ACC100 FM Transmitter Question?

You get what you pay for (generally). The best FM transmitter I've used (and I've experimented with most) is the Decade MS-100. I've had one running for me 24/7 for several years and nary a glitch (and it's in a weatherproof box on top of a roof, so the environment is not very friendly). It's expensive, but in my opinion, well worth it. And certified as well (in both Canada and the U.S., although the U.S. ones are tuned down to meet the more stringent requirements there).

You definitely want to transmit in mono to get the most range (if you look at the specs in car radios, most can hear an FM mono signal strength of 2 to 3uv, whereas they require a 30uv stereo signal - you'll see similar specs in good home stereos - and much worse in the cheapo home stereos).

As an aside, there are generally other considerations for certification than output strength. There are a lot of inexpensive, uncertified transmitters out there that splatter all over the map. Even the EDM (talked about here a lot), which has good quality audio, leaks into adjacent frequencies, which you don't find in professional quality transmitters such as the Decade.

I realized what the 100 stood for-- 100 feet! All i could get using the antenna.

They happily sent me instructions to increase the range-- but of course would make it illegal.

The Decade transmitters
They put out the full 250micro volts at three meters. They do not short cut you on that.
If you want to know what 250 micro volts will get you. I saw you mention the 2 microvolt sensitivity
on receivers. Well it actually 1.7 microvolts on really good receivers.. You have to ask the company producing the radio what the sensitivty is on the radio or the specifications.

The Decade will give you this range. If you have a tower put it in a weather proof box made out of white PVC material...It works the best. No metal boxes. Black color boxes absorb signal due to the carbon that make the box black. I am a Electronic Engineer and I designed alot of transmitters in my time for the military,and keep up professional AM and FM Broadcast Stations. Believe me the FCC knows who I am. I am also license in Amateur Radio,and many other services.

Let me pull out all my Folders on what the FCC wants to see if you meet the 250 uv output they do not care.

Ok my Best friend John Reed who was ahead of the part 15 transmitters,but he retired now.
Anyway here the deal most the companies that produced like the AC100 had to reduce it power to meet
Part 15 it was originally designed to be a 1 watt transmitter,so do't be shocked it sucks.

Now Decade designed theirs to be the very best Part 15 transmitter ever.
I know the people at decade... Antways if you are sitting this up to be a Church Station they will sell it to you for $385.00 that is way below regular price.

Now for distant on the Decade transmitter

3 meters 250uv basically 10ft
24 meters 31uv 78ft
48 meters 15uv 157 ft This is where most transmiters die at
192 meters 3.8uv 630 ft Radio Shack DX 440 world band receiver 4uv sens.
384 meters 1.9uv 1260 ft 1/4mile range not to bad good home stereo with out
door antenna or good car receiver 1.7uv sens.
768 meters .95uv 2520 ft 1/2 mile almost This could be done with a receiver
with a good outdoor antenna.Yagi type with lots of
elements on the antenna. Radio shack sold a good
out door FM antenna with a Range of 110miles try
That one and your signal should be picked up.

Anything past this is pure luck. Most good home Stereos have a 1.7uv sensitivity 20db to noise ratio
Anyways that type of receiver with a very large TV antenna may be able to receive the signal out
to 1/2 mile due to the gain the antenna has. Car Radios will loose you at th 1/4 mile range. Get the
transmitter high up on a tower in a White plastic box made of white PVC material is good. Run you some
very good shielded audio cables to your studio...You can get the range and be legal. It just takes
time and alot of hard work. I use to live two blocks from the FCC in Virginia and with the right tower,and
setup I manage to get out 2 miles to cars.. I was completey legal,and the FCC had no problem with it.

You will not do better than a Decade transmitter. Yes you want the Mono FM. Most Stereo receivers
stink on being able to receive stereo signals. Next time you tune a Stereo signal you are far from
see how noisy it is then turn radio to mono. It like night and day. Mono will sound clear while the stereo
signal will sound hundreds of miles off. Transmitt in Mono and you will never have people saying your
signal has alot of noise on it.

Well I hope this helps out some

Retired Senior field Engineer for Raytheon/Advance Technologies and Research/NASA

Sean

I think you're a little bit optimistic about the range of the Decade transmitters.

In Canada, we're allowed 4 times the field strength than in the U.S. - that translates to 1000uv/m at 3 meters (or 100uv/m at 30 meters, which is how the regulations read).

And that translates to about 3uv/m at 1km. However, that's the field strength - there have been threads here to calculate the actual signal strength to the receiver with a car antenna (around 1 meter in length), and it works out to be about 1.5uv, pretty much the lower sensitivity limit for a good car receiver (mono). Legal signal strength in the U.S. would give you a range of about 250 meters (800 feet). And that's the best you could do, outside in a weatherproof box, line of sight, with a sensitive car radio, transmitting in mono.

