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Antenna transmission problem

May 5th 2015, 14:30

patterson725

Joined: Dec 17th 2011, 03:41
Total Topics: 0
Total Posts: 0
I have a half-wave, folded dipole about 45 feet up a tower that I bought as a kit from MFJ. My radio is an Icom 718; 100 w transceiver. For no apparent reason, one day I was using the radio and was not able to get anyone to respond to me. I broadcasted for several days until I reached the conclusion that other hams simply couldn't hear me. I could hear everyone else just fine, but they couldn't hear me. Has anyone had any experience with a problem like this? Your input will be greatly appreciated.
May 5th 2015, 15:14

W1VT

Joined: Apr 4th 1998, 00:00
Total Topics: 0
Total Posts: 0
Most hams record SWR measurements--a fault often causes a high SWR. Sometimes it helps to know if the SWR is a little high or extremely high, but in many cases, you need to take down the antenna and do a close visual inspection--perhaps unscrewing the coax connectors to make sure nothing is amiss.

Zack Lau W1VT
ARRL Senior Lab Engineer
May 10th 2015, 14:09

patterson725

Joined: Dec 17th 2011, 03:41
Total Topics: 0
Total Posts: 0
Thanks for the input. The antenna is a 20 meter kit that I bought from MFJ. It has a balun, making it impossible to visually inspect the connection from the antenna wire at the impedance matching transformer or coax. I was thinking of doing a continuity check on both the antenna and the coax. Do you think that would be a good first step?
May 15th 2015, 19:19

KB9YOJ

Joined: Dec 20th 2000, 00:00
Total Topics: 0
Total Posts: 0
What kind of coax and how long of run? 1:1 OR 4:1 balun? To measure the SWR on the 718 follow these steps:

SWR
The IC-718 has a built-in circuit of measuring antenna
SWR—no external equipment or special adjustments
are necessary.
Measuring SWR:
1. Confirm that the output power is over 30 W.
2. Push [SET] one or more times to select the SWR
meter.
3. Push [MODE] one or more times to select CW or
RTTY operation.
4. Key down or push [PTT] to transmit; then read the
actual SWR from the meter:
≤ 1.5 well matched antenna
≥ 1.5 check antenna or cable connection, etc.

I would compare the dipole to a reference load (dummy load) across the 20 meter band. The SWR plot should be similar to what is listed in the instruction manual from MFJ. Hope this helps you trace out the problem. Also, make sure your MIC gain isn't at zero. Sometimes it comes down to a simple issue.

Matt
KB9YOJ

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