05 Volvo 780 CB radio/linear problem/quirk

I see you said the amp is fed from the battery and you have it grounded to the frame of the dash. Is the dash grounded to the frame? and what type of grounds are you useing. If you are using regular wire coated you mite try using flat braid ground wire and use it to ground every thing to the frame. You definatly have RF feeding back to your Mic and that is whats biting you if RF and those RF burns sure hurt. Your on the right track it is ground related try grounding every thing separate to the frame sometimes if you ground one piece of equipment to another it will cause a Ground loop just keep trying but you are on the right track i believe.

 

Grounding "boxs" any where but the batteries is asking for ECM cool down
Feed back thru the ex speaker is due to location of said speaker

Running insulated wire for grounding purposes only compounds RF issues

 

OK,good job a chasing this down. 1ST thing to try would be to move your amp somewhere else or put a rubber mat between the amp and the radio,i have had to do this is the past and its helped. 2nd,Throw that screwing metal mike cord in the trash and get the other style,those things are notorious for this problem!

Make sure that where the antenna is mounted that it is paint free bare metal,no paint at all between the antenna mount and where ever you have it mounted to. You may end up needed to run a larger ground wire from the antenna mount straight to the frame. Because your not getting enough ground the way its set up now. If 8 gauge wire wont do it then your going to need 2 gauge welding wire,i have the same problems with my 387 Pet and the ground is so poor in trucks these days that you just about have to get drastic with your install. If the mike is biting you then its a ground problem for sure. But it also seems to me that with an SWR that low that you are getting all the ground you need,strange. Does your SWR go up when you transmit? If it does then this would also suggest a ground problem.

It could also be poorly shielded coax causing this as well. Not all coax is the same and you may want to think about some larger RG213 coax. Check this site out to see what i'm talking about. http://www.ve3sqb.com/hamaerials/ocarc/ although i really dont think its a coax problem,but something to think about.

If you have a grab handle on the side of your cab faring, they make a mount called an Outback mount (goggle it),its meant for 387 Pet's and T-2000's but it may work on your truck as well. They run about $100.00 but those that who use them swear they work great!

One more thing,if you still have problems out of this you may want to consider having your modulation limiter put back into the radio. Anytime you put an amplifier on a radio that is over modulated to begin with you make it 10 times worse when you add an amp. This is why,allot of times,you have to turn your mike gain back to stop the squeal. Allot of times it wont matter how much ground you have or where your speaker is,you will still squeal if the radio is over modulated. My speaker is right behind my head and i dont squeal no matter what radio i use,but none of mine are over modulated ether. Remember. An amp is not meant to make you louder,only to make you heard further away,but you seem smarter than most so I'm guessing you already know this.

I wish you luck my friend.I have been fighting the antenna setup on my 387 Pet for over a year and although i have it close,its still not as good as i would like it to be. they just dont make trucks the way they used to!

 

I realise this is sorta old but, How did you make out with your TS 250?

I just went through the exact same problem with my 500V, Turns out after double checking everything I had to run a secondary ground from the amp case to a body ground. Now it works great with no feedback at all. I have inquired if this is just a band-aid fix to an underlying problem but so far I have not found any definate answers.

 

Who tuned the radio and matched it to the amp? What does the output look like on a scope? What is the phase angle of the feedline? Is the stud an actual 50 ohm stud or is it 30 ohms like most of the truck stop studs?

feel current in the mic wire, meaning it is grounding out through my hand. the astatic is one that has the tangle free cord that is made of metal, and it has burned the snot out of me on the leg once and on my hand.

anyone have any ideas? when it is talking, its walking the dog. none of this started till the amp was installed so it tells me it has to be a grounding issue but i was wanting some suggestions from a few of the people on here as i am sure this has happened before. i would like to think this mess is grounded enough but who knows these days. they are making these big trucks out of fiberglass and plastic these days.

any input or questions are welcomed. thanks in advance.

Rob[/QUOTE]