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I am looking at starting a FM or AM Part 15 Station to go along with my Internet based Radio Station.
I always thought AM would carry the signal farther than FM.
I am looking at starting a FM or AM Part 15 Station to go along with my Internet based Radio Station.
I always thought AM would carry the signal farther than FM.
But with Part 15 power does it really matter ?Thanks in advance 🙂
My internet Station is just getting started.
And I think a small Part 15 Station would be a great addition to it.
http://www.klnj.net.
Total posts : 45366AM Part 15 definitely does better than Part 15 FM.
That is, AM is EASIER to send for a longer distance.
HOWEVER, as we have recently found, if the FM antenna is very high way up in the air, it can also go far.
Total posts : 45366FM will always sound better than AM in terms of frequency response. Noise starts creeping into AM signals at a rather close range, and just increases as you go out further. Whereas your FM signal tends to either be there, or not. Having your transmit antenna up high so that you reduce obstructions to your listening antenna means that an FM signal should be there more often within your legally attainable range.
As for that range, it’s just the laws of physics that dictate that. Given the field strength allowed for FM broadcasting in the U.S., your signal can go probably at maximum 250 meters (750 to 800 feet) with a sensitive car radio at the receiving end (capable of receiving a 2uv signal or less with some quieting), much less with a typical portable stereo (the FCC uses 200 feet as the range barometer to a typical receiver). Having your antenna up high, as I said, will reduce potential interference, but you won’t get any better range than that (and be legal). Right at this moment I’m broadcasting on AM using a Rangemaster, legally tuned to 100mw output, mounted at ground level, and getting a good, listenable signal (with some noise, but not horrible) out to a mile or more in some directions.
Total posts : 45366Hats off to Artisanradio for one of the most accurate range estimates for Pt. 15 FM! Indeed, the only legal way to be heard beyond 750 – 800 feet would be if your listeners had outdoor 10 element yagi beam antennas aimed at your transmitter. The FCC’s 200′ estimate for a typical portable stereo is quite accurate also. Don’t forget, tho, that’s outside with no obstructions. One of the REAL challenges with Pt. 15 FM, is penetrating inside houses. With the antennas that “Joe Blow Public” uses on his stereo in the living room, (which is often NO antenna at all….) you’ll be lucky to be heard well inside the house across the street!
Sorry to be discouraging…just being honest! Ron Kocher, Palm Coast, FL
Total posts : 45366The bottom line is…your mileage will vary. I’m not sure why everyone else has so much trouble with FM range but out here a Ramsey 25b off its own little whippie sitting in a window covers FAR MORE than 700 feet.
Anyone is welcome to come on down for a see for yourself demonstration.
RFB
Total posts : 45366That’s probably because it’s not legal. I don’t think that particular transmitter is FCC certified (and even if it is, as you yourself have pointed out in previous posts, that doesn’t really mean much – it’s up to the user to ensure that the installation is legal). If you do the math, you’ll find the range estimates I gave are pretty accurate for a legal Part 15 FM field strength. Unless, of course, you have a field strength meter and can verify that your installation is compliant (not many of us have that piece of expensive hardware available).
When I was broadcasting in FM up here in Canada (where we are allowed 4 times the field strength of the U.S.), my range topped out at about 1 km, and that was with an Industry Canada certified transmitter in a weatherproof box, mounted high above a roof, and located on a hillside with my listening area down the hill (so antennas were pretty much at line of sight, with no obstructions). Typical range was 1/2 km, maybe a bit more. And that range is what the math indicates.
[Allowable U.S. field strength is 250uv into a 1 meter antenna at 3 meters. That translates to a field strength of:
25uv at 30 meters
5uv at 150 meters
2.5uv at 300 meters
Now, a field strength of 2.5uv doesn’t mean that you will induce a 2.5uv signal into an antenna. There’s some complicated math that will calculate that with a typical car antenna (found in other posts), but I usually rather simplistically estimate a signal level of 50% of field strength, so that means a 1.25uv signal at 300 meters. That’s at the extreme lower end of detectable sensitivity for a mono signal – very important – with an extremely sensitive car receiver. Recent Kenwood car radios will receive a 2 to 2.5uv mono signal with 40db quieting, most others top off at 3uv or worse, so expect plenty of noise (most likely nothing) at the 1.25uv level. A field strength of 4uv/signal strength of 2uv would be produced at approximately 180 meters with no obstructions, or close to 600 feet; that would generate a good signal on that Kenwood car receiver with quieting. Of course, if you just happen to have a gain antenna, such as a Yagi (as has been pointed out), attached to your car, you could extend the distance somewhat.]
