At 01:38 AM 3/23/2005, Peter Grillo wrote:
>I've had similar thoughts. Whoever is willing to answer this question might
>wish to suggest hanging vertical dipoles instead of requiring a ground
>planes under the vertical elements. Structurally, this would be a benefit.
>Same questions apply. Any takers?
>
>-----Original Message-----
>From: towertalk-bounces@contesting.com
>[mailto:towertalk-bounces@contesting.com] On Behalf Of StellarCAT
>Sent: Tuesday, March 22, 2005 7:56 PM
>To: towertalk@contesting.com
>Subject: [TowerTalk] Model done for 4SQ supported by center tower
>
>Alright .. .the consensus was to go with a 4SQ (over a dipole
>at 175'). The dipole actually shows more gain and a lower
>angle (with gain) than the 4SQ BUT - and it is a big one - it
>has a strong lobe that is straight up so the qrm would
>be obnoxious)...
>
>anyway... several have suggested to use a center tower to
>support (via ropes) 4 verticals. This would place the tower
>at the center. How does this interact with the 4 verticals?
>Has any one modeled this and/or is there anecdotal
>evidence it does or does not work?
>Also I assume the ground plane (I was thinking of 6
>elevated radials per vertical at minimum 8' above ground)
>would have a "hole" around the tower and not connect to it - correct?
>
>[this would also apply to the folded back dipole systems -
>do they "see" the tower in a detrimental way as well?]
Running a quick NEC model. 4 61 ft elements (1" diam) in a square (1/4
wave on a side), fed at the bottom. 175 ft tower in the middle (modeled as
1ft diameter wire). Using the 0,90,180 across the corner feeding strategy.
10.9 dB Fwd gan, 100 deg BW , 14.6 dB F/B
W/o the tower, 10.7 dB fwd gain, 100 deg BW, 28.3 F/B
Fair amount of current in the tower, 136+j168mA at the base. 101-j69.8 mA
nearer the top, all the elements were fed with 1 Amp.
So the tower actually increases the forward gain (by an insignificant
amount), but screws up the F/B.
You could probably adjust the phasing a bit to fix the F/B
_______________________________________________
See: http://www.mscomputer.com for "Self Supporting Towers", "Wireless Weather
Stations", and lot's more. Call Toll Free, 1-800-333-9041 with any questions
and ask for Sherman, W2FLA.
_______________________________________________
TowerTalk mailing list
TowerTalk@contesting.com
http://lists.contesting.com/mailman/listinfo/towertalk
|