Mark,
I think you mean 250 microvolts (uv)/per meter at 3 meters, not 250 millivolts(mv)/per meter at 3 meters. I think you're talking about the emission limits in 15.209, correct? O.K. I was just checking.
No, I meant micro volts, i use the m because using the u I found a lot get confused...at least I've always ran into that confusion by others.
Maybe italicized? m instead? 🙂
RFB
This part 15 website stimulates many thoughts, and in this thread we toy with the question of whether we, if asked, would help install a part 15 station.
It is a serious matter, no different than doing masonry or tree trimming. To do it professionally would require insurance, not only to cover one's own physical risk, but to defend against unhappy customers if perhaps their house is lost from lightning attracted by the 10-foot stick.
Our decision here in the one man think tank is "No, we don't do that kind of work, but you might consider checking out part15.us"
Good FM transmitters aimed for (legal responsible) Part 15 FM operation in the USA have variable output from 0-100 mW. If you have a 1/2 or Full wave FM antenna, then you cut the power back RFB. It's no big deal. You don't know if some one is running 500 feet RG8 coaxial, with -18 dB loss! You might need watts to get the signal to the antenna~! An extreme example but 200 feet of RG58 might not be unreasonable or about -11 dB. So you need 250 mW to get 20 mW at the antenna (50 ohm Z). What matters is the FIELD STRENGTH. Right? That's the first, middle and bottom line with Part 15 FM. Yes or No? All this talk of power and antennas is secondary, to me at least. Also the good flee powered FM transmitters adjustable (low) power with min harmonics and splatter, with out add on filters, another key in not getting unwanted FCC attention. No harm, no foul.
I don't doubt your estimate, but as you have said (and the FCC also says) YOU (the operator) are responsible for compliance. How you comply is variable, higher (milli) power and less efficient antenna, low power and more efficient antenna. I tend to go for the latter, low power better antenna. If you only need 10 mW or 15 mW so be it, good, bragging rights. If you want a compact antenna, put up a 1/4 wave, J-pole or dipole and turn up the power if needed. Again all the good Part 15 FM transmitters, serious about Part 15 compliance, are low power and allow you to adjust power (down) as low as you need to meet the regulating field strength..
However if going with LPFM or LPAM, where FCC gives you either 10 watts or 100 watts, FM is the way to go. You will have more range watt for watt with LPFM than LPAM, since it is a new game from milliwatt Part 15. Of course getting a low powered licence (10/100 watts) seems to be a magic unicorn. Not sure if LPAM or LPFM would be easier to get? I was reading that some LP stations were being fast tracked on Indian reservations. That's a different story. We are unlicensed, and most people don't want the hassle of LPAM or LPFM (which must be non-profit) even if you could get a license. Commercial AM stations are struggling to survive.
The question is how to accurately measure this field strength at 3 meters? In my way of thinking I would make sure the range is not much more than about 1/4 mile with a super sensitive FM radio. There are DIY field strength meters, from plans or kits. I don't think they are calibrated to FCC standards. I would talk to the FCC and say this is what I have. Just tell them. What can they say, turn your power down. Done. If no one complains I doubt the Feds will come out if you have 282 uV/m verses the max 250 uV/m at 3 meter.
"Want my opinion based on first hand experience from a 30+ year veteran of radio engineering in AM/FM/TV/RADAR and SAT as well as 30+ years of experimenting with Part 15.....go AM...you will be MUCH happier with the results...pre built gear or home made....legal or (and I don't recommend it) throwing watts." RFB
Your appeal to authority is noted. No one has said anything about your experience or watts. I have a degree in engineering, but that's irrelevant. This is kind of a non-sequitur or straw man. I don't have a dog in the fight RFB. AM has antenna, feed-line, ground issues; where FM is so much easier IMHO. That seems like a fact not in debate. However I think you would agree, AM has potential for more (legal) range, if you have a very good resonant antenna and ground. Doing that legal like is a challenge, but I like a challenge. If that's your only goal, make sound in a radio at greatest distance, in my opinion AM has more wiggle room. However FM does sound better with 50Hz-15Khz audio, where AM is topped out (with most receivers) to 6Khz audio, may be 8Khz. Many of my tube radios are 1948-1960 AM/FM. I enjoy both AM and FM. I have HP digital sweep/signal gens and an oscilloscope. I enjoy aligning them for best sound.
Have you ever heard wide band AM? How about C-QUAM stereo?
You seem defensive. Yes I have heard of WIDEBAND AM, and restore antique radios from the 1930's, 40's and 50's. I own many communication radios that cost big coin, with variable bandwidth. I also have heard C-QUAM and want to buy one of those transmitters. I don't think C-QUAM increases range. Down side of C-QUAM, most people don't have C-QUAM receivers. However the new crop of HD radios (like the excellent Sony XDR-F1HD), by default has C-QUAM capability. Other wise there is only one portable C-QUAM receiver I know of you can buy new today, Sony SRF-A300, sold in Japan, about $120 mail order. My old Acura Legend I still own has an AM stereo radio (Alpine I think). Not many commercial AM stereo stations.
