I'm also thinking that without a noise-bridge, my best bet is a trial and
error comparison. Joe Carr sez that at less than 1 wavelength, large loops
can reach a feedpoint impedance of up to 3000 ohms (I had to read it twice
to make sure); but at a full wavelength or longer, it pretty much stays at
around 100 ohms. Various sources show anywhere from no match needed, all
the way up to a 30:1 match is needed. I think there's just too many
variables to know for sure. So, trial and error it is. I'm going to try a
30:1, a 10:1 and a 1:1 toroid xformer to see what differences, if any, I
can detect just with the naked "earball". In the absence of any
discernable difference, I'm going to at least use the 1:1, if only to
maintain the DC seperation between the antenna element and the coax.

In addition to the end Z varying radically with frequency, you will also
find the classic 9:1 toroidal transformer only functions as a 9:1 over a
relatively narrow frequency range- whereas a binocular core will behave as a
9:1 over almost 2 decades. Somewhere here I have a network analyzer plot
comparing a toroidal vs binocular transformer.


--
Dale W4OP
for PAR Electronics, Inc.

Dale Parfitt wrote:

In addition to the end Z varying radically with frequency, you will also

find the classic 9:1 toroidal transformer only functions as a 9:1 over a
relatively narrow frequency range- whereas a binocular core will behave as a
9:1 over almost 2 decades. Somewhere here I have a network analyzer plot
comparing a toroidal vs binocular transformer.

It depends a lot on the size of the transformer. You can get two decades
from a tiny one made with a TV balun toroid. One trick is to keep the
total length of wire in the transformer below about 5% of a wavelength
at the highest frequency of interest.

The antenna's Z does indeed vary a great deal, from 10's to 1000's of
ohms. If you plot it in the complex plane, it makes a spiral centered at
the antenna's *characteristic* Z, which for an inverted L is generally
in the range of 300-700 ohms. Matching to an impedance near the center
of the spiral yields a system that is not perfectly matched at any
frequency, but is adequately matched over a wide range of frequencies.

-jpd

Yeah !
But the blinking NE-2 during a thunderstorm is kinda entertaining!

(I had the same brain fart) ;)

it seemed like the simple loading of the antenna thru the "Balun"
caused noise to drop by 50% and my station count at least doubled
(but I still cant get New Zealand---I need my sleeeep!)

I tested the concept first with a 300/75 tv-cable balun

Yodar


-=jd=- wrote:


That's the method I used with the end-fed random. I had built a static
bleeder to go with it, which was just silly. I experienced a mental vapor-
lock and didn't recognize that the xformer provided a direct DC path to
ground on it's own. It could have been that I just wanted to build
something - idle hands and all...

Volker Tonn wrote:
But for sure you can not do it by yourself and it will cost a LOT. And
at least there is NO insurance it will work under ALL circumstances.
Best (additional) way to go is to disconnect the antenna when leaving
the shack or lightning is coming up whilst you are in your shack.


Not true. You have to be anal-retentive as hell to make sure that it
is done right, but you can do it properly using the right equipment.
Polyphaser or I.C.E. protectors do the job well, but they must be
mounted on an appropriate ground window. The object of the game is
not to have your equipment at ground potential; rather the object is
to have the potential on all the equipment rise and fall together so
there is no differential amongst the equipment.

There is quite a bit of introductory material at www.polyphaser.com.

Eric

--
Eric F. Richards,
"Nature abhors a vacuum tube." -- J. R. Pierce, Bell Labs, c. 1940

Is there much one can do for sensitive electronics? For example, during the
summer at my QTH, late day thunderstorms are common and on one such day I
did have the antenna disconnected from my Drake R-8B but a FET still managed
to get fried and I needed to send the radio back to Drake for repair.

Regards

John Barnard

"Eric F. Richards" wrote:

Volker Tonn wrote:
But for sure you can not do it by yourself and it will cost a LOT. And
at least there is NO insurance it will work under ALL circumstances.
Best (additional) way to go is to disconnect the antenna when leaving
the shack or lightning is coming up whilst you are in your shack.


Not true. You have to be anal-retentive as hell to make sure that it
is done right, but you can do it properly using the right equipment.
Polyphaser or I.C.E. protectors do the job well, but they must be
mounted on an appropriate ground window. The object of the game is
not to have your equipment at ground potential; rather the object is
to have the potential on all the equipment rise and fall together so
there is no differential amongst the equipment.

There is quite a bit of introductory material at www.polyphaser.com.

