So If I were to set up a Radio camp and I want to get out the whole camp I could do this legally on AM? OK not that does make some sense. Thanks Rich for that clarification. Maybe the FM side is only going 800Ft. Now the AM side could go 2-3 miles. That could be the distance of the whole camp ground. The fact it was not inspected after advertising is still beyond my scope at the moment. Maybe something will come up that explains this. On a side note I'm glad to start seeing part 15 Radio for campus education and great projects like this. I'm not putting down their efforts. I just want to have a few things clear here.
Below is a link to the full text of FCC §15.221, which includes...
b) As an alternative to the provisions in paragraph (a) of this section, intentional radiators used for the operation of an AM broadcast station on a college or university campus or on the campus of any other education institution may comply with the following: (etc)
One's personal definition of a "radio camp" wouldn't necessarily be accepted by the FCC as meeting the definition of a college or university campus, or campus of any other education institution defined by §15.221(b).
This line taken from the rule... "or on the campus of any other education institution"... opens the liklihood that if a given summer camp is operated by a bonafide educational institution, which could include a religious organization, it would probably pass muster.
In a certain sense the definition of "educational institution" is as significant as the definition of "campus."
...In a certain sense the definition of "educational institution" is as significant as the definition of "campus."
That is arguable for unlicensed AM broadcast systems, perhaps.
But nothing in Part 15 permits exceeding the maximum field intensity limit given in FCC §15.239 for unlicensed FM broadcast systems -- whether or not they are located within a camp/campus that meets a definition acceptable to the FCC.
Chances are that further comments in a thread on this topic seen on another board will now appear only behind a "members only" wall :< )
I think the paranoia about advertising your station is a bit much. First of all, if you were 100% legal an inspectin wouldn't be an issue. I know, this is where ya'll chime in with your list of 100% legal stations that got a NOUO. Did they follow through with due process? You have the right of appeal. If you simply have a 100% legal transmitter running, you're going to be OK. Oh, wait, now we cue all the evil "out to get you agents" funded by the NAB, and all that rot. There are thousands of Part 15 stations running in this country. Yet people dig through every violation ever recorded to put together the consipracy theories, etc. Yes, it's entirely possible that some operators got screwed. This happens in everything. How many people can you find that will tell you how they got screwed over by a cop for speeding? The list is endless.
I don't think I could possibly advertise anymore than I do. When I came on the air two years ago the paper did a front page story, above the fold, with half page color photo. We have a storefront on mainstreet with a bright two color neon sign. We've adopted a highway with a big KEBS Bovey Radio sign -- right on the four lane highway passed by thousands of people a day, a highway by the way which is the main highway connecting towns that have several commercial radio stations. Their staff must certainly drive by the sign at least a couple times a week. I have an ad weekly in the newspaper. Our logo is on the posters for the Farmers Day Festival -- thousands of posters are put up all over the area. So, no, I can't say that if you advertise the FCC shows up right away.
I'm running a blatantly legal transmitter. Maybe the FCC drove by one day, looked at it in their binoculars, and said "Look at that, Watson. It's a certified Procaster and the ground terminal has no wire on it" and they drove on their way. I don't know. But the idea of having a station on the air and trying to keep it a secret is pointless. Unless you're trying to fudge the rules.
As you can see from a documented FCC bust here on this site the documentation done by the FCC is rather thorough. If you were legal that documentation would prove so.
Tim in Bovey
I think the reason these examples of inspections happened seems to all boil down to station operators talking about using uncertified FM transmitters. It seems in all examples there had been discussions of using other transmitters "turned down to legal power". We all know how rare and expensive it is for an operator to have the necessary device to actually measure field strength. So if the FCC gets wind of someone using something on FM that's not certified they can be relatively sure that it's not going to meet the rules and they've got an easy case on their hands.
There simply is no way that someone using any sort of non-certified transmitter can be sure they're legal without being able to take field intensity readings. You can't even go out with a radio, set it up at 200 fet and turndown the transmitter until the signal fades away, as the reult depends on the sensitivity of the radio and antenna. And near as I can tell every Part 15 FM operator doesn't believe 200 feet is the limit and would tweak it for a bit more. Heck, you can't even be CERTAIN that your Part 15 certified transmitter is legal.
It's so much easier with AM. Any relatively competent person with some radio knowledge can build a transmitter and verify that their final input is 100mw or less with simple, inexpensive, easily available meters. Then if you own a tape measure you can be sure your ground lead and antenna combined add up to 3 meters or less, and you're good.
I stay fast to my belief that the only real use for Part 15 FM is for the transmission of music etc in your own home and around your yard, for the convenience of transmitting sound into car stereos from ipods and such, and general purpose short range uses. That and if you have enough potential listeners living on your block. You can only do so much with the legal limit no matter how you try. you simply cannot change the laws of physics.
