Antennas for radio - AVS Forum
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post #1 of 19 Old 08-23-2008, 02:33 PM - Thread Starter
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If I'm in the wrong forum, my apologies. Please direct me to a more appropriate place if so. I did look over the list of forums here and decided to post here.

I don't know squat about HD radio, but am very into FM. In fact, I have my own FM show on college station KALX, Berkeley, 90.7 FM, which also has 3 internet streams (www.kalx.berkeley.edu for access -- we are a great station for music!).

OK, like I say, KALX is great, but I sometimes like to hear what else is going on. My equipment isn't the best. It ranges from a pretty decent AV receiver (Kenwood VR6070) connected to one of my two rooftop TV antennas, to a low end AV receiver that's around 20 years old, an Aiwa that cost me $150 maybe, hooked up to a Terk ($80, and a mistake!), to a mini-system (Sony with 50 CD changer) that's downstairs and hooked up to a rabbit ears that rotates horizontally (vertically too, but I keep it oriented in a cross configuration).

What I'm really tired of is the fact that all but my best receiver (the Kenwood) get crappy reception for low wattage stations unless they are very local.

I guess I need a rooftop antenna, maybe with a rotator and hopefully with more than one remote control. I could try putting an additional split on one or both of my TV rooftop antennas, but fear problems with attendant signal loss. Recommendations appreciated.
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post #2 of 19 Old 08-23-2008, 02:47 PM
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Forum member "k6sti" has lots of antenna stuff on his web page:
http://ham-radio.com/k6sti/xdr-f1hd.htm

Kevin
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post #3 of 19 Old 08-24-2008, 05:56 AM
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for low power transmitters, consider a yagi style FM antenna on a rotor. Anything else will be a compromise. Avoid splitters, you lose 1/2 of the incomming signal with each split. There are several commerical FM yagi antennas available...here is one
http://www.solidsignal.com/prod_disp...ource=googleps

a decent rotor
http://www.solidsignal.com/prod_disp...D=MTRTR200-100

good luck
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post #4 of 19 Old 08-24-2008, 08:51 PM
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Quote:
Originally Posted by Muse View Post

I guess I need a rooftop antenna, maybe with a rotator and hopefully with more than one remote control. I could try putting an additional split on one or both of my TV rooftop antennas, but fear problems with attendant signal loss. Recommendations appreciated.

Channel Master makes splitters and low-noise amps if you have several tuners. Cruise the SolidSignal site for some options.

Here's a list I compiled of various fringe FM antennas (munged since the bot won't let me post a link yet):
aphenos dot net slash misc slash electronics slash suppliers slash FM_DXing_Antennas dot htm

The APS-13 is the best consumer-grade antenna for FM, but there are less expensive options if you aren't reaching for Tierra del Fuego
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post #5 of 19 Old 09-01-2008, 03:37 AM
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You also might be surprised to find the BEST (most sensitive/selective) tuners in some of the older equipment. FM tuner design peaked in the 70s and 80s, and some of the tuners from that time (by manufacturers such as Onkyo, Kenwood, Pioneer, Sony, Yamaha, Sansui and others) were remarkably better than the average tuner section in today's receivers. My point? For analog reception, don't "dis" the old stuff!
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post #6 of 19 Old 09-01-2008, 07:03 AM
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However, tuners like the new Sony XDRF 1HD (DSP based) kick any vintage tuner's butt in terms of sensitivity and selectivity (see k6sti's page for more on this.)

At $99, you can't beat it.

