"Interesting analogy about the outer wall of the home acting as a reflector that makes a lot of sense. I am still running a Ramsey FM 25 B with the RF power at half setting or 12 o'clock position which should be about 10 mW, but since i have no way to measure that, i will call it a Hopeful Guess lol"
It would be great to measure it precisely, but I think you have nothing to worry about. Your signal is not going for miles, and it is quite obvious in the photos with your antenna setup, running any kind of high power would be a problem with VSWR and harmonics and such.
Mobile home parks are a unique puppy when it comes to measuring field strengths, for the simple reason there is so much reflective surfaces nearby that can and will throw off even a Potomac's readings. The FCC does not use directional antennas for measuring the field strength. They use a calibrated dipole antenna that is omni-directional and will pick up junk behind it as well as in front of it and on all sides. Now take the environment of a mobile home park and all the reflective surfaces, it will be quite a job to measure a flea signal accurately with all the multi-path reflectivity going on.
So what the field agent would most likely do is measure your signal outside of the mobile park to minimize the reflective affects as much as possible. When they see your signal is not saturating their Potomac, they will know right off your not purposely making your signal reach that parking lot behind you. They will recognize that small signal is merely doing what it does when surrounded by reflective materials, and bounce here and there, go in directions not expected and such.
Radio...gotta love its unexpected good results!
RFB
"One of the problems with the LPFM attempt here (their CP runs out Feb 10, 2012), is they can't get enough ERP without interfering with other stations, and they have no engineer(s) on their board. If they did, they might know that, if they could get enough directional power to reach even a limited range"
Indeed. Sounds like a very directional pattern would be their solution, and can be done.
Or applying for a different frequency to operate on, relocating the TX site, all sorts of different ways to avoid the problem.
But as you mentioned, if they had an ENGINEER on board....wow go figure! 😀
RFB
I was told in an earlier thread in the forum that an antenna's field strength and antenna were two different things entirely. And that increasing an antenna 's range through means of elevation wouldn't increase it's field strength. That no longer true guys? Higher power tx's, say 200-500 mw, give off ridiculously higher ground level field strength readings? Sheeezz...
I think your mixing up AM & FM. With AM Pt. 15, increasing the antenna height WILL usually increase your field strength because your longer ground lead radiates, acting as a longer antenna and increasing antenna efficiency. (Unless you use an RF choke in the ground lead...sometimes even that doesn't work)
On FM, raising the antenna will NOT increase the field strength. (At least, not 3 meters out, where it needs to be legal) On FM, your extra mast, coax, ground wire or whatever, don't act as an antenna, or increase your antenna's effeciency. The antenna itself is very efficient, if tuned for resonance.
Again, you CAN increase your RANGE and your far-field field strength on FM by raising the antenna above obstructions. You'll have a better, stronger signal by being able to shoot over those obstructions, but your field strength at 3 meters (where it needs to be 250uv/m to be legal) will be the same.
Naturally if you raise your power, your signal strength AND your field strengh reading will go up. You can't raise one without the other going up too. Cheers!
There are two ways to increase field strength without increasing TX power: 1..using a directional antenna...a yagi antenna, or 2..stacking dipoles or even stacking yagi antennas.
But this does not matter, the rule is clear about 250uV at the 3 meter point from the antenna, be it a single element or stacked elements.
There really is just no way around the rule. As I pointed out, and another member, the field agents know better and know the difference between a humble setup doing its best to stay compliant versus a setup with a bunch of "extras" that should not be there to begin with and would potentially be used beyond the allowed limits.
I think the concept of a shield may be a viable one for other applications...like perhaps a suit that could be worn by tower climbers to protect them from high level RF energy fields.
Or maybe they could replace all those aluminum foil hats those bozo's keep wearing and showing videos of on youtube! 😀
RFB
I am aware of the differences between Part 15 Fm/am installations and the effects to each. The a-m question i posted many threads ago about Hamilton's invention was just that. A question. No confusion there. This post of mine has drawn a ton of interest and feedback. I like assessing the "psychology"/mindsets associated with the tone of the responses. Love this forum! Thx.
here is a sketch for a typical trailer park part 15 am installation. a setup like this should cover an entire typical size trailer park with a strong signal.
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I have noticed a tone also, mpmiss, as to "psychology/mindsets" on the forum. Is that "tone" something that could be explored? Or, is it something best left to itself.
