[Elecraft] KX3 Audio output

[Rich - K1HTV]

Jim,
   Looks like the addition of an inline audio transformer between the wireless
transmitter's miniplug and the KX3 (or any device powered by the vehicle) would
resolve the potential problem which you have addressed.

73,
Rich - K1HTV

= = = 

-----Original Message-----
From: Jim Brown [mailto:jim at audiosystemsgroup.com] 
Sent: Monday, May 30, 2011 13:54 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