Bruce,
Carl and I have both used 3 tube Knight Kit AM transmitters. This is probably what you remembered.
Neil
kc8gpd is definitely right about the NAB trying to crush unlicensed FM, and he may also remember that CPB/NPR (Corporation for Public Broadcasting/National Public Radio) has tried to wreck not only part 15 FM but also licensed LPFM. Public radio serves itself first, tries to keep the public from broadcasting. The wireless mic industry, which Bruce suggested, may have played a hand because people using FM wireless mics were not purchasing expensive commercial products.
ABMedia1 makes me think that there might be more to the point I only hinted at, that because the transmitter is 100-feet high but only measured on the ground if the FCC shows up, the field strength at the ground will very possibly be legal. The height of an antenna does wonders to coverage. Or, maybe I'm wrong. I was wrong once before, which I now deny.
Bruce, the tube transmitter you may remember is an FM build-it-yourself project that was in Popular Mechanics Magazine (or some similar magazine), which I built, but the coverage area was very poor, as I think they tailored the circuit to match the lowered part 15 rules for FM. I spend many happy hours trying to goose the thing, but it stayed weak.
I think I may have once before discussed the 3-transistor transmitter, but if you're confused, think of how confused I must be.
FCC Part 15.239 permits a maximum legal field intensity of 250 µV/m in any direction 3 meters from the transmit antenna.
Field intensity over a free space path is inversely proportional to distance. So for a path length of 3,219 meters (2 miles), the FCC maximum, legal field strength will be 250 * 3/3219 = 0.23 µV/m. At 1 mile it would twice that, 0.46 µV/m.
Both of those field intensities are well below that needed by consumer-grade FM broadcast receive systems for good noise-free reception, especially those using simple, indoor antennas.
The peak, legal FCC field can be produced by a transmitter power of only 0.00001143 mW (11.43 nW) radiated by a 1/2-wave dipole.
The FCC issues quite a few citations (NOUOs) where it can be shown that the fields they measured at a given distance from the transmit antenna were generated by radiated powers that can be produced by transmitters operating at much less than 50 mW, using simple antennas such as a 1/2-wave dipole or a short whip.
Here is one recent example based on the FCC link below. That 24,004 µV/m field at 3 meters could have been generated by a transmitter power of about 10.5 mW radiated by a 1/2-wave dipole. That FCC-measured field is 96 times greater than legally permitted at that distance by Part 15.239.
http://transition.fcc.gov/eb/FieldNotices/2003/DOC-315968A1.html
Understand that some unlicensed FM operators might use transmitters with much more output power than 10.5 mW, also that for their own reasons some people may not object to that, and probably that most of those operators never will be noticed by the FCC.
Of course everyone is free to operate as they wish, but hopefully with an understanding of the risks that may apply.
"Understand that some unlicensed FM operators might use transmitters with much more output power than 10.5 mW, also that for their own reasons some people may not object to that, and probably that most of those operators never will be noticed by the FCC."
Is it really worth it? That question would go both ways at the current point of the rules.
For one, a 24,004uV/m field at 3 meters. Although the current useless limit of 250uV/m at 3 meters, the 24,004uV/m field, ie the 10.5mW, is it really worth the agency's limited resources to go chasing after 10.5mW, 24,004uV/m field intensity?
Calculate the number of those senseless busts that yielded a 10th of the
total fines collected versus the number of filed reduced an cancelled
NAL's and the bottom line at the end of it all as to the expense
undertaken by the FCC to chase down tiny tots.
Yet currently licensed stations are committing far more serious offenses to the rules, like false statements on official FCC documents for years.
For seconds, is it worth the risks of operating outside of the current useless limit?
Well the answer to the first point is no, it is NOT worth it to dump resources on miniscule stuff when the big boys are out there snubbing their noses up at the FCC and the rules. Anyone can simply look up the records and see that there are still outstanding cases unresolved, but those stations still get license renewals and on-going grants of STA's lasting far more than 180 days.
There is only one reason why those limits were reduced even further, and it isn't to prevent harmful interference.
