[R-390] SWL antenna

[Tim Shoppa]

John Kolb wrote:
>At 04:37 PM 11/6/2006, Dan Merz wrote:

>>  But I've been
>>wondering about the transmission line across and inside the attic
house
>>about 40 feet across and down about 16 feet into the basement.  My
first
>>idea was to use one of the better .240 diam coax types either 50 or
75 ohms
>>but then I starting reading about losses when mismatch exists and
thought
>>maybe RG8 might be worthwhile.  Or will I be just as well off using
the
>>cheap 300 ohm foam twin lead that I now use.

>The RG-8 won't work any better than the smaller coax and will be
>a lot stiffer and harder to handle

>>  I don't expect much noise from
>>things in the house but do know the current washer is a problem when
it's on
>>- probably has more electronic controls than the older one that I had
for
>>years with mechanical switching.  My current system picks that up
because
>>the lead-in wire drapes over toward the laundry room.  But I can hear
it on
>>a portable am radio operating on its internal antenna as well.  I
usually
>>lose interest in listening when the washing machine is running.

>Coax instead of twin lead should help with pickup from local QRM such
as
>washing machines.  Noise of your current washer probably comes from
>the motor, not the controls.

To build on top of what John and Roy have said:

Even better than coax is twinax or whatever they call shielded
balanced line today. I got a bunch and it works wonders on
MW and LW along with a magnetically shielded loop antenna.
Loops have a very real advantage in that they have a deep
null that is useful for eliminating a single point source of
interference. For the higher SW bands I have a dipole in
the air connected via the twinax. In all cases the reduction
in local RFI is profound compared to coax (worst) or coax
and a balun (slightly better than just coax but still not wonderful).

And the twinax is wonderful for use with the 390A, with
it's balanced antenna jack. You're using it exactly as it was
designed. Remember that the 390A was often used with noisy
mobile generators and in environments with lots of noise.

Twinax is often found surplus (meaning you should dumpster-dive!)
from IBM mainframe deinstallations, or you can buy it in quantity
and new on E-bay or other places.

Tim.