There's a "DX" setting for the TH-7 that moves the resonant frequencies
closer to the CW end of the band. It's intended to be a compromise for CW
operators who still want to have reasonably flat SWR at the low end of the
phone subbands. Sounds like it's perfect for your needs. It involves
changing one dimension on each side of the front and rear driven elements:
FDE-2 is set to 42 inches (previously 40") and RDE-2 is set to 33 inches
(previously 31".) I set mine that way and the curves are nearly dead on with
the graphs in the manual. I'm not sure about this, but the DX setting might
not have been documented in earlier manuals.
But even the standard dimensions should still match the SWR curves in the
manual. It's possible that some sort of interaction with the tower caused
problems for your friend, but not with any of the standard setups I've seen.
Could you describe the tower and its previous location? Was there another
antenna on the mast or nearby? It's possible that your friend may not have
constructed the beam properly, there might have been a defective trap or
balun, or the coax or connector joints might have been bad. I'm assuming the
beam is in large pieces now. It might be worth your time to disassemble it
completely and rebuild it from the ground up (plan on spending 2-3 days on
the project.) That way, you can be sure that the beam is built correctly and
can test the traps and balun for proper operation prior to reassembly. If
you do this, be sure to clean the contact points on all the elements and
follow the instructions carefully, using an appropriate anti-oxidant
compound like Penetrox (available from electrical supply stores.) If the
beam was one of the early production units, it might be worth getting an
updated manual from Hy-Gain.
73, Dick, WC1M
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