[opendtv] Re: VHF Stations Seek Solutions for Reception Problems, by Doug Lung

  • From: "Manfredi, Albert E" <albert.e.manfredi@xxxxxxxxxx>
  • To: <opendtv@xxxxxxxxxxxxx>
  • Date: Wed, 1 Jul 2009 11:09:29 -0400

Cliff Benham wrote:

> No.
> I was asking about a circularly polarized antenna being used only
> for receiving TV signals.
>
> If a circularly polarized antenna has a 90 degree phase delay
> between the H&V elements then it follows that it is only good for
> one frequency.
>
> This is because the 90 degree delay line is only 90 degrees at one
> particular frequency.

Right. When I saw Dale's and Ron's replies, I thought that might be what
you were asking. The question then is, can you use a variable delay
line, where delay varies as a function of frequency?

I don't know whether this is done in practice with CP or EP antennas,
but such devices do exist.

http://www.elmectech.com/variable_vda/vda.html

At 60 MHz, a 90 degree delay is 4.167 nS.
At 100 MHz, 2.5 nS
and so on.

Maybe Dale knows what's actually out there.

Bert
 
 
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