Re: LF: Noise R75 - rs232 from smpsu -

[Dave Pick <davepick@btinternet.com>]

Laurence

Well the input side was a surplus IEC filtered inlet I got at a rally, I usually buy them if I see them. Even though it probably isn't characterised for LF I guess that in conjunction with the PSU's internal filter it must be pretty effective. The short length of mains lead inside the metal box is wrapped round a toroid a few times before entering the PSU.
On the DC output side I used a pair of 3A 500uH chokes I got from RS, one in each side of the power supply, and decoupled the outgoing side to the box-earth with 100nF poly Cs. The DC then exits the box through a pair of feed-through caps just to gild the lilly a bit.  I don't know what all this does for Dell's PSU identifying system.... but it certainly shuts it up!

73
Dave.

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From: Laurence KL7UK <hellozerohellozero@hotmail.com>
To: rsgb_lf_group@blacksheep.org
Sent: Tuesday, 3 August, 2010 3:38:12
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
 

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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

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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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