One more aside here, RF. If an inspector comes to check on a set up it'd be based on two factors. 1. A complaint from a licensed operation due to signal interference. 2. A complaint from someone over objectionable content being broadcast over the air or even jealousy. Correct? I don't know if the FCC comes out for jealousy, but I could be wrong. Anyway, the NOUO sent by the FCC would list the reasons for the order and unlike the FCC rules for Part 15, it wouldn't be vague. Most NOUO's are pedantic in nature; they must be specific in order for an operator to fully understand how to bring his/her operation into compliance.
Short of these reasons, what other reasons would there be for a visit from the FCC? There'd have to be a reason. I've been told by inspectors to my face that they don't want to deal with Part 15 operators due to several factors. In short, he informed me that "these stations aren't even on my radar. You'd have to really offend someone for me to actually visit a guy's basement or room to shut them off". He went on... "Keep your broadcasts clean and do your technical homework and you'll be fine."
When you wrote that "it is up to an inspector", that much may be believed by some. But, he has to abide by the FCC's WRITTEN rules too. Right?! And if a visit to an operator is based upon a complaint, which has nothing to do with exceeding power limits at an installation where the "field strength" limits have NOT been exceeded, or objectionable format, well, I think you see where I'm headed. Are you saying a visit or NUOU would be acted upon, or sent for a "high power" tx? There is no definition for a "high power" tx for FM Part 15. For the record here guys, for my tests, we're talking about a 500 mw, 1 watt, 5 watt tx's here. In essence, RF, under your assumption, a visit for any reason, would/could morph into an inspector having to choose whether or not to "trust an operator" to keep the power turned down on say a 1 watt tx; regardless of the reasons for the visit-when in reality the FCC's own WRITTEN rules, which he is also governed by, do not contain any provisions related to power output, nor do they define what would be considered a "high power tx's" for FM stations. And he wouldn't want to leave an installation alone such as I've described because the operator might be tempted to turn up power when he leave? Who cares? Again, the purpose of this experiment isn't to blast more power illegally. It is to find ways to use more power whilst staying within the FCC's own WRITTEN rules. And if such an installation hasn't violated the 'field strength' rules, where's the violation? Why would an operator under my set-up and scenario be concerned with an inspector's trusting them if they are actively following the rules?
Thusly, I conclude, that the challenge for me is to find a way to comply with what IS written in the present rules under section 47 of the FCC rules for Part 15 FM and to comply with them while trying to maximize the greatest range I can achieve-with any 500 mw, 1 watt tx I choose. No laws or rules broken here. Just experimentation. Especially since there is nothing written governing what is considered a "high power" tx for Part 15 FM operations. The term "high power" is yours. Not the FCC's. And I argue that whether or not an FCC inspector "trusts me" is immaterial; his own rule book doesn't specify what he needs to "trust me" not to violate other than the previously stated "field strength emissions" being limited to 3 meters. Does what I'm saying make any sense, RF? Or is it just the mindless babble of the barrister in me seeking to emerge? Lol. I always enjoy the chats and responses.
"best thing to do is enlist the cooperation of select trailer park residences"
I wish there was some people i could trust around here, but there really isn't. There is one friend here i would ask to host a station repeater in a heartbeat but the rest i would not.
This is not the best neighborhood in town.
As for carrier current, i would like to do that but it would take me some time to save money for the right gear. Probably something from Radio Systems. I actually set out to make a video today to show my coverage but for some odd reason the camera recorded video with no sound. Looks like i will need to re-do that video some other time.
"for fm in addition to the f/s rules it does state unit shall use nothing larger than a fixed 20" antenna attached to back of unit. or something to that effect.
it is allowed to have a unique connector to allow for broken antenna to be replaced in the field by end user."
For certified units marketed in the US they have to have a fixed or unique antenna connector. I do not recall any 20 inch limit to the whip though.
RFB
Pretty much all of the visits and tags by agents are sprung from a complaint, be it a signal running 1/1000 of a watt or 100, or if someone tips you off to the FCC. Doesn't matter when the knock comes to your door.
Having been through inspections and discussions with a variety of field agents, they have a set of guidelines they follow when conducting inspections. At one time these guidelines were readily available to the public for viewing on the FCC site, but now even with someone here attempting to get that information via the FOIA, and was refused...well that means
your only guideline are the published rules we know of now.
Thing to remember is that high powered illegal FM has been around a long time..and so has the routine of inspections and what those field agents do and what they do not do. It doesnt matter who comes up with the words "high powered", that is irrelevant. What is relevant is what the inspecting agent decides to do upon seeing your high powered transmitter in operation or even before seeing it, taking the measurements prior to that agent even stepping one foot onto your property.
Now do not think that the field agents cannot calculate what kind of power your system is putting out without being on site looking at a watt meter. They will know what power level you are running the first time they fire up their monitors and tune to your frequency and point their directional antenna your way. They know by experience, and education, that a compliant signal will have X amount of field strength at X distance. If those measurements are way above the limits, they are not that daft to believe they have to know for sure by a visit. Their gear tells them this long before that.
