FM Antenna over Ethernet

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.

Comments

[jaydenthorup]

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. http://www.crompton.com/wa3dsp/hamradio/antcalc.html 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.

[lukethedog]

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

http://www.educypedia.be/electronics/antennadipole.htm

[static]

 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.

[jasen]

I have "some" rf knowledge. one pair should be enough. cat5e works to 350Mhz so it will work ok in the fm broadcast band but it has the wrong characteristic impedance (100 ohms each pair instead of 300 ohms or 75 ohms) probably the best compromise is wiring one pair to the 75 ohm terminals (as you did) and using a balun at the antenna end. for am it appears that your receiver uses a lonewire mine expects a loop antenna, not a longwire, network traffic may contain signals that intefere with am