Tim in Bovey
Rich quipped: "Chances are that further comments in a thread on this topic seen on another board will now appear only behind a "members only" wall :< )"
We must ask, if things get said behind a member's only wall has anything been said?
We do know that things not said on the public forum are probably being talked about behind the member's wall.
I agree with Tim's estimation that good publicity is not being policed by an FCC eager to deploy tigers.
But publicity is also open on the crumby breakfast tables of licensed operators and self-righteous HAMs who might sniff a chance to be Roy Rogers vs. the cattle rustlers.
i have a harris MS 15. it's old, 1980 vintage solid state exciter, but heres the thing about it. it tops out at about 15 to 20 watts but bottoms out at a power level so low that my marconi 2955 didn't even register a power reading. and it does this stock, no modifications. i'm assuming it drops down to single digit micro or nano watts. i fired it up on it's lowest power level feeding 30ft of rg58 into a tuned dipole and it didn't even go as far as my certified waio / broadcast vision transmitter. that tells me that it is a good candidtate for part 15 fm use under 15.239. since i have a spec-an, and a certified fm transmitter as a calibration source i am confident that i can set this harris to part 15 levels with no issues and without a $15K FIM. unfortuneately i have to remove the external pot and replace it with an internal pot for the power adjustment so that once it is set someone can't come along and change the power setting. this is the primary reason it is not currently in use on my part 15. when i make that little modification i will give it a shot at trying to match it up to my certified unit. i also have an optimod 8000 clone here that someone built from the 8000 schematics. and the big boot is not only does it sound so much cleaner and better than the certified unit it is spectrally cleaner than anything i have ever seen at that power level as compared to my certified unit which is a spectral nightmare and just barely complies with fcc spectral emissions for part 15. so it is possible to use a commercial exciter for legal part 15 uses. that is my story.
Yes, of course it's possible to use a variety of exciters and transmitters for legal FM Part 15 use. The flaw in the plan is that you plan to use a certified FM transmitter as a standard and you have no clue what that certified transmitter might actually be putting out. you may be able to use a spectrum analyzer to match your output to that of the certified unit but it's my suspiscion that your certified unit won't be putting out 250 uV/m. My bet is that it will be less.
And no matter what you use for a transmitter, no matter how pure the signal, how beautiful the audio, the legal limit will still only give you so much coverage. 250 uV/m is just that, no matter how you're generating it.
Hopefully next week sometime I will have, at least actual FIM readings from a brand new Decade CM-10 and a brand new Wholehouse 3.0 as measured at 3 meters. These numbers will be determined with both the FIM-71 from Potomac and the ZTechnology R-506. Both units used by the FCC, as well as RF R&D labs and broadcast engineers.
My bet is you get coverage over a block and you're using a non-certified transmitter, you've just opened yourself up to scrutiny.
Tim in Bovey
Reply to Tim Bovey
I agree with your assessments of Part 15 FM ... to a point.
We've all learned a lot in these discussions about FM. Certainly enough to know that talking about range is not simple and linear.
Yes, if you have a legal FM transmitter installed close to the ground, then 200-250 feet maximum to a sensitive receiver is probably about all you're going to get. But mount that transmitter up at 10 meters (about 33 feet) and you'll get 3x + that range to the same receiver. Rich's simulations have predicted that, and my experience has borne that out in the real world (Rich's simulation just explained what I observed and quite frankly I was perplexed up to that point).
There are plenty of applications for which you can use 800+ feet range in a car (which generally would have the best receiver) - car shows, ferry lineups, parking lots, construction zones, bridge lineups, etc.
That would also cover about a city block, particularly if you had an outside antenna to go along with that sensitive receiver.
Would it go as far as Part 15 AM. No, of course not. But it still has its uses over and above personal entertainment.
FM still sounds better (even in mono) and some music practically demands that higher quality, such as classical.
And I can also state categorically that if you increase the allowed field strength by 4 times (as in Canada), the potential uses increase even more (especially if you can get that transmitter antenna up high, as I did on Bowen Island).
I look forward to your test results, which should be very telling and hopefully will match with Rich's simulations. And if, as you (and others) suspect that most of these certified transmitters deliver less (maybe even far less) than the legal field strength, it will certainly help guide others' decision as to which transmitter to purchase if you want the most range.
I also wonder if there are easy ways to field retune those transmitters you're testing to take them up to the maximum legal field strength. But that's a topic for another day.
Building on the comments just posted by Artisan, knowing also from experience that height is the key to range improvement with small transmitters, I also tell you that improved antenna technology can improve the signal within the same field strength, leading to better reception by reducing multipathing without actually extending range.
