Those little things you often see at Walmart or Target or whatever other places that use a car's cigarette lighter plug to power them, and use a USB or 1/8 aux cord to send audio from a phone, tablet, etc. to the car's FM radio...
1. Would you get any Part 15 type range out of them at all if you used one of those cigarette plug to wall plug adapters and used them at home?
2. Would they be Part 15 compliant? (it seems like these could be good cheap starter Part 15 FM transmitters until there was enough budget for someone to buy a Whole House or C.Crane)
The one thing is that you'd only be running it from a 12 Volt power supply. That in and of itself may not be an issue. Here is a possible problem:
The Transmitter was originally meant or certified to run in a car with a short audio cord. Once you put a longer cord on the transmitter it acts like an antenna. It will raise your field strength. If the transmitter is already transmitting at 250 uV at 3 meters and you increase its strength by a longer cord whereas the shield becomes an antenna. So you could then be violating part 15 rules for FM.
AM is really the way to go.
I have a 3.5mm aux cord that's 6.5 inches long and a 3.5 female to RCA male connector that's about 8 inches long. Would just over a foot together to connect my audio source to one of these transmitters be within limits?
Only use an FCC Part 15 certified transmitter. There should be a sticker on it.
Generally, these things come with the audio cable the unit is certified with. Use it and you should be OK.
Remember that just because the unit is certified, it might not even be close to legal field strength (certification only means that it is at or less than 250uv/m at 3 meters - it could be less, even much less). Many of these things are engineered to transmit only a few feet, and won't be of much use for broadcasting.
Generally, you won't get more than 200 feet range to a portable radio with a compliant FM transmitter (more using a car radio). Regardless of anything else, unless you have a field strength meter, you should use that as a barometer of whether you're legal or not, particularly if you're using a different audio cable or a transmitter that is not certified.
Power for these devices should not be an issue. If it's powered using a USB cable, then just use a cell phone charger plug. If it uses a cigarette lighter connector, you can purchase a wall adapter for a few dollars.
If you do decide to go this route, I'd stick with a name brand transmitter, and one that has been proven to have close to legal field strength. I got a new Maxell P-13 (battery powered) on e-bay for just $1. The earlier version, the Maxell FMT-100, might still be around, particularly used. There are others, the ones designed to transmit music from computers or ipods/iphones are generally the best bets.
As far as sound quality goes, they generally are OK, pretty much on a par with the Whole House and the C Crane.
Part 15 "range" is always exactly the same no matter what kind of transmitter is used.
That is, the field strength on FM cannot exceed the numbers specified in Rule 15.239.
The FCC Certification requirement applies mainly to the manufacturer who cannot legally build or sell transmitters in the U.S. UNLESS they are "certified".
The buyer of the transmitter only has a truly certified transmitter IF he uses it exactly as intended by the manufacturer and stated in the documentation.
ANY changes made to the transmitter voids the certification, but the FCC 15.239 Rule must still be met.
Obviously the ordinary hobbyist isn't going to be able to accurately make changes to a transmitter beyond using it according to the certification instructions from the manufacturer because the field measurement equipment costs $25,000 and requires engineering school to operate.
Aside from that I have a Scosche Certified FM Transmitter which has an 8"cord that plugs into an audio jack and is powered by 2-AAA batteries.
The antenna is attached to the shield in the audio cable and if I were to extend the audio cable length it would extend the antenna size and void the certification.
Make life simple by using the guidelines given in an FCC statement suggesting that an FM range of about 200' is the most that can be legally expected on FM.
I've searched eBay for the models previously mentioned, as well as other fairly known ones like the Belkin Tunecast II, Belkin Tunecast Auto and the Pyle PLMP2A. Seems like they either have the FCC logo on the box, the transmitter itself, or both. Based on what's been said, all I have to do is use what jack comes with it (only using my roughly 1.25 foot 1/8 to RCA jack if no aux jacks come with it) and connect to my laptop to see what happens. 200 feet was mentioned, but 100 feet before fading is what I was truly shooting for. That should do for some on site youth sports play-by-play.