In actual practice in Canada, I was able to get that 1km range from my Decade MS-100, mounted on the rooftop on a hillside, overlooking my intended coverage area (which was just about at the ferry dock on my little island). Past that point it was very dicey. Older, less sensitive car receivers couldn't even get it there.

I've found that most home stereos have specifications that are far worse than car stereos. That can be compensated for somewhat with good antennas, but who's going to put up a monster, directional antenna to listen to a Part 15 pea-strengtth signal? Most relatively inexpensive stereros with their small antennas had trouble picking my signal up beyond about 100-125 meters (that translates down to about 25-30 meters in the U.S. for a legal signal, or around 100 feet).

Sound more Realistic to me. I gave you the Distances the FCC thinks you will get with 250uv@3meters.
That list looked over done for me too. I had a decade transmitter up on my 200ft Amteur radio tower
in a weather proof box and managed to get real close to a 1/2 mile. I had really long Audio cables double
sheilded to keep noise out of my audio. I have been able to get out more than 2 miles on a Ramsey
transmitter with a 10mw ouptut,but that way over FCC limits and that transmitter is no longer used.
Matter in fact on a 25ft Tower and 5/8 wave FM radio antenna I acheived close to 8 miles to a car,so
you really have to be careful about using Ramsey transmitters. Their so call best FCC part 15 transmitter
puts out a full 25mw and on a 5/8 wave antenna it will get you out very far. That their Professional FM
Transmitter you build by kit. The FCC will nail you to the wall using this transmitter. It far exceeds 250uv
at 3 meters. I figure it put out more like 10,000 uv at 3meters...We are talking about 25mw...Decade
transmitter is only rated at 1mw and I am not sure if that the canada version or the America version.
Either way 25mw is far more power than 1mw.... Well anyways I know Decade says their america version
only radiates 250uv@3meters and that is the safest way to go and stay legal. The FCC has told me they have fined many people using the Ramsey FM transmitters,and they say it ok to use the Ramsey transmitter,but you better take antenna measurements...They said that Ramsey transmitters have a adjustment inside of them for power out put, so they just sid to get a very senstive Field streingth meter.
One that give a digital readout in micro volts. If you test it and make sure you are not over then the Ramsey transmitter will be ok. The FCC say the first thing everyone does is turn the power to max on those transmitters. Well that from the FCC not me. I found out it best to use a transmitter that already FCC certified
and you will run into no problems.

Yes I think that distance the FCC gave me is really blown out of proportion,but that what distances they think 250uv@3meters will give you. I think the FCC needs to come to reality that those distances are impossible unless you use some really large FM type antenna.

Sorry one thing that 1/2 mile I achieved was really fuzzy,but I could hear my signal...I did not want you to think I achieved a 1/2 mile clear on a decade transmitter. It was real fuzzy,but audable..Yet it took a 200 ft
tower....1/4 mile out was almost crystal clear. I hope that helps out. Radio I used had a tuned RF front end and three stages of IF then the detector and limitor stages.....a 1.5uv sensitivity on a true FM radio. This
radio had no Stereo in it. It was made in the 1970's for Long distant FM listening. Lafayette type Radio well
made.

thanks Sean

Seankw40,

When did John Reed retire? Has he been replaced by somebody else (as being in charge of the Part 15 rules)?

He Retired this December of 2008. Yes I was sad to see him go,and I really don't think he has been replaced yet. There is a couple of people filling his spot but as a new person being a head of the FCC part15 it has not happen yet. There is a group of people working in that section. He been a friend of mine for years,so I will
deeply miss him..He was a good frind to me after my wife had passed on.

Sean

I dug into my storehouse of past projects to find an ACC100 - it appears to be stereo (it has the stereo encoder installed). Range was what could be expected on a US Part 15 FM transmitter transmitting in stereo. It sounded OK too (not up to the standards of the Decade, but then it costs a lot less). I e-mailed away and got both the manual and the modifications that you can do to increase power (but then it isn't legal, at least in the US). The mods would have been a pain with the encoder installed (they required removing the circuit boards, doable but not easy with the encoder) and then adding/moving a wire jumper on the bottom of the transmitter board) so I didn't do them. From what I gather, the range increases a lot with these 2 mods.

So I wouldn't count out the stock ACC100 as a reasonable, Part 15 approved FM transmitter.

I love the ACC 100. Have installed 2 in churches – great for transmitting within the building. However, in one case I HAD to use an isolation transformer to get rid of the hum. The manual says there's one built in and, with the right modifications, you shouldn't need an external one. I just about went nuts assuming that was true.  Only an esternal isolation transformer (an inexpensive car audio part) solved the problem.

i own one of these, come with a 3 year warranty, little pricy but on a good day to a very sensitive portable all band receiver i measured 1200ft in some directions at this range the signal is barely listenable but was there. it is part 15 certified and it's parent comapny is broadcast vision.

http://www.waio.com/