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:[email protected]] 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 >> > > _________________ Topband Reflector Archives - http://www.contesting.com/_topband
