Thanks Perry, looks like you are on the right trail for this
rabbit................
I found this at repeater builders -
http://www.repeater-builder.com/antenna/440fdipl.pdf
it says 23 inches between each element, mine are from top to
bottom - 22 13/16, 25 1/2, 22 5/16 then the next set are 22 7/8, 25
5/16, 23 1/16.
----- Original Message -----
Subject: Re: question on a DB420 - from KG8ID
Hello Perry,
Good to hear from you again. The DB-420 is probably a 460 mhz
cut antenna and you will have some reflected power. Usually we
have about 1 watt reflected for 60 watts and sometimes 1/4
watt. Decibel for some reason stopped making the 440 mhz cut
antenna three years ago. This is unfortunate because it was the
antenna of choice and best performer.
This is what I would do:
1. Make sure there are no damaged or cracked elements or
problems with harness.
2. Assure that the spacing of the antenna dipoles are in the
omni configuration. In other words the top 4 bays are in the
same direction and the bottom 4 bays are in the same direction
with both 180 degrees apart between top and bottom with elements
at 90 degrees.
3. Then measure the distance between the center of all folded
dipoles. Take a magic marker and mark the positions and
document measurements.
4. Use a analyzer to check the antenna out on your output
frequency and maybe move the dipoles further away from one
another as much as the harness allows you to see if there are
any improvements at ground level.
5. If it improves that is good, if not you just move it back to
the original markings and assure proper alignment.
6. Usually they will improve once mounted on a tower. If a
VSWR is present you could incorporate a circulator on the
repeater to absorb the reflected power.
7. When checking VSWR, check between the transmitter and
duplexer first, then check after the duplexer to see the
difference in watts output and reflected power. You may also
want to reduce your power output from 57 watts to 40 watts
output.
The antenna cut for 460 mhz with 40 watts and reflected power of
2-3 watts may still out perform other antennas as long as you do
not have de-sence. I think it will improve once it is in the
air on the feed line.
Hope this helps and please let me know your findings on your
project.
We are seeing higher then normal SWR from our top repeater
antenna (Hustler Spirit Series) so we took a recently aquired
DB420 8 bay folded dipole antenna to the site and connected it
to a Telwave SWR meter and the meter to the duplexer antenna
port, the RF power out was 57.5, the reverse or reflected was
4.5, so the calculated SWR is 1.8:1, which is acceptable, is
this SWR showing an antenna that is tuned higher in the band say
for the
Business Band? And after knowing this will the antenna still
perform good for us?
There is more to the story but I did not want to take too
much of your time, thanks
Perry/KG8ID