If the resources were directed where it is most needed, perhaps the world of broadcast radio (commercial radio) would be in far better shape.
The answer to the second point is, well only yourselves can answer the second point of operating outside of the current limits being worth the risk.
RFB
I always concentrated on the AM
installations. To me, those
set-ups were what made Part 15
radio exciting. I am disappointed
because we will be moving and I
will probably never have the
chance to do the "3 meter stick -
100 mW DC input" thing again.
The carrier current set-up will
probably continue in some form.
I have 3 FM transmitters. The
C Crane transmitter has been
loaned to a friend. It is falling
apart from heavy use for almost
10 years. When it comes back,
I'm going to repackage it so
it is mechanically more secure.
It has also been converted to mono.
The Maxell P-13 gets used for
in-house relay from the main
computer in the living room
to the area where DOG RADIO
used to be. There is still
a stereo system in that room,
and I usually sit and listen
to streaming Part 15 stations
in there when the living room
computer is free. Which is
usually late at night. That's
on 88.3, which I jokingly
refer to as SLUG 88.3. That
transmitter is certified, and
it is an extremely convenient
package for relaying audio. I
have rechargable batteries for
it, and they work fine. I have
not modified the P-13 transmitter in
any way.
The transmitter for 90.9 (jokingly
referred to as GNAT 90.9) is a
North Country Radio MPX-96, which
was given to me as a gift by a friend
in California. A really great friend
by the way, who built a great Part 15
station in 1971 which was called WQRM.
He built a beautiful homemade control
board from a street sign that he painted
and made holes for knobs, meters, and lights.
I still
can't believe it. It was a great job.
He went into engineering and worked on
some fantastic projects in his career.
And he is still doing that.
The MPX-96 was delivering about 1/2 a
milliwatt to a standard FM dipole from
Radio Shack. I put the dipole into
a bunch of plastic pipes shaped like
the letter "T"- and made a cool looking antenna.
It's self supporting and can just sit
it a room whatever you want to put it.
it is rather large though.
In order to get the MPX-96 to run 1/2
a milliwatt, I used 4 old 6 dB RF attenuators
in series. This is about 24 dB of attenuation
connected to the output of the MPX-96. So
you can just do the math and figure out
what the MPX-96 power out is without the attenuators
in line. So that's the GNAT 90.9 set-up.
And that rig is set for stereo right now.
There is a switch to put it in the mono mode.
The transmit antenna is on the first floor
of a 2 story house in a room. I am not running
this installation right now. I do really love
the antenna. I think it looks really cool.
The house we are in right now is in the
bottom of a steep narrow valley. FM doesn't
get out of here anyway. 1000 feet away the
houses are much higher up. It is rather
dramatic, actually.
In my opinion, what other people run on FM
is not my affair. This is what I'm doing
and it's fine with me. I just thought it
would be fun to describe the set-up.
Bruce, SLUG 88.3, GNAT 90.9, TICK 1020 CC, etc.
I would just like to add that the original poster said he has been broadcasting for 6 years with a range of 2 miles. Obviously this is in violation of FCC rules, but we can learn from this.
We know the FCC operates on complaints. If he hasn't gotten any, then no problem. If he gets a complaint and an NOUO, then he can just shut down, no problem.
I can see your point.
One of the reasons I'm so conservative
with the FM is because a guy
from Clear Channel lives only
a few houses down from me.
I know he's there. He doesn't
know I'm here.
And I want it to stay that way.
And when we move, I guess that
(at least) won't be a potential
problem anymore.
But I will always keep the FMs
at very very low power. That's
just what I'm used to doing.
Best Wishes,
Bruce, SLUG 88.3, And also a proud owner of 2
AMT-3000s, but I guess I've said
that before.
"because the transmitter is 100-feet high but only measured on the ground if the FCC shows up, the field strength at the ground will very possibly be legal."
Given one can run the numbers to determine what kind of FS will be measured at ground level from the transmitting antenna 100 feet up, I seriously doubt you will find that the FS will be "legal" 100 feet below.
