Adjacent Channel Rejection

[cbshack]

I have 3 Uniden Grant LTs that I am testing. Radio number one has a Lou Franklin Filter in it. Adjacent Channel Rejection with my signal generator all the way up is awesome. It drops to 1 s unit 2 channels above and below channel 19 . Radio number two is stock and takes about 4 channels either way of channel 19 to drop to an s 1 level. Radio number 3 has had some transmit and receive mods done to it by a shop in California. It has had the 1st If and 1st rf transitors changed to higher gain lower noise parts. The radio is a little more quiet and little more sensitive than the other two stock radios, but the adjacent channel rejection suffers. It takes 5-6 channels in either direction to get the s-1 reading from channel 19. Interesting. I have spoken to Ray at Galaxy about this and he agrees with me. Interesting. Just some food for thought. I copied the testing methods from the website of Bob's CB and Wireless.

 

[NorthStar]

Ben,

That is very interesting My guess would be these were built with different part tolerances in the reciever circuitry. But I could be wrong.

 

[cbshack]

I guess that is possible. I did use the Cobra 148 service manual and adjust all 3 radios to s-9 with 30% modulation, 27.185, 1000hz, 100uv before I proceeded. All radios manufactured in 2004. I have installed many Lou Franklin filters in the past with good results. I was talking to Ray about another radio and he offered me this information and advise. Something to think about. I am going to go back and check some of the tolerances.

 

[cbshack]

Tried the same test with my Icom 706mkIIG and two channels up and two down to s-1 reading with the generator cranked up all the way on channel 19. I guess this should not surprise too many people though. Just trying to share some information.

 

[frmboybuck]

That Channel Guard filter works wonders. I have one in my Lincoln and love it. Best $30 I have ever spent