Hi Bob,
Our club could use some ideas on combatting a bad crackle in our 2M
repeater.
The site is a mountain top where there is almost always some wind. The
system
has behaved very well for years, but for some weeks there has been a bad
crackle on user transmissions. The crackle is worse during high winds, and
is
only present when the receiver hears a signal. That is, the carrier is
perfectly clean when only the transmitter is up, such as during the dropout
delay or IDs. This leads me to think it is not a bad antenna connection. The
site is very busy, with the continuous addition and removal of commercial
and
public service RF gear. A high-power TX was recently added.
Note that we actually have two identical systems on the same frequency, with
one being a hot standby. The repeaters are on separate towers a couple of
hundred feet apart. The crackle is the same on each repeater! It is bad
enought to cover up many user transmissions.
Sounds like a general problem at the site.
We had this problem at our Conifer Mtn site several years ago. The guys
thought I was crazy when I planned the fix...
First, test for the problem. Inject a weak signal into the repeater so
that it just quiets the repeater. Climb the tower. Take a screwdriver and
a handheld to listen to. Rub the blade of the screwdriver on the metal
parts of the tower. The part of the tower radiating the noise is the one
that causes the most static in the repeater.
At our site, it was the guy wires. The galvanized thimbles were acting as
diodes where they went thru the torque arms of the tower. I took up short
pieces of galvanized guy wire and some galvanized guy wire clamps. I
clamped these short pieces from the guy wires to the horizontal braces on
the tower (Rohn 25). By electrically bypassing the the thimbles, the
static disappeared.
BTW, we also did the same thing at the bottom of the guy wires at the
anchors. Clamp guy wire from each main guy wire to the ground rod
installed at the guy point. (You DO have ground rods there, don't you?)
I made this change many years ago and have had NO problems since then.
73,
Dave
-----
Dave Maciorowski, WA1JHK
Colorado Repeater Association, Inc.
¿ªÔÆÌåÓý Colorado with Voice and Data, 6-Meters to 1.2 Gig
Internet: wa1jhk@...
CRA:
