: Rabbit Ear Array: will it work?
2009-04-12, 05:17 PM
Will the signal reception of analog UHF (Channel 32) TV improve by connecting several 'rabbit ear' TV antennas in the form of an array (i.e. connected in parallel)? instead of using just one.
If it does, what should be the separation of the individual 'elements' rabbit ears.
The rabbit ears have to be mounted outdoors, and i've got coax cable to wire the ant. to TV. so will this DIY balun work: http://en.wikipedia.org/wiki/File:Dipolehalfwavebalun.png
PS: not sure where to post this question
2009-04-13, 12:04 AM
Well, doubling the signal of rabbit ears by adding another will give you 2.15 db plus 2.15 db equals 4.30 db. Doubling that with a total of 4 rabbit ears will give you 4.30 db plus 3 db equals 7.3 db. Not a whole heck of a lot. If you want some serious gain for channel 32, build the narrow-band GH shown here :
The coax balun will work if you cut and make it right for channel 32. But youre overall better off buying a quality commercial balun for a few bucks.
2009-04-13, 04:45 AM
Thanks for your response.
1. So what should the spacing be between the elements.
2. For channel 32 (f=581MHz), the coax balun is 12.9cm (approx. 5 in.). Should I make it in form of a coil?
2009-04-13, 09:26 AM
hster2: How many are you putting in the array? If two then try 15 1/4". You will not need the 4 to 1 balun because you are starting with a dipole (73 ohm). You will need to match to 36.5. You will need to make a Q section match (85mm of 50 ohm coax between antenna feed point and 75 ohm coax.) Note that this is just like a two bay whisker antenna. You would be better with 4. Look at Mclapp's (M4).
2009-04-13, 10:05 AM
I presently have 3 unused rabbit ear TV ants.
First of all, I believe the impedance of each rabbit ear type ant is 300 ohms.
so when 3 are connected in parallel to form a 'rabbit ear array', will the effective impedance drop to one third? (like with resistors connected in parallel). Also, if the above is correct, using 4 elements implies that there is no need for a balun since 300/4 = 75 ohms, the characteristic impedance of the coax transmission line.
What should be the length of the coax balun in this case. since my previous calculation is based on 300 to 75 ohm matching, or 4:1 matching.
Also how do i determine the element separation.
2009-04-13, 11:49 AM
Are you going to tear the rabbit ears apart or use them as is ? Each manufacturer of rabbit ears uses different tricks for setting the impedance. I wouldnt assume anything without modeling the specific ones. It looks simple, but in real life, it can get very complex. If you stil want to do it, just experiment with different spacings etc. If you do it right, you may get 4.5db from the 3 rabbit ears. You can get close to that with the Radio Shack classic bowtie antenna for $3.95.
2009-04-13, 12:12 PM
I agree with 300ohm;in real life to get an antenna to work well, is complex. There is no good rule of thumb for spacing(like 3/8 WL to 3/4 WL). The phasing of the elements is the tricky part.
2009-04-13, 12:23 PM
Thanks for your responses.
I intend to use them as is. How can i model the antenna design, pls?
but will the impedance change?
2009-04-13, 12:39 PM
but will the impedance change?
I can pretty much guarantee it wont stay the same, heh.
You can get free modeling software from here : http://home.ict.nl/~arivoors/
2009-04-13, 12:44 PM
Thanks 300 ohm.
Pls. will the impedance change as i assumed above. (i.e. like resistors in parallel)
Thus, will using 4 elements imply that there is no need for a balun since 300/4 = 75 ohms, which is equal to the characteristic impedance of the coax transmission line?
Or how do you mean?
2009-04-13, 12:56 PM
If you dont really know what the impedance of each of the antennas is in the first place, dividing, adding etc wont get you anywhere. Like I said, different rabbit ears can have different impedances due the techniques the manufacturer uses in the build.
2009-04-13, 01:04 PM
Ok. but is the logic correct?
Assuming the char impedance is 75 ohms. Is the above assumption correct?
2009-04-13, 01:28 PM
For resistance calculation, yes. But you would still need a 1:1 balun anyway, because youre going from a BALanced line to an UNbalanced line.