Loggings > FM Free Radio

Antenna Height vs Gain

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ThaDood:
Well, not me, but someone whom kindda' resembled me, did well with 25mW, 40ft up a fur tree, on a home brew copper, 1.1:1VSWR tuned 1/4-wave GND Plane. It was heard over 5 miles away in one direction. Then, 400mW was heard almost 10 miles away in the next state. (Damn, that station is sadly missed.) And, even got a letter writing back to a Radio Garbanzo broadcast from a town over 70 miles away. Even Fearless Fred said, "Ya never know!". (Temp inversion that night?) CP wasn't done since it was just seen as wasteful. 1/2 the signal either goes straight up, or straight down. (OK for worms or ET.) FM is no longer done, due to the huge FM witch hunt the Federal Corporate Coddlers are so hard on about. Any chance to get your antenna in a tree, just above the tree? I remember a station, in fairly flat terrain, used just 3W up a 60ft pine tree on one of the custom made 1/4-wave GND Plane. It MAX'ed out to 19 miles in one direction! Huh... Wonder what ever happened to that dude whom resembled me? 

Josh:
A vertical calculated for beam tilt would help in the range dept, or a vertical dipole(s). The big boys use cp because they're trying to fill concrete canyons with flutter - free fm stereo as well as horizontal fringe antennas at the same time as vertical car antennas.

OgreVorbis:

--- Quote from: ButchKidd on July 19, 2018, 0200 UTC ---Can you guys give me your general thoughts on this?  I know there is no right answer.

I've finally built a circular polarized antenna to try to get a more consistent signal no matter what type of receiver.  My original idea was to build a second CP antenna and feed it in phase a wavelength below the first.  Now I'm having second thoughts on the two-bay idea.

I'm in a rural area and my existing ground plane antenna is nearly 100 feet above the terrain.  It doesn't quite clear the treeline, but it's as high as I'm likely to get without a real tower, which isn't going to happen.  It's a good transmitter site, but despite some pretty cavalier power levels, I just can't get the signal to my house.  I think I'm terrain-limited rather than power limited.

Here's my thought.  I'm not really comfortable using high power long-term.  It seems like asking for trouble.  I'd like to get the most out of a lower output power, but if adding another CP antenna will just lower the center of radiation by one half wavelength, would you expect to get any additional range out of the higher gain?

All things considered, I can just run more power to a single antenna at the same height.

--- End quote ---

I have some decent experience with this although I've never tried a CP antenna. I've tried ground plane antennas, dipoles, and the "dominator" antenna (which is a 5/8 wave with interesting matching). Anyway, in a hilly location, I've actually found the ground plane type antennas work better at a lower height than anything with higher gain. The lack of gain almost compensates for low height (I'm considering 100ft - low). It shoots the signal up more. Yes, some of it will be lost in space, but on the low end of the FM band, there's some bending that can occur and the GP will cause the signal to go over hills a bit better.

With the amount of power you're using, you should be getting farther than that. My guess is the transmitter site is just in a bad location. Something I've thought about doing, was putting a solar powered TX on a hill nearby with a directional wifi dish for streaming audio and controlling the transmitter. You could get away with only 15W on a hill and go much farther than 150W on the ground. Height is pretty much everything, not power. I did a test with a 30W transmitter on a mountain that I lugged up with a car battery (wasn't easy). The signal went about 30 miles.

Another thing to consider if you just want to make it from the site into town is a yagi.

One more thing - Don't use stereo. Give mono a try. When you're really close to the TX, it won't sound as good, but I came to find that with my setup, using mono made the signal much clearer longer distances away. And at those distances, nobody is going to be hearing the advantage of stereo because receivers default to mono with low signal level anyway.

Are you getting multipath distortion? When you drive listening to the signal, does it pop in and out. Sounds  pretty clear, but with bursts of static. If yes, use mono or SSB stereo mode instead of normal stereo.

ButchKidd:
I put the turnstile antenna up yesterday, and even with the -3dB from the CP antenna, I'm already getting better results.  It's not vastly different, but certainly better.  That makes me think it is at least partly multipath issues.  Since the parts for the turnstile weren't expensive, I'm thinking of stacking two again.  If it doesn't help, I can always take the second one back down.

My wife's car has one of those horizontal trace antennas on the glass, and I can pick my station up all over town with it now.  I realize that's cross-polarization for the old ground plane, but that seems to be what many cars have like it or  not.  I notice much less picket fencing when I drive around town between steel and masonry buildings, even with a vertical receive antenna.

And I can receive it at home if I use my attic mounted TV log periodic. It's too weak for stereo and RDS, but I can hear it.  Certainly not strong enough for a casual listener to stop on it, though.

I agree that I think I should be getting way more range for any given power level.  Do you think I could be under-modulating?  I don't have an accurate way to check the deviation like an oscilloscope or FM analyzer, so I've tried to look at the bandwidth on an SDR dongle and keep it about as wide as the other stations.  The nearby stations sure seem to take up more than 150 KHz on my waterfall, so maybe I've been too conservative.

JimIO:
Keeping it short, using a V tx ant. and H rx ant. you will be up to -20db.
As for modulation, crank it up until you are as loud as other stations.

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