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[K9VER]

I went to go on 20 meters with my A3 beam and when I tuned up the SWR was off the charts.  The previous day I was on and it tuned up perfectly.  I looked at the feed line coming into the house and there did not appear to be anything wrong with the coax.  Does anyone have any ideas on what to check before climbing to the antenna and checking the connections there.  I am afraid that it has something to do with the connection at the antenna.

73

Tom K9VER

[W1VT]

A time domain reflectometer can be used to estimate where a fault is located.

[K1VSK]

I went to go on 20 meters with my A3 beam and when I tuned up the SWR was off the charts.  The previous day I was on and it tuned up perfectly.  I looked at the feed line coming into the house and there did not appear to be anything wrong with the coax.  Does anyone have any ideas on what to check before climbing to the antenna and checking the connections there.  I am afraid that it has something to do with the connection at the antenna.

73

Tom K9VER

I would agree with you first reaction. It isn’t the antenna

[K6AER]

Check VSWR at the antenna and the coax with a load.

Check connections on the beam.

Check the traps for corrosion.

[AF5CC]

How is the SWR on 15 and 10 meters?  If it was the feedline, I would think the SWR would be very high on those bands as well. Could be a 20 meter trap failed somewhere.

73 John AF5CC

[WA3SKN]

Water and connection troubles.
Gotta dummy load?

-Mike.

[K9VER]

I checked the SWR with an analyzer and it is bad on 20/15/10 meters.  Not sure what a dummy load will do for me as it will not use the coax to the beam.. I have tuned up  my OCF and it is working fine.

[WA3SKN]

"Time to climb!"

-Mike.

[WB0U]

I had a problem with critters biting and shorting out a length of RG-58 laying on the ground.  I found this with a resistance check in the shack using a VOM.  After investigating, I found the teeth marks in the coax outside jacket.

The A3 beam uses  coiled coax as a common mode choke with an insulated driven element.  The A3 beam looks like an open circuit at DC which allows a check to be made for a shorted coax without disconnecting the antenna.

Lynn, WB0U

[N1UR]

Before you climb, you should bounce a TDR signal and see if it approximating the beam location on your coax.  Its always funny when I see that a connector issue is a few feet from the radio.

Ed  N1UR

[KE6VG]

In case someone reading this doesn't know, Nano VNA, Rig Expert meters along with several others have a TDA function built in. It will measure your transmission line and tell you where a fault is if there is one.

[N0GV]

This is a connection issue. Either the coax is bad or a connection has failed. The traps should not matter unless a coil has failed in one.

Run an impedance sweep across 14 to 29 MHz and see if any of the bands match ok or come close VSWR < 2. If they do then the trap for the lowest band that is close to matching has opened the inductor. If the match is really not good it is the trap on the driven element. Otherwise it is a measure for dc continuity across each trap and see....

Tdr will localize cable issues... often to within a few inches....

My money would be on the connection to the driven element on the top of the tower but animals gnawing on the cable anywhere are a possibility.

IF you have an angry neighbor look for pins thru the feedline....

Grover

[K0UA]

Old Cushcraft beams are noted for this problem. It is a trap connection failure inside the trap. It can be fixed, but you need to take the traps apart to repair it. Lots of articles on the internet on this.

[ZS5WC]

 :)IF its all 3 bands, it points to either the coax or the connection at the yagi at the Balun,
Could also be the innermost traps, i.e. 10m traps on driven element.
Best way disconnect at yagi and connect dummy. Prove the coax, then take it from there.
I had a similar problem with water ingress into PL259 / SO239 junction.
Best to put silicon grease into that junction, and tape up any joints with self vulcanising tape.

William, ZS4L / ZS5WC

[W4JFA]

Have you had rain lately? I've also read about trap connection problems like Jim said. Maybe you'll get lucky and you find a bad PL-259 in the shack. Fingers crossed 4 U.