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An FM Broadcast Transmitter For Your Home
Bruce Perens writes "I wanted to be able to listen to net audio and my ham station around the house and yard. Those iPod FM transmitters don't have enough range. So, I bought a digital controlled, 100 miliwatt transmitter that covered my whole block the first time I plugged it into what was, until then, a recieving antenna."
Just look in the DIY kit section of any electronics store, there's always a number of small FM transmitters, some of which get 2km range.
They usually have an electret microphone, but it wouldn't be very hard to modify one to take a line-level source.
Yes - they could. Radio stations are typically required to pay licensing fees for the music they play. Although, if you are transmitting at such strength so as to get the RIAA on your back, the FCC is going to have some fines for you as well.
THIS ACCOUNT IS OFFICIALLY RETIRED/RETARDED.
It used to be. As a ham you SHOULD know this. The rules regarding unlicensed broadcast transmission in the FM band changed. You can, in fact, use any amount of power you want. That is, as long as you don't excced 250uv/meter measured at a range of three meters.
For most of the unlicensed stuff that translates to roughly 10 to 20 mw. This is governed by part 15 of the FCC code and you can read even more about it at http://www.fcc.gov/mb/audio/lowpwr.html#PART.
Going to the store page reveals that a 0.3W transmitter costs a wild $140. Yes, there's an LCD and menus, but no self-respecting budget-minded geek would lay down that much money to broadcast music over a short distance.
There's plenty of circuit designs at ePanorama that are relatively simple and powerful. DIY; save your money and your honor.
I bought the CCrane transmitter http://www.ccrane.com/fm-transmitter.aspx/ and perfomed the easy mod http://www.xmfan.com/viewtopic.php?t=3257&postdays =0&postorder=asc&start=0/ to increase it's output power.
It works great and covers the entire house. It's cheaper than the original post and includes a case and power supply (problems that the original poster had with the ebay one).
Not so insightful. If you read the article, you'll notice that Bruce set the output to 100 mW. There was a reason for that: unlicensed transmitters at 100 mW or less are legal in the FM broadcast band.
1: You might get surprisingly long range reception. From my experience on the 145 MHz Ham band, I can easily communicate 30 miles with less than 1 watt with a roof-mounted antenna (of course the receiving station also has a good high antenna). There are differences that will reduce your range (particularly the wide bandwidth of the signal), but in general 2 watts can potentially cover a very wide area..
2. Yes, particularly if the antenna is high up and your signal gets into the city, or if your transmission annoys anybody for any reason.
3. $10,000 a day fines and your equipment (and possibly other nasty things I don't know about!)
Ultra cheap FM transmitters use a tuned tank circuit to control frequency (ie - a variable capacitor). These are very difficult to get to the exact center of the frequency you choose, the result will more than likely be poor audio response.
Furthermore, your receiver is probably digitally controlled to an exact FM frequency and the variable cap system will change frequency slightly with temperature and humidity, so that the transmitter will slowly go in and out of channel. The receiver is phase locked to the correct channel, and the result is that the system will gain and lose quality over time. Digitally controlled frequency is a must for this application.
Kit systems are usually poor at doing audio; making a noise-free circuit is somewhat of a black art and it takes a lot of research and tinkering to get it right. For example, Ramsey Electronics makes an FM transmitter kit with digital frequency control and all that. The problem is that the board layout introduces an unacceptablt amount of hiss into the audio signal. No amount of adjustment will fix this, and the average hobbyist is unprepared to even figure out what the problem is.
Finally, Be very careful of high end ($300) transmitters used for gyms. Some of them are mono only (!) but do not specify this on the advert.
Your best bet is to look on the net for reviews of any transmitter you're thinking of buying. When people have good things to say and don't point out the obvious flaws, then the product might be OK.
I purchased several poor FM transmitters before I got one that worked well, and I use it for transmitting FM throughout the house.
That would be the C.Crane FM transmitter. You can get it for about $80, and Froogle lists several vendors.
On FM frequencies, these devices are limited to an effective service range of approximately 200 feet (61 meters).
/ Documents/bulletins/oet63/oet63rev.pdf
source:
http://www.fcc.gov/mb/audio/lowpwr.html
see also:
http://www.fcc.gov/Bureaus/Engineering_Technology
Bottom line:
The transmitter described is not even close to complying with FCC regs. FCC compliance depends not only on transmitter power, but also on antenna gain and several other factors. You cannot simply say "X milliwatts is safe". Not only that, but 100mW into almost any antenna is going to be a violation. Something in the range of 1mW into an omni antenna would be more like it.
