I read a neat NOUO, http://transition.fcc.gov/eb/FieldNotices/2003/DOC-332408A1.html
The actual field strength was not given. I am not sure if it was left out on purpose or just accidently omitted. But what made the NOUO neat was there is a list of spurious signals. For a transmitter on 101.1, the 202.2 and 505.5 are sloppy but where they came from is clear enough.
The 112.7 was interesting. My first thought was “mixing product”. 2 x 101.1 – 112.7 is 89.5. There is at translator 2000 feet North West of Victor’s city center (K208DZ) on 89.5. http://transition.fcc.gov/fcc-bin/fmq?list=0&facid=94059 (If you look at how far 10 watts goes for that translator from being up high, it is easy to imagine why even a tiny bit of power on 101.1 got someone’s attention and they contacted the FCC.)
The moral of the story is if you have a FM transmitter close to another FM transmitter, watch for mixing products.
If you look at Victor CO on a map, it is quite small. I would guess a part 15 AM transmitter could have covered the city pretty well without the FCC having anything to say. I wonder how far a part 15 am signal would go from the ridge K208DZ is on if ground radials were run as far as practical down the ridge.
Frequency mixing can occur anywhere within a system but usually this happens at the receiver when strong signals are present. In the NOUO cited the problem was apparently that the transmitter was radiating harmonics and somehow was also producing a non harmonic "spur" in the aircraft band so in this case it was not the receiver causing the problem.
One similar example from my past is that one fine day I received a polite call from a local police department and they informed me that my two meter ham band mobile signal (146.28 MHz) was interfering with their police radios in the 154 MHz band. (They found me from my ham callsign.) I thanked them and assured them that I would take prompt action to remedy this. I was using an external power amplifier with my hand held and checked it on the lab bench and found that in addition to amplifying the 2 meter signal the amplifier was oscillating at about 8 MHz which produced spurs up and down the band. This is a very common problem with RF power amplifiers if proper neutralization is not used. I junked the amplifier since it was poorly designed and not to be trusted.
One misconception I have seen cited many times is that interference from Part 15 FM transmitters can be eliminated by using filters on the transmitter output. While such filters can suppress harmonics, they seldom will suppress spurs.
The lesson is that interference is likely when strong signals are present at the receiver but it is also possible that the transmitter is producing signals which are not intended. Any interference observed should be carefully examined to determine the cause.
Neil
As much as I hate the cheap design I might be forced into the Whole House FM transmitter 3.0 but at $125 it a steep price for someone with a limiteed income. Still I'm concerned about harmonics wth the SainSonic AX-05B and need to hear from those who actually owned one. I don't want nor can use a 10 Ft transmitter.
What about a band pass filter that only allows 88-108 Mhz and other frequencies beyond or below would be filtered out? What about the FMUser transmitters?
If a transmitter is certified, as is the Whole House 3.0, then it definitely doesn't have a 'cheap design' - it has to meet the FCC (and Canadian) rules for spectral purity. There are reasons why certified transmitters cost more.
You also don't have to worry about operating with an illegal field strength, as you do with the cheaper transmitters that are readily available. The absolute best range you can hope for with a LEGAL transmitter in the FM band in the U.S. is 800 to 1000 feet, and that's line of sight (absolutely no obstructions between your transmitting antenna and receiving antenna) and a very, very sensitive car radio (with sensitivity well under 2uv). If you are getting more range than that, under those conditions, then it is pretty much guaranteed that you are operating outside of the Part 15 rules (i.e., illegally). Whether you will get caught or not - well, that's another matter.
If you want more range than that, then there's always Part 15 AM, which can legally get you up to a mile, maybe a bit more (depending on a whole host of factors which have been discussed in this Forum).
@ArtisanRadio Did the SainSonic AX-05B cause harmonics? It does have an FCC ID on it and claims to be certified like the Decade CM-10 and if it is certified I found on SainSonic I can get it for $50 from SainSonic's web site using Pay Pal. What I meant by Cheap Design was that the Whole House Transmitter 3.0 was made of plastic which looked like it would break the first time it got dropped say 6 to 12 inches from a wooden floor where as the SainSonic is aluminum and would last longer because of the way it was made. I've also read reports about the Whole House Transmitter 3.0 having that little antenna connector just glued to the circuit board via Amazon. This means that I'd have to never unscrew the antenna when I want to put the transmitter away like I use to do with my hand held police scanner when I had one. I'd unscrew the antenna and put it into a drowar. I guess if the SainSonic is prone to harmonics which I have a greater concern about I could get the WHT 3.0 and hope it won't break but at $125 (99 for me cuz I got the facebook code) it would be a shame to only have it a day because the buttons, connectors are not made well. Do you know where I can get a referbished one with a warrenty for a affordable price? I've even heard that there is issues with the left channel popping out due to the issue with the 3.5 mm imput jack but I do like the 75 uS pre emphasis. The Maxell P-13 would have been nice if it had a digital readout (Deal Breaker) and could run on electric I can't see well enough to modify it to run on electric outherwise I'd do that as it already transmitted pretty far under good conditions and had a wire antenna that you could make longer if you were brave enough and the transmitter probably causes less harmonics and spurs than the SainSonic if it is prone to do so as the reviews for the Maxell was good. The 11.6 Mhz harmonics some of these transmitters cause howeve is a greater concern than anything so what other part 15 transmitter or reasonable power transmitter can I get that won't wage a war on other services preferably Stereo for my Album Rock listeners?
The only issue I heard bad about the SainSonic was a little hum if you don't use heavy 3.5 mm audio cable and if you try and overmodulate the transmitter it causes issues as any transmitter would if your not careful. I just want to make a wise decission. AM though it goes further I'd have an issue putting up an outside antenna in the rented house and putting together a kit. No album Rocker listens to mono either as Progressive Rock fans are picky and want stereo only. Maybe I'm wrong. I'd like to have a nice clean FM Transmitter. I hope I win the WHT 3.0 on Facebook I try every time they give it away but chances of winning is slim. Yes the transmitter I had years ago was metal and wore out after yrs of use and I used it pretty hard every weekend 8PM-4AM I'd do a show. Thanks for your help I appreciate you all's time.