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Re: [IRCA] Antenna Project
- Subject: Re: [IRCA] Antenna Project
- From: "Craig Healy" <bubba@xxxxxxxxxxxxxxxxxxxx>
- Date: Sat, 11 Mar 2006 22:18:48 -0500
- Organization: Hazzard gang
I've had some time to work on the copper tube flag antenna. The current
configuration is a three foot square loop made of 1" and 3/4" copper tubing.
The vertical uprights are split in the middle and a length of 3/4"
fiberglass rod is inserted to make a roughly 3" gap. Right now I have two
9:1 transformers feeding to two SO-239 jacks, one from each side. These are
symmetrical.
Here's a picture of the antenna:
http://www.am-dx.com/Graphics/miniflag.jpg
And, one of the two identical feeds. Sorry it's a bit fuzzy:
http://www.am-dx.com/Graphics/flagfeed.jpg
I spent a fair bit of time with various resistors, but could only come up
with about a 20db null. It is a nice cardioid, though. I also tried
hooking the two outputs to a phasor. That really didn't work at all, for
some reason.
The best results were obtained by connecting the output to one side, and the
other side to an old home-made antenna tuner. This provided a good null on
several locals. Here are the results:
Station Null 180 degrees from null
WPRO-630 S-7 S-9 +32db
WSKO-790 S-8 S-9 +38db
WHJJ-920 S-8 1/2 S-9 +30db
WRNI-1290 S-7 S-9 +28db
What I did was to get the best null on the station, record the reading, and
then simply turn the antenna 180 degrees without changing anything else.
That gives a pretty good measure of the front to back ratio of the antenna.
Gain is very good. I am using a DX Engineering preamp, but it probably
wouldn't be needed for most use. The receiver is a Drake R8B.
Next I will make a specific tuner with a variable pot in series with a coil
and variable capacitor. This will give the desired complex termination. I
suspect this needs both a resistive and reactive component to work properly.
Overall, I am very pleased so far. It's been worth the effort. Full
article to follow soon.
Craig Healy
Providence, RI
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