Last year, the sponsorship for my "tape-delayed" softball broadcasts that I "aired" on Soundcloud put enough in the budget for the THII that I currently have (had it since mid-July), but even though I promoted the heck out of being on AM, it just didn't resonate with my target demo during basketball season (not one person carried a Walkman or anything to listen with in each gym I went to, my listeners were 100% from Soundcloud), so I'll air softball live on AM with tape-delayed broadcasts on Soundcloud (starting in a few weeks), build the budget and get one of the cigarette transmitters to start testing so that I can do play-by-play on FM (with AM as a backup/simulcast). I'm leaning towards the Tunecast II or the Tunecast Auto.
The Belkin Tunecast & other similar devices were designed to work in a car, in which you only need a few feet range. Remember, that just because a device is Part 15 certified, it could be radiating much less of a signal than the rules allow, and that is likely the case here (from what I've read in reviews). You'll get 200 feet (more to a car radio) with a certified Part 15 device operating at the legal limit.
The devices that have been mentioned in other posts are intended more for what you're looking for - broadcast to nearby radios in the house. They're more likely to do what you want than something designed for a car. I've had car devices that had trouble even within a car.
I'm not discouraging you, just encouraging you to read the reviews. Even if you have budget issues, you might be better off waiting and getting a used Whole House 2 or something similar, than wasting your money on a device which doesn't do what you want it to do.
I just did a quick search, and found a Maxell P-13 on e-bay for US$14, a Scosche FMT4R for around US$5, and I'm sure there are others available. The biggest drawback of these devices is limited transmit frequencies, but if you can live with that, they will most certainly work better than any in-car FM transmitter.
I recall one member here used one of those cigarette lighter fm modulators with the wall adaptor and some how got decent range. Fm usually doesn't work well with house wiring or the same way as AM works with carrier current.
His station i guess was the exception.
Crane FM2 is certified and advertises 75 feet. Has a modulation monitor so doent over deviate. I've seen it as low as $35.
Yes, the C.Crane FM2 is certified, but the stereophonic generator cannot be turned off.
Since your planned use is mainly speech you will want the most solid reception possible in your signal area, and keeping in mind that the human voice is mono, an FM signal is far more stable if the stereophonic capability is turned off.
Perhaps someone can explain the technical reason for this.
The Wholehouse 3 transmitter does have control over the stereo, it can be switched off.
Yes I can explain it but that would be another subject for another thread.
This was discussed with me posting a few articles on mono vs stereo in past posts(you'd have to search the past) on this forum.
If you can't find it I will explain in a new thread.
Mark said: "Yes I can explain it but that would be another subject for another thread."
We'll be o.k. talking about FM stereo in this same thread because it all relates to the same opening question... about using an FM transmitter for a special application.
http://www.engineeringradio.us/blog/2011/08/fm-stereo-vs-station-coverage/
This article talks about the transmitting part of why mono goes farther than stereo with the same transmit power.
Here's more... http://lowpowerradio.blogspot.ca/2011/08/broadcast-low-power-fm-in-stereo-or.html
Also, ANY radio/reciever is way more sensitive in mono then stereo.
On hi fi tuners check the sensitivity specs in stereo and mono, a big difference. This applies to all radios.
On Decade's web site for the specs on the MS-100 the frequency response of the mono model is 20hz to 20klz. The stereo model 20hz to 15klz.
Better audio fidelity with mono.
With our little allowed power(BETS-1 included) to get the best possible coverage mono is best as reciever sensitivity is half the battle.
More info:
https://www.prometheusradio.org/sites/default/files/lpfm_tech_box_guide.pdf
One of my hometown college FM stations near Nashville, TN and a commercial FM in Louisville, KY use mono. They get decent distance for their power. Sound quality is ok, but leaves a little to be desired though. With whatever transmitter I wind up buying, I should get about the same sound quality as those full power stations. My THII's output pretty much rivals WSM whenever I'm in my station's current listening "sweet spot" (within 40 feet of it in any direction), so that's the sound quality I'll shoot for on FM.