Super Penetrator 500 above a Sirio SY 27-4?

[Shockwave]

Marconi's model now clearly shows why this is a bad idea. The effect is actually much worse then I thought. The 4 element version I experimented with showed approximately 10 degrees of downward tilt. I suspect this has to do with the 2 directors trying their best to refocus that energy back inline with the boom. The free space model shows that simply adding the SPT500 above the beam caused the beam to nose dive its pattern 20 degrees downwards! That would be a very bad thing as far as performance.

So why don't we hear many more people saying how much the performance of the beam was messed up after placing a groundplane with horizontal radials above it? The answer has to do with how the earth will reflect that pattern back upwards in the far field. This is why when you model over real earth, you see distortion in the pattern but the far field TOA remains virtually unchanged.

One might be quick to think if the height above earth is going to correct the angle, then you don't have to be concerned with this interaction. Not so because the near field radiation will still be directed downwards by the radials above the beam and will increase RFI. Even though the primary lobe TOA does not change over earth, the gain at that angle has been reduced by the loss of power that is radiated downwards.

 

[binrat]

So the simple answer maybe to place the 500 tight above the yagi without and radials, using the yagi as radials?
I know having 10' of space between the 2 when I had it up was a royal pain for servicing the vertical. Just don't like standing on a small step while being tied off to a pipe to reach way overhead. My next set-up will have the Ringo ranger 2 metre above the yagi.

 

[PONYEXPRESS]

Read forum posts about 5/8 verticals coexisting in harmony over horizontal beams, but have not found references to an SPT-500 above an SY 27-4. I contemplate this set-up on a 40' tower but worry that the ground radials on the SPT-500 (which would extend parallel & above the beam's elements) may cause changes of the radiation pattern (or other ill effects) on the signal of the SY 27-4. Is this a viable array or do I have a legitimate concern? Is there a ‘minimum’ height to maintain the SPT-500 above the SY 27-4?

What would be interesting would be what would happen if you rotated the radials around so they were not directly under a element but perhaps a 45 degree angle off of being directly above the beams element. This would help eliminate some of the pattern change
Myself I would just run a antenna like a Gainmaster or Imax 2000 without ground radial kit and be 9 ft above the beam.

 

[W5LZ]

The only 'best' way of reducing inter-antenna effects is distance, the bigger the better. Any two antennas 'near' each other will affect each other. How much and in what way is the 'biggy'. There's almost always a 'work around' to compensate for that interaction (commonly a part of 'tuning' an antenna). You do the best you can then accept what you get.
- 'Doc