Antennas for radio

Forum member "k6sti" has lots of antenna stuff on his web page:
http://ham-radio.com/k6sti/xdr-f1hd.htm

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

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

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!

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.

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.

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!"

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

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?

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.

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)

Where can one find plans/measurements for an APS-13 clone?

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.

Alright.... as promised, here are some photos and a drawing of my antenna: http://picasaweb.google.com/radioguy/FMAntenna#

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.


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

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.

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

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?