----
All of whose base are belong to the what-now?
Pump up the volume
it is only after a long journey that you know the strength of the horse.
In Europe it is not permitted to use any transmitter on broadcast frequencies, unless you are a licensed broadcaster. And it doesn't matter how low the output power is, so those Ipod thingies are not allowed either.
Such devices (including the ipod fm transmitter) are illegal to use in Europe.
As i have written in another post, These things are illegal in the UK (we have to use special transmitter/recievers that work on the 2.4Ghz band). So thank god, I dont need to listen to "Johny next door", who loves to broadcast crappy songs, drowning out my regular channels.
Have a nice day!
To comply with the unlicensed rules, you need to turn that thing down by a couple orders of magnitude. The lower limit isn't actually in watts, it's actually something like 85uv @ 3 meters. I don't recall exactly, but it's not my ass on the line here... go read the rules before yous gets busted. :-)
To comply with the licensed rules (you said you don't wanna lose your ham license), you need to start broadcasting your call sign periodically. Worse, you need to stop broadcasting music - mostly because the FCC will kick your ass for abusing your amateur license (again, go read the rules), but partly because the artists' organizations may kick your ass for not paying royalties. Yeah it's only your neighbors you're entertaining, but they can be every bit as abusive as the FCC.
Wait... did Bruce P write that article, or does the story just link to some random guy who bought one of these things?
or how about anyone come over..
what he is doing is already in violation of the FCC rules. 100 miliwatts is the maximum allowed into the antenna provided in the kit. hooking it up to a gain antenna is illegal as he now went past the 100mw ERP.
all it will take is one phone call by a pseron that does not like him to get the FCC and a 10,000.00US fine on his arse.
Unlicensed operation on the AM and FM radio broadcast bands is permitted for some extremely low powered devices covered under Part 15 of the FCC's rules. On FM frequencies, these devices are limited to an effective service range of approximately 200 feet (61 meters). See 47 CFR (Code of Federal Regulations) Section 15.239, and the July 24, 1991 Public Notice. On the AM broadcast band, these devices are limited to an effective service range of approximately 200 feet (61 meters). See 47 CFR Sections 15.207, 15.209, 15.219, and 15.221. These devices must accept any interference caused by any other operation, which may further limit the effective service range. For more information on Part 15 devices, please see OET Bulletin No. 63 ("Understanding the FCC Regulations for Low-Power, Non-Licensed Transmitters"). Questions not answered by this Bulletin can be directed to the FCC's Office of Engineering and Technology, Customer Service Branch, at the Columbia, Maryland office, phone (301) - 362 - 3000, e-mail LabHelp@fcc.gov.
PENALTIES FOR OPERATION WITHOUT A PERMIT OR LICENSE
The Commission considers unauthorized broadcast operation to be a serious matter. Presently, the maximum penalty for operating an unlicensed or "pirate" broadcast station (one which is not permitted under Part 15 or is not a Carrier Current Station) is set at $10,000 for a single violation or a single day of operation, up to a total maximum amount of $75,000. Adjustments may be made upwards or downwards depending on the circumstances involved. Equipment used for an unauthorized operation may also be confiscated. There are also criminal penalties (fine and/or imprisonment) for "willfully and knowingly" operating a radio station without a license. DON'T DO IT!
He also far exceeds the distance limit set by the FCC.
Nice way to publically admit you are violating FCC rules.
Do not look at laser with remaining good eye.
Program restrictions are not relevant for my purposes, which are not broadcasting. Those who want to open a broadcast station for their own neighborhood can potentially run into them.
Bruce
Bruce Perens.
Bruce
Bruce Perens.
Bruce
Bruce Perens.
Bruce
Bruce Perens.
Low power broadcasting is legal under FCC part 15 as long as you stay under radiated power limits that they set.
Bruce
Bruce Perens.
It is absolutely untrue that unlicensed transmitters at 100mW or less are legal in the FM broadcast band in the U.S.
Well, actually, it is true that some unlicensed transmitters at 100mW or less are legal in the FM broadcast band. But only those that operate at far, far less than 100mW.
