[Premium-Rx] NDB Receivers

[Carcia, Francis A HS]

Isolation transformers on the power line are also great in the EMI test
world when
testing below 100 KHz. Good coax is a must!!!!!!!!!!! RG223, RG214, RG
141BU, RG400
RG58, RG8, junk.

-----Original Message-----
From: Ben Dover [mailto:quixote2 at ix.netcom.com]
Sent: Monday, April 04, 2005 3:49 PM
To: Doug Millar; premium-rx at ml.skirrow.org
Subject: Re: [Premium-Rx] NDB Receivers


>I, too, like NDB listening. Other than running the entire 
>receiver off of batteries, is there any easy way to keep noise induced from

>the AC line out of the receiver?



It all depends on what you mean by "easy". In LF / VLF noise zapping, that 
word becomes quite relative. ;o)

The Name of the Game here is break the AC ground loops. EVERY television
engineer
is adept at that game; ground loops cause "hum bars" in video.

First, and most effective step; break the AC loop induced in the antenna
that goes
to ground thru the receiver. That means a broadband RF transformer; primary
winding
is the antenna going to an ISOLATED (i.e., non AC electrical service)
ground. The
secondary goes to the coax feeding the receiver...  and the shield is NOT
grounded
at the antenna / transformer end. It only gets grounded at ONE point, at
the receiver
end, and your coax surge suppression gizmo & receiver are tied to the SAME
clean 
ground. Such transformers aren't commonly sold items; you have to design
and make 
your own usually, but it's not that hard an engineering and fabrication job.

Next, an isolation transformer to power the receiver is a big help,
especially if
it has low interwinding capacitance and / or Faraday shielding. Much of the
RFI on 
longwave is capacitively coupled into the receiver thru the AC line,
especially the 
15.734 KHz horizontal oscillators in TV sets, and the COPIOUS harmonics of
same!

Finally...  if possible, make sure that your receiver ground is TOTALLY
isolated
from the AC power company ground.


73's,

Mr. T., W9LBB





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