In article ,
Cecil Moore wrote:

Fred McKenzie wrote:
I've collected the parts but haven't assembled it yet. It will be
interesting to see how the monstrosity works!

Hope you enjoy 75m QRP.

Cecil-

I can appreciate that a mobile whip used on an auto, does not have the
efficiency of a full quarter wave vertical over an array of counterpoise
wires. But it does work.

I want to use a pair of mobile whips as a horizontal dipole. (Or more
in the case of the Octopus.) Are you suggesting that such a dipole on
75 or 40 Meters, will not perform as well as just one of the whips
mounted on an automobile?

Fred
K4DII

Fred McKenzie wrote:
I want to use a pair of mobile whips as a horizontal dipole. (Or more
in the case of the Octopus.) Are you suggesting that such a dipole on
75 or 40 Meters, will not perform as well as just one of the whips
mounted on an automobile?

The radiation resistance of a 75m hamstick is roughly
about 0.5 ohms. The feedpoint impedance is roughly
about 20 ohms if one subtracts out the ground losses.
Very roughly, that would make a 75m hamstick dipole
have a radiation resistance of about 1 ohm and a
feedpoint impedance around 40 ohms. That's about 2.5
watts out for 100 watts in. I would say that qualifies
for QRP and is actually an improvement over a 75m mobile
hamstick with a measured signal strength that is 12 dB
down from a good screwdriver which itself is about 10 dB
down from a 1/2WL dipole.

Almost any other antenna in the world will beat a
75m hamstick dipole. One can radiate ten times as
much power simply by lengthening it by 50% and using
high-Q loading coils.
--
73, Cecil http://www.w5dxp.com

Cecil Moore wrote in news:2KTMj.8379$V14.7229
@nlpi070.nbdc.sbc.com:

Fred McKenzie wrote:
I want to use a pair of mobile whips as a horizontal dipole. (Or more
in the case of the Octopus.) Are you suggesting that such a dipole on
75 or 40 Meters, will not perform as well as just one of the whips
mounted on an automobile?

The radiation resistance of a 75m hamstick is roughly
about 0.5 ohms. The feedpoint impedance is roughly
about 20 ohms if one subtracts out the ground losses.
Very roughly, that would make a 75m hamstick dipole
have a radiation resistance of about 1 ohm and a
feedpoint impedance around 40 ohms. That's about 2.5
watts out for 100 watts in. I would say that qualifies
for QRP and is actually an improvement over a 75m mobile
hamstick with a measured signal strength that is 12 dB
down from a good screwdriver which itself is about 10 dB
down from a 1/2WL dipole.

Almost any other antenna in the world will beat a
75m hamstick dipole. One can radiate ten times as
much power simply by lengthening it by 50% and using
high-Q loading coils.

Hi:

As I reported some time ago, I compared Hamstick dipoles to a full size
dipole at about the same height. The Hamstick dipole was about 20d down
from the full size antenna. The 2:1 SWR bandwidth was about 65KHz. They
work as an antenna but are in the better than nothing class.

John Passaneau W3JXP

John Passaneau wrote:
As I reported some time ago, I compared Hamstick dipoles to a full size
dipole at about the same height. The Hamstick dipole was about 20d down
from the full size antenna.

So I was generous in estimating 2.5 watts radiated
out of 100w input. In your case, it was more like
1 watt radiated out of 100w input.
--
73, Cecil http://www.w5dxp.com