At 50 ft HAAT, which looks as what you have, 10 mi ideal situation
coverage (dist=(sq root (2 x 50)).
A good DB224 or fiberglass like the RFS 220 or Telewave ANT150F6-2 (I am
assuming 2 m) would give good coverage of what you have. Feed line 1/2"
heliax a min. At this run going to larger would gain little. I like
the fiberglass, but for top mount DB224 would better stand the
lightning.
However, you seem to have put lots in a PA and little in anything else.
The PA except for suppurious emission specs, is the last to worry about.
Good antenna and receiver should be what you are talking about.
All of what Nate said is good advice. Mainly height and antenna is the
name of the game.
I hope you did not spend much on this repeater, but guess is a start.
73, ron, n9ee/r
Ron Wright, N9EE
727-376-6575
MICRO COMPUTER CONCEPTS
Owner 146.64 repeater Tampa Bay, FL
No tone, all are welcome.
On Sat, May 31, 2008 at 4:15 AM, Nate Duehr wrote:
atms169 wrote:
Hey guys, I'm trying to find radiation patterns or a calculator to see
what would be the best possible coverage for our repeater.
There's a number of calculators on the web, and some good links in the
RB website for Excel spreadsheets where you can see the math if you
like.
We are in the very flat lands of Texas and our repeater is only up 50
feet (total of 530 above sea level). With 120 watt output.
120 watts after the duplexer loss, or before? What kind of duplexer,
feedline, etc.
Assuming 50' for the transmitter and 8' (I'm being generous) for a
mobile rig, the radio horizon between those two is approximately 14
miles, according to the popular calculators.
Anything else isn't line of sight propagation.
Which do you think would work better? A dual folded dipole antenna
with low angle of radiation or a fiberglass vertical at 6db?
Let's assume power doesn't matter for a moment, and just break it down
into comparison of the antennas.
Remember, altitude trumps all, antenna gain and feedline losses next,
and the PA is *last* place you want to make up for a weak antenna
system. The antenna is gain both directions, transmit and receive. The
PA only helps people hear the repeater... it doesn't help them get into
it.
So... the important info is missing in your question...
What band? Can't answer the antenna question without knowing what band
you're looking at to compare different sized antennas. Makes a big
difference. I will assume VHF for these answers for the moment.
You say 6dB. Is that 6 dBd or 6 dBi? That also makes a big difference,
since we're going from your numbers for the one antenna, and don't know
which other antenna you're comparing to.
What specific antennas are you looking at? Spec sheet on the web
somewhere to reference? For both... the dipole array and the stick.
Most dual-dipole- array antennas claim about 6 dBd gain when set up in
an
elliptical pattern. That assumes a 1/2 wave spaced (from the mast)
dipole array, like this Sinclair:
http://www.sinclair technologies. com/catalog/ product.aspx? id=1680
<http://www.sinclairtechnologies.com/catalog/product.aspx?id=1680>
There are different configurations for 1/4 wave spaced (from the mast)
dipole arrays, the lowest gain being the purely omni-directional setup.
The "offset" setup where you pick a direction to "push" your RF one
way more than the others, gives you a little more gain that direction at
the expense of the other side.
http://www.sinclair technologies. com/catalog/ product.aspx? id=326
<http://www.sinclairtechnologies.com/catalog/product.aspx?id=326>
Generically, there's no free lunch. The same sized antennas exhibit
much the same gain, but you can do tricks with the dipoles a stick can't
do... like offset the pattern a bit.
You could always go for an enormous VHF corner-reflector!
(Yep, they make 'em...)
http://www.sinclair technologies. com/catalog/ product.aspx? id=1403
<http://www.sinclairtechnologies.com/catalog/product.aspx?id=1403>
It's ONLY 10' wide... hahaha...
More info needed... the devil is in the details.
Nate WY0X
<http://www.sinclairtechnologies.com/catalog/product.aspx?id=1403>
