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Antenna Height vs Gain

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ButchKidd:
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.

JimIO:
You don't say what power or range. If the antenna is above the terrain then a ground plane is not a good antenna to use. I would have started with a center fed half wave vertical. What design is the CP antenna?

ButchKidd:
With 20 watts, I was getting 3-4 miles.  At 50 watts, about 6 or 7 miles.  I did some quick tests at 100 and 150 watts, but the range didn't improve.  RDS lasted much closer to the edge of the signal,  though.  There's a hill roughly 7 miles from the transmit site.  When I crest the top of that hill, I lose my station and most of the time  I can just make out the next nearest station on the same frequency 60-70 miles away just above the noise.  I live a couple miles past that hill.  Most of the town can hear the station just fine, but my neighborhood can't hear it at all.

I realize I'm already getting better range than a lot of licensed LPFM stations.  I guess that's because we're so far away from cities and the noise floor here is comparatively low.

JimIO, I agree with what you said about a ground plane antenna that is very high above the terrain.  I just didn't consider 100 ft to be very high when commercial antennas are 800 ft high.

The CP antenna I built is a turnstile, so it's pattern should be much more like a center-fed dipole.  Well, like two of them, but you know what I mean.  I just took the designs for 2m and weather satellite antennas, removed the reflectors, scaled them up, and turned it on it's side.  It seems to work well in the yard, but I won't really know how well it performs until I get it up in the air.

There are a couple churches kind of near here that have LPFM stations, and it looks like they're both using Jampro Penetrators or something similar.  I might try to build something like that in the future, but I understood how a turnstile worked.  I don't know what type of matching the Jampros use.

JimIO:
Big stations on tall towers use beam tilt. Way beyond free radio.
It sounds like you are terrain limited. Where is your studio?
What about a second transmitter to cover your neighborhood?

ButchKidd:
Thanks for the help, JimIO.

I record my shows at home and upload them to the computer at the transmitter site via WiFi when I'm nearby.  There's no internet service at the transmitter site or I'd stream it.

A second transmitter is probably the most practical solution.  I've been reluctant to set up a pirate transmitter at my house, since I thought all the existing antennas would give it away.  I still have the cheap Chinese transmitter I started with years ago.  I could probably find a friend who would be willing to host it as long as I keep the power really low.  I'd like to find a way to get the two broadcasts in sync, but I guess that's more complicated than it's worth.

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