[Elecraft] Noise with KUSB

[Mike Harris]

Hi Svend,

I do not normally use the KUSB but I have just tried a simple 
experiment.  I measured the change in noise in the following 
conditions:

PR6 - ON
PRE - OFF
AGC - OFF
K3 - SSB mode, 2k7 BW
ANTENNA terminated with 50 ohm.

Nothing connected to KIO3:  +0dBV
K3 <> RS232 cable <> PC communicating with K3:  +1dBV
K3 <> KUSB <> PC communicating with K3:  +10dBV
K3 <> RS232 cable <> KUSB <> PC communicating with K3:  +0dBV

All readings +/-  0.1 to 0.2dBV

My RS232 cable home made to K9YC design using CAT6 UTP cable is 
approximately 3 metres long.

The presence of band noise naturally masks much of the PC noise 
but the increase in background noise level at this QTH when 
connecting the KUSB alone is still approximately +3dBV.  With band 
noise I do not detect any increase in noise due to the RS232 cable 
alone.  With the PR6 OFF and the K3 internal pre-amp on, noise 
from the KUSB is approximately +.3dBV.

It seems in my configuration PC noise is least with K3 <> RS232 
cable <> KUSB <> PC combination.  Interesting.

Maybe others would like to try and replicate this, perhaps using 
better test equipment than that built into the K3.

It might be worth testing to see if this reduction in KUSB noise 
can be achieved with a much shorter RS232 tail to the K9YC design 
or even an appropriately wired back to back RS232 gender changer. 
This set me thinking that it might be a good idea to make a short 
cable for the K2 I/O to enable use of the KUSB or a regular RS232 
cable without the danger of damage to the K2 I/O.

I have not had much opportunity to play with the PR6 due to lack 
of 6M activity here at present other than EME.

Regards,

Mike VP8NO


----- Original Message ----- 
From: "Svend Spanget" <spanget at privat.dk>
To: "Mike Harris" <mike.harris at cwimail.fk>
Sent: Wednesday, August 05, 2009 5:54 AM
Subject: Re: [Elecraft] Noise with KUSB


Hi Mike.

Thank you for answering!
I have the KUSB adapter from Elecraft. Do you suggest that I make 
a short
cable like you did between the K3 and the KUSB?
The noise is specially irritating on 6 m. I don't have a preamp 
yet, but
building one is on my to-do list. What is your experience with 
PR6?
After I discovered the source it has become clear to me, that the 
noise
is on all bands more or less....
My old laptop has a serial port, but I went for the USB solution 
because
I plan to buy a new PC, which likely will only have USB ports.
It is not grounded though - I will see if there is possibility to 
ground
the PC.

Lots of 73's de Svend, OZ7UV