I'm writing for the original poster about installation, who may not know what band they want, but they mentioned LPFM. When it comes to installation, FM is a winner! BTW I'm running my Talking House right now on 1380 Khz, listening to some MP3's through a vintage Zenith tube radio. I like the AM because it is more of a challenge. Also lack of AM radio programing forces me to make my own station. I'm blessed with one good local oldies AM station. That's not really my main taste, but it beats endless talk radio. In the end AM or FM is a choice and both valid.
I am not being defensive. I merely express my experiences in working with all aspects of radio and television engineering. And that extends much further and beyond Part 15 but does not exclude Part 15 as Part 15 is in fact a part of the radio world.
I have experienced all the up's and down's with both AM and FM, not just in the Part 15 world but also in the Part 73 world, where if you want to get down to the mud and the blood and guts...Ive stood up with the best and have had the sore feet standing on hard cement floors for hours and even days in many a transmitter sites and worked with the best of them in the industry.
As you stated earlier pilot, there are pro's and con's to each. And every installation has different conditions, therefore calling for a variety of solutions and choices. There is no one magic formula or method that blanket resolves the problems. And if anyone has had the experience to see that first hand, then you know exactly what I mean and do not need a long winded overly detailed post explaining it. But I will give a nutshell example.
My current location has a good ground conductivity rating compared to my previous location...which was a very dry desert climate and practically flat terrain. In the previous location, I found FM to work better than AM. However here where I am at now, AM works better than the FM becasue of that ground conductivity and the fact there is a river less than 2 blocks from my transmitter..no doubt making AM the better choice in this location.
Imagine what a 3 meter stick with a simple ground can do planted right on that river bank or shallow compared to an FM faced with very tall dense trees everywhere and some of them as old as the days of the frontier exploration era of the 1800's. Some exceeding the height of the utility poles by a huge margin. Not much good for that LOS if things are in the way to which clearing them would require a 70 foot plus tower..if the city code would even let you throw up such a structure in your neighborhood much less the neighbors allowing it! Ever hear of the Homeowner's Association? Many of them pitch a gripe if you want to put up solar panels on your roof much less an ugly tall tower in the back yard.
So ya there are pro's and con's to it gmcjetpilot..no argument there. However your solutions based on your experiences alone are NOT the be all end all..and neither are mine for that matter simply because every location is different and will require different solutions..be it choosing AM or FM.
Now...for my decree:
All I am doing here is posting from my experiences and ideas and first person prospective as well as voicing my opinions like everyone else is here. Let me be quite clear here with this..very easy to comprehend...
I do not need lecturing. This place is supposed to be fun and for everyone, a relaxing place, a place to unwind and share experiences and ideas, which is all that I am doing..trying to share what I have experienced and have done in my years in the engineering industry and time spent with my hobby. Isn't that what this is all about in the first place? Or am I wrong?
There is a reason why I state my experience of 30+ years (37 to be exact)...because lately when I post something..there seems to be others who have to pound the sand with their stick and state their years of experience blah blah...so in that respect and in short...TOUCHE..expect the same in return.
Or to put it in even more simpler terms...I am no newbie to any of this by any means. If some typo sets some off or what I post from my experience seems to ruffle feathers..well 1-900-WAHH...ok? Simply do not read what I have to contribute. There are other threads and discussions. No one forces anyone here....at least that is how it should be..right?
I did not start to participate here to be treated with any different respect than anyone else is expecting to be treated with. I love what I do and gladly share that with anyone. I certainly am not perfect or declare myself as Mr. know it all.
However I will not allow anyone, and I do not care who they are, to prance and dance all over me and my posts about my experiences when I am merely sharing them openly and freely because I enjoy doing that. Quoting codes and decimal points to me as if trying to attempt to be one peg above is pointless and not worth my time even reading much less responding to...and I will no longer respond to them.
In the short time I have begun to post after being a member for over a year, a few have expressed the warm welcomes one would expect while others throw around weight and scales as if this is some sort of rank and file pick and choose preference club. I do not participate in such childish games and gladly yield the floor to those who have to feed that already over-bloated ego and I certainly will not give it any more attention than it deserves.
So with all that in mind...I gladly yield the floor at this point. I have a station to run and although it is Part 15, it IS a commercial Carrier Current operation and it would not exist or be successful if I did not know what I am doing. Want to know more..simply ask. I will be happy to tell you all about it and share my first hand experiences. But do not get in the way while I share that with those who wish to know. Fair enough?
So save all the tutoring and nit picking for the beginners. No one is perfect and if anyone believes they are..try that perfection on the much bigger issues facing this world at this point in time. It could use those perfect world answers.
Decree over.
Thought for the day:
One way communication traffic never works in a two-way repeater.