Eric

--
Eric F. Richards,
"Nature abhors a vacuum tube." -- J. R. Pierce, Bell Labs, c. 1940

JB,

Three things "To Do" during Thunder and Lightening Events:

1. Dis-Connect 'all' Antennas and Ground them to the Ground Bus
in your Shack.

2. Use Shorting Plugs and Wires on 'all' your Radio/Receivers
Antenna Inputs.

3. Have a small 'all' Metal Foot Locker or Cabinet to place
your Radios/Recivers in for Safety.

iane ~ RHF
..
..
= = = John Barnard wrote in message
= = = ...
Is there much one can do for sensitive electronics? For example, during the
summer at my QTH, late day thunderstorms are common and on one such day I
did have the antenna disconnected from my Drake R-8B but a FET still managed
to get fried and I needed to send the radio back to Drake for repair.

Regards

John Barnard

"Eric F. Richards" wrote:

Volker Tonn wrote:
But for sure you can not do it by yourself and it will cost a LOT. And
at least there is NO insurance it will work under ALL circumstances.
Best (additional) way to go is to disconnect the antenna when leaving
the shack or lightning is coming up whilst you are in your shack.


Not true. You have to be anal-retentive as hell to make sure that it
is done right, but you can do it properly using the right equipment.
Polyphaser or I.C.E. protectors do the job well, but they must be
mounted on an appropriate ground window. The object of the game is
not to have your equipment at ground potential; rather the object is
to have the potential on all the equipment rise and fall together so
there is no differential amongst the equipment.

There is quite a bit of introductory material at www.polyphaser.com.

Eric

--
Eric F. Richards,
"Nature abhors a vacuum tube."
-- J. R. Pierce, Bell Labs, c. 1940

..

In article , John Barnard
wrote:

Is there much one can do for sensitive electronics? For example, during the
summer at my QTH, late day thunderstorms are common and on one such day I
did have the antenna disconnected from my Drake R-8B but a FET still managed
to get fried and I needed to send the radio back to Drake for repair.

I You do not know what happened. The radio might have been damaged
before you disconnected it. Sometimes the damaged FET does not fail
right away. There might have been a static charge on the antenna that
blew the FET when you went to reconnect it.

I consider myself very fortunate that I do not live in a lightening zone
and so do not have these problems but I do not use the type of antennas
most susceptible to this kind of damage.

Loop antennas are the safest to use as long as you make ground contact
first with the radio upon reconnection. If you use a Marconi type of
antenna, be sure to use a coupling transformer that is grounded in some
way to give the static charge a place to go.

The damaging pulse from lightening needs some kind of clamping device.
Those can be bought at the same outfits that sell antennas.

--
Telamon
Ventura, California

John Barnard wrote:

Is there much one can do for sensitive electronics? For example, during the
summer at my QTH, late day thunderstorms are common and on one such day I
did have the antenna disconnected from my Drake R-8B but a FET still managed
to get fried and I needed to send the radio back to Drake for repair.


First off, it could have been damaged by a surge and failed later.

Second off, with reputable lightning supressors such as Polyphasers,
properly set up, the radio is actually safer than it is when
disconnected because the supressor will crowbar (dead-short)
nanoseconds after the strike starts, when the threshold voltage is
reached. It remains shorted as long as current is flowing.

It should be noted that a simple static discharge such as touching a
doorknob and getting a spark has to be about 3000 volts before a
visible spark occurs. That is way above the crowbar voltage of the
Polyphasers.

Regards

John Barnard

"Eric F. Richards" wrote:

Volker Tonn wrote:
But for sure you can not do it by yourself and it will cost a LOT. And
at least there is NO insurance it will work under ALL circumstances.
Best (additional) way to go is to disconnect the antenna when leaving
the shack or lightning is coming up whilst you are in your shack.


Not true. You have to be anal-retentive as hell to make sure that it
is done right, but you can do it properly using the right equipment.
Polyphaser or I.C.E. protectors do the job well, but they must be
mounted on an appropriate ground window. The object of the game is
not to have your equipment at ground potential; rather the object is
to have the potential on all the equipment rise and fall together so
there is no differential amongst the equipment.

There is quite a bit of introductory material at www.polyphaser.com.

Eric

--
Eric F. Richards,
"Nature abhors a vacuum tube." -- J. R. Pierce, Bell Labs, c. 1940

--
Eric F. Richards

"The weird part is that I can feel productive even when I'm doomed."
- Dilbert