[NLRS] Power supply question

[Doug Reed]

At 05:37 AM 5/26/2003 -0700, Eric wrote:
>I am looking to buy a power supply that will power
>some small VHF bricks.  I am looking in the 20-30 amp
>range, but was just wondering what people are using
>and any positives or negatives about the supply.

I own a couple Astron RS-11 supplies that I use for small radios. My larger
radios are usually run from a combination of regulated power supply and
battery. I usually buy surplus linear supplies and modify them. I have
several industrial switching supplies that I use on the test bench but so
far none on the air. At Ramsey County ES we use primarily Astron linear
supplies, 10, 20, 35, and 50 amp versions.  

>Switching vs regular any quick comments?

Many years ago the .85 repeater in Oakdale installed a new RF amp and used
a switching supply to drive it. Within half an hour there was a complaint
from a repeater owner in Afton saying he was hearing a strong spur from the
repeater on his output frequency about 50 KHz away. It didn't take much
thought to blame it on ripple from the switching supply modulating the RF
amp. Since then I've been wary of switching supplies in RF duty. 

On the other hand, several manufacturers now sell switching supplies for RF
duty and I haven't heard of any repeat of the problem. I used a IBM PC
switching supply on a packet station recently and I have another industrial
switching supply I plan to use on another packet station soon. But I took
the added precaution of putting some additional hash filtering on the
output of these supplies.......

At Ramsey County ES, we've been using Astron linear supplies on our radios
for a long time now. About the only problems I've had have been when using
them as standby float battery chargers. One problem is that the current
limiting on the supplies does not prevent them from over heating and
burning up if the battery is deeply discharged. That problem has mostly
gone away since I started putting resistors or PTC fuses in the "battery
charging" circuit. 

The second problem is that not all supplies have all the protection diodes
they really need. Over the course of 15 years Astron kept adding protection
diodes each time they found a new failure mode. Some information can be
found on the Civil Air Patrol web page and most of the needed diodes can be
found by comparing schematics with newer supplies. 

In general I do consider the linear supplies to be more reliable than
switching supplies. On the other hand, if a linear supply shorts, it dumps
20-30 volts on the output. When a switching supply dies, I expect the
output to go to zero. A well designed switcher is reliable, we've been
building using them at work for over 15 years. But a linear supply is
generally much easier to repair...... 

Chances are that I will begin to use more switching supplies at home
because I have them and don't want to spend new money. I do like the looks
of the Alinco DM-330-MV supply and I'd probably buy one of them if I was
buying a new supply and wanted something portable. High current linear
supplies are HEAVY. 
 
If you do buy a supply, I'd suggest something with meters, particularly an
ammeter. The lack of meters is usually what I bitch about first. Good Luck!

73, Doug Reed, N0NAS.