RFB
I've said that before and we all laugh about it, but
you are all engineers and I'm just a dude. Also,
I was born prematurely in 1954 and have a lot
of damage from that, so I really am NOT as smart
as you guys, however.
On the FM field strength thing:
(Really loose math here.)
250 uV/M @ 3 meters - about 10 feet
Now in my house, with the C Crane
running on 90.9 MHz in the studio
where 2 of my dogs sleep, on the
first floor - if I take my Grundig S-350DL
upstairs (admittedly not a great FM
receiver, but not a horrible one) I have
to have the whip antenna up to get the
signal without any noise. And the C Crane
doesn't put out much, as we all know.
If I get a ride in the car down the street:
125 uV/M @ 6 meters ~ 20 ft (street)
~ 62 uV/M @ 12 meters ~ 40 ft l
~ 33 uV/M @ 24 meters ~ 80 ft l
~ 16 uV/M @ 48 meters ~ 160 ft l
~ 8 uV/M @ 96 meters ~ 320 ft l
l
Somewhere around here, the l
signal starts to collapse. l
l
l
l
l
l
~ 4 uV/M @ 192 meters~ 640 ft l
l
Somewhere in here the signal goes away...
(And this car radio can hear stations 80-
100 miles away on a normal day.) l
l
~ 2 uV/M @ 384 meters ~1280 feet l
Then car runs out of gas at stoplight.
Also, I tried to make a straight street with
a whole bunch of ls, but it didn't work.
Best Wishes,
Bruce, MICRO1690/1700
First RFB you spent three paragraphs talking about your experience and so on. This is not in question and is irrelevant.
Your next two paragraphs are interesting and I agree, Part 15 AM has much more legal range, and it works for you and me. However if some one is asking about a transmitter for church so people can hear the sermon from the cry room or from their car in the adjacent small parking lot, range about 150 feet, through a glass window or LOS, I'm going to recommend VHF, FM!
Then your next paragraph is personal. I never said MY opinion was the be all end all. I am a pilot. I also have a degree in engineering from LSU, post grad UW. I worked hard for that, but it's as irrelevant as your "mud and the blood and guts...Ive stood up with the best...." This is not rocket science, and there is room for opinion. I was just pointing out that power of the FM transmitter does not matter, just the 250 uV/m field strength at 3 meters. Everything else works backwards from there, antenna gain, coaxial loss, SWR, RF low pass filter if installed (good idea). The FM transmitters final stage is not what the antenna sees was my point, which no one mentioned. You might have -20 dB to -10 dB loss! That means 10 mW or 100 mW of loss. That is all I was pointing out. That seem to have set you off. It is true a high gain FM antenna needs not milli-watts but micro-watts, to achieve the 250 uV/m at 3 meters.
Your next ten paragraphs under "Decree" or manifesto .... good grief. No comment. You really have some crossed wires. I can see the sparks from here. This is supposed to be fun. I ADDED some points that you did not disagree with, and I really don't disagree with you, except for your tone and apparent manic energy you are displaying. I am not challenging your authority or knowledge in the RF field, which you seem to think I've threatened apparently. You seem very sure of yourself, and I have no desire to take anything away from you. For gosh sakes you sucked the fun out of the room RFB. This is not about you. Stick to the facts and don't get personal about yourself or me please. I look forward to more of your good technical factual posts. Cheers
Isn't the max allowable range 200' for Part 15 FM?
If I get a ride in the car down the street:
125 uV/M @ 6 meters ~ 20 ft (street)
~ 62 uV/M @ 12 meters ~ 40 ft
~ 33 uV/M @ 24 meters ~ 80 ft
~ 16 uV/M @ 48 meters ~ 160 ft
~ 8 uV/M @ 96 meters ~ 320 ft
Somewhere around here, the signal starts to collapse.
~ 4 uV/M @ 192 meters~ 640 ft
Excellent test. Good range for the C. Crane
How did you determine field strength? Did you
calibrate the S-meter. How was the audio?
When was static apparent? Was this mono?
The Grundig is mono but the car I assume
stereo.
I took my Degen DE1103, a decent radio and
used an accurate signal Gen to figure out the
field strength needed to move the LCD segment
signal strength meter. Pretty crude but it gives
me some indication for antenna experiments.
OK fine...can we get on with the program then?
RFB
You know boys, if you don't play nice, I'll have to ask you to sit in opposite corners in "time out". Now put down the knives and the spears, and shake hands. Let's focus on the radio stuff and less on the personal stuff. The truth is: we all have our egos invested in what we do with our Part 15 stations; some apparently more than others. That's O.K. That's the way it has been the last 40+ years for me personally. So why should things be different here? Let's play nice with each other and leave the spear chucking for other sites. Somebody's gonna get hurt. I'm just sayin'...
Now put down the knives and the spears
Indeed...I never was a good aim at throwing knives or spears for that matter....don't want any innocent bystanders getting hurt! :p
RFB