The most frustrating weakness with out of the box certifieds has been for me the raucous multipath distortions as I move within the field. By viewing a spectrum analyzer I have reduced this unpleasant affect to near zero while maintaining the same field strength (actually I lost 2dBu), but the signal is more constant and less prone to disturbance.
You have guessed by now that I am talking about vertical and horizontal polarization in transmission, regardless of which one your receiver is set for.
I'll be doing some "height" testing as well. My house was built in 1905 and has a third story walk up attic wih a front window that faces the street. This is roughly at about 30 feet above the ground. This window has no screen or metal nearby, the construction of the house is metal free, and I am able to set the transmitter right outside that window on the front of the house. I have every plan on doing so and continuing my range and possible FS tests with the transmitter at that level, so see what happens. It's about the best and easiest way to test height range that might simulate what someone may do in real life. The house is all wood, the windows are all wood framing and the only wiring in the attic is one line to a lightbulb at the top of the pyramid ceiling.
This is all the sort of testing that can turn into a real mess. I only have two FM transmitters, both brand new Decade CM-10 and a Whole House 3.0. Once I have the field strength readings at 3 meters so I know where they stand legally I'll decide which to use for height testing, etc. But there seem to be a ton of transmitters out there, although mostly not certified. I was quite surprised to see today (I had never looked before) and the HUGE variety of FM transmitters on ebay, that clearly will be sold to anyone, with a ton of varying outputs listed -- 5 watts, 7 watts, 10 watts, etc. Clearly not certified. Certainly not Part 15 legal.
Tim in Bovey
I also wonder if there are easy ways to field retune those transmitters you're testing to take them up to the maximum legal field strength. But that's a topic for another day.
Certainly this would destroy their certification. And the only way to really retune them to know is to have a FIM at hand. Trying to use a spectrum analyzer to compare output would have to rely on a true tested source to establish the limit, then make all tests and adjustments under the same circumstances.
I was surprised to see the Wholehouse 3.0 with it's "reverse SMA connector" for the antenna was not *really* an SMA connector. On the transmitter it's just a reversed bolt with a 1/4 x 36 thread. This doesn't really prevent anyone from using whatever they want for an antenna, as you can easily clip a lead, or for that matter, use a matching reverse thread nut and attach a nice wire with a round lug terinal on it right to this antenna "bolt". No coax connector necessary.
Of course the Decade has a metal whip antenna. What are the odds the metal cabinet is RF ground? Probably not. I was intending to take output readings from these transmitters to see what their actual output is in watts (fractions of watts I imagine) but it looks like I'll have to open them up to gain ground access for this. It would be interesting to know power output and also field intensity at three meters to see what sort of power is being intentionally lost in the antenna design to make them legal LOL.
Heck, for all we know these turn out to be over the limit (but I doubt it)
Tim in Bovey
... Once I have the field strength readings at 3 meters so I know where they stand legally I'll decide which to use for height testing, ...
Tim -
Your results using your FIM-71 and/or R-506 instrumentation will be interesting to read.
Some caveats intended for the casual reader ...
Field strengths measured X meters in any direction away from the radiation center of a VHF transmit antenna system will depend on (at least):
1) The effective radiated power in all directions and all polarization planes
2) The elevation above the earth of the radiation centers of the transmit and receive antenna systems
3) The polar patterns, physical orientation, and antenna factor of the receive antenna
4) Earth characteristics (conductivity and permittivity)
5) Obstructing and/or reflecting surfaces other than the earth, on/near that measured propagation path
6) Ambient r-f noise and other interference present at the input terminals of the FI meter, at the measured frequency
From what you have posted about your decades-long broadcast experience, probably none of this is new to you, Tim.
But it might provide some background to those who read the results of any such measurements made and posted here, or on other "Part 15 Hobby" websites.
Yup, always variables. But the FCC doesn't factore too much into account when taking a FS reading or your transmitter, LOL.
For my 3 meter FS tests I'll be in an open field well more than several hundred feet away from anything but the Earth itself. The FIM-71 manual suggests 7 feet about ground for such tests, which I will do, using wood stands to hold the transmitter and FIM at height.
Once I have these numbers I plan to revert to my front yard and street, where it will be easy to compare "field" readings to "residential" readings at 3 meters and see if I can note any significant difference, then I'll proceed to take my 50 feet, 100 feet, 150, and 200 ft readings, and further if necessary. Mostly because I have the markings already made on my street, measured with a tape measure.
The FIM-71 allows for calibration taking into account cable losses (probably non even measurable at the couple feet involved here) and antenna factor as well. The R-506 has the antenna factor and cable loss data already loaded into it's internal computer and provides direct readings. (Oddly enough, I still prefer the FIM-71, probably because I've used one for years, the R-506 is relatively new to me).
So, we'll see. Hopefully some data next week.
Tim in Bovey