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[TowerTalk] Cushcraft Thunderbird traps.

To: "'Tower and HF antenna construction topics.'" <>
Subject: [TowerTalk] Cushcraft Thunderbird traps.
From: "John E. Cleeve" <>
Reply-to: "Tower and HF antenna construction topics." <>
Date: Thu, 15 Apr 2010 18:59:33 +0100
List-post: <">>
Good afternoon gentlemen,

I have to mention, off topic" that it is so quiet around here today, I can
hear myself think once again. My Qth being about 20m from Heathrow.the
entire UK airspace, together with other EU countries has been closed, in the
case of the UK for the first time ever, due to ash clouds from a volcanic
eruption in Iceland, and a non cooperative high pressure zone over the North
Atlantic sweeping the cloud down across the UK and EU...


However back to the topic, I have been reading some adverse comment about
the performance of the Cushcraft Thunderbird X7 and X9 yagis, which relates
to the performance of the traps placed in the directors of the yagis. One
author measured his traps, but he did not specify how, and found that their
resonance did not match and were about 0.5 MHz apart. I presume that if the
two traps for each band, are not matched and "spot on" the design frequency,
then the expected performance from a given example of either antenna, will
not match the claims of the manufacturer...


My questions are these; does anyone out there know the design frequencies
Cushcraft chose to preset those director traps? Assuming that design
information is available, and you then discover that the traps in your
example of the X7 or X9 are off the design frequency, are they adjustable?
What would be an "approved" method of measuring the trap resonance on the
bench, and how might you readjust them, because they look pretty well sealed
up to me. I will be refurbishing a Cushcraft X7 during the summer, and I
want to have all the facts available, should any adjustments be necessary.


Sincerely, John. G3JVC. 



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