[R-390] Balanced Antenna Input

[David Wise]

The balanced to SO239 adaptors do indeed defeat the purpose of the
balanced input.  The idea behind the balanced input is that if your
shack is a high-noise environment, you can cancel some of it by
running a balanced line out to the antenna.  That way, any crap
picked up by the feedline is applied equally to the + and - inputs
(my terminology) and cancelled.  This phenomenon is called
"common-mode rejection".  As soon as you ground either wire, that
goes away and you're back to the conventional unbalanced line.
(By the way, in this mode there is no point in adjusting
the balance caps, since it's not balanced anyway.)

That said, the majority of today's users (and some in the past -
witness the Navy mod to swap the rear-panel connectors) go
unbalanced, simply because stuff is more available.  And
remember, in the HF range, if you have a decent antenna and
your shack isn't an EMI hellhole, most of your noise will be
atmospheric and far-field QRM anyway.

73,
Dave Wise (SWL in Portland OR)

> -----Original Message-----
> From: r-390-bounces at mailman.qth.net
> [mailto:r-390-bounces at mailman.qth.net]On Behalf Of n4buq at knology.net
> Sent: Thursday, April 13, 2006 8:58 AM
> To: r-390 at mailman.qth.net
> Subject: [R-390] Balanced Antenna Input
> 
> 
> I have seen some adapters that mate a given connector type to 
> the "twin-ax" 
> style used at the balanced antenna input.  I might be wrong, 
> but it appears 
> these typically have one connection to the shell which 
> grounds that side of 
> the connection.  The balanced connector is designed to work 
> with both sides 
> of the feedline ungrounded, right?  If so, don't these 
> adapters defeat some 
> of the proper workings of this input?
> 
> Barry - N4BUQ
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