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Posted: 1/30/2006 9:10:16 PM EDT
[Last Edit: 1/30/2006 9:10:57 PM EDT by AZ-K9]
I have Sirius, and there is an 8 square block in my city in which I cannot get the signal. My receier says "aquiring signal".

Our police radio experienced a lot of problems within the same exact area a year ago. Turns out a building in the area has Nextel towers on it, and after negotiating Nextel altered their power or freq's and it no longer interferes with the police radio.

Is it possible it also blocks the Sirius reception?
Link Posted: 1/30/2006 9:15:26 PM EDT
Well, if it always drops out when you go into that area and picks back up when you leave, then that's a pretty big clue...

Seriously though, it is possible. Is yours direct wired or using an FM transmitter?
Link Posted: 1/30/2006 9:23:55 PM EDT

Originally Posted By Hoplophile:
Well, if it always drops out when you go into that area and picks back up when you leave, then that's a pretty big clue...

Seriously though, it is possible. Is yours direct wired or using an FM transmitter?



FM, why? Has nothing to do with the receiver displaying "aquiring signal"....
Link Posted: 1/30/2006 9:40:36 PM EDT
I may be able to help here. If memory serves me, Sirius and XM downlink in the Ku-Band satellite frequency band. In North America this is generally 11.7-12.2 Ghz. What may very well be happening is one of a few things.

1. Harmonic interference
When a signal is broadcast especially using high powered signals, harmonics are also broadcast. A cellphone tower is generally broadcasting in the 800 Mhz range, putting harmonics at 1.6Ghz, 3.2Ghz, 6.4Ghz, 12.8Ghz. Yes that is outside of the Ku-Band Rx range but with a high enough carrier even a 4th harmonic can be taking up so much bandwidth that it could affect the Rx only signal of a satellite radio reciever.

2. Broadband Noise
The cell tower may not be filtered enough and by amplifying the cellular signals, they are also amplifying a lot of noise (Gaussian White Noise) acting as a jammer of sorts.

3. Command and Control
While aiming a satellite terminal, I crossed a cell tower and picked up what seemed to be a carrier in the Ku-Band Rx freq that I figured (possibly mistakenly some cell guy will probably chime in telling me I'm wrong) was a command and control link between that cell tower and another or perhaps another location.
Link Posted: 1/30/2006 10:03:29 PM EDT
Wingnut coverd a lot of my ideas. I was thinking that the high signal (energy) level near the cell site could possibly overwhelm the satellite receiver. Here is another. Both XM and Sirius use terrestial repeaters. In other words, they have placed transmitters in many cities to 'fill in' when you drive between buildings for example and the satellite antenna in your vehicle can no longer see the satellite. The satellite receivers automatically switch to the land based transmitter (if available) when it doesn't 'see' the satellite. Now...the land based transmiters are around 2300mhz or 2.3ghz. PCS cellular is around 1.9ghz. So, another possibility could be that (assuming a city 8 block area) buildings were blocking the radio and it was using the land signal. That could make it even easier for the cell transmission to overload the radio. I'll turn this back to wingnut as my experience limited to TVRO and C/ku uplink.
Link Posted: 1/30/2006 10:10:23 PM EDT
Agreed Tallbob, the potential lack of filtering of that high-powered signal probably raises the noisefloor of the receiver, reducing the Signal/Noise ratio and producing a corresponding rise in BER thereby making any signal you do recieve unusable. The reciever simply cannot sort out the actual satellite signal from spurious noise from the tower.
Link Posted: 1/30/2006 10:29:11 PM EDT
AZ-K9 is probably reading some of these posts wondering what we are talking about so here is what I'd do ( without a very expensive spectrum analyzer and other stuff). Get the book for you satellite radio and see if there is a signal meter or "antenna aiming" as it is called on my XM Delphi. Then when you drive around see what changes from when you have radio and when it quits.

Find out who maintains your police radios. My guess is he knows the engineer of the Nextel site and may have the answer if not a solution or cure.

I'll assume you have the antenna properly mounted on the roof of the vehicle and the installation was a quality job. You'd be surprised what bad grounds and poor connections in general do to rf (radio frequency) devices.

More and more wireless services are making things interesting.
Link Posted: 1/31/2006 4:50:13 PM EDT
and more and more of those various wireless gadgets transmit RF and, as noted. harmonics. Look at the FCC small print on your radio. It must accept interference and not cause interference. Unfortunately one of the easy ways to not cause interference is to use the lowest possible singal strength. Your receiver is made sensitive to pick up extremely low power signals. You get near a high power source of RF and it may get overwhelmed.
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