Hi John,
I'm providing a disclaimer now...: I'm somewhat unorthodox,
unconventional, and have a terribly dry sense of humor. I've been known
to dispense what others feel is bad advice. With that in mind, feel
free to try any of my suggestions with great caution. I'm leaving
myself open for a lot of heckling, but I'll try to keep my sarcasm down
to a minimum. I don't find the repeater "business" to be a great
science like some do-- a lot of it is common sense and elbow grease.
You can learn a lot by monkeying around and throwing stuff at the wall
to see what sticks.
So, moving right along, and in the words of Bill Clinton, "I feel your
pain." A couple of months ago, I started a new repeater project and had
all sorts of de-sense and noise problems. To me, it sounds most of your
problems are within your antenna system. Here are some suggestions (and
my stories) on how to get rid of noise problems...:
First, I like to put some space between any rigid feedline and my
duplexers. The physical strain of the hardline might be wreaking havoc
on your duplexer's wiring harness. I usually add anywhere between three
and six feet of LMR-400 (which many claim to be evil) between my
duplexers and my feedline entry point. RG-214/U might be a better
selection, due to its double shielding. However, its losses are a bit
higher per foot than LMR-400. I've been told (and have read) that when
LMR-400 moves around, it makes noise. While I believe that's
technically true, it probably is about any type of coax. I don't know
about you (or anyone else), but I don't go to the repeater site on a
daily basis and shake my feedline jumpers around, just to see if I can
see if they're going to make noise. ("HA! I got you now, you sneaky
noise demon!") I don't believe the repeater moves around-- unless it
gets up and goes out on the town at night while I'm sleeping. (Maybe it
just gets high on RF and "drunk dials" instead?) So, don't be afraid to
give it a try. In fact, I use LMR-400 between the repeaters themselves
and the duplexers. Even worse, I have a $47 diplexer (not duplexer)
separating 2m VHF and 70cm UHF, feeding into one antenna. SWR is fine
and I haven't noticed any loss in sensitivity. Both repeaters are tied
together, which means when it is in use, one receiver and two
transmitters are sharing the antenna and moving three virtual RF paths
simultaneously-- unless, of course, two people "double" on each band, or
if the repeater is ID-ing between talk times, et al.
Second, if you're not using silver plated connectors, seriously think
about using them. Don't even consider the run-of-the-mill teflon ones,
they're nearly useless in your repeater application. Anyhow, I bought
two sets of duplexers, one being Telewave TPRD-1556 VHF duplexers (6
cavity), the other being Telewave TPRD-4544 UHF duplexers (4 cavity).
Both sets were used, very clean and well kept, except the silver plated
connectors and coupling loops. I pulled each and every connector off,
soaked them in C-L-R overnight, rinsed them off, dried them off with a
cloth, then used silver polish and an old Ronson Roto-Shine shoe shine
kit to buff 'em and bring the shine out. After that, I rinsed them
rather well again and took a toothbrush to them to remove any remaining
polish paste. I put them on a baking sheet and into the oven for about
an hour at 200 degrees Fahrenheit. They dried nicely-- no moisture! I
disassembled the entire wiring harness and used RG-214/U for the coaxial
ties. Then, I pulled the coupling loops out, took copper polish to the
loops, rinsed them off, and put them in the oven for a little bit too.
After I was convinced that they were dry, I used clear spray
polyurethane on the loops to prevent tarnishing and inserted them back
into the duplexers. I took them back to a local, reputable two-way shop
to re-tune them. They're doing much better than they ever did before.
My temporary, 'el cheapo' antenna has an SO-239 connector. I have an
eight inch piece of coax with a PL-259 on one end and N female on the
other end coming out of the base of the antenna. I get a little crazy
with heat-shrink tubing, but I haven't had any problems there, either.
That was good at relieving any strain at the antenna connector.
Third, I have to agree with the pre-amp issue. That could very well be
the entire root of your problem. But, if you have the time and
resources, snag yourself about 20 feet of decent coax, a cheap $50
collinear antenna, and take the repeater home. Stick the antenna out in
the back yard. Try your pre-amp on the repeater, then without...note
your differences. The goal here is to see if your noise levels are
higher at the repeater's designated site or not-- whether your antenna
is behaving or not, and whether your feedline is behaving or not. That
would give you an idea of whether you have to climb the tower and poke
around or not. Might sound obvious as well, but I've known a few hams
who are inherently sloppy and don't like to put covers back on things.
Then they have RF noise and can't figure out where it's coming from.
Always put the RF shielding back on, even when you're testing. I have a
Maggiore R1 UHF repeater and a Hamtronics REP-200 VHF repeater. If I
have the lids off when I'm testing, they love to leak RF everywhere and
can terribly skew any test results. I make every effort to keep the
lids on when I'm testing, since that's the nature they'll exist in when
I'm done. I've also seen funny things happen with desense when I pull
repeaters off of the rack and then put them back on. While it may not
apply in your situation, the principles are the same-- try to test with
all of the enclosures on, so you can see how the repeater will tolerate
in its standard environment.
Fourth, double check each duplexer cavity. You could have a loose
connection somewhere, perhaps a connector that's not too tight, and so
on. I have tried time and again, but am somewhat poor overall when it
comes to tuning duplexers. I freely admit to that defeat and I
outsource the work. If you have any doubt about your capabilities (and
I'm not implying you're not an intelligent or capable individual), take
'em to a reputable two-way shop who will tune them RIGHT. I paid $75 to
have two sets done in Western Pennsylvania and it was worth every bit!
Good luck on your project-- let us know if we can be of more help!
All the best,
John, NF3Q
> > Hi,
> >
> > I have read the large majority of messages on here and the Repeater
> > builders site, and I am still lost.
> > This is the first time I have worked with a repeater in my 30 year ham
> > career and am learning something new everyday..
> >
> > We installed a GE Mastr II running into pre-amp, a BandPass and then
> a 6
> > can duplexer. The antenna is Hustler G7-144 and 1/2in hardline up 65
> feet.
> >
> > The duplexer was set up with service monitor at the test site prior to
> > installing it here.
> >
> > When I go above 10 watts out all we hear from the users is a lot
> noise and
> > very little voice. As the power goes higher (when radio heats up) the
> > noise gets so bad that we can not make out a thing the people are
> saying.
> >
> > The SWR between the radio and the duplexer is 1.1 at 5 w and 1.15 at
> 7.5
> > watts. Of course as we go up in power to 20 watts out we have 1.3 SWR.
> >
> > On the antenna side of the duplexer the SWR goes up to 1.4 at 20
> watts and
> > 1.2 at 7 watts and very little at 5watts (meter hardly moves).
> >
> > I am thinking it is either the hardline or connectors and/or antenna.
> >
> > The antenna and hardline are used. The connectors despite being new are
> > very hard to put on. The guy that installed them even had to use
> pliers on
> > the tower to attach the connector up there and I have to use pliers
> to get
> > it tight on the duplexer.
> >
> > Any suggestions on how to fix this?
> >
> > Thanks and 73
> > John, W3ML
>
