CAPACITANCE HAT AND WHERE TO PUT IT
EZNEC MODELS WITH BUDDIPOLE PARTS
In the Buddipole user Group, Steve opened a thread about the effects of Capacitance Hats (Message 28930 ff.) and the contribuitions of Steve, Budd and Ralph made me curious and I opened EZNEC.
I refere to the model of the "longest vertical configuration" for the 60m Vertical from Scott Andersen's book "The Buddipole in the Field" Chapter 10, p.138 ff.
I had to replace the 9.5 foot whip by a 5 section shock cord whip (106" instead of 114" for the long telescopic whip) to allow for fitting the capacitance hat. I assume the use of the TRSB, set to 2:1. The 3 first models are of the same antenna height, but different inductances, in the 4th model I used the same inductance as in the 1st model, but reduced the radiator length.
1.) Antenna without capacitance hat:
Coil inductance 16.38 uH
2.) Antenna with capacitance hat, placed between the top of the 4 antenna arms and the shock cord whip. (This setup is not possible with the Buddipole capacitance hat without modification, I used it for modelling purposes only)!:
Coil inductance 13.75 uH, slightly increased bandwidth, slightly more loss (!), not much effect compared with antenna without capacitance hat, as Ralph mentioned.
3.) Antenna with capacitance hat at the end of the shock cord whip:
Coil inductance 11.8 uH, increased bandwidth, better VSWR, slightly less loss
4.) Antenna with capacitance hat, same inductance as model 1, reduced height:
aaaaah! Coil inductance 16.38 uH (as in model 1). The antenna height is reduced by more than 5 feet, that's exactly what Budd claimed! Performance pretty much the same as with "full-size" Buddipole radiator!
You find the EZNEC-files in the "Files" section of the BUG under "Capacitance Hats"
73, HB9MTN/5B4AGV, Ed
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