Beam Interaction - FYI

[pph at dc.dk]

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From: PALLE PREBEN-HANSEN at datacentralen_di_cpr
Date: 10/9/95 4:31PM
To: cq-contest at oampc12.csg.mot.com at INTERNET
To: kurscj at oampc12.csg.mot.com at INTERNET
Subject: Re: Beam Interaction - FYI
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      Hello,
      
      Stacking a beam for the same frequency within a stack seems like 
      looking for troubles. Also I think the 2 elm Cushcraft 402CD is not 
      full size and has some kind of high-Q loading, making is more 
      sensitive.
       
      In the good old days (pre computer age) a stacking distance of 2/3 of 
      the boom length, but no less than 1/2 wavelength, was considered 
      resonable.
       
      Today we know better how to calculate stacking distance of similar 
      beams for max. gain. It is a function of the 3 dB opening angle of the 
      beam measured in the stacking plane (= opening angle in the vertical 
      plane (H-plane) for a vertical stack of horizontal polarized beams). 
      At this distance interaction is usually not severe.
      
      At HF stacking is not so much done for max gain as for filling in the 
      vertical radiation pattern. Still the beams requires a reasonable 
      seperation to avoid interaction. Your 20 m beams are most likely not 
      too far from the calculated optimum stacking distance.
      
      I have stacked beams for six. The seperation is only little smaller 
      than for max gain and the interaction, when they are rotated 
      individually, is minimal on the SWR.
      
      At 40 m your seperation is 1/4 wavelength and on 20 m more than 1/2 
      wavelength.
      
      It is said, that stacking beams for different bands requires a 
      seperation of half the max-gain-stacking-distance of the beam for the 
      higher frequency. Interlacing stacked beams for different bands is not 
      good, but what else can one do when the credit card will not give 
      rotating poles for all 5 bands .... ..
      
      Stacking beams is great for contesting and switching BLU (Both-Lower- 
      Upper) or BIP/BOP (Both In Phase/Both Out of Phase) could be added. 
      Individual rotators is great, and so is one linear to each of the 
      beams in the stack!
      
      Has anyone programs for calculating a stack feed out of phase? TA by 
      K6STI and YTAD does not handle this. Well, I am building a BIP/BOP 
      switch even without computer modelling.
      
      73, Palle, OZ1RH (OZ9EDR-OZ5W contest team) Internet: pph at dc.dk

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