Total posts : 45366I think one reason Pt. 15 FM range reports are often so super-sized, is because so many people assume: “as long as you use a certified transmitter, you’re guaranteed to be legal.” But that’s only true until you diddle with it, and/or put a different antenna on it.
But what’s the first 2 things most operators do when they fire up a certified FM xtmr for the first time, and discover it can only be heard 100 feet away or less? It’s even recommended in many product review posts that you do those 2 things before using your new “certified” xmtr.
As soon as you do even one, you’re more than likely above the field stregnth limit. For that reason, and factoring in human nature, I believe most “Pt. 15 FMs” are technically illegal. But, the FCC enforcement bureau being mostly “complaint driven”,you should be OK as long as you’re careful to select a clear frequency, use a GOOD low-pass filter, don’t have any ememies, and aren’t grossly overpowered. Happy trails!
Total posts : 45366“But, the FCC enforcement bureau being mostly “complaint driven”,you should be OK as long as you’re careful to select a clear frequency, use a GOOD low-pass filter, don’t have any ememies, and aren’t grossly overpowered.”
We could bang our heads on the table about signal strengths all day long and not get anywhere with the real world here.
Fact is that there are a lot of marketed transmitters that even with that comfy FCC number on them, exceed these field strength levels. And the FCC really has no time chasing after a transmitter a couple of mW higher than the rule thumpers preach.
I know..I keep in contact with a field agent on a regular basis and their plates are so full and manpower so weak and budgets so low that they can barely keep up with the REAL enforcement they need to do.
You hit the nail on the head stating select a clear frequency, use a GOOD low-pass filter, don’t have any ememies, and aren’t grossly overpowered.
Now if a TX, certified or not, puts out “x” amount of signal, and that unit/s are still being marketed and sold within the US, then I do not see what the problem is when someone firing up their TX for the first time notices that signal reaching out a lot farther than 200 feet.
If these units were “illegal” then they would have been taken off the market a LONG time ago. But for some reason, and let’s use a well known brand for this…Ramsey still sells their FM 25’s and FM 100’s and AM 25’s and 1 watt amps and so on.
Saying that those who do have a signal reaching beyond 200 feet are illegal is a shot in the dark unless you have inspected these stations and found blatant pirating with booster amps and multi-bay antenna systems etc. We do not know what they are using. They could have very good conditions in their area, or have their TX’s high up on a pole or serving a small village or community HOA lot for all we know. We can quote the limits, but that doesn’t mean anything when it comes to an operator running their FM-100B unit stock into the internal whip…or attached to an external antenna via the supplied external antenna connector.
What is on paper is not what is in the real world, all those agents out there are very well aware of this, as well as being aware that transmitters are on the market that do exceed the field strength limitations…but we do not see any massive movement by government or anyone else to force these manufacturers to discontinue marketing and selling of them do we?
Just accept the fact that more than 200 feet happens and that not everyone is a terrorist!
RFB
Total posts : 45366That was kinda sweet.
Total posts : 45366Well it is not intended to berate or put anyone down. Even I quote rules and field strengths etc. But I also recognize that what is on paper is not what is in the real world, especially when it comes to propagation. It is just as much in flux as is the environment.
Another bottom line is what has been quoted many times before, use your discretion and simply stay within the rules. It is not a user’s fault that a kit they buy still on the market can throw a signal a lot further than 200 feet even off its own supplied whip.
But in keeping with the spirit I firmly agree that AM is the way to go for range than FM. But FM, even from a iPod transmitter having NO antenna other than the audio input wire can do some surprising things.
RFB
Total posts : 45366In the Pt. 15 world there’s no doubt AM range is greater than FM range…but Oh the audio frequency response on FM! And the stereo! And it’s noise free in most of your coverage area, small as it is. Plus, it’s so much easier to set up right. (Don’t need radials and all that) AND, (finally) 80% of radio listeners are already on FM. I especially love FM for those reasons, but that’s just me. What the heck! Try them both! Then stay with the system you like best, or stay with them both and give your listeners a choice. Good Luck & Have fun!
Total posts : 45366Illegal FM transmitters were the bane of my existance when I was legally Part 15 transmitting using FM on Bowen Island in Canada.
I made the effort to ensure that I was within the rules, to get the maximum possible legal range, even to the point of consulting with Industry Canada, our watchdogs. And there were others who really didn’t know what they were doing (or care) who were interfering with my signal with illegal transmitters – even leaving these transmitters on 24/7 with an unmodulated carrier. So while the FCC/Industry Canada may not have the time or budget to pursue these guys, they still have an effect on both Part 15 operators and listeners, never mind the licensed stations.