I also second the whole rotor/rooftop antenna approach. I tested out my (finally) completed DIY APS-13 antenna in the driveway yesterday, and was blown away! Static free reception from 75 miles ... in a valley (with a cruddy 00's Yamaha stereo reciver). I can't wait to install it up on the hill (which will hopefully be completed this weekend) and hook it up to an XDRF 1HD.

http://rochestermnhd.blogspot.com/ - Tech 55901. Tech news for Rochester. Authored by mattdp and gjvrieze.
http://tvfmantennas.a.wiki-site.com/index.php/Hardware
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post #7 of 19 Old 09-01-2008, 12:32 PM
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channel master ::sigh:: I used to work at a place that sold at one store decent stuff from them. Now I don't even think they sell outdoor antennas.
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post #8 of 19 Old 09-01-2008, 01:05 PM
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Ain't that the truth, mattdp! I tried one of the Sonys, and was floored at how well it performed. Unfortunately, the display on mine lasted about two hours. Back to J&R! Just "one of those things", I'm sure. But DAMN, Dude, that thing was a hotrod, ESPECIALLY ON ANALOG FM STEREO! Stations 120 or more miles away came in with quiet, WIDE stereo! "Holy Yagi, Batman!"
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post #9 of 19 Old 09-01-2008, 02:51 PM
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Yep Sony radios are the true DX machine thanks to my XDR-S3HD Sony table top radio!!

I manage to lock in with text and HD audio as well too KOA Denver, here in Albuquerque and not only that I also got a lock just the call letter text on KSL Salt Lake City, during the summertime storm static crashs season.

I am looking forward to fall and winter for extreme radio DXing!!

9-1-08

"73's N5XZS"
From Timothy C. Johnson
Live Long and Prosper...
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post #10 of 19 Old 09-01-2008, 07:14 PM
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Quote:
Originally Posted by mdovell View Post

channel master ::sigh:: I used to work at a place that sold at one store decent stuff from them. Now I don't even think they sell outdoor antennas.

I really wish Channel Master still made good stuff. Where's a Stereo Probe 9 FM Antenna or the Quantum TV antenna line, when you need 'em?

http://rochestermnhd.blogspot.com/ - Tech 55901. Tech news for Rochester. Authored by mattdp and gjvrieze.
http://tvfmantennas.a.wiki-site.com/index.php/Hardware
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post #11 of 19 Old 09-02-2008, 09:14 AM
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Does the industry still rate FM tuner sensitivity in microvolts (I believe that used to be the term used.) I once had a Pioneer SX535 tuner (from the '70's). If I recollect, the tuner sensitivity was rated at 1.3 microvolts. That tuner was really sensitive and I believe you could keep it in stereo mode which eliminated the anoying transition back to mono on weaker signals.
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post #12 of 19 Old 09-02-2008, 02:23 PM
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FM tuner sensitivity used to be specified in microvolts but now is usually specified in dBf (dB relative to 1 femtowatt).

dBf can be converted to microvolts if you know the RF impedance. For example, the Sony XDR-F1HD tuner has a 75 ohm input impedance and a 50 dB quieting sensitivity of 13.5 dBf. This converts to 1.3 microvolts, as shown below:

power = 10^(13.5dBf/10) femtowatts = 22.4 X 10^-15 watts
voltage = sqrt( (22.4 X 10^-15 watts) * 75 ohms) = 1.3 X 10^-6 volts
(^ denotes exponentiation)
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post #13 of 19 Old 09-05-2008, 12:50 PM
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Quote:
Originally Posted by mattdp View Post

I also second the whole rotor/rooftop antenna approach. I tested out my (finally) completed DIY APS-13 antenna in the driveway yesterday, and was blown away! Static free reception from 75 miles ... in a valley (with a cruddy 00's Yamaha stereo reciver). I can't wait to install it up on the hill (which will hopefully be completed this weekend) and hook it up to an XDRF 1HD.

Where can one find plans/measurements for an APS-13 clone?
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post #14 of 19 Old 09-07-2008, 07:52 AM
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I'll post dimensions and pictures. It's still sitting on top of the hill (were waiting on a rotor bearing, then the entire thing goes up).

As far as I know, I'm the only person on the internet to try and duplicate it. I make no guarantees about the accuracy of my design to theirs. I did all dimension estimation off of wavelength calculations and some pictures of the APS-13.

Mine is made of an old Radio Shack antenna and a scrap Winegard HD-8200P, etc...

I can tell you it does have good directionality and gain.

