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From: "Alan Melia" <alan.melia@btinternet.com>
To: <rsgb_lf_group@blacksheep.org>
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Date: Tue, 3 Aug 2010 11:35:41 +0100
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Subject: Re: LF: Noise R75 - rs232 from smpsu -
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Hi Laurence I have found some problems with the "two wire" versions where
the powered instrument has no proper ground connection....VLF receivers etc.
But often this can be cured by grounding one side of the low-voltage output.
As they are in plastic cases you can do much about radiation from the
"brick" itself. Lead radiation seemed to be worse from two wire than 3 wire
mains supplies (of course).

Lyle Street !! .....tut tut another youthful indiscretion :-)) Service
Trading were still going just a few years ago with an address in Chiswick!!

Alan G3NYK

----- Original Message ----- 
From: "Laurence KL7UK" <hellozerohellozero@hotmail.com>
To: <rsgb_lf_group@blacksheep.org>
Sent: Tuesday, August 03, 2010 3:38 AM
Subject: RE: LF: Noise R75 - rs232 from smpsu -



Dave - can you enlighten me on the filter values both on the X and Y caps
and inductance AC side and filtering on the DC?  I have about 5 bricks here;
some I picked up in a market in Beijing (Beijing Lu akin to the old Lyle st
in london (dont think you spell it like that - that dates me)) - Ive taken a
couple apart and I have some that are 2 wire AC and some 3 wire - all appear
to have pretty good filtering and various screening materials even the
Chinese cheapies. Any values to knock off 137 especially welcome - of course
each psu has a slightly different osc/pulse freq - some at 60 some at
300Khz! The opto isolator really helped the AK rx with good/reasonable
signals from Japan every nite so far...

Im running out of good Oklahoman LF projects!

Laurence



Date: Fri, 23 Jul 2010 22:26:06 +0000
From: davepick@btinternet.com
To: rsgb_lf_group@blacksheep.org
Subject: Re: LF: Noise R75 - rs232 from smpsu -






Laurence

In my remote station I put the Dell brick in an Eddy box (die-cast box) with
a proper mains filter on the input and chokes and feed-through capacitors in
the DC output lead. Drilled some holes for ventilation. Quiet as a mouse.
A linear PSU should also be fine but quite large.
The RS232 is unbalanced of course, but if you run it in screened cable and
use a ferrite common-mode choke dies it not help?

Dave G3YXM





From: Laurence KL7UK <hellozerohellozero@hotmail.com>
To: lowfer@mailman.qth.net; rsgb_lf_group@blacksheep.org
Sent: Friday, 23 July, 2010 21:47:56
Subject: LF: Noise R75 - rs232 from smpsu -




Anyone done any common mode noise mitigation from the RS232 port of the R75
Rx> - the noise coming up from the SMPSU/processor from the old Dell puter -
cable is double screened - choking off using J (75) type has seen little
improvement - this is my last hurdle to unimpeded remote rx on 137 - any
pointers appreciated - everythings bonded and Ive tried the on/off earth
tricks at various locations -

Anyone had any success of powering a Dell D series from a non standard non
switched PSU? (the noise goes away when the DC from the Black Dell brick is
removed but it may also be partially screen/processor noise...)

with thanks

Laurence Kl7UK



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