Re: Sent DB2 back: Homemade HDTV antenna idea?

In article <9a17d83c-8750-450b-9bd2-665ff9cfd170@xxxxxxxxxxxxxxxxxxxxxxxxxxxx> Jim Wilkins <KB1DAL@xxxxxxxxx> writes:
On Mar 5, 1:00=A0pm, nos...@xxxxxxxxxxxxxxxxx (Alan) wrote:
Jim Wilkins <KB1...@xxxxxxxxx> writes:

It's actually a home-made replacement part for a Radio Shack UHF
antenna that was damaged in a storm.
Depending on whose formula I use, the end-to-end distance should be 15
to 16 inches. The original was 14.6" but it was made for older, higher
UHF channels.

I don't know what formulas you are using, but a good start is 468 feet=
/f
(in MHz).

That, also this, set to Channel 59, which is currently the highest one
worth receiving here.
http://www.k7mem.150m.com/Electronic_Notebook/antennas/yagi_vhf_quick.html

Actually, you should look at:

http://www.k7mem.150m.com/Electronic_Notebook/antennas/dipole.html

which gives the formula 468/f. The page you give is for building yagis,
and the reaction between the elements makes the lengths different than
for dipoles.

With that, you are not in *any* television band, as your antennas
are all in the 300-400 MHz range.

End to end = BOTH elements.

Yes, exactly, as in the web page I referred to.

Why are you using an impedance transformer?
Remember the impedance of a dipole is about 73 ohms.

Two 6" rods = open dipole, like the original. They are hex standoffs
because I didn't have any 3/8" aluminum rod or tube.

I was asking about why you used the 300 ohm to 75 ohm impedance
transformer. You have 75 ohm cable, and an approximately 75 ohm
antenna -- the transformer just makes things bad.

Two 6 inch rods adds up to 12 inches, not 15 inches.

Alan
.

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