Antenna for Volvo

The Volvo perch mount is a great solution for a new mount, but the OP has a system that was working at one point, after which something failed.
Getting 35 watts out of a Cobra 29 sounds bizarre. There are tricks some "techs" do to fool a wattmeter, like spreading out the coils in the matching network inside the radio, so that the radio is no longer looking for a 50 ohm antenna system, and the radio puts out lots of garbage along with the signal.
Carlitos, how long did your previous arrangement work? Was the tuneup on the Cobra recent? Were the original antenna or coax old? Are the door hinges rusty or loose?
You mention that you tested both the radio and antenna (or antennas?) as good -- how did you do that?
Something changed on you during the time that everything seemed fine. A faulty coax connection, a break in the wire that's wrapped around a fiberglass antenna, or the all-too-predictable burnout of something in the radio after being pushed that hard are all ideas that come to mind. I suspect that, since you've replaced the coax (did you use a proper harness for the new pair, or a single line for the original coax? They can't be interchanged...) either the radio, or the nylon washer on the antenna mount, has failed.
At this point, before you put any more money into buying more stuff, I'd recommend having a tech with a decent wattmeter or antenna analyzer check your system for you. And maybe have some shop, other than the one who made your Cobra put out 35 watts, go through your radio and undo some of the....ummmm..... mods that have been done so that it reads actual, in-band, clean watts.
I get repeat business by returning radios to stock and cleaning up how they sound, because their owners get compliments on how they sound on the air, and their radios last a long time. So most of my business comes from referrals; the repairs don't have to be redone
Just some thoughts for you, before you spend a heap more cash on stuff to replace things that are already OK.
-- Handlebar --

 

thanks for your help

 

Volvos have a multiplexor system in them. There is a box under the dash that the antenna coax goes to then cable goes from there to the am/fm and one to the CB. There is really nothing special about the stock Volvo antennas other then they are made by Rami. The multiplexor box does not like extra power. It can and will go bad and cause all kinds of issues. You can use any antenna you chose on the volvos.

Here is what I did. I got a bird perch mount and used that for an antenna for the AM/FM.

I took the covers off the mirrors and routed new cophased antenna into them and to the dash. Worked great especially for higher powered radio setups.

 

Rat,
Thanks for that explanation. I haven't had any Volvo trucks in here, so that's a new one for me to remember.
I've used diplexers that are supposed to function like the one you describe in the past, with moderate to poor results. I like your idea better.
-- Handlebar --