FM Radio Antenna

Discussion in 'Local Radio Discussion' started by Chuckmeister, Apr 5, 2017.

  1. I live in the city facing the ocean will a giant hill behind me. I have trouble getting most radio stations but I really love listening to my local radio station and have invested a lot of time and money in my stereo/speakers throughout the house/garden etc.

    Often my favorite station fades in and out--its a college station 88.1Mhz and is usually very strong.

    I read about how to build an antenna by wrapping wires around a square frame at certain dimensions and have mounted it inside my attic. I used 14G speaker wire (single) to wrap the frame and connected it to a coax cable via a balun/adaptor at both ends of the cable running through the wall to the stereo.

    I believe the balun does some type of modification to the signal and I am wondering if having two of them (one on each end) is a problem. I've also read that there are so many different types of baluns that you never really know exactly how one brand will work compared to another.

    Essentially, I am using them to simply make a connection between the wires on the antenna to the coax, and from the coax to my stereo. I have a receiver that provides a signal meter and used it to test the signal--it made little difference on the 88.1 (even though I built the antenna especially for that end of the spectrum) station but increased reception on other stations by around 20-30%--so I know there is at least a connection but I still dont get the "super-solid" signal I was expecting for my effort.

    I took electronics in high-school 30+ years ago and and I have no soldering gun so I am trying to do this with caveman-level mechanical skills and the advice from anyone who responds to this posting!

    :)

    Chuck
     
  2. Most of my recent audio receivers have featured F-type coax connectors rather than the old 300 ohm screw terminals. The newest ones did away with screw terminals on the AM side in favor of spring terminals like some speakers use.

    Without knowing what station you're talking about, I'd guess that they turned down their broadcast power or they fiddled with their antenna. Anything down that low on the dial is going to be relatively low power to start with. College stations are notorious for having output power levels under 1000 watts. My alma mater sends out their signal at 340 watts. One nearby school has a 29 watt transmitter.

    Attic mounting an antenna is a pretty excellent way of killing the gain. Putting it in a window or at least where there isn't all sorts of trusswork would probably be better.

    FM features wavelengths conducive to using a dipole antenna. A neat property of the dipole is that they're somewhat directional so if multipath is killing your signal, you get some rejection from off-angle. For 88.1MHz, a dipole with 2'8" legs may be just the ticket.

    When I was at school, I used a six foot piece of weather-worn RG59 connected directly to my receiver to pick up stations from as far away as 80 miles. I named it "Mr. Coax".
     
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  3. There are many cheap commercial FM antennas available that might help you out. I assume the station you're after is KKJZ-FM? I would go to fmtool.com and input your address. It will show you what FM signals are strongest for your area, and whether any outside stations might be interfering with the one you're trying to receive. It also will give directional information that might help you aim your antenna. As far as an antenna goes, there are several already made cheap ones from MCM electronics that you might want to try. The latest catalog I received has their omni-directional antenna (part # 30-2435) on sale for $10.99, and the directional larger one on sale for $24.99 (part # 30-2460).

    That station also is listed as being on iHeart radio. You might come out better buying a Bluetooth transmitter and/or receiver and streaming it?

    Edit: Here are three antennas on MCM
     
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  4. I should have looked it up (actually, the TS should have offered up the callsign). This is no fly-by-night college station at 30KW. I'd start with a short piece of bare copper wire. Lamp cord would probably work.
     
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  5. I've noticed performance differences from one balun to the next. Some of them just don't seem to work well.

    You could also check if aiming your frame up/down a bit makes a difference.
     
