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Author Topic: Short Commercial AM Broadcasting Antennas  (Read 209 times)

Offline NQC

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Short Commercial AM Broadcasting Antennas
« on: May 18, 2021, 1655 UTC »
Hey All,

Just ran a few of these for grins :

WCNL ,1010 Newport ,NH :1/4 wave would be  231 ft. They run 10 Kw day on   63 ft (!!) of guyed tower with a Zillion panel antennas (cell/ 800/900Mhz ??) attached . AM almost looks like an "afterthought"  and that it seems most of the  dough is coming in  from repeater rentals. LOTS of   juice lost  on this  antenna  , but I still   hear them daytime ( fair to weak )
 through hilly  terrain / poor ground  conductivity at around 113 miles away.

WZBR , 1410 Dedham, MA : 1/4 wave would be 165 ft. They run 2Kw day into free standing 75 ft fiberglass whip (helical wound inside). I'd love to see this one in 75 MPH winds ! Fair signal at 9 mi ,  terrain path  maybe not too bad.

WJIB 740 Cambridge MA : 1/4 wave would be 316 ft. They run a 285 ft free standing tower, so it would be  thrown into our "not too bad department" at  31 ft short of 1/4 wave.Line of sight "Band Bully", even at 5 W night time  power at around 4 miles out.

Can anyone else give  any examples that you know of, the shorter the better. Maybe 1/8 wave or less ?   I am just curious how LOW some of these guys limbo and STILL make it "work", but obviously WITH a serious  electric bill as a "penalty".

FWIW /  a bit OT, I have worked out to 27 miles using  a high mast mounted 50 ohm resistor with very short leads soldered on   75 ft of 9913 (a "sort of"  "near isotropic " radiator :)  ?? ?)  on 440 Mhz FM. Rig output hyper low ,  got around  2 to 4 mW output  at radiator ?? QRPpppp- THAT was fun ! I also ran ridiculously low  outputs on 2 M SSB/FM as well.

K

« Last Edit: May 18, 2021, 1724 UTC by NQC »
Station main receiver : Bed springs to  blue razor blade detector to 2000 ohm cans to steam  radiator. Grid FN 42

Offline ThaDood

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Re: Short Commercial AM Broadcasting Antennas
« Reply #1 on: May 18, 2021, 1818 UTC »
Well... TIS Stations come to mind, with antennas from 10ft to 20ft in length. However, most of them have large capacitive Tophats. I remember when Rochester, NY downtown got a TIS station on 970kHz around 2000. I was actually able to hear that all the way to the town of Wheatland, a.k.a. the Monroe / Livingston Co. border. That's considerably more than 10 miles. Then, you still have Part #15'ers trying to push the distant limit with flea-power by making those 10ft antennas, or shorter, more efficient with heavy gauge load coils, large diameter pipe, and capacitive Tophats. Some of these dudes boast up to 3 miles! They also must have great GND conductivity to make that. Super-weak, I've heard my AM1620 that far, but on a cold winter day and in a lot with virtually no noise. Any bit of electrical buzz would wipe that out. So, how low, or short, can you go?
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Offline NQC

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Re: Short Commercial AM Broadcasting Antennas
« Reply #2 on: May 18, 2021, 1847 UTC »
Hey Dood,

VERY interesting re TIS and part 15 installations.

I too have heard some of these at amazing distances.The X band especially can be very kind at times.

But you donít hear much ( or anything) about commercial music/talk stations that are really limited on what they are allowed to build.

Just curious about what those guys have
run into.

K
Station main receiver : Bed springs to  blue razor blade detector to 2000 ohm cans to steam  radiator. Grid FN 42

Offline redhat

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Re: Short Commercial AM Broadcasting Antennas
« Reply #3 on: June 09, 2021, 2230 UTC »
You may hear more about this in the future.  I read recently that the commission is considering relaxing the rules on AM antenna efficiency in order to provide stations more latitude with regard to finding replacement tower facilities for stations displaced by urban sprawl and gentrification.  Usually you have to have a full proof done by measuring field strength at many points and requesting an operating variance, or something to that effect.

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Offline RobRich

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Re: Short Commercial AM Broadcasting Antennas
« Reply #4 on: June 10, 2021, 0317 UTC »
Amatuers have been known to work 160m contacts on loaded mobile antennas operating under 1% efficiency.

Likewise for 630m when using the common technique of shorting the legs of a 160m dipole to create a top-loaded t-antenna fed against ground radials.

Then there are the 2200m ops. Often a cage or similar vertical of severely compromised length (versus wavelength) with a massive base loading coil operating under 0.25% efficiency. Potentially four-digit voltage on the antenna, too.
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