[Elecraft] KUSB Noise Query - K3

[Matthew Zilmer]

USB uses differential signaling.  Your problem may not be conductive noise, but instead it could be radiated directly from the adapter, where the ferrite won't help.

KeySpan makes a USB - serial adapter that is pretty much noise-free.  Its model  is HS19, I think.

Matt Zilmer
Consultant - Product Management Dept.
Magellan Navigation / MiTAC Digital Corp.
Tel: (909) 394-6052
Cell: (909) 730-6552
In status quo voluntas non sufficit


-----Original Message-----
From: elecraft-bounces at mailman.qth.net [mailto:elecraft-bounces at mailman.qth.net] On Behalf Of john petters
Sent: Thursday, December 13, 2012 9:25 AM
To: elecraft at mailman.qth.net
Subject: [Elecraft] KUSB Noise Query - K3

Hi Folks,
I posted a query about K3 Serial ports a few months back - we could not get the K3 to work properly with the RS232 connection. It turned out to be a fault with the sound card, which took out the serial connections.
When I first built the K3, I bought a cheap Prolific USB converter, which radiates awful noise over the spectrum. I decided to bite the bullet and buy the proper lead, which arrived today.

Using my Toshiba laptop, on battery power, I get a couple of s points of noise on 10M with the KUSB connected and HRD fired up. This is using my
2 element DJ4VM quad, which is fed with 300 ohm twin into the shack, i.e. near the laptop.

On LF, I can hear the pulsing information, in sympathy with the flashing LEDs on the KUSB on 160M at quite a high level. I can even detect this when fed into a Marconi dummy load. The K3 and the tuning units are bonder to an RF earth - a copper stake about 8 feet away from the K3.

I have tried choking the USB lead at the laptop end, which does reduce the noise to a degree.

The question I have is - am I being unrealistic in expecting zero noise to be radiated from these adaptors?
Does anyone else have this problem - or has anyone looked for it?

It is not very noticeable on CW or SSB. To hear it best, listen in the AM mode with the AGC off. On SSB it sounds like band noise.

Is this a problem JUST with USB adaptors or can I expect silence when connecting a computer via RS232 to RS232.

If not we are sacrificing a low noise floor for the convenience of computer control.

Any views appreciated,

73




--
John Petters
www.traditional-jazz.com
Amateur Radio Station G3YPZ
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