Topband: Adding a parasitic reflector to a vertical

[Joel Harrison]

I believe you could get by with less radials with a phased array. In that
case all of the elements are "driven" so the current distribution in each
element will be forced.

With a parasitic element proper current distribution and thus gain is
impacted by ground resistance so a good, effective radial system is really
mandatory to achieve maximum efficiency.

Modeling data supports this. ON4UN has a chart in Low Band DX'ing that
depicts gain -vs- ground resistance for parasitic elements.

As a comparison, my 80 meter 4 square has a little less than half the
radials I have on the 160 meter parasitic array and is a stellar
performer.

I have no experience and have not modeled a phased array other than a 4
square so I base the above on nothing more than my study and experience
with the arrays in question.

73 Joel W5ZN



> 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
>>>>>
>>>>>
>>>>>
>>>>>
>>>>>
>>>>>
>>>>>
>>>>>
>>>>>
>>>>>
>>>>>
>>>>>
>>>>>
>>>>>
>>>>>
>>>> _________________
>>>> Topband Reflector Archives - http://www.contesting.com/_topband
>>> _________________
>>> Topband Reflector Archives - http://www.contesting.com/_topband
>>
>
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