Originally Posted by JHBrandt
KJRH/2 is actually on RF 8; KTUL/8 is actually on RF 10, and KOED/11 really is on RF 11. All other Tulsa-area channels are on UHF.
So for VHF, he needs 180-204 MHz. The average wavelength works out to a bit over 1.5 meters. 1/2 wavelength works out to .78 meter or about 31 inches. That's the total
length of a half-wave dipole (which is why VHF-Hi+UHF antennas like RCA's ANT751 are so much smaller than the old antennas that were designed for VHF-Lo also).
However, you can get a few dB more gain by treating each half of a pair of rabbit ears as its own
dipole. In this case, you want each ear to be somewhat longer than 1/2-wavelength; otherwise the impedance doesn't match where the rabbit ears are connected to the balun (which is usually inside the rabbit-ear housing). Each ear may resonate well, but the signal doesn't make it to the cable. So the "best" length to use is actually a compromise between low reactance and a good impedance match, which is a bit of a black art.
I based my results on the info at http://www.hdtvprimer.com/ANTENNAS/RabbitEars.html
. The author of that page actually ran simulation software to determine the ideal length to set rabbit ears for any given VHF channel. In general his results came out a bit longer than 36 inches (except for channel 11); that's why I suggested 42-44 inches.
But if you have one of those 12-position tuner knobs on your antenna, it lets you alter the impedance match, possibly letting you shorten the ears back toward that 31-inch, 1/2 wavelength ideal. It can be finicky though; the OP may just have to find the best combination of rabbit ear length and tuning knob setting by trial and error.
BTW, I agree RCA's ANT751 would probably be a good antenna for the OP's environment.
The best recommendation IS to play around with the size. For a while I used a cheap RCA rabbit ear/loop combo (which may be what the poster is using), still fed through an "unbal" to the presumably 300ohm flat-wire posts on my trusty Radio Shack antenna amplifier. It's been a while, but I do seem to remember having to significantly shorten the rabbit ears to pick up the VHF high digital stations in my area (physical channels 7, 9, 10, 12, 13). With them fully extended, I didn't get those channels, which was quite different than my experience using the same antenna for analog VHF stations, which required full extension to get fairly lousy reception on channel 2, and halfway-decent on the remainder of the VHF dial (3, 4, 5, sometimes 6, 7-11, 13).
So they say there's no such thing as a "digital antenna" but there you go, what worked for analog didn't work for digital, and it was all about the size.
This is why the ANT 751 is a "rational" "digital" antenna for most areas, because they essentially eliminated 3/4 of the size of an old VHF log periodic dipole array, and it probably gets better digital reception (most areas) as a result than the old huge antennas. (Oh, BTW, if you're concerned about a pole, the ANT 751 does contain its own short wall mounted pole, but you may not like that, I certainly didn't, and the mounting gear for the antenna doesn't work well with the pole in my attic, which I don't like, ONE of the reasons I usually use my own homemade antenna.)
As far as impedance matching is concerned, that is another whole black art, but one of the beauties of the half-wavelength dipole is it greatly reduces the reactance of the whole transmission circuit in the first place (which is why it is a "reference antenna"). Actually the EXACT length of the "half-wavelength" varies depending on the thickness and construction of the pole elements, so again, you have to play around with it...
Of course, the single most important thing to play with is direction and location of the antenna; the cheapest antenna you can buy will work quite well located properly (outdoors up high and avoiding trees and other scattering influences generally), which is not of course what the makers of antennas (or even Internet pundits on antenna theory such as myself) would necessarily care to admit. It's not so much how it's designed as where you put it and aim it (well, within reason, but I've definitely found that for digital, HOURS spent finding just the right location and direction of a simple antenna is worth more than spending $hundreds on an antenna that has a higher "distance" rating (which, antenna theory/reality again, probably will get you FEWER DIGITAL stations than the cheap antenna, ANALOG again is actually a different story).