Saturday, April 30, 2011

40m Double Bazooka build.

I just built another bazooka, this one for 40m.  I used the Carol rg-6 and the same method of build I used before with one exception;  this time I used 1/2" cpvc with caps on it to create a tube to enclose the shorting point.  I drilled a hole just large enough for the mixing tip on the epoxy to fit and "injected" the epoxy into the tube.  So far it seems to be a strong joint on the 40m antenna.  I had it in the air last night and most of this morning with winds gusting to around 20mph.

The bandwidth on this antenna has exceeded my expectations.  I have the entire band below 2:1.  This antenna is actually resonant toward the low end of the band so it is hard to get an accurate 1.5:1 bandwidth, unless you are willing to TX out of the amateur spectrum.  (I am not.)

I believe if I trimmed the ends it would put the entire band below 1.5:1.  This antenna is slated to go to WB8CHE so I left the antenna as is so that he could trim it to his preference. I have been using the antenna to make a few contacts and test it out before mailing it to Russ.  I have went from the bottom of the SSB segment to the top without the use of a tuner and get full output from my Yaesu ft-450AT.

Most of the antenna on the 21' pole.  I have the antenna pretty tight just to make sure it will hold together.
The unpainted conduit body at the feed point.
The epoxy filled tube over the shorting point
(Kind of looks like a caterpillar!)
Close up of the epoxy filled cpvc tube over the shorting point.
My method of attaching a rope to the end.
The complete antenna rolled up and ready to go.

 The ends of the antenna are left raw.  During installation the SWR gets checked and the ends can be trimmed to raise the resonant frequency of the antenna.  This antenna is a bit long so that it is resonant more toward the bottom of the band.  This allows the antenna to be tuned for the particular installation.  (Better to trim than figure out how to add!)  After it is tuned, the ends should be sealed with epoxy, or silicone sealant would also work.

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