[ARC5] restoring hacked vhf receiver

[Bob kb8tq]

Hi

“Best practice” for RFI reduction is to ignore the fact that there is a ground on the converter board. 
Run the two input wires through a toroid or a big ferrite bead (maybe both). Do the same thing 
for the two output wires with a second big bead.  Dump the whole thing in a metal box (possibly 
along with a fan). Run the inputs through feed-thru caps and do the same with the output. Yes it 
seems a bit stupid to run a ground wire through an expensive cap. Some sort of honking big cap
inside the box on the input and another on the output may help some. 

If one layer of this utter nonsense does not do the job. Go to a second layer. Yes, another box inside
the first box and another set of chokes and caps. The inner box sits on insulated standoff’s in the first 
box. Eventually you will either cure the problem or go insane with all the work you are putting into 
packaging a cheap regulator. 

Once it works (or is close to working. Ground a single point on the box. If things get worse, move the 
location of the ground. If things get better, either go have a beer or see if the are better in a second
location. 

Why this approach? It’s the magnetic side of things that is the problem. It’s current loops and ground
currents that are eating your lunch. There’s not enough voltage involved for capacitive (E field) 
issues to be as big a deal. 

Bob

> On Mar 6, 2018, at 1:14 PM, George Babits <gbabits at custertel.net> wrote:
> 
> Last December I bought a 350 watt (15 amp) 24 volt unit.  It put out a strong signal every 90 KC from 2 MC to infinity.  No amount of RF filtering on both the input and output helped at all.  If you can live with the hash I guess it is OK, but not me. I finally bought an Astron linear regulated supply.
> 
> 73,
> George
> W7HDL
> 
> 
> ----- Original Message ----- From: "Bob kb8tq" <kb8tq at n1k.org>
> To: "David Stinson" <arc5 at ix.netcom.com>
> Cc: <arc5 at mailman.qth.net>; "Robert Eleazer" <releazer at earthlink.net>
> Sent: Tuesday, March 06, 2018 10:40 AM
> Subject: Re: [ARC5] restoring hacked vhf receiver
> 
> 
> Hi
> 
> Most of what you see runs a square wave at 20 to 60 KHz. Without added filtering
> on both the input and the output you *will* see RFI out of them. They also require
> some amount of air flow to cool them. If you are putting out 30W, you should count
> on getting rid of 6W or so. The cooler you keep them, the longer they will last ….
> 
> All that said, they are a good way to get the job done. You can’t build something
> better for the same money.
> 
> Bob
> 
>> On Mar 6, 2018, at 12:16 PM, David Stinson <arc5 at ix.netcom.com> wrote:
>> 
>> 
>> 
>> From: Robert Eleazer
>> 
>> Subject: [ARC5] restoring hacked vhf receiver
>> 
>> By the way, I am wondering about those buck-boost converters you see for sale for a few bucks the ones that can take in around 5 to 30VDC and put out 1.5 V to 35 VDC.  I have been trying to build am LM350 circuit to provide a little over an amp at 28 VDC to power a radio and while it worked at first it's been driving me nuts.  Is the power out of those buck/boost converters fairly clean or are there lots of harmonics?
>> -----------------------
>> 
>> They are very useful, and they are very RF-noisy.  One really needs to build it into an RF-tight enclosure with filtering in and out.  I posted about this a few days ago.
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