Min » Sunday 16th Dec 2007, 18:50

The Mod Board Installed

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Post by Min » Sunday 16th Dec 2007, 18:52

7805 Regulator with a heap of Silicon Heat Transfer Compound and a decent heat-sink aswell.

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Post by Min » Sunday 16th Dec 2007, 18:53

Channel 108- 28.085MHz

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Post by Min » Sunday 16th Dec 2007, 18:54

Channel -79= 26.175MHz

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Post by Min » Sunday 16th Dec 2007, 18:56

All I have to do know is the clarifier mod, which I will be doing Ricks way. This should fix the slight off frequency problem.

Then all is done.

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Post by Min » Sunday 16th Dec 2007, 20:35

Rick, I have just done the Clarifier mod the way you described except for R175- change to 1K. Just cause I dont have any on hand and will have to wait till tommorrow for the shops to open. The clarifier still slides great and I can now get it on frequency.
What is R175 for? Does it have to be changed? What will the difference be once its changed?

Actually, I`m gonna look through my parts radios and see if I can find a 1K. I`m wanting to finish this radio now that I`m in the mood.

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Post by Min » Sunday 16th Dec 2007, 21:03

Channel 40 and frequency counter readout.

Thanks alot Rick. I did the clarifier your way and all is good now.

Cheers :occasion5:

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