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Tom Ring[_2_] · September 28th 08, 02:34 AM posted to rec.radio.amateur.antenna

wrote:
On Sep 27, 12:31 pm, "Frank" wrote:
"Richard Fry" wrote in message

...

"Art Unwin" wrote
... Now the antiresonant point will be between 100 and 200 ohms
resistive which allows me to feed it directly from a 50 ohm
transmission line (3/4 andrews) with negligable losses as
the mismatch is resistive.
__________
Art -
An antenna with an input impedance of 150 + j 0 ohms has a reflection
coefficient of 0.5 (50%), a return loss of 6.02 dB, and an SWR of 3:1 to a
50 ohm source. Probably not many transmitters would be happy with that
magnitude of load mismatch.
Do you maintain that the losses defined by these parameters are negligible
to amateur radio operators?
RF
In fact the losses are very low. 1000 ft of 7/8 hardline at 1.9 MHz has a
total loss of 0.68 db when terminated in 150 ohms. The total loss includes
0.26 db due to a the VSWR load of 3:1. Data from: "TLW, Transmission Line
Program for Windows", version 2.02.

73,

Frank

Feed line losses maybe, but total system loss will probably be
overwhelming.
Or at least to someone like me who likes to actually radiate most of
the
power I feed to an antenna.
The feed losses feeding a dummy load at 1.8 mhz are likely to be
quite
low also. Doesn't mean I would want to use it as an antenna though.
In one of his posts, he even goes as far as to claim appx 9 dbi gain
from his very small vs wavelength device.
This is appx equal to the gain of a FULL SIZE 3 element NBS yagi.
The only thing I keep observing here is a full load of horse hockey
that keeps emanating from a certain delirious old fart now living in
Illinois.
9dbi gain on 160m with a radiator the size of two shoe boxes,
consisting
of loads of wound 22 gauge wire. I don't know how many feet, but
probably in the hundreds anyway.. Can we spell some serious loss?
In some posts he seems to infer that he is now winding it on some
plastic barrel or garbage can, but I wouldn't expect a drastic
increase
in performance, considering the frequency being used.
I won't mention that in other breaths he takes, he claims no real
gain, but basically an omnidirectional antenna.
The wind changes direction depending who he wants to listen.
This is some good stuff. The comedy channel is missing the boat.
Heck, the feeder losses are really not much of an issue being
at 1.8 mhz, the loss of most any decent coax is very low.
Nearly ladder line performance.. You could be 10/1 SWR and
it wouldn't kill you as long as the radio didn't shut down.
In his case, the coax probably radiates more than the antenna.
His antenna is not a whole lot different than someone using an
Isotron. And in the case of that small antenna, it's not unusual for
the coax cable to do a good bulk of the actual radiating.
At least the people that make the Isotron have the common
decency not to proclaim some miraculous discovery of science,
and/or claim 9 dbi gain from their dinky antenna on 1.8 mhz.
So I don't heckle them like I do Art.
If Art did likewise, he'd never hear a peep out of me.
But we all know Art is not going to follow that plan... :/

He also stated he would possibly be putting a 6 foot or so dish behind
his antenna to add gain. Wonder at what frequency he expects that to
work? I think it was in the 80m or 40m range. Hmm.

tom
K0TAR