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[N4SRN]

We have a Kenwood TM-V71 in my local Makerspace club with a 2m/70cm antenna on the roof. Last week, I was able to join a local repeater 2m net loud and clear on 50W. Yesterday, I was just above the noise and hard to hear.

Those who installed the roof antenna are gone but they were knowledgeable Hams. A  RIGExpert meter found SWR ~1.5 at the station feedpoint.

How might I go about troubleshooting the issue?

Bret/N4SRN

[W1VT]

You would want to know that other folks weren't impacted by a temporary noise affecting the repeater.

[N4SRN]

You would want to know that other folks weren't impacted by a temporary noise affecting the repeater.

The others could hear one another just fine. One could make out my Callsign and commented that I was loud and clear last week. I could hear the just fine too.

[WB6BYU]

The first thing I would look for is an intermittent
connection in one of the coax connectors or
jumper cables in the shack.

When doing an SWR sweep with the analyzer,
wiggle the various connections and see if the
SWR jumps around.  Sometimes an intermittent
Mat show yo when the cable is bent one way, and
in connecting the analyzer you’ve changed it from
how it was when attached to the radio.

If the radio is regularly moved around (for example,
if it is only set up temporarily when the space is
in use), then there are lots of opportunities for
the cables not to get connected back properly.

Some possible causes of intermittent connections:

Cables not crimped or soldered properly.

Ground braid broken off from connector shell
due to repeated flexing.

Not enough thread length on the female connector
for the plug to seat all the way (crimp connectors
often rely on a snug connection).

Center pin of socket expanded due to plug with
too much solder on the tip (I had a particular
problem with one old SWR meter that worked
with old fashioned PL-259 plugs but was
intermittent with crimped plugs where the tip
was tapered.)

If you have one, put an SWR / power meter in
the coax and check both readings on transmit.
One thing to confirm is that you are getting the
expected output power into the coax.  There
could be something wrong with the radio
(running full power into an intermittent antenna
connection is not a good idea) and make sure
there is plenty of air flow around the heat sink.

How much do the panel lights dim when you
key the rig?  I would expect a little change due
to the higher current draw, but not a lot.
Excessive dimming may indicate a problem
with the power supply or cables, no difference
at all may indicate that the transmitter isn’t
working (due to a protection circuit or a blown
final).


That’s not to say that there aren’t other potential
problems with the antenna (did it blow down?  Is
it covered in snow?) or the feedline (Chewed by
birds or squirrels?  Soaked up water due to poor
weatherproofing of the joints?), but the first step
is to confirm that the radio is working properly
(into a dummy load, if one is available).  But if
you still hear the repeater as well as you did last
week, those aren’t as likely (assuming that you
needed 50 W to hit the repeater:  when
the repeater is very strong it may still be full
scale on your S-meter with no antenna connected).


Those are the easiest places to start, because
they don’t require roof access, daylight, or good
weather to accomplish.

[KA3IGW]

Along with checking your in shack connectors as WB6BYU suggests, make sure your microphone wires are in good shape or maybe try a different microphone if you have one. Of course that wouldn't affect your signal strength into the repeater but low audio may lead those listening on the repeater output to misdiagnose your issue.

[W3PX]

If you have had had any rain lately, check for water ingress in your connections. Water in connectors or your coax will usually make the VSWR look better due to additional loss, but reduce the amount of signal in both directions.

[WB8VLC]

N4SRN in New Hampshire in the winter time?

To me this seems like icing or snow on the antenna as a possible issue also.

[K5LXP]

Snow/ice is nearly RF transparent.  For such a drastic change being caused by the antenna, the receive strength would be impacted as well.  First check I would make is if this is the same on other repeaters.  If RX is OK on other repeaters but you're noisy then it's a TX problem.  First check would be with a wattmeter right at the radio, then if that is OK, verify that power is making it to the antenna.  Lastly a VSWR check at the antenna.

Mark K5LXP
Albuquerque, NM

[WA3SKN]

I would check the antenna system and verify the 50w output.

-Mike.