LDF4.5-50A
http://www.tessco.com/products/displayProductInfo.do?sku=466137&eventGroup=4&eventPage=1
1.05dB loss at 450MHz @ 100'
DB420 spacing -- spacing and mounting per DB Products/Andrew/ComScope,
etc. :) instructions, I agree, it's never perfect, just wanted to be
clear that it is all "by the book".
Will keep looking -- measuring power at the feedline-antenna
connection is my next step. Thanks for the input Robert -- this helps!
On Oct 16, 2008, at 9:18 PM, KD4PBC wrote:
Cort,
Do you really have 5/8" ?
Here are the part numbers for the coax
LDF4-50A 1/2 50 ohms - loss at 450MHz ~1.447
LDF5-50A 7/8 50 ohms - loss at 450MHz ~ .808
LDF6-50A 1 1/4 50 ohms
LDF7-50A 1 5/8 50 ohms
So if you have the real deal feed line loss doesn't look like your
problem
If you have something else all bets are off send me what number is
on the
cable.
The Telewave antenna (actuality ANY Telewave antenna) is problematic.
We tried using several in the paging business most likely for the same
reason you did they are cheap.
They never performed as well as advertised.
If you want a "cheap" antenna the best for the money is and ASP705K by
Decibel Products (or whatever they are this week)
They work well have a nice round pattern. And will generally out
perform a
DB-420 because of less pattern distortion.
The statement "The DB420 is spaced correctly from the tower"
concerns me as
there is no "correct" way to side mount an antenna.
You must take in to account the desired v. undesired coverage areas
and
optimize the mount and elements to achieve the desired coverage.
On that antenna with an 18" face tower mounted 16" off the point of
the
tower set in an omni configuration
You will see peaks of around 10.5dBd and nulls of around 5dBd.
I see nothing here that would indicate that the Telewave system is
performing correctly.
Remember to take into the feed line loss when calculating SWR. That
is if
you are putting a 100 watts into the feed line and get 50 watts back
That indicates a fault at the top as you have 100 watts and 2.894dB
loss
(1.447*2 up and down) that would be half power of 50 watts.
Do some more looking before you call the antenna bad.
Robert / KD4PBC
-----Original Message-----
From: Repeater-Builder@yahoogroups.com
[mailto:[EMAIL PROTECTED] On Behalf Of Cort Buffington
Sent: Thursday, October 16, 2008 9:17 PM
To: Repeater-Builder@yahoogroups.com
Subject: [Repeater-Builder] UHF Repeater Antenna Discussion
Folks,
My repeater partner and I have recently placed our new 440 machine. We
have realized some odd issues. We bought a new Telewave ANT450F10 to
put on top of the 100' tower, fed with a new piece of Andrew 5/8"
heliax. We also side-mounted an old DB420 with the top a few feet down
from the top of the tower with about 85' of old 7/8" Andrew heliax.
So, we put smokin' new gear on top, and smokin old below it. The DB420
is spaced correctly from the tower and is set up with each half 90
degrees rotated.
The tower is on relatively high pasture land (for NE Kansas anyway)
with a nice clear view all around. I'll not say we're on a hill, but
on relatively high ground. We are attempting to cover two towns
approximately 25 miles apart. We are 1/3 of the way from town 1 to
town 2 and about 3 miles N of the highway that pretty much is a
straight shot connecting them.
The Telewave setup on top performs poorly. The DB420 on the side is
working great. By this difference, I mean signals that are getting in
full quieting on the DB420 are very noisy on the Telewave. Transmit
differences mirror receive. S9 reception on the DB420, switch to the
Telewave and it's S1-S3. We experience this phenomenon in all
directions.
Wattmeter (yes, it is a "real one" -- Telewave 44) says that things
look good as far as loading both antennas -- DB420 is 1.43:1, F10 is
1.39:1. We are about to climb and take readings at the top to make
sure there is no feed problem with the Telewave 'F10, and I admit that
has not been done yet. We did have a discussion with Telewave, who
advised that vertical alignment of the F10 (as they refer to it) is
critical. We have checked alignment and even implemented a little
down-
tilt in the most important direction (just a few degrees). We see not
real appreciable difference.
For you repeater elmers out there: If we don't find a problem with the
feedline on the Telewave antenna, does this make any sense? Telewave
also HIGHLY recommended that the F10 isn't a good fit for this
installation due to its extremely narrow vertical beamwidth, and
recommended that a 4-bay dipole of theirs would be MUCH better because
of the ability to tune the pattern to our desired coverage area and
the increased vertical beamwidth. I always thought I wanted NARROW
vertical beamwidth to keep the RF on the horizon. I would have thought
that 100' up on relatively high ground (this is Kansas, after all)
wouldn't have a real problem shooting over the top 10 - 30 miles away.
In any event I seek advice and wisdom, and yes, we are planning to
check the coax for loss at the earliest convenience. I would like to
take advantage of the top slot on the tower for improved performance
rather than stay on the lower spot, and will try another antenna if
necessary. I'm just having a hard time imagining that the F10 has
appreciably narrower vertical beam as a 9.something dBd antenna than
the F10 as a 10dBd antenna, etc. etc. And it also seems counter
intuitive that a taller vertical beamwidth and less gain on the
horizon in this application would be better. I trust the experience
and knowledge of Telewave, but I also trust the wisdom from this list,
which has saved me many times.
Your thoughts gentlemen?
--
Cort Buffington
H: +1-785-838-3034
M: +1-785-865-7206
------------------------------------
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--
Cort Buffington
H: +1-785-838-3034
M: +1-785-865-7206
