[TowerTalk] Loaded Boom, Didn't tune on 40

[Mike Foerster]

Well guys, I spent about an hour up on my tower this evening installing an
omega match (box) to try to tune up the boom of my TH11DX using the truss
support wire.

What I did was to build a box (5x3x7) and mounted 2 variable transmit spaced
capacitors with a coax connection (with ground) on the bottom and a single
wire out to connect to the insulated truss wire.  The box was built water
tight.  The idea is to leave the box up there.

I insulated two truss wires and connected it up.   Using an MFJ-259 to tune
it, I could not get it to tune up on 40 meters.  SWR started to dip, but the
capacitor to ground was a minimum, and it wanted to go lower (was at minimum
capacitance.   I could find a low SWR point above the band.

I was able to get it to tune up on 30 meters reasonably well, but once I
tried it here in the shack, the SWR didn't show the same as up on the tower
on 30 meters.  The minimum SWR had moved on me.  Not sure why, but I may try
it again sometime if we have a warm day again.

Surprisingly, I can load up the boom on 40 using the internal tuner of my
rig, but I'm not so sure how efficient that is.

Any idea why I couldn't tune up on 40 meters?  Do I need to add some
inductance to the feed?

The TH11DX boom is 24 ft long, the truss wires are 103" out from the mast.
The reflector is full length on 20 (37ft) and is grounded to the boom, as is
the front director (with traps).  The 6 feed elements are insulated from the
boom (log periodic feed).

By the way, for those other's that my be contemplating something like this,
the ONLY way to do it is with the MFJ-259 or something similar.  I can't see
trying it with a friend in the shack...

Mike


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