Cobra receive adjustment?

[stingray]

I have 2 identical radios (87 GTL's) on receive i get the same signal from people but on one radio i get 1 s unit of noise and on the other i get 3-4.
can anything be done to quiet the other one own?

 

[RatsoW8]

I have 2 identical radios (87 GTL's) on receive i get the same signal from people but on one radio i get 1 s unit of noise and on the other i get 3-4.
can anything be done to quiet the other one own?

Maybe the s-meter on one of them isn't calibrated the same as the other. They may be receiving the same noise level but showing different readings on the s-meter.

 

[stingray]

Maybe the s-meter on one of them isn't calibrated the same as the other. They may be receiving the same noise level but showing different readings on the s-meter.

maybe. but i wonder why i get the same s unit readings from people talking but just more noise level on the one radio.

 

[RatsoW8]

maybe. but i wonder why i get the same s unit readings from people talking but just more noise level on the one radio.

Could be internal. Not all transistors are created alike. Or maybe they both just need to have the receive alignment done.

 

[Robb]

Since both of these radios are relatively old; I suspect the electrolytic caps are getting weak. In reality, it could be a few things. The internal power supply filter caps are often the source of noise in an older radio - BTW. There is a 13.8v plug on the back of the radio that will bypass the internal supply. IF you hook it up to an external power supply and the noise goes away; then the problem is definitely the radio's power supply filter caps.

The alignment will make a difference too. It is hard to say w/o the radio in front of me. How do they work with the ANL switched on? Any difference?

http://www.cbtricks.com/radios/cobra/87gtl/graphics/cobra_87gtl_sch.pdf

 

[stingray]

Since both of these radios are relatively old; I suspect the electrolytic caps are getting weak. In reality, it could be a few things. The internal power supply filter caps are often the source of noise in an older radio - BTW. There is a 13.8v plug on the back of the radio that will bypass the internal supply. IF you hook it up to an external power supply and the noise goes away; then the problem is definitely the radio's power supply filter caps.

The alignment will make a difference too. It is hard to say w/o the radio in front of me. How do they work with the ANL switched on? Any difference?

http://www.cbtricks.com/radios/cobra/87gtl/graphics/cobra_87gtl_sch.pdf

running it on a pwr sup. i still get the 3-4 lb noise level. the anl/nb does quiet it but the meter reading does not go down.

 

[Robb]

Switching PS or transformer-type PS? A switching-type supply can make some noise on just a few channels - or even all of them. A transformer-type supply usually doesn't have this kind of problem.

Do you have a mobile radio in your car? Does this noise go away when you drive a few blocks from your base station? Can't do much about that kind of local noise; sometimes you can. Unless you have the time/means to track it down - like having a CB walkie-talkie to locate the source - that should work.

Could also be noise brought through skip propagation too.

Other than noise generated by an outside source, it may just need all new electrolytic caps in the radio and an alignment.