Topband: Adding a parasitic reflector to a vertical

[W0MU Mike Fatchett]

Could you not get more out those elements if you had phased them?  
Obviously there would be more work required for the phasing system.   
One element short of a 4 square.


On 2/1/2018 6:01 PM, Joel Harrison wrote:
> As Tim noted I built the K3LR version of the 3 element parasitic array
> this past fall. I used my original and existing shunt fed tower as the
> driven element. It is switchable in four directions and I have an
> extensive radial system (120 radials)under each element.
>
> My initial assessment indicates a forward gain of around 5 dB and a
> minimum F/B of 25 dB. It performs very well from out here in fly over
> country.
>
> I am in the process of completing a paper detailing my construction and
> experience with the array and will also be presenting this at the Dayton
> Antenna Forum on Friday of Dayton.
>
> I have spent the past 10 years improving my 160 meter RX systems here at
> W5ZN and had reached a point of needing to improve the TX system beyond a
> single shunt fed tower. I struggled with whether to build a stand alone 4
> square for 160 meters however the appeal of the parasitic array is that I
> could use the existing shunt fed tower to support the T elements without
> having to erect an entirely new mechanical structure for a 4 square while
> achieving basically the same result. I have been pleased with the
> performance for the short few months it has been in operation.
>
> Obviously it doesn't provide the broad bandwidth a 4 square does. I have
> about 40 KHz between 1.5:1 points however in reality a 4 square has
> limited bandwidth since beyond the resonant points you dump a lot of power
> into the dump load!
>
> 73 Joel W5ZN
>
>
>> 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 at 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
>>
>>
>>
>>
>>
>>
>>
>>
>>
>>
>>
>>
>>
>>
>>
>
> _________________
> Topband Reflector Archives - http://www.contesting.com/_topband