In article ,
Richard Harrison wrote:

I apologize for causing confusion. The Isotron is only a large capacitor
with a trimmer?

Well, from what I can see of it (based on the diagrams on the Web), it
looks rather as if it's intended to behave like a very short dipole.
It's center-loaded and resonated with a large coil, and has a really
humongous capacity hat (the plates). The center coil, and the short
conductors leading from the top and bottom of the coil to the two
capacity-hat plates, would do the radiating.

If this is a correct description, then I'd expect the Isotron to
suffer from the same limitations as any short, loaded dipole - a low
radiation resistance (perhaps only an ohm or two) and a relatively
high loss resistance. Used in isolation (e.g. on an ungrounded mast,
with a choke on the feedline) its efficiency would be quite poor.

The fact that it's stated that it _must_ be grounded to a metal mast
for proper operation raises a big red flag (in my own humble view, at
least). This suggests that other folks are correct in asserting that
the mast, and the outside of the feedline are doing a lot of the
radiating.

It's even possible that in this configuration, the antenna system does
its best radiating when the Isotron itself is tuned _away_ from a good
match with the feedline, thus forcing significant currents onto the
feedline and the mast. One might (in this case) even view the Isotron
assembly as being something akin to a transmatch, with its reactivity
matching the impedance of the "antenna" (the mast and feedline) to the
feedline.

It'd be quite interesting to have somebody set up an Isotron as
directed, tune it to get the best signal in and out, and then run an
RF current meter over the mast, mast-grounding wire, and feedline when
transmitting. If there are relatively high currents present on
these conductors, it'd certainly be diagnostic!

--
Dave Platt AE6EO
Hosting the Jade Warrior home page: http://www.radagast.org/jade-warrior
I do _not_ wish to receive unsolicited commercial email, and I will
boycott any company which has the gall to send me such ads!

This suggests that other folks are correct in asserting that
the mast, and the outside of the feedline are doing a lot of the
radiating.
============================

What's wrong with radiation from the feedline? It's just as useful as
radiation from elsewhere.

On Tue, 23 Mar 2004 19:44:47 +0000 (UTC), "Reg Edwards"
wrote:
What's wrong with radiation from the feedline? It's just as useful as
radiation from elsewhere.

It's like promoting your SUV enjoying 80 MPG (but failing to disclose
that is with a 100 MPH tailwind).

Reg Edwards wrote:
What's wrong with radiation from the feedline? It's just as useful as
radiation from elsewhere.

Maybe for an Isotron, but not for a beam.
--
73, Cecil http://www.qsl.net/w5dxp



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What's wrong with radiation from the feedline? It's just as useful as
radiation from elsewhere.

Maybe for an Isotron, but not for a beam.

Or in cases where radiation coming off of the feedline would be
inconvenient for other reasons - e.g. the feedline runs in close
proximity to other wiring (RFI and telephone interference, or signals
getting where they don't belong in a multi-repeater shared site), or
metal pipes or metal-loaded walls (e.g. stucco).

--
Dave Platt AE6EO
Hosting the Jade Warrior home page: http://www.radagast.org/jade-warrior
I do _not_ wish to receive unsolicited commercial email, and I will
boycott any company which has the gall to send me such ads!

"Reg Edwards" wrote in message
...
This suggests that other folks are correct in asserting that
the mast, and the outside of the feedline are doing a lot of the
radiating.
============================

What's wrong with radiation from the feedline? It's just as useful as
radiation from elsewhere.

If I have a nice yagi array aimed at the moon and thus a low system noise
temp, and the feedline is allowed to radiate, I would think that might have
a bit of an effect not only on the array's pattern but also ruin the system
noise temp. The return loss then is also a function of cable length, routing
etc. Hardly a predictable array.
I can think of other examples. Although I admit in the case of the Isotron,
cable radiation is probably an advantage.

Dale W4OP

Reg Edwards wrote:
This suggests that other folks are correct in asserting that

the mast, and the outside of the feedline are doing a lot of the
radiating.

============================

What's wrong with radiation from the feedline? It's just as useful as
radiation from elsewhere.



If your interest is to spray your rf all over the place then a radiating
feedline is really FB.

If you have a $1500 tower, a $600 rotator, a $800 beam, a $3000
amplifier all connected to a $3000 transceiver, then you really want to
steer your RF in a controlled direction. Under these conditions a
radiating feedline destroys the nature of the antenna pattern and you're
not getting what you paid for.