So with that in mind, do you really think the field agent is not going to note the higher power being detected at a far greater distance than what should be detected and measured at the known limit distance?
The measured field strength at that greater distance is going to tell that agent everything they need to know right off. They just have a procedure they have to follow, thus the visit and inspection.
And they do not announce it either, so you will never know if one is lurking about or if a complaint went in or anything until that knock on the door, or nice little envelope stuffed with a field NOUO notice in your mailbox.
No one here, including me is telling you not to do what you would like to do or experiment or anything else. That is the neat thing about living in the US..you can choose to do whatever you want to do. Just recognize its your behind that is up in the air taking the risk if what your doing is outside of the law.
And the activity being outside of the law is that signal emitting a stronger field strength at 3 meters than what it is supposed to be. In order to make sure that signal is within the 250uV at 3 meter limit, you will need something better than a CB field strength meter in order to measure it properly. The inspecting agent is not going to take your readings as conclusive evidence your complying. They wont even look at your measurements until after they conduct theirs....with their incredibly fancy and highly accurate Potomac FIM which WILL tell them EXACTLY what your system is doing..on site or at a distance, and they will know what kind of power level is being thrown into that antenna producing those measurements.
Well to conclude all I can say is it's up to you what you want to do. Run a high powered transmitter, run the risk. And if you succeed in getting only 250uV at 3 meters from an antenna being fed by 10 watts, that is great..but only great to the point if the inspecting field agent also thinks its great and goes away.
50/50.
RFB
i just reviewed part 15 rules. your correct no mention of a 20" limit on a fixed radiator. i think at one time though this was the case. maybe back in the 80's when i first was studying part 15 rules via ernie wilson and jr cunninghams books.
to the poster get the best certified fm you can. probably a decade ms100 put in in a weather proof enclosure and sit it dead center on top of the roof of your mobile home. as long as it's certified even sitting it over a aluminum roof won't make it go that much over part 15.239 limits not enough to matter. test with a portable and find which clear frequency gives best reception. they are not broadband and uniform in power output across the fm band so every certified tx has it's sweet spot where it will perform best and it differs from manufacturer and product. decade ms100 is regarded as the best part 15 fm available.
Thanks for the info Kc8. RFB, last question/comment. It all goes back to the initial query I posted many a thread ago. Can it be achieved via the shielding methods I've posted? I've heard from a few, their opinions of enforcement by the FCC. I get it. Now I'm asking essentially if you or anyone has ever attempted my experiments? Or, tell me, do you think it would work? Either way, please expound. Perhaps, the answers I seek gentleman await the labors of mine own efforts, heh?
I do not think it is a question of "will it work". Meaning will the shield method attenuate RF.
If the material is meant to absorb RF energy, the shield method will do its job depending upon how much RF energy needs to be absorbed, how much absorbing material there needs to be to adequately absorb the excess RF down to where you need it, and the costs involved building it. Then there is the question of effect upon the antenna, VSWR, antenna mount wind loading etc.
But as to this shield thing specifically working to assure Part 15 FM field strength limits....even NEC or CAD or wild guess cannot tell you the real world result.
Since it has never been done before, then yes the answers you seek will have to be discovered by the labor of your experiments.
RFB
get a i.AM radio unit and external ATU. you'll cover that whole trailer park with just the atu mounted above the roofline and grounded.
A FIELD STRENGTH READING IS A MEASUREMENT OF YOUR SIGNAL'S STRENGTH. It is physically impossible to increase your signal strength, without increasing the field strength reading.
Yes! I HAVE experimented in this area. All you'll be doing by running extra power and then shielding the antenna, is having the shielding reduce the radiation from the antenna, which will reduce the signal strength required to produce a legal field strength reading. (No increase in signal)
As mentioned before, you can increase the RANGE (not the strength, just the RANGE) by raising your antenna so you don't have to cut through as many obstructions. But you cannot increase your signal strength without also increasing field strength.
Sure you're free to test until the cows come home...But you can't do the impossible. Just trying to save you frustration. Good Luck!
Hamilton's approach was not a coax shield. It was an RF choke made from a toroid core and wire. This was attached inside the Rangemaster box to the ground lead to prevent that ground path from radiating.
It did its job just fine and prevented the long ground path (water tower) from radiating, drastically reducing the station's range, which is what is to be expected since it was the long ground pathway that was the cause of the signal reaching out so far. It was radiating MORE than the radiating element at the top.
RFB, I may be wrong about this.. (don't feel like searching the info right at this moment).. But I'm almost positive that the rf choke which Hamilton designed and provided to KENC to remedy the radiating ground situation ultimately DID NOT pass muster with the FCC agent... and this is why Hamilton returned to the drawing board to redesign it - and as of yet still hasn't come out with any new design (his website just says it's "coming soon").
I'm pretty certain the FCC agent actually deemed that the choke did not sufficiently stop KENC's ground path from radiating.
