Satellite radio antenna vs. Motorola Radio

[LT-EMTC9]

I've been installing sat radios in our towns crusiers for at least a couple car cycles now. There is a mix of both XM and Sirius. All sat radio antennas are mounted on the rear of the roof, while the VHF and UHF antennas are on the trunk (the only antenna on the roof is the MDT which runs on a cell phone freq). The radios that are used in the car are VHF CDM 1250 as the primary, a CDM1250 for low band, and a UHF CDM 1250 for the Officers portable repeaters (rat packs). Just recently, there started to be some interference on the sat radios when the VHF radio is keyed, or rcv'ing a transmission. I am totally baffled, has anyone had or heard of a problem similar to this? Thanks!

[tvsjr]

Absolutely. My first XM install... got it all nice and installed, turned it on, made sure it played properly, reinstalled all the plastic. Decided to drive somewhere, hit the master switch, and poof, XM went to no signal. A four-letter aria ensued.

The XM antenna isn't just an antenna. They mix the receive products down to some IF (not sure if it's 10.7 or what, but something much lower than the native DBS frequencies) to allow the signal to traverse that tiny coax with no issues. When I installed mine, I paralleled the XM coax along a bunch of Spectra coax - my guess is that leakage from the Spectra's IF was getting into the XM and tearing it up.

I reinstalled the antenna/receiver, ensuring that the antenna/coax/wiring/etc. at no time came close to the existing radios, and never had another problem.

[resqguy911]

I fried a RoadyXT by holding my VHF Saber too close to the unit while TXing. It was less than a second of RF within 5", but I even saw it blink out forever right there in from of me....

At least I got to upgrade to an Xpress.

[alex]

I didn't have any issues with the XM Commander unit in my old truck, antenna was the stock mag mount one, and have had no issues with the Delphi setup in my Chevy with XM.

Granted, on the old explorer, I didn't drill in an XM antenna, but I don't know how Chevy does theirs, I could ask one of my engineering friends over there and see what they say... I've found the built in antenna to be pretty good on my truck so far.

-Alex

[KitN1MCC]

a real good spot to mount them is on the front on the hood. on my 2003 silverado it is on the hood near the driver door and it works great

Burn up an XM unit call them up they will usally send a new one for free

or go to http://www.myradiostore.com and support Opies brother elmo

[LT-EMTC9]

Well, glad I am not the only one that is seeing this. On one of the cars, I moved the antenna to the front of the roof (above the windshield) and it is working fine. The other car I have not had a chance to fix yet. The reasoning you all mentioned is making sense, cause I used to run the sat coax along the drivers side and never had a problem. On the new cars, I have been running them on the passenger side (due to almost running out of coax on the drivers side), which is also the side where the VHF/UHF antennas are. I will work on the other car and let you know how things turn out. Once again, thanks for everyones input/help!

[Quarterwave]

My sirius does this when I Tx on high pwr (40) on my Uhf M1225, but not on low pwr (5). I usually run in low power mode as I am just hitting the local repeater. My Sirius is near the back right roof of my Silverado and the UHF is a glass mount on the back glass about 8in away. Bad combo, but as I don't talk much and use low pwr when I do, I havent had any real problems. However if I do, I will move the antenna, can't let UHF block out my NASCAR 128!.

[bobbyaa]

It's probably your radio desensing the XM antenna. I've seen the problem before with people transmitting on in car radios when their MVR antennas in close proximity. The only real solution is move one of the antennas. We've tried notch filters but when they are that close pushing 35-50 watts, sometimes even 110, its not going to matter...move the antenna

[Tom in D.C.]

My new 2007 Subaru's XM antenna is mounted inside the windshield
on the passenger's side. The radio runs somewhat more than
50 watts on VHF and UHF FM, analog, and does not bother the
XM reception at all. The comm antenna is mounted on the roof
well behind the sunroof and is a 17-inch dualbander. Just FWIW.