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  6. Thank you all for your responses. I guess what I am specifically asking about it whether or not using the baluns to convert from the coax to "spade" terminal connectors at both ends is negating the antenna's effectiveness. The tuner has connections for either 300 or 75 Ohm but I seem to get the same results either way--essentially a marginal increase in reception. I am using a pre-fab coax cable with factory connectors and a balun at each end because I didn't want to have to deal with stripping/crimping/soldering, etc. and those were the only things I found. I had the blissful ignorant's optimism that this setup would just work. Now I'm left question every component in the system; are the two baluns too much?, is one balun too much?, is the extra coax cable coiled up under the house bad? If I get rid of the baluns how do I connect the ends of the coax cable to the antenna (14g speaker wire) and the stereo (thumb screw posts)?, does my tuner have an issue? Should I connect up my iPod and forget about the radio? (KJAZZ is getting more like "the Wave" (soft jazz and Kenny G-type stuff) more an more everyday :-/ I don't know where to start but my guess is that the two baluns is not good--I also don't have a simple way of measuring the effectiveness of the antenna (can an ohm/volt meter be used?) I had a semester of electronics in high school so I'm not afraid of using a soldering iron (much, anymore) so if removing the baluns and creating my own connections is recommended I can go that route--but some direction on how to do it would be appreciated.

    Sorry for the run-on reply--I spend a lot of time "wondering" about this since I spent a lot of time making the antenna, mounting it in the attic and running the cable down to the receiver. Before I had much time to do anything about it we decided to move the stereo (console) and so its been disconnected for a while but now got the speakers and antenna re-connected. Its important to me that I maintain the pure analog nature of the signal/sound source (I'm using all c.1972 equipment/components and I'm probably a little OCD) which is why I haven't gone with a more off-the-shelf or digital kinda setup.
     
  7. I think it more likely that the antenna is too much for the application. Given the "decrepitude" of the tuner, you may be overdriving its ability to limit the gain (AGC) on what is likely a very strong signal.

    The coax connectors are 75 ohm and the screw terminals are 300 ohm so you can't use them interchangeably and hope for "maximum power transfer". The job of a balun is to convert a 300 ohm antenna to a 75 ohm cable. The balun doesn't "modulate" anything; it just converts the antenna to an impedance that is compatible with the cabling you're using..

    I'd try a short chunk of speaker wire on one of the FM screw terminals without any formal antenna and see what happens. If that isn't enough, I'd move on to a dipole made out of twin-lead. They have a version on Amazon that sells for just over $6 and features a built-in balun. A twin-lead model with fancy U terminals is thirty cents cheaper.

    Come to think of it, since you already have the coax laid out, you might try it without the antenna and see what happens.


    There's also a chance that the signal is sailing right over your antenna due to land features and all you need is some elevation.
     
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  8. When they were KLON I used to get them on my SCPC receiver with my C band dish. They were a really good station back in the 90s. Come to think of it, they may have been on an audio subchannel of one of the video channels.
     
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  9. "The balun doesn't "modulate" anything; it just converts the antenna to an impedance that is compatible with the cabling you're using.."

    Okay, so if I understand that statement, the fact that I'm using the two baluns wouldn't / shouldn't affect the effectiveness of the antenna/cable's capability of transmitting the signal?

    "Come to think of it, since you already have the coax laid out, you might try it without the antenna and see what happens."
    I may just do that--I can't remember if I tried that yet--it'd be a shame though if my super-cool antenna wasn't being used. :-/

    "There's also a chance that the signal is sailing right over your antenna due to land features and all you need is some elevation."
    The antenna is in the attic, I'm not inclined to go any higher. Come to think of it though--I think what mostly disturbs my radio reception may be occasional interference of some nature and that seems to have gotten better since I hooked this all up.

    I will try disconnecting the antenna itself and see how that goes--thank you!
     
  10. There is a small amount of loss known as "insertion loss" that comes from making the connections in and out of the baluns and some loss in the balun section itself. The loss impacts everything so the net is that the undesirable signals are attenuated just as much as the desirable signals. In the grand scheme, the loss totals about 2.7dB with two F-connectors and two baluns. Twin-lead would likely have a little more loss depending on how the wire was installed and would do little to protect from picking up undesirable signal.
     
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