Ah, the OP cannot do roof or outside antennas.
Thought I'd post this anyway.
This is my latest build the 10', 88-92MHz high performance yagi design from High-Performance Yagis for 88–92 MHz
Thought I'd post this anyway.
This is my latest build the 10', 88-92MHz high performance yagi design from High-Performance Yagis for 88–92 MHz
An externally hosted image should be here but it was not working when we last tested it.
An externally hosted image should be here but it was not working when we last tested it.
FM radio antenna (indoor)
The antenna wizards hang out at Hugh Thompson's Digital Home .. It is a great resource for multimedia home entertainment. The Toronto/Buffalo region is like a "big bowl" so I can receive all the UHF tv stations using a small fractal antenna. But CTV moved down to channel 9 which I don't get on the fractal. For CTV, I have a loop about the size of a bicycle wheel hung on the wall. The loop is made from an extension cord with the sockets cut off and the 75ohm balun attached to the plug. Something like that will work for FM radio.
The antenna wizards hang out at Hugh Thompson's Digital Home .. It is a great resource for multimedia home entertainment. The Toronto/Buffalo region is like a "big bowl" so I can receive all the UHF tv stations using a small fractal antenna. But CTV moved down to channel 9 which I don't get on the fractal. For CTV, I have a loop about the size of a bicycle wheel hung on the wall. The loop is made from an extension cord with the sockets cut off and the 75ohm balun attached to the plug. Something like that will work for FM radio.
I'm in love with the Moxon antenna. Never tried one for 75 ohm though, but according to this link: http://www.moxonantennaproject.com/fmdxer/The Indoor Moxon FM Antenna.pdf it's doable.
No need to use plastic pipes, I use a wooden frame, and for indoor use, it's more than enough.
It doesn't take much time to make one, and the result is well worth it.
Good luck with Your Dx'ing
No need to use plastic pipes, I use a wooden frame, and for indoor use, it's more than enough.
It doesn't take much time to make one, and the result is well worth it.
Good luck with Your Dx'ing
For broadcast reception you can often get away without a balun. The skeleton biconical linked from an earlier post can get some balun action by leading the coax cable away between the arms of the lower element. Not as good balun action as a full biconical, but that would be a bit large for indoors!
In the US all FM radio stations used to transmit with a predominantly horizontal polarization. The transmitting antennas are multi bay arrays. The common practice was to tilt or rotate one or more bays to improve reception with vertically polarized car radio antennas. That is still the case for older station equipment.
Today most new broadcast installations employ hybrid antenna systems using a combination of vertical, horizontal and even circular polarity. This is done to offset the loss between horizontally polarized home receiving antennas and vertically polarized car radio antennas. Some information about FM transmitting antennas can be found here:
SWR Products
It is highly possible that the best polarity at the receiving end may not be perfectly horizontal. My experience in South Florida is that the strongest signal is usually received with a horizontal antenna, but it may be possible to reduce troublesome interference by tilting the antenna to reduce reception of the interferers signal. We have a lot of pirate broadcsters that radiate all sorts of random junk, but most seem top be vertical.
My experience has all been done with outdoor antennas and good measuring equipment. Indoor antennas will require much more experimenting since the signal strength can vary a lot with a small change of antenna position, especially in a concrete and steel building.
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.
Here's a useful site for diy FM antenna builders: 88–108 MHz and FM tuner enthusiasts.
I built one of these: Wideband Vertical Omni - Works quite well, and can also be used in an attic, closet, etc ..
All of the materials required can be purchased at online metals here: http://www.onlinemetals.com/ and your local hardware store/home center.
Note that Beezley states in the latest edit on the above omni that only 6% of U.S. FM broadcasters still use horizontal polarization.
I built one of these: Wideband Vertical Omni - Works quite well, and can also be used in an attic, closet, etc ..
All of the materials required can be purchased at online metals here: http://www.onlinemetals.com/ and your local hardware store/home center.
Note that Beezley states in the latest edit on the above omni that only 6% of U.S. FM broadcasters still use 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.
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.
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.
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:
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.
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.
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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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
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
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.
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.
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.
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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