An illegal field strength is the ONLY reason why an FM transmitter would have a range exceeding what has been discussed here. It’s just physics. There are reasons why Ramsey’s and others are marketed as ‘kits’ – they could not be legally sold as assembled transmitters, since they could not be certified. And 1 watt amplifiers – just an invitation to break the rules.
You’re effectively arguing that it’s OK to break the rules on FM, as long as no one complains or you’re caught (just don’t break them too much). And yet you used the argument for AM transmitters in previous posts that just because you install a certified transmitter, it doesn’t mean that you are legal – and you exhorted people to ensure that the installation is legal. So which is it?
[As an aside, I experimented with various Ramsey FM transmitters and an early version of the EDM at their lowest power setting, no tweaks or amplifiers. As I stated earlier in this thread, my absolute maximum range using the legally tuned Decade MS-100 was 1 km to a very sensitive car receiver line of sight & no obstructions, typical was 1/2 km or so. I was able to hear the Ramseys almost across the island, a distance of about 2 miles (just outside Snug Cove), and the EDM right across the island to the ferry terminal in Snug Cove, probably 3 miles, with whip antennas no less! The EDM also had lots of signal splatter. Needless to say, I shut those things down right away – there was nothing gray or theoretical at all about their legality]
Total posts : 45366Precisely, rlkocher. FM transmitters are easy to setup and use. Non certified ones are also easy to purchase from online sources. All in all, a definite invitation for those who don’t really know what they’re doing to get one (and a temptation for those who do to get that extra range).
I really don’t know why Industry Canada allows 4 times the U.S. field strength here, but I’m glad they do 🙂 At least Part 15 FM is useable as a broadcast vehicle.
Stereo broadcasting is great, but it sucks power and reduces the listenable range of your signal; you’ll get the greatest listenable signal range broadcasting in mono. I like mono. Given the material that I broadcast (vintage jazz, 60’s music, old time radio) there’s no reason to broadcast in stereo, and I usually dig up the mono song versions in any event. It allows me to reduce the Internet streaming bitrate with no loss in quality of the source material (I also run my own server, so it then gives the potential for more listeners). And greater range. Win-Win-Win.
FM signals tend to either be there, or not – there’s a narrow band where you start to lose the signal and then it’s just gone. So if you hear the broadcast, you’ll generally hear it well.
On the downside, the FM band is crowded, and it’s tough to find an open frequency, particularly within urban areas. When there is one, every Tom Dick and Harry with an FM transmitter, certified or otherwise (usually otherwise due to cost considerations) gloms onto it and hammers your signal.
The AM band is relatively open, so it’s easy to find a frequency, at least during the day (night is another matter, signals just come rolling in on those daytime open frequencies). You won’t get the frequency response, but there are transmitters that sound really good – I use the Rangemaster and it’s particularly nice, even without audio processing (but I use VST with a software compressor plugin, combined with an Inovonics 222 to get 122% peak modulation). When I listen to the station in the car, you notice a difference between AM and FM, but surprisingly, it’s not as much as you would think. And also not surprisingly, I’ve found that the more inexpensive assembled transmitters don’t sound as nice – you get what you pay for.
I’ve also found that FM is troubled more by obstructions than AM, perhaps because of the much weaker signal. I use AM now because I’m located in an urban subdivision; if I was more in the open, I think that I would go back to FM, particularly if I could get the antenna up high (an option that is really not there with AM, given the need for a non-radiating ground).
Total posts : 45366apparently in florida and texas. it’s unofficially legal to run 1 watt on the fm band and run 100mW on am with a long ground lead. the fcc apparently shows leniency in those areas. canada is more progressive with LPFM and AM but does not allow for multiple transmitters running the same programming whether carriers are synced or not.
Total posts : 45366Hi,
I’ve read the pros and cons for FM vs AM and I agree with most. But I just want to chime in about AM audio quality. AM may never sound as good as FM, but with proper audio conditioning it can give FM a run for it’s money. More so with a car radio where the acoustics are not like a living room.
I broadcast on AM (big band stuff mostly) and when I’m well within range, on the road I can’t tell AM and FM apart. Keep in mind that many commercial AM broadcasters set their compression very high to enhance vocals so the audio quality for music takes a hit. Well that, and the fact I don’t hear as well as I used to either 🙂
I’m just saying, it’s possible to get very decent audio quality with AM.
Andre
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