RadioBanter - Snow / Disconnecting Antenna

On Sun, 12 Feb 2006 19:56:25 GMT, Telamon
wrote:

In article . com,
"junius" wrote:

Thanks for the expanded explanation, Telamon!

So basically, then, one is fine doing shortwave listening during a snow
storm, provided that one is not using an outdoor antenna that is
exposed to the falling snow (or alternatively -as per David's post- if
one has an outdoor antenna which employs an unbalanced transformer and
the low side is grounded).

You have two options I can think of to mitigate the static problem.

1. A voltage transformer of some type not a current type.
2. Some type of static discharge unit on the coax lead-in to an outdoor
ground stake.

#1 You can get more signal out of the wire by using the transformer so
this solves two different problems of improving the wire reception
performance and blocking static electricity from reaching the radio
input at the same time.

Technically the amount of static protection provided by two windings in
the transformer is called voltage creep-age. This factor goes up with
distance and the insulative value (voltage breakdown) on the wires used
to make the transformer.

The wire antenna and outside ground stake are connected to the ends of
the primary winding. The coax lead-in shield and center conductors are
connected to the ends of the secondary winding. The coupling between the
windings is magnetic only and with the wire insulation the static
electricity can't cross between them but the signal does magnetically.
The static on the wire goes to the ground stake keeping it at a very low
value, a value far below the insulative value of the transformer wires.

Depending on the wire height above ground and the wire gauge you change
the turns ratio of the windings to accommodate the wires impedance but a
9:1 transformation will do the job in most installations.

#2 This is basically an air gap from center conductor to ground where
the coax shield is directly connect to ground at an outside ground
stake. Usually the device is a kind of tube filled with a gas that
squelches the gap current after the voltage spike so it doesn't stay
permanently shorted. The voltage will rise to the gap value, the tube
will conduct for a period of time sufficient to drain the charge to a
value below the gap value and then the current to ground is stopped.

I favor #1 (blocking) because the transformation of the wire impedance
is useful by itself and 0 volts of the DC static voltage is all that
ever reaches the radio input. #2 (shunting) will allow the DC static
voltage to reach the radio input to the specified gap value of the
static suppresser that is in use and the suppresser supplies no other
benefit by its inclusion in the antenna system.

???

Just get one of these autotransformer types. All parts of the
antennal system are at DC ground.

http://www.geocities.com/qrp_baluns/QB-9E.html