The APS-13 is really just a souped up Radio Shack FM antenna with extra directors.

http://rochestermnhd.blogspot.com/ - Tech 55901. Tech news for Rochester. Authored by mattdp and gjvrieze.
http://tvfmantennas.a.wiki-site.com/index.php/Hardware
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post #15 of 19 Old 09-07-2008, 10:41 AM
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Alright.... as promised, here are some photos and a drawing of my antenna: http://picasaweb.google.com/radioguy/FMAntenna#

http://rochestermnhd.blogspot.com/ - Tech 55901. Tech news for Rochester. Authored by mattdp and gjvrieze.
http://tvfmantennas.a.wiki-site.com/index.php/Hardware
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post #16 of 19 Old 09-07-2008, 10:59 AM
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Quote:
Originally Posted by mattdp View Post

I did all dimension estimation off of wavelength calculations and some pictures of the APS-13.

There is no possible way this can work properly. The APS-13 is a highly optimized design derived from extensive computer modeling. The dimensions are critical. Correct response depends not only on the element lengths and spacings, but also on the phasing-line spacing and diameter (which is odd) and construction details, such as the size of the element mounting brackets.

Quote:
Originally Posted by mattdp View Post

The APS-13 is really just a souped up Radio Shack FM antenna with extra directors.

The two antennas were designed decades apart for different purposes by different people using entirely different methods. Both are Log-Yagis. The similarity ends there.

Brian
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post #17 of 19 Old 09-08-2008, 07:15 AM
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I had heard somewhere that the RS was very similar to the front section of the APS-13. They look fairly similar.

I never said it worked properly, but it does work nonetheless. ...and it works quite well (compared to rabbit ears). I'd be glad to build a more accurate model, but apart from sinking $225 into a real one, I don't know what else I can do.

http://rochestermnhd.blogspot.com/ - Tech 55901. Tech news for Rochester. Authored by mattdp and gjvrieze.
http://tvfmantennas.a.wiki-site.com/index.php/Hardware
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post #18 of 19 Old 09-08-2008, 09:26 AM
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What the APS-13 is famous for is not so much forward gain but its spectacular pattern. No backlobe anywhere in the rear half-plane is less than 29 dB down across the entire FM band, according to my computer model. A clean pattern is much more important than gain in situations with adjacent- and co-channel interference, which is just about anywhere these days except in the far boondocks. 30 dB is a factor of 1000 in power. Power from the rear is 1/1000 of that from the front. To achieve that kind of rejection requires precise cancellation of the currents in all of the elements over a wide rear angle, all the way across the FM band. A small construction error here or there can seriously disrupt the cancellation at one frequency or many.

My favorite high-performance antenna for home construction is the Körner 17.5, described here:

http://ham-radio.com/k6sti/korner.htm

This antenna has more gain than the APS-13 and a pattern almost as good, but it uses a single driven element and no complex phasing line. Unless you're really careful mechanically, it would be difficult to make the couple dozen electrical connections required for the APS-13 phasing line robust against wind and weathering. If any go bad, so does the antenna pattern. I don't have construction details for the 17.5, but Peter is a very nice guy and I'll bet he wouldn't mind supplying them if you're serious about building the antenna.

Other antennas, both commercial and home-brew, are described and modeled here:

http://ham-radio.com/k6sti

You can compare forward gain and F/B curves here:

http://ham-radio.com/k6sti/curves.htm

Brian
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post #19 of 19 Old 09-08-2008, 04:36 PM
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Thanks for enlightening me. I thought the APS-13 was just a nice high gain design, nothing more. The whole thing about the polar pattern and f/b ratio makes sense, I just had not considered that before.

I've heard the old Channel Master Quantum antennas had really good f/b ratios, has anyone used, say an 1110 or 1160 on FM?

http://rochestermnhd.blogspot.com/ - Tech 55901. Tech news for Rochester. Authored by mattdp and gjvrieze.
http://tvfmantennas.a.wiki-site.com/index.php/Hardware
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