Persistant High SWR Problem

[K5MBV]

I have an antenna problem doesn't go away even with
a new M2 yagi and different coax. MFJ 3 el yagi had the same problem. Here's the problem:

The SWR bridge shows greater than 5:1 over the entire 6m band with the antenna, and the transceiver
cuts the power back to just a few watts. Taking a 50 ohm 100W dummy load out and attaching it
to the coax, the SWR/power meter shows about 1.05:1 and 150W. The power seems a little high. It's set to 100%.

The antenna is mounted to a piece of PVC pipe attached to a 55 gal trash can and is 8 ft in the air
and in the clear of any metal, trees or anything.

The only thing I can think of (and I hate to think this) is that the transceiver is putting out wide
band trash and since the dummy load impedance isn't frequency dependent like the antenna
it shows a low SWR. Can this be?

I don't have another 6m signal source to check the antenna with. Also I don't know anyone who works on the FT-100D. I'm sure Yaesu would disclaim it since
it's no longer built.

What should I do? I'm at the end of my tether with this problem. I don't want to put the antenna in the
air until everything is OK. How to troubleshoot the problem?? Most shops would just put the radio
on a dummy load and the SWR would look fine like it does here.

This has become a real downer for me. Do you have any suggestions? Know anyone who works on
old Yaesus? Have you ever heard of a problem like this?

Ken K5MBV
 
       

[NA0AA]

I don't know anything about your antenna but I would check the following:

1.  Continuity of the coax center conductor and shield, also make sure the coax is also not shorted somewhere [use a VOM]

2.  antenna:  What does the instructions tell you about tuning?  Usually M2 has decent information but again, I've not got yours in hand.

3.  Any possible obstruction or RF coming back?  Are you missing a Balun?

4.  Build a 6 meter wire dipole or 1/4 wave vertical and see if your radio will behave.

[KJ4FUU]

I would recommend borrowing an antenna analyzer from some place and double checking:

a.) What the resonant frequency is,

b.) What the impedance is at that frequency.

Can you get a hold of one? If you buy one, I wouldn't get one of the non-LCD display ones, unless you have a frequency counter handy, and the analyzer has an output for a frequency counter.

-- Tom