Thread: A DTV antenna
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Old April 26th 09, 01:04 AM posted to rec.radio.amateur.antenna
Richard Clark Richard Clark is offline
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First recorded activity by RadioBanter: Jul 2006
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Default A DTV antenna

On 26 Apr 2009 00:56:11 +0100, Gordon wrote:

I've done the math. Channel 2 has a wavelength of about 18 feet and
channel 50 is about 1.4 feet. More than a 2:1 ratio. I do catch a
break since the VHF lo band is going to be vacated in this area. So
channel 8 is the lowest frequency I need to worry about (wavelength
of approx 5.5 feet).


Hi Gordon,

Yes, you've got the minimum specifications there. The widest part of
your antenna, at an optimum, would be something under 3 feet (half the
channel 8 wavelength) - still pretty big for indoors, especially if
the stations are in an awkward angle.

And speaking of stationS (accent on the plural), your design
requirements are going to be complex if they are not all on the same
axis/direction. And speaking further of stationS, you will need to
cover a broad range of frequencies.

The usual, optimal design is called a Log Periodic Dipole Array (or
variants of Log _______ ). It would qualify for being both
widebanded enough for one, or many, adjacent channels (growing in
length and element count for additional channels). This is why I
described the optimal antenna as being "honestly" big.

Smaller antennas are not going to deliver performance - but, again,
you may not need optimum, nor performance when the time comes. The
bow tie you've described elsewhere seems a suitable compromise.

Actually, I tried to keep the situation as controlled as possible.
I initially had the leads just drapped down the "mast" (dowel) to
a balun. It was my wife that tried to improve the asthetics by
neatening up the twinleads. Then she complained that reception
was bad. That's when I was experimenting with the dressing of
the leads. Right now I have it "dressed ugly", but it works.


Twinlead is fairly robust "except" when it is in close (three widths)
to metal or an RF absorber. As marginal as your situation sounds, my
bets are still with clutter near the antenna which is MORE prone to
disturbance than the line is.

No, the rabbit ears didn't work very well at all. That's why I have been
experimenting. I have seen a lot of the DIY designs littering the
WWW. This dual bowtie design is mine, tho.


When the band shift comes, rabbit ears could work quite well. Don't
take the plunge into elaborate designs until you have some basis of
comparison is all I am suggesting.

73's
Richard Clark, KB7QHC