Sirus program on FM?

[TPO]

A friend asked me the other day why he was still hearing Stern on FM. I wasn't sure what he was referring to so I asked him some questions. Turns out his favorite station is on 88.1 MHz, and that when he is in the car he often hears Stern's morning show interfere with the semi-local college station. I asked him to check whether or not this mostly happened when he was in traffic or near other cars and his answer the next day confirmed what I assumed was happening. He is hearing the miniature FM transmitters used by some Sirius radios to get their signal into the regular FM car radio! He was able to pace some guy on the highway and listened to Stern for quite a while!

Has anyone else noticed this?

 

[Chuck]

> He is hearing the miniature FM transmitters used by some
> Sirius radios to get their signal into the regular FM car
> radio! He was able to pace some guy on the highway and
> listened to Stern for quite a while!
>
> Has anyone else noticed this?


This is getting to be more and more of a problem. Many of the Pubcasters are geting complaints about it. In fact, a couple of engineers report that they have had complaints that their licensed station was interfering with someone's satellite radio! Go figure.

It seems that most people program their XM or Sirius radios to rebroadcast in the noncom band.

 

[wkbam1690]

> > He is hearing the miniature FM transmitters used by some
> > Sirius radios to get their signal into the regular FM car
> > radio! He was able to pace some guy on the highway and
> > listened to Stern for quite a while!
> >
> > Has anyone else noticed this?
>
>
> This is getting to be more and more of a problem. Many of
> the Pubcasters are geting complaints about it. In fact, a
> couple of engineers report that they have had complaints
> that their licensed station was interfering with someone's
> satellite radio! Go figure.
>
> It seems that most people program their XM or Sirius radios
> to rebroadcast in the noncom band.
>
There's a thread on the Community Radio board about this, with some reports of half-mile or so reception. FCC, are you listening? You like busting kids with Ramseys going a few blocks, but allow these into the marketplace?

 

[Russty]

> ...88.1 MHz, and that when he is in the car he often hears
> Stern's morning show interfere with the semi-local college
> station...
> He is hearing the miniature FM transmitters used by some
> Sirius radios to get their signal into the regular FM car
> radio! He was able to pace some guy on the highway and
> listened to Stern for quite a while!
>
> Has anyone else noticed this?

Yes, I too have done this. I drove to the beach this summer listening to someone else's XM radio. Friends of mine have bought Sirius to hear Stern. The Sirius FM modulators come from the factory set to 88.1 MHz. Apparently most people are too dumb and or lazy to change it. My friends changed it to 87.7 MHz, which suprised me because that is the TV band (Channel 6) and according to Part 15 Rules is strictly prohibited, yet these devices are accepted by the FCC as Part 15 approved. It makes one have to wonder. Their transmitter gets some good range too, which also suprised me as there is a Channel 6 LPTV in the area. A lot of people set their modulators to 87.9 (also still TV band and prohibited). There is a much more in depth and lengthy discussion thread about this topic on the Community Radio board.

 

[webcastboy]

> from the factory set to 88.1 MHz. Apparently most people
> are too dumb and or lazy to change it. My friends changed
> it to 87.7 MHz, which suprised me because that is the TV
> band (Channel 6) and according to Part 15 Rules is strictly
> prohibited, yet these devices are accepted by the FCC as
> Part 15 approved. It makes one have to wonder. Their
> transmitter gets some good range too, which also suprised me
> as there is a Channel 6 LPTV in the area. A lot of people
> set their modulators to 87.9 (also still TV band and
> prohibited). There is a much more in depth and lengthy
> discussion thread about this topic on the Community Radio
> board.
>

FYI...87.9 is not the TV band. It is Channel 200 of the FM Band. There are a handful of stations using it nationwide...but I think it's only open to Class D licenses. Actually, a quick Radio Locator search turned up only two: K200AA in Sun Valley, NV and KSFH in Mountain View, CA (SanFran).

It's damn hard to get on 87.9, too...you have to have absolutely no other place on the dial to go, AND be hundreds of miles away from the nearest TV channel 6. There are precious few areas in the country that meet both criteria.

87.7 is not a wise choice for an FM retransmitter since TV Channel 6's audio is on 87.75 (IIRC) and therefore even more likely to get interference from a Ch.6...but I'm relatively sure there's no rule in Part 15 prohibiting using it for Part 15 purposes.

Retransmitters have always been made to favor the NCE band because, for many years, in a lot of the country, there aren't as many stations in there and those that were, were lower power. That's become a lot less true in the past 10 years, thanks to public radio's rise to prominence and mostly thanks to useless satellite-translators popping up everywhere. But the retransmitter manufacturers have been slow to catch on...

 

[Grrradio]

I'd be amazed to see half a mile out of any of these devices, at least in their store-bought forms. Not that ANYONE would ever mod such a thing, just to see what they'd get out of it. No sirree. ;-)

Last year, a friend and I employed our old buddy the Capture Effect to get an approximate idea of how far a modulator might throw a barely-car-detectable signal of 30 dBu. This was a mid-grade off-the-shelf KMart model (about $20; I forgot the brand name.) We parked his car in a nice, flat, open area in Iowa, tuned to a signal whose strength we knew (from calculators on the FCC site) to be approximately 55 dBu at that location; aligned the radiating portion of the modulator (in this case the audio cord) with the car antenna; then walked away from the car until we had taken over the audio AND stopped hearing the "squeaky" static of two fighting FM signals. We used that distance as the approximation to 60 dBu, i.e. a 5 dB window for capture effect... the 60 dBu got out for approximately 6', meaning the 30 dBu (1/316th of the signal) should get out for six feet times the square root of 316... i.e., around 110'.

I'm currently using a GE that tunes via a combination of range selector and dial -- it knocks out a known 60 dBu signal cleanly for seven feet. But even with 65 dBu at 7', 30 dBu is about 1/500th of the signal and should go about 160' at most. I'd like to know what these half-milers are doing! ;-)