But please correct me if I'm wrong, in which case I'll make it a point to purchase one of them!
From what I read on various forums about the choke-n-ground thing, the unit did keep the tower from radiating but another member said they decided to go off the air due to the drastic reduction in the range after installing the choke.
Understandable too..the reduced range I mean. Basically that choke prevented the RF path from being complete. It choked off the return RF going back into the transmitter.
KENC should have re-located that transmitter closer to the ground to reduce the ground from radiating. The range would still reduce, but perhaps not as much as it did with that choke.
It's a shame KENC went through so much trouble and a shame they decided to call it quits. I certainly would not have let that get in my way. I would have found new solutions to keep the station going. But perhaps the decision to shut down was their best move.
RFB
"I thought i would keep my FM signal on 105.3 Mhz inside the mobile home park by having it as low as it is now."
Usually that works. It also creates the potential for multi-path within the park, and possibly is the reason why in certain directions from the park, you can pick up the signal fairly well.
Here is probably what is happening. Since the antenna is lower, and it is surrounded by nearby conductive objects, ie the mobile homes, the signal is reflecting off those mobile homes and going in those unexpected directions. Add the sensitivity of car radios and its understandable that even with the antenna so low, your still picking the signal up fairly good in that parking lot. The passing vehicles affecting the signal is an example of conductive objects effect on an RF signal. In the case of the mobile home park, the metal objects are stationary, and the mobile homes are sitting in different directions, it just so happens they are in the right position to bounce your signal in those directions your detecting it.
The passing vehicles are simply re-reflecting the signal as they pass by, causing the signal to drop out for a second or two as the vehicles pass.
This may be an advantage for you since the signal can get to the shopping center parking lot. I see an opportunity there!!
Using a shorter antenna does help keep the field strength in check. But it also presents an incorrect load to the TX and causes the final to work harder and run hotter due to the VSWR created by the shorter off-resonance antenna.
In-line attenuators are the better method to keep the field strength in check. But if it works and the TX seems to be ok with the shorter antenna, why not!
Your mobile home is also acting as a reflector. And depending upon the distance between the antenna and the outer wall of the mobile home, it very well could react like a feed horn in front of a dish, except in this case the dish is flat..ie the mobile home wall. If the distance is right, that wall will act like how a dish focuses the signal, or opposite like how a transmitting dish works, taking the signal from the feed horn and the signal bounces onto the dish, and the dish re-focuses and provides gain to the signal being applied from the feed horn. Depending upon the size of the dish, the distance from feed horn to center of the dish and power output of the feed horn, that signal off the dish could reach into the Megawatt range.
But in this case it wont go that high. The dish would have to be quite large. But side by side comparison, your mobile home's metal wall could be contributing to the signal's strength in the direction of the antenna itself, just like how a dish and feed horn would work.
Question...I noticed all the Christmas lights on the porch. Do they cause any co-channel noise when fired up while your transmitting? Just curious. Oh and btw, the wiring of the lights may absorb some of the signal and couple it to the AC lines, giving a little bit of FM CC action there! 🙂
I think your setup is fine. Its obvious your not trying to pump the megawatts, or put up a system capable of high power. I would run with what you got and enjoy its coverage!
RFB
"Question...I noticed all the Christmas lights on the porch. Do they cause any co-channel noise when fired up while your transmitting? Just curious. Oh and btw, the wiring of the lights may absorb some of the signal and couple it to the AC lines, giving a little bit of FM CC action there! :)"
RFB,
I have checked for co-channel noise before and after the Christmas lights were strung out on the porch and noticed nothing out of the ordinary.
In fact you might even say i check to often for interference of any kind just to make certain i am not giving anyone a reason to file a complaint against my station. (paranoid? maybe lol)
Never gave it any thought that the lights could act as an FM CC. Coverage is about the same with or without the lights which are regular incandescent bulbs. My wife & I avoid those l.e.d. lights like the plague.
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
Thanks for the input.
"Reason for such a decision by a field agent is because you have too much box that could be cranked up, attenuators bypassed and exceed the limits, that kind of thing."
I may have missed it, but I'd think a field agent would take one look at such a box and know it was never intended for Part 15 applications and become very suspicious that attenuating the signal is just an attempt to hide real intentions of getting his blessing ... only to crank up the power when he leaves the area ... pirate station trying to look like they ain't.
'Course, these guys aren't that dumb. That suspicious nature is part of their job ... rest assured, if the signal is heard at unreasonable range, and if they know about your 'attenuated' TX, they'll be coming back.
Unless you're applying for a Class C Construction Permit, and want to just do Part 15 'til you can get it. Otherwise, it makes no sense.
Seems like, with the recent rule changes (became law about this time last year), if you want to service a smallish area with more power and range than Part 15 could ever get you, gathering interest and finding financial resources for building an LPFM station should offer a good solution.
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, they could supplement with Part 15 AM in fringe areas. Not FM stereo, but better than nothing.
carrier current or an i.AM w/external ATU unit are his best bets.