Hi Mark:
The tower (driven element) sits on a base insulator. So it is series fed.
73
Tim K3LR
-----Original Message-----
From: Mpridesti [mailto:mpridesti@yahoo.com]
Sent: Wednesday, January 31, 2018 4:46 PM
To: k3lr@k3lr.com
Subject: Re: Topband: Adding a parasitic reflector to a vertical
Hi Tim
Following this thread. Assume the tower is grounded so just how are you
connecting your L network to the tower? A gamma wire? Tapped where?
Appreciate your help!
Regards,
Mark, K1RX
> On Jan 31, 2018, at 2:28 PM, Tim Duffy <k3lr@k3lr.com> wrote:
>
> I have been using a 3 element parasitic vertical beam on 160 for at least
20
> years. K9CT, NR5M, AA1K*, VE3EJ and most recently W5ZN have the same
array.
> It has instant switching in 4 directions.
>
> With 4 parasitic cut directors around the center driven element tower - it
> is pretty easy to get over 5 dB of forward gain (over 40 KHz wide) and
over
> 30 dB of front to back (over a narrow bandwidth). Easy driven element
match
> with an L network at the base. Each parasitic has 3 modes. Director,
> Reflector or float. Going from directional to Omni is easy as well.
>
> *AA1K has an additional director toward Europe. So he has 4 elements!
>
> As was pointed out - the magic in any vertical antenna is all about the
> radials. Each parasitic wire (4) and the center driven element tower has
120
> radials that are 130 feet long (unless they cross the junction bus). I
have
> 67,000 feet of radials under my 160 array.
>
> I use a 120 ft 24 inch face solid leg tower as the driven element. The
tower
> sections are welded together to decrease any joint loss. The parasitic T
> wires are #12 Copperweld.
>
> The last three editions of the Low Band DXing book describe this antenna
in
> the Yagi chapter.
>
> 73
> Tim K3LR
>
> -----Original Message-----
> From: Topband [mailto:topband-bounces@contesting.com] On Behalf Of W7RH
> Sent: Tuesday, January 30, 2018 11:39 PM
> To: Topband
> Subject: Re: Topband: Adding a parasitic reflector to a vertical
>
> I've played with parasitic elements in antenna arrays for almost three
> decades and the current antenna system I have used parasitic elements
> both director and reflectors.
>
> With very careful tuning performance that of a all driven array can be
> achieved. Tree is correct they due tend to be somewhat limited in in
> bandwidth with relation to F/B ratio. Gain remains fairly constant.
>
> The tuning procedure that Tree suggested is absolutely correct. You
> detune all unused elements and adjust the center frequency of the
> parasitic for best F/B one element at a time. Parasitic elements I might
> add are no different than driven and must have extensive ground system
> to be effective. No exceptions. You know you have right by F/B ratio.
> You can go one step further and measure the actual antenna currents
> which I have done. In my system the parasitic elements achieve 80-85% of
> the theoretical current at the base.
>
> de Bob W7RH
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
> --
> W7RH DM35OS
>
>
> It has become appallingly obvious that our technology has exceeded our
> humanity.
>
> Albert Einstein
>
> _________________
> Topband Reflector Archives - http://www.contesting.com/_topband
>
> _________________
> Topband Reflector Archives - http://www.contesting.com/_topband
_________________
Topband Reflector Archives - http://www.contesting.com/_topband
|