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Old 4th November 2011, 05:36 PM   #71
rdf is offline rdf  Canada
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Quote:
Originally Posted by tubelab.com View Post
In the US all FM radio stations used to transmit with a predominantly horizontal polarization.
Most stations I've built are circular polarization. Horizontal antennas were reserved for mountainous terrains with crippling multipath. Some sites I inherited were elliptical; instead of the 50% V, 50% H polarization of circular they employed less vertical power to balance the higher gain benefits of horizontal against the penetration benefits of circular.
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Old 4th November 2011, 05:46 PM   #72
hags is offline hags  United States
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Quote:
Originally Posted by DF96 View Post
AM MW ground wave is essentially vertical polarisation. We were talking about VHF FM. In the UK this started horizontal for best high quality long-distance propagation to fixed roof antennas, then added some vertical to help the majority who wanted portability and were not interested in quality.
That's correct, I was just giving two examples of vertical polarization.
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Old 4th November 2011, 06:02 PM   #73
Colin is offline Colin  United Kingdom
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This might be of interest. An experimental DIY FM antenna by John Linsley Hood, specifically designed to be mounted flat against the wall and be as unobtrusive as possible.

Lofty FM Arial.jpg

I built one years ago and it worked quite well but my location is line of site to an FM relay station, just over a mile away. It worked better than the usual rabbit ears wire.
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Old 4th November 2011, 07:39 PM   #74
Nanook is offline Nanook  Canada
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Default readu made options...

er...some ready made options: the original poster was looking for an indoor antenna setup. Being a Canuck myself, he should have just looked in his own backyard:
  • Magnum Dynalab has the SR-100 "Silver Ribbon" antenna, an easy to tune dipole type, with proper termination. The ST-2 is a verticle type, including a choke. This is similar to the Fanfare. Magnum based in Bramford,Ont.
  • UHF has a TV rabbit ear type, that has been apparently "hotrodded", based in Longueuil (Montreal), Quebec.

The J-pole looks interesting as a DIY type. Here's a thought: I get great reception on 99.3 (FM, but not in a metro area) with my Tivoli Model1 radio. It uses cell phone technology to receive and tune stations. Even without an antenna I can get a signal from over 100 miles away. With an antenna I am sure even better. Another option could be an old CB "whip" antenna.

Regarding many of the other "pre-made" and inexpensive options, I have an old Terk tabletop "square" FM antenna/tuneable amplifier, that simply doesn't work. At least not the way I think it should. I would stay away from many of these types, unless also suitable for HDTV, whether rabbit ear types or not. Perhaps I can attach this tuneable amplifier to an antenana and get som distant stations.
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Last edited by Nanook; 4th November 2011 at 08:01 PM. Reason: typos
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Old 4th November 2011, 07:57 PM   #75
hags is offline hags  United States
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Really for indoor FM it's hard to beat a big ol' pair of rabbit ears. I've seen these at many local garage sales that seem to dwarf my 10' yagi. You can also check your local CL.

IMO the biggest bang for you indoor FM antenna buck.
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Old 4th November 2011, 10:55 PM   #76
Nanook is offline Nanook  Canada
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Default rabbit ears...

I agree, however the balun should be taken out . There' are significant drops across inexpensive baluns. Get a good balun or just cut the existing one out.

Apparently any "HDTV" rabbit ears are suitable as indoor high performing antennas. I gave a set away to a friend who could not get FM in his trade shop. Now he gets good reception. Often available for $10 or so new

An old CB antenna with a suitable choke (at least I think that's what the thing housed in the cylinderical housing on the ST-2 is). Make your own choke suitable to filter out TV, CB, etc Again, similar to the Fanfare FM-2, and Magnum Dynalan ST-2
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Old 4th November 2011, 11:08 PM   #77
hags is offline hags  United States
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Absolutely, if you're serious about FM RF/AF performance replace the cheap baluns with coax baluns/chokes or toroids.
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Old 6th November 2011, 04:59 PM   #78
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Wow - a couple of pages of helpful responses to a post on a thread which was years old. Thank you very much everybody. I shall make my way through people's ideas and see where I end up.

Thank you again.
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Old 5th October 2013, 09:41 PM   #79
wa2ise is offline wa2ise  United States
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Exclamation J pole antenna with feedline other than 50 ohms

Oh, there's tons of instructions on how to make a J pole antenna fed by 50 ohm coax. But there's absolutely nothing I can find if you want to use feedline of some other impedance, say 75 ohm coax, 300 ohm twinlead, 450 ohm ladderline, or even a twisted pair in ethernet cat 5 cable (100 ohms balanced, I ran some to extend a POTS phone line, and had a leftover twisted pair, and hey, Cat 5 runs in the VHF spectrum anyway, but not on this cat 5 cable or else the FM radio would suffer too much leakage). This must be classified or something...

As a scientific wild *** guess (SWAG) it looks like you can locate the feedpoints for these other feedline impedances by taking the square root of the ratio of (desired impedance/50 ohm), and taking that resulting number and multiply it by the length from the bottom (shorted end of the J pole) the instructions tell you to place the 50 ohm coax connections. It seems to work on a J pole I made for my FM broadcast receiver, though I realize there's a ton of variables, like receiver mismatches, stray conductors near the antenna and so on.

Yes, I know that all ham rigs are 50 ohm, and thus why noone ever says anything about any other impedance location. But if I wanted to make a J pole to receive say an FM broadcast station at 101.1 MHz and couple it to the 75 or 300 ohm FM tuner input, I'd want to know where these impedances exist on a J pole antenna.
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Old 5th October 2013, 09:56 PM   #80
dmills is offline dmills  United Kingdom
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Actually, on receve almost no radio is actually 50 ohms (Well, some measuring recevers), and 50 to 75 ohms is only 1.5:1 VSWR anyway, so I probably would not worry about it.

Note that given the reality of the recevers, there will be a mismatch anyway and thus the cable can be used to form part of a matching network (Take the mismatch and rotate it around the smith chart by the electrical length of the cable to see what you end up with).

If I was feeling picky, it is possible to tweak the feedpoint for best return loss, but note that obtaining a 75+0j ohm feedpoint will also depend on element spacing.

Regards, Dan.
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