[Hallicrafters] tech question please!

[joel hallas]

Glenn,

They do require extreme care in selection and operation to be 
satisfactory. If possible, when buying switching supplies for radio use, 
stay within supplies especially designed for the purpose, although 6 V 
may be tough to find.

As a part of my "Emergency Power" article (Dec 03 QST) I tried using 
marine battery chargers and found that they all seemed to put out lots 
of hash, some not even legal under FCC rules. On the other hand, I have 
had very good luck with various sizes of Astron switchers.

In order to make a noisy supply quiet, I would suggest the following, in 
the following order, and keeping the previous steps in place:

1. Move the supply some distance from the radio (6 feet may help, as far 
from the antenna as possible),
2. Determine whether the noise is conducted or radiated. Pull the 
antenna off the radio, if the noise stays the same it is likely being 
conducted into the radio on the power leads. If it drops, it is being 
picked up by the antenna.
3. In my experience, the chargers were putting the hash on the ac power 
lines and it was picked up on my outside antenna! By taking a large 
toroid  (CWS (formerly Amidon) FT-240-61, but not too critical I 
suspect) and getting as many turns as possible near the supply end of 
the ac power lines, I gor rid of most of it. Note if you can disconnect 
the line (or the plug from the wire) you can fit more turns through the 
toroid then if you have to pull the plug through the middle.
4. If it is conducted try the same type of toroid choke on the dc leads. 
Once I did (3) I still had noise and by also doing (4) it was about gone.
5. If still not good, you could try finding a metal case to fit the 
supply. Ground the green wire of the ac cord to the case, as well as the 
dc ground lead. Bypass all leads in and out and include the toroids 
inside the case with the bypas caps on both sides.
6. Number 5 is a lot of trouble. If it were me, I'd get a 6 V battery 
and use the supply to charge the battery and then turn it off and use 
the battery to run the radio. Just don't try to operate HF while you're 
chargeing!

GL and 73, Joel, W1ZR

Nash4447 at cs.com wrote:

>Gotta question for the technical experts ...
>
>I noticed that the modern "switching" power supplies are able to develop 
>quite a bit of current in a very small package.   I found one of these units that 
>puts out 6 volts regulated at about 15 amps. The reason I bought the thing was 
>that I wanted a supply to run mobile tube radios on my bench. Well, I hooked 
>the supply up to my tube radio and it handled the current load beautifully 
>without even getting hot ( 7 amp load), BUT the damned thing creates so much hash 
>that I can't hear anything through the radio. 
>
>Does anyone have any good ideas how I might be able to eliminate the hash? I 
>haywired things up just to try it out. The exposed supply was sitting next to 
>the receiver.  Do these supplies have to be in a metal box for shielding ?  
>Would some sort of RF choke arrangement in the output lead help?
>Or are switching type supplies just not suitable for my purpose?
>
>Glenn K6PZT
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