[Elecraft] KX3 Audio output

[Igor Kosvin]

Knowing Elecraft design practices most likely the audio output is isolated,
so your concern is notwithstanding.
73
Igor, N1YX

-----Original Message-----
From: elecraft-bounces at mailman.qth.net
[mailto:elecraft-bounces at mailman.qth.net] On Behalf Of Jim Brown
Sent: Monday, May 30, 2011 1:54 PM
To: elecraft at mailman.qth.net
Subject: Re: [Elecraft] KX3 Audio output

On 5/30/2011 8:50 AM, Rich - K1HTV wrote:
> Do a Google search for "Coby CA-745", an FM wireless transmitter that
plugs
> into a cigarette lighter. You can find them at Amazon, Wal-Mart and Best
Buy for
> between $16 and $19. The input is via a stereo miniplug at the end of an
> attached cable.

There is potential for significant difficulty using a device powered 
from one point in the automotive DC power with another device powered 
from a DIFFERENT point in the same automotive power system. The reason 
is simple -- there can be a lot of DC resistance between different parts 
of the system, and a lot of noise, both audio and RF, between those 
points.  The audio interconnect is unbalanced, so any noise that is 
present is likely be added to the audio feed.

Consider the use for which these modulators were designed -- a 
BATTERY-powered personal music player, like an iPod or CD player.  With 
these devices, there is only ONE connection to the automotive power 
system, the lighter plug.  Ditto with a wired AUX plug-in for those 
players.

BTW -- this issue requires VERY CAREFUL attention to the design of DC 
busing and both audio and RF interfacing between the KX3 and the power 
amp if those units are to be physically separated (for example, the 
power amp in the trunk or under a seat).

73, Jim Brown K9YC


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