[Elecraft] RS232 Noise

[Mike Harris]

G'day,

Finally got around to making a replacement RS232 rig control cable using 
CAT6 patch cable, about three metres long.  Method used was as detailed in 
the reference below.

Results; spectacular!  Noise on 6m increases approx 1dB when the cable is 
connected to the K3 (no antenna).  Using the old cable the noise jumps up 
approx 9dB and was 6dB up on the noise floor when the antenna is 
connected.

I can no longer hear the CRT monitor updating when the seconds tick over 
in WSJT.  This was audible even when the old cable was disconnected from 
the K3 so it was probably being radiated from the cable and picked up by 
the antenna.

Regards,

Mike VP8NO

----- Original Message ----- 
From: "Jim Brown" <jim at audiosystemsgroup.com>
To: "Reflector Elecraft" <Elecraft at mailman.qth.net>
Sent: Thursday, April 23, 2009 10:10 AM
Subject: Re: [Elecraft] RS232 Noise


| On Wed, 22 Apr 2009 19:11:51 -0400, Mike Harris wrote:
|
| >This extra noise vanished when I removed the "RS232" cable from the
| K3.
| >The cable is actually the one I made up for the K2.
|
| There are several problems in the setup. First, the K3 connector shells
| are not properly bonded to the chassis, so the cable shield is useless.
| Second, the cable Elecraft sold with the K2-series products used
| parallel conductors, not twisted pairs. That's a recipe for noise and
| RFI.

<snip>

| 1) Build the serial cable shown in my RFI application note.
| http://audiosystemsgroup.com/RFI-Ham.pdf  It uses CAT5 cable. When VHF
| noise is a concern, shielded CAT5 may offer further improvements.
|
| 3) Fix the pin 1 problem in the K3 by bonding the DB-connectors to the
| chassis. Pin 1 problems couple RFI in both directions -- that is, they
| let RF into equipment and they put RF onto cables that radiate it.
|
| 73,
|
| Jim Brown K9YC