[Antennas] Crude Capacitive Hats and observations!

[Ron & Madhavi]

In case someone out the would be interested in my lazy Sunday =
afternoon's "backyard" experimenting with capacitive loading of a WIRE =
element........here goes!

Having read that most of the useful radiation off a dipole is done by =
about 66% of the element (about 22 feet at 20m), I decided to settle for =
the 23' wire. I next found 4 unequal size brass welding rods. I shaped =
these into triangles and soldered them up. The sides of the triangle =
were 21" each and the base was 17"=20

I soldered a triangle each to either end of the 23' dipole -- 1.5' from =
either end. I chose that placement simply because I did not want to =
solder it to the end of the wire as it might have touched the aluminium =
pole I use as a mast. I fixed the centre of the base of the triangle to =
the wire, using a tie wrap. Even though I know that a short dipole's Z =
is closer to 50 ohms I fed the antenna with 75 ohm coax as that was all =
I had in the junk box!=20

The element was hoisted up the pole and oriented as a sloping dipole. =
The end was about 6' off the ground (this height enabled the coax to be =
opulled into thew shack through the space between awnings! The coax was =
pulled at right angles and the measured minimum SWR was 1.9 at 16.45 =
Mhz. I guess this would correspond to around 1.3 if fed with 50 ohm =
coax. Did the element look pretty? NO WAY!   =20

As 23' corresponds to around 20.35 Mhz, I conclude that the capacitive =
hats moved the resonance by about 3.90 Mhz?=20

What I plan for tomorrow is to increase the loading by having another =
triangle within the first (like an egg beater). Whilst this might not =
look pretty, I guess I can learn from this crude experiment that similar =
amounts of loading could be used to make an efficient shortened element =
out of aluminium. In the past, I had simply lumped inductance -- I know =
this is not as efficient as capacitive loading. This system with far =
less inductive loading might make an excellent shortened 40m =
vertical/sloping dipole. =20

I am no guru (hi) just an ordinary backyard experimenter trying to =
reinvent the wheel! Any advise, suggestions etc would be most welcome. =
Oh BTW, I have only a small lot (32x12) and one anchor point at 40' =
above ground. Thus, compressed antennas are all I can run on the low =
bands.=20


                     =
------<--------------------oo------------------------->-------

That's what it looked like, only vertical ! I hope this info would be of =
use to someone else I me!

73,
Ron, 6Y5/4S7RO =20


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