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#1




Capacitive Hat
I know a capacitive hat (or capacitance hat) lowers the resonant frequency
of a whip by electrically lengthening it, but by how much? When I was in the service, one of our techs loaded an AFRTS BCB transmitter (1520 kHz, I think) into a 35foot whip that had a capacitive hat. The hat was a five foot diameter ring of #10 wire with four spokes off the top of the whip. I don't recall (or never knew) what other matching he did. 50 watts went about ten miles, so it worked OK, not great. The ARRL antenna book makes it look like the physical length is about 2/3 of the electrical length (60 degrees physical length plus 30 degrees from the hat). 
#2




Capacitive Hat
On Thu, 27 Jul 2006 21:43:15 0700, "Sal M. Onella"
wrote: I know a capacitive hat (or capacitance hat) lowers the resonant frequency of a whip by electrically lengthening it, but by how much? Hi OM, The hat replaces roughly double its length in height  or so goes one proportions of one magic formula. So, for your example of: a 35foot whip that had a capacitive hat. The hat was a five foot diameter ring of #10 wire with four spokes off the top of the whip. hat would say it is equivalent to a 40 foot radiator (35 + 2 · 2.5). I've often wondered why anyone would go to the trouble to wrestle with the mechanical details of keeping a top hat aloft, when they couldn't manage what would be 5 additional feet of whip in this case. Top hats built out of guys is another story, but freestanding hats seems more like adornment than being necessity driven. You may note this doesn't come even remotely close to resonant for 1520 KHz  if that was the implication in your posting. Further, it would be an amazing top hat that could for a 35 foot whip. 73's Richard Clark, KB7QHC 
#3




Capacitive Hat
Sal M. Onella wrote:
I know a capacitive hat (or capacitance hat) lowers the resonant frequency of a whip by electrically lengthening it, but by how much? What I do to answer questions like that for myself is to model the antenna system using EZNEC.  73, Cecil http://www.qsl.net/w5dxp 
#4




Capacitive Hat
Sal,
A capacitance hat allows you to drive your car into the garage without breaking off a whip of 15 feet equivalent height. A capacitance hat loads a short vertical without suffering the loss in a loading coil. To calculate capacitance of a hat, above an antenna of given height, with N spokes of given length, surrounded by a halo, plus resonant frequency, download program TOPHAT from website below. The program also calculates L and C values of the tuner. The whole job can be done in a couple of minutes.  .................................................. .......... Regards from Reg, G4FGQ For Free Radio Design Software go to http://www.btinternet.com/~g4fgq.regp .................................................. .......... 
#5




Capacitive Hat
Sorry! The correct name of the program is TOPHAT2.  .................................................. ......... Regards from Reg, G4FGQ For Free Radio Design Software go to http://www.btinternet.com/~g4fgq.regp .................................................. ......... 
#6




Capacitive Hat
"Reg Edwards" wrote in message news Sal, A capacitance hat allows you to drive your car into the garage without breaking off a whip of 15 feet equivalent height. A capacitance hat loads a short vertical without suffering the loss in a loading coil. To calculate capacitance of a hat, above an antenna of given height, with N spokes of given length, surrounded by a halo, plus resonant frequency, download program TOPHAT from website below. The program also calculates L and C values of the tuner. The whole job can be done in a couple of minutes. That's outstanding! I see the original antenna was only about 15% efficient and the capacitance hat improved it by about 2 dB. I will play with that program. Thanks. "Sal" (really KD6VKW) 
#7




Capacitive Hat
"Sal wrote That's outstanding! I see the original antenna was only about 15% efficient and the capacitance hat improved it by about 2 dB. I will play with that program. Thanks. ======================================= Sal, enjoy yourself with it. I do not wish to dampen your enthusiam, but 2 dB is only 1/3 of an Sunit. Hardly noticeable! ;o) ;o)  Reg. 
#8




Capacitive Hat
Reg Edwards wrote:
Sal, enjoy yourself with it. I do not wish to dampen your enthusiam, but 2 dB is only 1/3 of an Sunit. Hardly noticeable! ;o) ;o) Hardly noticeable? That's enough to be crowned champion of a 75m mobile shootout with all the attending honors. :)  73, Cecil http://www.qsl.net/w5dxp 
#9




Capacitive Hat
1dB is a humandetectable change.
2dB could make the difference between a QSO and no QSO with marginal S/N ratio. 1 "standard" Sunit of 6dB can probably make the difference between marginal S/N and armchair copy. If copy is already armchair, Reg's totally right. No change. I like to make a lot of QSO's that are down in the noise, though. 73, Dan 
#10




Capacitive Hat

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