[South Florida DX Association] TH-11 Problems

[Pete Rimmel - Marine Chemist - N8PR]

>>Wally and interested members,

>>The SWR is 5:1 on all bands as measured both in the shack and at the
antenna...

Wally wrote:
12 meters never had a good SWR.  Always hovered around 2:1 and the 746 I had
at the time would shut back the output power unless I used the internal
tuner.  I remember that the SWR started to climb at the high end of 20 and
15 pretty quickly.


>>Two of us put it together and triple checked everything.

Make sure the correct traps are mounted in the correct positions.  If the
antenna was sitting on a wall waiting to be installed and water moisture got
into the vents you could have a problem.

>> We have built, repaired and/or rebuilt many antennas, and did not use too
much or too little No-Al-Ox on the antenna joints.

Dont go too crazy with the penetrox.  It isn't DX-butter!  All it is
supposed to do is to keep metals from seizing together.

>>> NO, this did not happen.

 If you get a bunch of it in your pipe clamps they can loosen prematurely.


>> I discovered that the BN-4000 is a 1:1 balun and it seems to be OK...
Putting the dipole connection in line should have also been a 50 ohm match
aothough unbalanced to the antenna, but it did not seem to be much better...
3:1 on most bands, but I did not write it all down...  On the low end of 10
M it came down to 1.5:1   Go figure !!

>>I used my MFJ antenna analyzer with a 50 ohm resistor across the output
both with and without the "impedance matching" coil across the balun and got
about 1.2:1 on all bands from 1.8 to 30 MHz and all freq's in between.


I used a hy-gain balun  on my antenna.  Don't recall any issues with it.

>> We did check the Coax  with a 4 watt  ~50 ohm load on the coax, and got
less than 1.5:1 on all bands.  The coax is old, but I don't think it is the
problem.

>> the MFJ on the antenna, directly with a 2 foot jumper,  showed the same
5:1 SWR as in the shack.


Isolate the problem.  Is it in the coax?  Pull the coax off the antenna and
put a known 50 ohm load on it.  PL-259's Okay?

>>Yes traps  are holes down...

Look at the bottom of the traps.  Vents down?


>>Again. everything was triple checked and all dimensions are to spec.
checked by two of us...


Then, look at your OAL and spacing measurements.  An inch here, an inch
there..... Can cause a problem if you miss something.

>>  We have about 28 man hours in the construction of the antenna...  we
really took our time and made sure it was AOK.

>>We double checked to see if there were any shorts or kinks in the matching
network after it was up, and all is FB.

>>  I was really hoping that it was the balun, but now, I have no idea where
to go next... we really don't want to take thaantenna back off the tower...,
That would take another 4 hours and crew of 10...

>>>>>>>ANYONE HAVE ANY OTHER IDEAS???

>73,
>
>PeteR  N8PR