Antenna questions


Hi, I have a roofmounted FM-only omnidirectional antenna. It works great except for one station (important to my wife) which suffers from multipath distortion/static, so I am looking to install a directional in it's place.

1. APS is mentioned here, but their website says the antennas are non-returnable. I think it's pretty important to be able to try the antenna in your attic before installing on the roof, and return if necessary! Does anyone sell these antennas with return privileges?

2. The Radio Shack website has a chart that shows specs for their various antennas. "FM Gain" is 2.2 on the largest of the their antennas, and only 1.0 on the antennas (including a directional FM-only) that I am considering. What is up with that? Aren't directional antennas also high-gain? Should I worry about it? Since signal strength isn't a problem, maybe just a unity-gain directional is enough?

Thanks for any ideas.
ehart

Showing 2 responses by subaruguru

Sean, you nailed this one down nicely!
Yes, I'd try the RS $22 one. You can fairly easily estimate relative gain by counting element count and geometry. If the others have significantly more elements than they'll probably have more gain.....
On a similar tack I just decided to relive my preteen years as a Ham by buying a 1957 Hallicrafters SX-100 receiver, and found on the net a couple of guys who sell "universal dipoles" using two long slinkies and a T connection and downlead! Amazing stuff. You simply string it up in your attic, and pull the slinky ends out to match wavemength. It'll go to 130 feet (gulp!), but works nicely at 15-16 feet for the SW bands normally used. For FM youd only need a few feet...hence normal dipoles. The point here is to confirm Sean's: height IS might. Even a lowly dipole, if set high enough, will offer great FM reception. Adding a few more elements (as in the $22 RS unit) simply makes it better. Don't worry too much about needing to spend more. DO use a good low-loss twin-lead instead of coax for a down-lead, though. I was surprised to hear from all the Hams that good foam twin-lead easily outperforms coax. Hmmm....
Have fun on the roof...I settled for the attic, as a couple of slinkies blowing in the wind could get a SWAT-team over to my house, I fear.
SEan, thanks for the refresher on Q. The Hallicrafters has SIX selectable bandwiths (0.5kHz for code up to ultra-wide for "phono"...HA!), and an amazing selectable Q-adjustable "notch" filter to move in to squash a strong adjacent broadcast. Results in amazing bimodal bandwidth curves! Didn't know they could do that in the 50s...and with tubes....
So the APS must be a lot of similar-length elements all stacked in a plane, as 88-108 megs is only a 20% change in frequency. Interesting. But isn't the Rat Shack also a tight-Q for FM (but with less gain, of course)? Gotrta get back to Radio Rwanda with its 10dB S/N ratio! Talk about low fi....