Broad banding the 148st ?

[Harley3315]

So I did the simple 2 switch mod for channels notice that on the Lowe end 26.81.5 not much forward swing and the same at 27.45.5 anything I can do to make it spread a bit better its great around 27.16.5 thanks in advance...

 

[M0GVZ]

How are you testing it? Are you using a dummy load or an antenna? If its an antenna you may find that the tuning of that antenna is playing a part.

 

[Harley3315]

Nope using a dummy load for all testing.

 

[Shadetree Mechanic]

It might need an alignment to make use of the new range of frequencies.

 

[Harley3315]

Yes that's what I've done but it doesn't spread well with the older 858 radios there were some broad band mods to get full power nearly top to bottom.

 

[9C1Driver]

Yes that's what I've done but it doesn't spread well with the older 858 radios there were some broad band mods to get full power nearly top to bottom.

You can expect issues with that radio, they got the nickname Soundcrapper for a reason. The ST versions were the worst of the 148 breed.

 

[sonoma]

I have one of the ST 4 pin versions that the channels work well in. I had to change the varactor diode with one that came in a galaxy radio. that made it work better. in fact I have a L kit in it and it wotrks 40 below and 40 above the regular 40 channels now. not sure if it would help yours but a thought. I did this because the 1st cobra 29 ltd radios did not want to give all the channels above and below 40 so you had to change that diode out on them so they would track all channels. so that was why I tried the better diode in my 148 gtl st radio and it worked.

 

[sonoma]

here is a schematic Rick Jackson made up for the st models. he put lots of notes on it to help with the radio. see if this will help you.

http://www.cbtricks.com/radios/cobra/148gtl/graphics/cobra_148gtl_sch_redraw.pdf

 

[sonoma]

here is a page from cobra that you might look at to see if your radio has had the campain done to it or not.

http://www.cbtricks.com/radios/cobra/140gtl/graphics/cobra_140gtl_142gtl_148gtl_tb1226.pdf

 

[sonoma]

here is the install for the channel kit which will help with what you are having. read the capacitor change in the 1st box about channels dropping out.

http://www.cbtricks.com/miscellaneous/vco/expo/model_l.htm

 

[Harley3315]

here is a page from cobra that you might look at to see if your radio has had the campain done to it or not.

http://www.cbtricks.com/radios/cobra/140gtl/graphics/cobra_140gtl_142gtl_148gtl_tb1226.pdf

Thanks but this bulletin is irrelevant to the 148gtl st in fact this has a kia audio chip not the Toshiba the out pin is 10 not 9 like the old ones.

 

[Harley3315]

I have one of the ST 4 pin versions that the channels work well in. I had to change the varactor diode with one that came in a galaxy radio. that made it work better. in fact I have a L kit in it and it wotrks 40 below and 40 above the regular 40 channels now. not sure if it would help yours but a thought. I did this because the 1st cobra 29 ltd radios did not want to give all the channels above and below 40 so you had to change that diode out on them so they would track all channels. so that was why I tried the better diode in my 148 gtl st radio and it worked.

Off the top of your head do you know which one it is d35 for some reason I'm thinking. Also it's not channel drop out it covers them all fine. I was hoping to even the out put power out through them. Rather that more on low end and way less on high iend

 

[sonoma]

look at the cap change and see if it helps.
I do not know what diode position it is. about 20 years ago I did the st radio for my self. still have it

I do remember the diode I put in its place was a svc-251spa diode. I believe thats the right part number.

 

[sonoma]

after looking at the schematic Rick drew up D35 looks like the one I changed. its in line with the 11.325 crystal

 

[Harley3315]

Thanks man appreciate the information.