I think the tones are best left alone. People are the same here as everywhere else, and you can just ignore the ones that irritate (I'm sure that set varies from person to person, again, because everyone is different). A manual kill filter, so to speak.
There are actually other ways to increase field strength, even with FM. I found one out, quite by accident.
I was transmitting with a Decade MS-100, mounted in a weatherproof box about 6 feet above a metal roof - it was trimmed to meet Canadian field strength regulations.
When I changed transmitting locations, I mounted the transmitter just above the peak of the metal roof (a few inches at most) - what can I say, it was easier, I had damaged the metal tripod I was using and I was a bit lazy (too lazy, at least, to fix it).
To make a long story short, my range bumped up by a factor of about 50%. I surmise that the roof acted as a large ground plane, improving the efficiency of the antenna, even though there were no physical connections (you still need a ground, even at FM frequencies, although it's nowhere near as important as in using AM). Needless to say, I raised the transmitter back up to its former level and my range dropped down to what I had estimated were legal distances (about 1 km max with direct line of sight to the antenna with a sensitive car radio).
I suspect there are other ways - I noted a funnel affect when testing FM transmitting - the signal definitely went farther in some directions than others, particularly through a valley between two rather large mountains. Of course, there was virtually no signal in the mountain directions.
he wants to cover his trailer park with a good signal. he is not going to legally do that with fm. that is plain and simple. no tone intended. if he has a metal roof he has a untapped resource he can use to his advantage either with a certified part 15 fm on top of roof or a part 15 am setup like in my diagram. after 40 posts i don't even remember the original question unless i go back and re read it.
That raises a question that I've been wondering about lately - if someone owns a piece of land, say a trailer park, can you legally increase your FM field strength, as an example, to cover that private land (and to make matters simple, only that private land)? Seems to me I've read something about special circumstances for university campuses - as long as your field strength at the edges of the campus doesn't go over the legal limits, you're OK. Or am I all wrong?
If, for example, you owned a huge tract of land and your signal just covers that land, then who would care what your signal strength is?
Maybe I'm being lazy again and should just read the rules. Once again.
The idea of having special rights on your own land is very worth discussing.
A friend of mine owns a huge tract of land in the country. There aren't really any people other than his family living on the land, but why can't he put out a signal over the entire area, so that maybe he could listen to music while mowing all the grass?
Here's another example. My wife and I named our lifestyle "Homeshool College", because we were always studying and researching. We were not an actual college, but then again, what is a "college?" Could we have used the special part 15 campus rules?
Yeah don't think i haven't thought about putting something up on the roof, that isn't an option.
I can't even keep the roof from leaking most of the time lol.
I mentioned putting something up there but they said no way and after having the maintenance people fix it twice i don't think it's a good idea anyway. But your right, it would be a great place to have the FM antenna. I am limited to what i can do here which sucks big time.
ask don imus why you can't. he did and got fined 🙁
http://www.mediageek.net/2002/12/mediageek-news-headlines-for-12-6-02/
Don Imus Ranch Gets Visit From FCC
It looks like the FCC has been focusing on bigger fish in the pirate sea. On Monday morning, nationally syndicated radio talk show host Don Imus announced on his radio program that the FCC made him shut down a low-power FM transmitter on his cattle ranch near Ribera, N.M., 50 miles northeast of Santa Fe. An unlikely pirate, Imus had installed the FM transmitter so his ranch-hands could listen to an Internet simulcast of his radio show, which originates in New York and is not carried locally in New Mexico. It’s not clear just how much wattage Imus’s unlicensed station was running, but Don claims it couldn’t be heard oustide his seven-mile-wide ranch property.
On his Monday program Imus vowed to have frequent guest, incoming Senate Commerce Committee Chmn. John McCain (R-Ariz.), place a call to Colin Powell’s son to resolve the matter. As Imus producer Bernard McGuirk pointed out on air, the Commerce Committee oversees the FCC, and Imus said McCain is known for “follow-through,” unlike another occasional guest, Sen. Domenici (R-N.M.), in whose state transmitter was located.
Back in 2000, Sen. McCain came out as the only republican senator to strongly support the FCC’s creation of a licensed low-power FM radio service, and floated serveral unsuccessful pieces of legislation that attempted to broaden its reach. However, these rules would do Imus no good because has no license.
An FCC spokesman said any transmitter that wasn’t licensed and exceeded a certain geographic range would be in violation of law regardless of wattage and would be subject to removal, although he didn’t know specifics of the Imus case.
For further info:
http://www.diymedia.net/archive/1202.htm#120402