[TowerTalk] HF beam antenna decision

[Bernard]

    I believe that they use a 2:1 balun inside the motor control housing of
the driven element.  It is on their website somewhere.  There are also some
pictures of it.

            73


            Bernard, WA4OEJ


----- Original Message ----- 
From: "Tom Rauch" <w8ji at contesting.com>
To: "Joe" <WD0M at centurytel.net>; "Peter Sundberg" <sm2cew at telia.com>
Cc: <towertalk at contesting.com>
Sent: Saturday, April 17, 2004 6:20 AM
Subject: Re: [TowerTalk] HF beam antenna decision


> > Just curious, how is the matching done on the SteppIR so that it
presents
> > 1:1 SWR over the whole range. I understand the fundamental properties to
> > set the length of the elements with stepper motors, but normally a yagi
> has
> > a lower impedance than 50 ohms at j0. Is the 1:1 shown on an SWR meter
> > built up of a complex R + j or is the feed impedance really a pure 50
ohms
> > resistive on all frequencies ?
> >
> > 73/Peter SM2CEW
>
> Hi Peter,
>
> I'm sure you know this but there is no possible combination of resonant
> feedpoint resistance and additional X that fools a meter into reading 1:1
> SWR. There is a myth that adding some reactance to pure resistance causes
a
> low SWR in a 50 ohm system, but that isn't true. Any noticeable reactive
> component mixed in pure resistance load (even a mismatched load) would
> increase SWR. If you add a -15J capacitor in series with a 35 ohms
> resistance, the impedance is 35 -15j which is a HIGHER SWR than 35 -0j.
>
> I don't know what they do, they could detune the elements from optimum
gain
> or F/B and instead compromise for SWR, or maybe they handle it some other
> way.
>
> Maybe someone who has a SteppIR knows what they do. I'd be interested
also,
> because SWR should vary a good bit from electrically close-spaced element
> bands to wide-spaced element bands.
>
> 73 Tom
>
>
> _______________________________________________
>
> See: http://www.mscomputer.com  for "Self Supporting Towers", "Wireless
Weather Stations", and lot's more.  Call Toll Free, 1-800-333-9041 with any
questions and ask for Sherman, W2FLA.
>
> _______________________________________________
> TowerTalk mailing list
> TowerTalk at contesting.com
> http://lists.contesting.com/mailman/listinfo/towertalk
>