Re: LF: Re: G7NKS multiple spots

[John P-G <gm4slv@sighthound.demon.co.uk>]

James,

The classical method is to use audio isolation transformers between the 
rig audio in/out and the soundcard, and opto-isolators on the serial 
port line(s) used  for the PTT switching (assuming you use serial port 
handshaking lines for this) so that there's no DC connection between 
radio "earth" and PC "earth".
I've got the audio transformers in my homemade interface, but no 
opto-isolators - so there's still some connection between radio and PCs 
(and I mean 3 radios and 2 PCs....) but still have no mains hum evident. 
Perhaps I'm just lucky?
Ferrites are good to keep RF out of places it's not wanted, but not sure 
what they'd do to keep 50Hz out.
John


James Cowburn wrote:
> Ferrite, Ferrite and more Ferrite then!
>
> Any suggestions as to where best to place clip on cores?  
>
> Mains lead? 
> Power lead from PSU (Icom PS55) to rig (IC735)?
> All leads from ZLP interface to laptop? (Dell D610) (I currently have
> ferrite clip ons on the microphone and speaker leads from ZLP to laptop)
> Dell Laptop PSU?
>
> All the above??
>
> With best regards
>  
>  
> Jim
>  
>  
> Dr. James Cowburn
> -----Original Message-----
> From: owner-rsgb_lf_group@blacksheep.org
> [mailto:owner-rsgb_lf_group@blacksheep.org] On Behalf Of Graham
> Sent: 16 September 2009 21:59
> To: rsgb_lf_group@blacksheep.org
> Subject: Re: LF: Re: G7NKS multiple spots
>
> JIm,
>
> I think you  find that is  caused by 50 hz mains hum .... may be a hum loop 
> in the  audio system / pc-tx earthling , not likely to  be psu problem as 
> frequency is 50 (fund)  and 150 ( 3 rd harm)
> I had a similar problem with my  valve HF set , that was a slight  ripple on
>
> the PA  HT line caused by the  100% duty cycle of wspr, not part of the 
> design criteria for  ssb/cw , caused  spots to appear +/-  100  Hz due to 
> the  full wave  rectification in the  psu
> G .
>
> --------------------------------------------------
> From: "James Moritz" <james.moritz@btopenworld.com>
> Sent: Wednesday, September 16, 2009 9:40 PM
> To: <rsgb_lf_group@blacksheep.org>
> Subject: LF: Re: G7NKS multiple spots
>
> > Dear Jim, LF Group,
> >
> >
> > > Me too.  I am getting 3 traces (!) from Jim M (he is 9+10 and audible!)
> > > and
> > > a biggish one from Gus too
> > I am seeing low-level (about -25dB) sidebands on your signal  at +/-50Hz 
> > and
> > +/-150Hz, which are giving rise to the extra spots.  I think something
> > similar is happening when you receive my signal. I am not getting similar
> > multiple spots from other nearby stations, nor am I seeing the same
> > sidebands on other strong signals, so I think they must originate in your
> > station somewhere - possibly audio being affected by mains noise, or some
> > sort of residual FM of an oscillator in your rig?
> >
> > Cheers, Jim Moritz
> > 73 de M0BMU
>
>
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--
IP90gg
Clousta, Shetland
http://gm4slv.blogspot.com