I'm really surprised that the person who wrote the original article (i.e., the one who posted on technocrat.net) admits to being a ham operator, but then seems to know nothing about part 15 of the FCC regulations. If you want to know all about the limitations on unlicensed operation, you need to know part 15 -- no excuses. And the 100mW limitation applies ONLY to unlicensed transmissions in the AM broadcast band, and NOWHERE ELSE. Instead, each band in which any kind of unlicensed transmission is permitted is subject to its OWN RULES.
See: FCC rule regarding unlicensed operation in the band 88-108 MHz (Note that although this document is served by akamaitech.net, the source of the document is the U.S. Government printing office)
FCC PDF document with all you ever wanted to know about unlicensed operations under Part 15
Ramsey Electronics kit page with FCC information regarding lawful use of low power transmitter kits
American Radio Relay League (ARRL) information on part 15 of the FCC rules (The ARRL is the largest national organization for ham radio operators)
Note that the actual permitted field strength for unlicensed operation translates into the a signal of only a few nanowatts -- around the single digit range -- certainly not anything even remotely resembling 100 milliwatts!
Thus, the immediate parent of this comment should be modded WAY down -- it certainly isn't "informative." If anything, it is perpetuating misinformation that could get someone into serious trouble.
So, instead of paying $140, plus shipping, plus mods, and transmiting at above the FCC's legal limit, why not pay half the price, make no mods and be legal?
Oh! I get it. You make some money on the sale of these on eBay. Maybe even indirectly? That's cool.
(Thanks, Salshdot for the nice ad.)
Soldering for idiots:
1. Heat what you are trying to join. Don't melt the solder onto a cold component.
2. Let the joint cool at it's own rate. Don't blow on it!
3. Don't solder something delicate (like a CMOS chip). Solder in a socket and plug in the component afterward.
There. Now you don't suck at soldering anymore.
Any ideas on a suitable attenuator? I would imagine that you can attenuate the 100mW output down to 20 or 30, and bring it within limits. According to the FCC link in the grandparent, the FCC seems to be concerned more with your transmitter having a range of 200 feet or less, regardless of output power or antenna design.
There is no reasonable defense against an idiot with an agenda
:wq
Roy Neset's Tioga, N.D., farm isn't quite in the middle of nowhere, but it's close. Neset wanted to listen to talk radio while cultivating his fields on his tractor. But the only radio station in the area plays country music and refused to change its programming.
So Neset bought a low-power radio transmitter, got written permission from a Colorado station to carry its signal and began transmitting that station via satellite. Neset's station extends only about five miles in each direction, most of which consists of his farm. His station is also listened to by a handful of people in the area.
When the local radio station manager learned of Neset's broadcasts, he complained to the FCC's field office in Minneapolis. The FCC sent an agent to Tioga on at least two occasions to monitor the station. On learning that Neset was broadcasting on 88.3 FM without a license, the FCC convinced the U.S. Attorney in North Dakota to file a lawsuit.
During a hearing, the FCC admitted that Neset wasn't interfering with any existing station. In fact, no FM stations broadcast in the area. But the agency stuck with its argument that it's illegal to broadcast without a license.
That that is is not that that is not. That that is not is not that that is.
Bruce
Bruce Perens.
I am giving you the benefit of the doubt - and could just toss this off as a troll.
I have a weblog called Technocrat.net and write reviews of stuff that I've bought on that weblog. The review before this was a flashlight. I would like to get traffic on my weblog, but that's all I get out of this.
For a living, I do consulting for $300/hour, which beats the heck out of anything I could make by hawking flashlights on slashdot.
Bruce
Bruce Perens.
Yep, VHF (2m) packet is limited to 19.2kbps, though the vast majority of packet operators run at 9600 or even 1200bps. I think some folks have run up to 56K on UHF (70cm) in Germany.
.05%.
AFAIK these limits are per the FCC, not technical limits. You should be able to hit a data rate of 50% of the carrier frequency under perfect conditions. So, 100MHz would theortetically give you 50Mbps. But whether or not you could successfully demodulate that more than a few inches from the transmitter without pumping lots of watts through it is anybodys guess. I think most encoding schemes have a data rate in the neighborhood of 1% their frequency. 11Mbps 802.11b @ 2.4GHz is around
DRM 'manages access' in the same way that a prison 'manages freedom'