[TenTec] On Switching Power Supplies

[Don Jones]

My Ten Tec 961 Linear Pass Pwr Supply failed CISPR 22 Conducted RF 
Emissions -- BAD

In Feb 2013 I hosted a open house of my company's EMC test lab. I 
invited local amateur radio clubs to come have a look see.

One of the demo's I set up was a CISPR 22 Conducted RF Emissions demo in 
our FCC listed full scan height EMC chamber (A2LA accredited). The 
equipment used for the demo was a typical ham radio HF station 
consisting of a Lenovo Lap top pc, and a Ten Tec Omni VI with a Ten Tec 
961 linear pass power supply.

The Lenovo PC (powered by a switching power supply) passed conducted RF 
emissions with flying colors, the TT power supply failed miserably which 
I found quit surprising. Hideous broadband noise exceeding the limit by 
20 dB was measured. The excessive emissions rolled off at about 600kHz 
and was below the CISPR 22 limit the rest of the way up to 30MHz. The 
interesting thing was that these emissions were present with the 
transceiver in receive mode and only 6 db worse transmitting a 45W CW 
carrier @ 14MHz.

So much for assuming Linear Pass Power Supply's are clean... Just sayin'

73, Don KO7i



On 1/18/2014 6:36 PM, Al Gulseth wrote:
> Speaking of "switchers" - I've been looking around for a small 3-4A PS
> suitable for use with QRP/QRPish rigs (TT examples: Argonauts, 1220, 13xx,
> etc.) and would like something a little more portable than the surplus
> Power-Mate linear supply I have now. Has anyone had any experience with the
> MFJ, Samlex, RS etc. of this ilk and/or any of the open frame stuff the
> surplus outfits sell? (I know quality and RFI output can vary widely with
> these: what I'm thinking might be the best possibility would be a good name
> brand - Condor comes to mind, especially their medical grade products.)
>
> If it's an open frame type, I'd assume a suitable enclosure and a Corcom-type
> line filter as well as some additional output filtering would be in order.
> Also, would a 12V or a 15V be a better starting point to readjust to 13.6-8?
>
> Or, even though it's a little bigger would I be better off just going for an
> Astron SS-10 or 12 since they seem to get pretty good reviews regarding RFI
> along with the added benefit of having enough "oomph" for an Argosy or Scout?
> Comments/suggestions?
>
> TNX/73, Al
>