The FCC will take a measurement on the ground yes. But they won't limit themselves to just a ground measurement, especially if the antenna is easy to get within 3 meters to measure, like mounted on a flat root top or in a room next to a window.
Even if the transmitting antenna isn't within a point to measure at 3 meters, calculating the field strength at the measuring point and back-track that field strength (mathematically) to determine exactly what it would be if they did measure 3 meters from the transmitter antenna...even 100 feet away or below.
Phil is right, the FCC responds to complaints. If OP has local support, especially from area licensed broadcasters, that would explain the hassle free operating for 6 years @ 2 miles coverage.
Given the description of the system by OP and taking into account the specifics pointed out by Neil regarding receivers and receiving antenna configurations in common use, I doubt everyone listening to this station hearing it 2 miles out is listening with an elaborate outdoor FM antenna system.
All of this is not to discourage. All of this is meant to inform you (OP) and anyone else who may not be aware of the actual specifics to 15.239.
However OP keep going, especially with the support by the community you have! There are cases where an unlicensed station would have the local support that said stations would eventually get special authorization or a CP for a higher power licensed station.
Back to the subject...a translator. Setting one up is no big thing, but feeding it audio and having a way to monitor it will be somewhat more complex. You could use the web and feed the remote translator with audio from a direct stream feed between your studio with a "closed loop" stream (non-public) which feeds only one computer located at the translator site. This same computer could also have a stream encoder with an FM radio receiving the translator signal and streaming that audio back to you at your studio. This will let you hear the actual received signal from the translator. Note however that you will have a bit of delay between everything, but the listening audience won't know the difference.
RFB
In 1994, in this house in
this valley, a guy actually
did hear my FM a mile away.
I was using a Ramsey FM-10
running 5 mW with a partially
collapsed antenna, indoors, on
the second floor of my house.
My friend was using a Technics
ST-9030, a very nice FM tuner
that both Carl and I have. He
was also running a directional beam
antenna on his roof, which was
elevated somewhat, but I don't
remember how high up.
I was on 91.9 then, because it was
clear in those days.
Yup, he heard my transmitter. But
with that set-up, he could hear
at least 9 states regularly. The
states out here are small, but
still, were talking about:
Maine, New Hampshire, Vermont, Massachusetts,
Rhode Island, Connecticut, (where we
live - I guess that counts) New York,
New Jersey, and Pennsylvania.
Now, he has a McIntosh MR-78, one of the
best vintage FM tuners ever made, if not
THE BEST. But his antenna rotor is
broken and pointed away from me.
By the way, I understand that the greatly
revered MR-78 is not as good as the
HD FM/AM tuner that Sony produced for
several years. I have one, but I can
never remember the model number.
Hang on a second while I go into the
other room... ...It's a Sony XDR-F1HD.
It's such a teeny little box and it
runs so hot. I don't use it very
much because I want it to last a long
long time. I bought it specifically for
FM DXing - not for HD radio. And, man -
does it cook!
Bruce, 88.3, 90.9, etc.
Yeah Sony always had an issue with some of their products running hot. Not a surprise considering those products are housed in non-vented enclosures!
RFB
Unless.....you live in Florida where operating in excess of FCC Rules is a 3rd degree felony. So that would be a problem.
In addition to your FM service, since your mission is to disseminate the message of praise, you might also want to add part 15 AM and shortwave, which can extend your possible audience.
From your high location the coverage might be very large.
" There are cases where an unlicensed station would have the local support that said stations would eventually get special authorization or a CP for a higher power licensed station."
RFB - Very interesting ... Can you cite an example? Could such a precedent be used to switch us from taxiing around and actually get us onto the runway for launch?
"Can you cite an example?"
How about a visual example.
Multi-part video Hunting Pirate Radio
And there is the station in Pahrump Nevada that got special authorization.
"Could such a precedent be used to switch us from taxiing around and actually get us onto the runway for launch?"
Why not. Local representatives live in our communities. They know as well as we do how much commercial radio these days really suck. They too would like to hear local coverage of their community activities, local high school games, basketball games, baseball games, local coverage of parades or other civic sponsored events.
RFB