Samlex SEC-1223 12VDC Switching P/S - RFI Reduction

[Tom Hammond-3]

Greetings folks:

Thanks to Nigel Hayton, ZL2DF, I have just posted to my web site at

     www.n0ss.net

an article which described Nigel's efforts to reduce the not insignificant
switching spurs he was experiencing from his Samlex 1223 power supply.

Basically, Nigel, with only a couple additions to the output circuitry of
the PSU, was able to reduce his 160M birdies from the S-9 level to a level
of S-1 to S-2... a pretty significant reduction, for a small investment.

The PDF of this article can be found about 1/3 of the way down my rambling
home page, just below the photo of the Samlex 1223.

If you happen to have a Samlex 1223, you might also be interested in some
service info for this power supply which can be found at the same location
on my home page. The schematic which came from Samlex, was pretty shoddy,
and after many photocopyings had become pretty difficult to read. I have
now included an newly re-drawn copy of the schematic, along with the
original copy I received. I hope you will find the new schematic a bit
easier to work with.

Enjoy.

73, and MANY thanks to Nigel for sharing his success with us.

Tom Hammond    N0SS

_______________________________________________
Elecraft mailing list
Post to: [hidden email]
You must be a subscriber to post to the list.
Subscriber Info (Addr. Change, sub, unsub etc.):
 http://mailman.qth.net/mailman/listinfo/elecraft   

Help: http://mailman.qth.net/subscribers.htm
Elecraft web page: http://www.elecraft.com

[Marcus Busch [DL1EKC]]

Hi Tom,

just would like to thank You very much for Your (and Nigel's) very
valuable information You have put on Your web site.

I stumbled on the birdies on 160/80 some time ago on a fieldday and was
thinking about looking into the circuits one day. But the birdies are just
S3-5 here.

Just to add a few notes:

I added a hard DC connection from the negative output to chassis/ground.
This was done because modern 12 V rigs do not have any chassis ground
connection when using symmetrical antennas (dipoles) and those ground
isolated PS. This makes the rig chassis and coax braid eventually floating
on unknown voltages. I observed this on several field setups, especially
when using vertical antennas. The protective ground of Your mains may not
be a good RF grounding, though. But it prevents static charge up of Your
chassis (and the "connected" operator) via the coax braid.

I also added a surge arrestor to the 13.8 V output of the PS. One day on
the field there was a thunderstorm around, but it was still some miles
distant. But a surge came via the mains line killing not the Samlex PS but
the TR switch in my K2! Fieldday over. The only destroyed part was the
1500 V rated ZVN4424A! Ouch.

After christmas I will add the ferrite beads ...

Have a good time.

VY 73 de Marcus, DL1EKC

_______________________________________________
Elecraft mailing list
Post to: [hidden email]
You must be a subscriber to post to the list.
Subscriber Info (Addr. Change, sub, unsub etc.):
 http://mailman.qth.net/mailman/listinfo/elecraft   

Help: http://mailman.qth.net/subscribers.htm
Elecraft web page: http://www.elecraft.com