Topband: Adding a parasitic reflector to a vertical

[W0MU Mike Fatchett]

I was going to try to phase 2 80m verticals but just could not find the 
room.  You get endfire and broadside.

I assume you have to put down the same radial field for a Parasitic 
element as a driven one?  Maybe I am wrong here.


On 2/9/2018 3:38 PM, Joel Harrison wrote:
> Interesting question Mike!
>
> Possibly, however my focus was to achieve maximum gain with minimal
> effort. This direction allowed me to accomplish that objective.
>
> Don't know if anyone has documented experience in doing what you pose. I
> would certainly be interested in reading the work anyone conducted along
> that line for amateur use. Would be interesting.
>
> 73 Joel W5ZN
>
>
>> 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
>>>>
>>>>
>>>>
>>>>
>>>>
>>>>
>>>>
>>>>
>>>>
>>>>
>>>>
>>>>
>>>>
>>>>
>>>>
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>> _________________
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>