Sirius causing static on CB?

I had a similar experience to many of you. I'm already used to listening to switch mode chargers on AM radios (broadcast, CB, and ham). Even though my Sirius doesn't have a battery to charge, it does have a power supply -- not everything inside runs on the raw 13.8 volts from the power cord.
Ever the inquisitive type, I plugged my Sirius box in on the bench and set it a few inches from the antenna port on my spectrum analyzer. There was a veritable forest of low level signals from around 150 KHz (the lower limit of my gear) up to about 40 MHz. I was able to confirm it was from the Sirius box by turning it off & on and watching the display.
There were considerable spikes around 10 MHz and 26 MHz, but not nice clean spikes like a carrier would show; nay, there were broad curves (a couple of MHz wide) centered around both of those frequency points.
Remember that the satellite band for things like Sirius is up in the microwave region. Mixer circuits "lower" the frequency to something that can be more easily manipulated, like filtering and amplification, so the signal will be usable. And every mixer has four output frequencies: both originals, and their sum, and their difference. Unless the three unwanted signals are filtered and suppressed, they're ripe for being transmitted a short range.
Like from the Sirius box to any other AM receiver in the cab. In the intended use, drivers just have their radio set for FM and dial up the link frequency, so it doesn't come up.
But, as has been said, give the world a better mousetrap, and it will spawn a better mouse. If the "non-typical" Sirius user *also* has an AM receiver of one type or another running at the same time, it gets to hear the garbage leaking from the Sirius box's enclosure.
Et voilà! Static in those other receivers.

I don't have the kind of lab that would be necessary to measure the absolute value of the incidental radiation from the Sirius box well enough to see if it's within Part 15 guidelines, but presumably they're designed to be within FCC's specs. But at least it let me know that it isn't a matter of some external ground not being adequate.

Guess it's "just one of those things" to put up with. It's possible that putting the Sirius box into a shielded enclosure and RF shielding/bypassing all the leads would fix this, but it would be some cumbersome as to render it unworkable for most folks, I think. At least the ones with a remote would allow the Sirius shield box to stay closed -- a piece of copper screen in front of the IR detector on the Sirius box would allow for changing channels, etc.
But is a puzzlement, to quote the King in "The King and I".

73

 

I checked mine out yesterday evening.
No noise at all on the CB when the Sirius is turned on.This is with the FM transmitter turned on or off.
It may be because my CB is in the overhead and the Sirius is mounted low on the dash near my cup holder.

That was good info there Handlebar! Thanks!

 

Well, whaddya know? 10MHz is a common IF frequency.

 

I'm used to seeing 10.7 I.F.s of course, but 10 MHz seems more prevalent (in my modest experience) as a master osc freq in synthesizers & in test gear. This Sirius had its major spike within a couple of Kc (oops, KHz) of 10.000. They may have used it because crystal filters are cheap, but I dunno. Of course there's lots of stuff to mix with in modern vehicle cabs, too.

 

Several years ago I had the same problem with my XM radio. Turn the XM on and the static noise would go sky high on the cb. Turn it off and noise would go away. Eventually the power cord for the XM went bad and I replaced it with a new cord. Never had the noise issue again with the new power supply.

 

I put a choke on my power cord and it seems to have cured my problem.

 

Try running your CB off the power/ground wires in your cubby hole and not off the post on the dash. I had the same problem when my XM Onyx radio was plugged into the cigarette lighter and the CB was ran off the post. Now that I run the CB off the ignition I dont get the noise.

 

It's caused by "stuffing" and also if you have other antennas by each other. Don't tie your extra coxial wire together. That causes stuffing. After I moved other antennas away from each other, static was eliminated.

 

I was going to post a thread about a similar issue but I think it may already be solved, I just need to test the theory now. I have a Cobra 29LX thats dash mounted to factory coax and antenna. The antenna is tuned properly by myself with SWR meter so before I was puzzled. I also have my iphone mounted on the dash being used for Pandora radio and ipod function and plugged into the FM radio jack with ipod charger plugged into the cigarette lighter. Perhaps this is causing the interference? I did notice that I am noticing static bursts on the FM radio as well as the phone's internal antenna searches for phone signal.

 

I've noticed that the static is coming from the 12V cigarette light plug. When the static builds up, unplug the plug and reinsert. That fixed the problem for me. I probably need new plugs since mine are old and worn.

"Do what thou wilt."