FM Antenna Over Ethernet





Introduction: FM Antenna Over Ethernet

Problem: I ran cat6 and coax throughout my house. But for some reason the notion of installing an extra coax or simple antenna wire never occurred to me. Now I have no way of using my nice FM tuner unless I hang an ugly dipole from the wall.

Solution: I have an extra Ethernet connection available near my audio equipment. I simply used the cat 6 run as an extension - allowing me to hang a dipole antenna in my data closet out of site.

Step 1: Tuner Side

(pictures could be provided if there is adequate interest)

I made the connection at the tuner by putting an rj45 connection on one end of the cable. Then at the other end I simply unjacketed about 1.5 inches of wire. then stripped off one inch of insulation from all 8 wires. Then I twisted 2 pairs into one bundle and the other 2 pairs in the other. Then connecting one of each of the wire bundles to the two FM antenna connectors on the tuner. The pairs you use doesn't matter just as long as you stay consistent. I used the Blue pair and green pair together and the orange and brown pair together.

Step 2: Antenna Side

At the other end in my data closet, I basically repeated the process.
1) Putting a rj45 connector on one end of my cable (using the same wiring order as the connector at the tuner end)
2) then I measured to see how much extra wire is needed to get the antenna dipole up and way from the wiring hub. ***
3) then I added another 50cm of wire
4) then I stripped a full 50cm of jacket off.
5) then stretched approximately 49cm of the Blue/Green pair along one half of a 100+cm dowel , and then stretched the other 49 cms of orange/brown pair along the other half. Then i firmly taped them to the dowel to ensure they don't sag (apparently keeping both legs the same length is essential).

*** in case you dont know better - DONT attach your antenna to your router/hub - you want only dead wire - no network traffic anywhere near your antenna.

Step 3: Where It Might Be Improved

I suspect there is a person out there with some RF knowledge that could fill me in on some balancing issues - but hey it definitely works!

1) I suspect I didnt need all 4 pairs to make the antenna. And if a person didn't have a full ethernet connection avaialble they could just pull a couple pairs off an existing ethernet or availalble phone line to do the same (being very cautious abour any current in the phone or network connections)

2) Sure I could have bought a digital tuner and used that on the ethernet - but that would have been more expensive.

3) I suspect the same could be done for AM tuning - simply eliminating the dipole and using the ethernet as a long wire antenna.



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    for wifi, use a pi microcomputer and a wifi dongle, connected with ethernet to your router. or use LMR-1200 cable. using cat 5/6 with wifi will radiate the signal in the transmission line, and you will get very little signal out.

    cat6 has 100ohms between twisted pairs so your impedance when using all 8 is 25homs. best stick to 4 not all 8 and balun between the antenna, and cat6

    I wonder if this would work for WiFi. I really would like to extend my WiFi coverage around the house and if only I can utilize existing CAT5! The telephone wire antenna hack also sounds intriguing!

    Awesome idea! On the tuner you should have both those cable bunches screwed into the 300ohm input, as with one connected to both the 75ohm and 300ohm, you are losing more than half power. However this is a great idea, and I will recommend it to some of my friends. Thanks!

    That is a store bought wire enclosure and packs

    Another thing that may help is that the length of the antenna is a direct ratio to the frequencies received. For instance your 49 cm half of the dipole will recieve 120 mhz best.... just outside the frequency. can help you calculate the length... also half  and double the length act the same way. Approx measurements needed is either 74.30 cm or half at 37.15 cm converted from inches.

    Fantastic, I was trying to fathom out how to add an FM antenna without a dipole on the wall, your suggestion reminded me I had installed a phono system thru my house. Hey presto, plugged it in with a dipole on the other end. Tremendous. Thanks.

    1 reply

     At one time it was a common trick to run a wire from the radio to the metal finger stop on a telephone to improve reception. I don't think the finger stop was connected to the phone wiring, but just bring the radio into closer proximity to the wiring was enough to help. Then miles and miles of phone line was up in the air, not buried.

     Respectfully this is an antenna that resembles a dipole. I have no doubts it works, but under the theory that when it comes to reception the more wire the better. The standard dipole has a feed point impedance of 75 ohms. The impedance  at the feed point of a folded dipole is 300 ohms. The reason I call this an antenna that resembles a dipole is because there is no distinct feed point, the "feed line" is also acting as part of the antenna. Not a problem when it comes to reception unless it passes by something that creates inference, but it means  there are no "balancing issues to be concerned with.

    How about using an ohm meter to test out the impedance. Start out by using one pair and test by putting the probe on each end. Then add a pair at a time and see if you can get to the impedance that you need.

    I also once knew but have long forgotten the length that a dipole needs to be to receive 88mhz to 108mhz (US FM broadcasting).

    I found loads of information at this site in my search

    1 reply

     An ohm meter is used for measuring DC resistance, not useful for measuring impedance. The "standard" formula for designing a dipole is 468/ frequency = the length of the dipole in feet. I'll mention more about the antenna in a comment to the article.

    There is so much you can do with ethernet cables, they are amazing.

    Nice Idea, and it's good that you do the experimentation on this. I wasn't sure how I would get my FM (and AM) signals out to my various sites. You prove it works.

    However.. I would point out one simple change that may make an improvement on your system.. or may not. The test would be very interesting to me.
    The idea is that each twisted pair rejects the pickup of radio interference if each wire of a twisted pair is connected to opposite sides. The way you have wired it, each twisted pair is actually a single long antenna wire, and picks up radio waves. So, the wire traveling from your radio to the computer closet itself is a very long antenna.
    IF you changed the wireing by untwisting the pairs at the ends, and wired them as 4 wires "solid" and 4 wired "striped", then each twisted pair would reject noise from Flourescents, computers and other EMI generators.
    The big question in my mind is does your method gather more radio waves, or more interference from other devices....
    In any event, I will try it both ways myself one day.
    I would also wonder if 1 pair of the 4 pairs could be dedicated to AM connections. I hate to have something unusable. In that case, I am certain it would be best for 1 twisted pair to be used on both sides of the connection. AM will pickup huge amounts of EMI, unless you use a twisted pair. I even have a wired loop antenna I got with an AM radio that uses twisted pair as the antenna lead in wires, so I am certain it will work.  If you try it, I would be interested to see the results in your "improved" PDF
    Thanks for an intersting Instructable

    good idea, don't mind noah, he's just old and crabby. (I really don't know him)

    4 replies

    Old and crabby? I am young and vital! The robot makes me say those things! Please believe me!

    *ERROR* :#(6c:6f:6c) Does not compute, shutting down. lol, I'm just messin' with you.

    *puts ubuntu flash drive in**lets hd eraser software

    Screws Ubuntu *puts windows XP+Windows 7 Unattended install Flash drive in(that means it does everything for me without asking)*

    "*** in case you dont know better - DONT attach your antenna to your router/hub - you want only dead wire - no network traffic anywhere near your antenna."

    LMAO could be interesting... but I don't want to try it with any of my current networking or radio receiver equipment

    From the pictures, the wire could have been any type. The author is probably within the strong signal area of the fm station. Receiving antennas are very forgiving if the signal is strong. I would avoid locating the antenna near live network wires, especially parallel to them. Finally, what is ugly about an antenna? I have decorated my house with 8 outdoor antennas. Santa uses the front yard here.