Mobile Radio Interfering with Stereo Head Unit.

[ericsze]

I have a CDM1550 VHF ~50 Watt mobile installed in a 99 ML320. Fused directly to the battery, remoted and antenna is mag mounted towards the rear of the vehicle. I noticed recently that whenever I key up the mike, I'll get some constructive interference which results in a "awful" noise coming out from my stereo speakers. Anyone ever run into this problem, and anyone know if it's damaging to anything? I know the MCS 2000's have a mute line...but haven't heard of any other radio that does.

[jcobb]

Two quick things. High power transmitters do get into other electronic gear - you will probably have to move the antenna around to see if you can get a lessening of the interference. You may have to provide additional shielding for the stereo/amp.

My FM radio goes "out" (no volume) when I transmit on the 2 way VHF, depending upon the freq tuned on the FM broadcast radio.

The "mute line" on a transmitter radio will do nothing to help the stereo interference. If your stereo has a mute button, you might try that before you transmit.


Jack

[ricciticcitembo]

And benzes usually have remote mount Amplifiers (in the trunk) and
in 1986-93 even remote trunk mount receivers. Both of which
exaggerate the problem. I have a collection of Beckers that were
replaced with "upgraded" radios. I've used the Benz radios without
the remote tuner but with external Blaupunkt Amplifiers with my
two-way radios without a problem in my Saab 900 and Ford Van.
I even have the audio output from the two-way's pumped into
the head unit (mixed with head unit audio) without problems.
The use of Balanced wiring or at the very least extremely well shielded audio lines are required as well as properly GROUNDED
Antenna System. Also no 110 Watters need apply.

Too bad the same setup as stock doesn't work that well at all
in the very car it came out of (a benz) especially where TX RFI
is concerned. I had Problems with a 93 Toyota Camry as well with
RFI. Never was able to solve it to my satisfaction either. Thats why
I replaced the Car. I was afraid the Air Bag was going to pop out
on TX since the light on the dash always came on when I TX'ed.

If I had a Benz with the RFI problem I would simply rewire the Stock
Stereo with better cabling and add a few amps while I was at it
since I'm already quite sure the head unit/tuner/amp is not really
the problem at all. It's the way they have it strung all over the car
and use unshielded wires to interconnect with that is the problem.
There was another post somewhere about a 320 with the same
problem of RFI in the Stock radio. I think there was a fix for this.
I also think the RFI is getting into the unshielded speaker leads.

And actually, I NEED a tuner for a BE1432 anybody got one??

[larryepage]

If these other suggestions don't work, you might want to check into replacing your mag mount with a trunk lip mount. A general problem with mag mounts is that they provide no ground connection at the antenna, which can frequently lead to problems. (A side benefit is that you'll get a better ground plane, which will give you a better transmit pattern and maybe even improve your SWR.)

Beyond that, remember that there is lots of wiring in an automobile that ends up being close to one wavelength or a half wavelentgh (or a multiple) of a VHF signal...in other words, a good receiving antenna. That's why you can have so much fun with a VHF transmitter and other folks' car alarms.

I have a 94 Ford Explorer, and when I transmit (50 watts, antenna toward the rear, good quality feedline) operation of my cruise control is significantly affected. In addition, about a year ago, I had to replace the in-dash portion of my factory stereo system due to a total failure of the control section. Inspection inside revealed several locations where there had been arcing from various components to the metal shields. Now I make sure the stereo is turned off when I transmit.

Most manufacturers of recent electronic equipment do not provide shielding necessary to provide protection from a nearby (legally operating) transmitter. Specifically, we have two recently manufactured televisions at home. One is a relatively top-of-the-line model. Both are just plastic boxes with circuit boards inside...nothing to keep stray RF out of the circuitry. Some of the RF boards are inside Faraday cages, but many important circuits are in the open.

In my experience, there are basically four ways that unwanted RF can get inside a stereo system--
-- power leads
-- antenna lead
-- speaker leads (or leads to remote power amp)
-- front panel (many times made of plastic even if the rest of the system is shielded)

Protection may have to be provided at all these points (ferrite beads, etc). And there is usually not much that can be done about the front panel.

Good luck!

Regards,

[MO_TRASHER]

Since you use a mag mount, move it to the roof and try it there. The ground plane may be better and that could help. Of course if your car is a convertible, nevermind. You should also "bond" your trunk lid and if that doesn't help I'm at a loss as where to go next. Make bonding straps with braid from coax cable. Scrape the paint away so you have good shiny metal. Use "star washers" to get a good bite in the sheet metal. Attach at both sides of the trunk lid. Best place is around where the hinges hold the deck, and where the brackets attach to the fenders. If nothing else, it should improve your SWR.
HTH
Bob