Yes! Found It.

I wrote earlier in the week about a disturbing amount of power line noise. It had sprung up sometime in the last couple of weeks and was a deafening S9++ on 160m. Not good at all for the start of the low-band season.

A day later, I had an opportunity to try scope it out. I found the noise was readily apparent on an AM broadcast radio. In my car, I tried to find the noise, but found it diminished greatly when I left the driveway, and returned once I parked my car near the church. This mean that it was very local, it wasn't something propagating along the power lines in the front yard.

Getting a little portable broadcast radio, the noise was quite loud in the shack, but diminished as I walked to the church. This meant the noise was likely coming from the parsonage itself.

Next step was to flip every breaker off in the parsonage as I listened to the radio. Of course, once I flipped the very last breaker, the noise disappeared. Turning all the other breakers back on -- no noise.  Then it was a matter of deducing what was being powered from that circuit breaker.

The circuit breaker in question, number 15, was powering a few outlets that supplied power to my internet router and other pieces of equipment on my wife's desk. A bit more unplugging found that the parsonage wiring wasn't the culprit, but something plugged into the wall. A bit more, and the cause was found -- it's a wall wart power brick that powers my AT&T Microcell.

When we got the Microcell back 3 years ago, the coverage underneath the parsonage's metal roof was extremely bad. Since then, it has gotten a little better. Until I can replace the bad power brick, we can live without the Microcell.

And no more noise on 160m. Hurray!

Crap. Line Noise

OK, perhaps I could use stronger language. Here it is, the start of the fall low-band DX season, and I have line noise.

In the three years I've been out here in Floyd county, the low bands have been very quiet, so it has been easy to hear other stations. You'd think being out in the country like this it would stay that way.

Well, something has changed in the last week or two. On 160m, I'm reading constant line noise 24/7. In an SSB bandwidth, it is S9+20. In a CW bandwidth, it is still S9. Terrible. On 80m, it is a little better, about S7 in SSB, and S5 in CW -- about the same level as the atmospheric noise. Above 80m, I don't notice it, really.

It's been very dry, as is typical of this part of the fall here in Georgia. However, even a recent downpour didn't silence the noise.

This is very bad. I guess I'll have to hunt down the source and tell Georgia Power about it. I sincerely hope they can fix it before the ARRL 160m contest.

Samlex SEC 1223

Unit #2 - before modifications.

I guess you can say I'm pleased with the Samlex  SEC 1223 power supply. After all, I own three of them.

Back in 1988, I bought a CB-grade 12 volt linear power supply capable of 25 Amps output. It needed a little work to function correctly, but it powered my venerable TS-430S and later the K2/100 for 19 years. It finally went west one day when the power transformer opened in the primary winding.

Soon after, I was hunting for a replacement at a hamfest. I found a Samlex SEC 1223 that fellow had replaced with an Astron SS-25M. Used, the price was right, at about $50. The unit is impressively small, and it had no trouble powering the TS-430S, K2/100 or K3/100 to full output on every band.

However, this unit had numerous spurs on 160m. I found the loudest one was around 1845 kHz, about S7 on the very scotch K2 S-meter. Note that the location and strength of the spurs varies with the supply load. Using snap-on ferrite cores as an experiment, I found that putting them on the power cord and the output power leads led to a reduction in the spurs.

Unit #1 - showing seven FT50-77 ferrite
toroids on power input leads.

My first modification was to de-solder the white and black power cord jumps inside the unit and slip on seven FT50-77 toroids. That reduced the spur to about S5.

Unit #1 - Output lead modifications.

I then made a modification designed by ZL2DF and published by N0SS. My unit was different from that of ZL2DF. It did not have the screw / compression power terminals. Instead, my unit had binding posts soldered directly to spade terminals on the PC board.

I pulled out the PC board and removed the spade terminals. I replace them with 16 gauge wire fed through eight type 43 ferrite beads. The wire is a bit small, but is the largest that will fit through the beads. The output terminals are bypassed across each other and to ground with .1 50v multi-layer ceramic caps.

With this change the 1845 kHz spur was just audible. Atmospheric noise covers it up at night.

Last year, I found another one of these gems at a hamfest for $20. Took it home and sure enough, a few spurs on 160m. Made similar modifications -- toroids on power leads, ferrite beads on output, caps across output terminals. Again, the spurs don't disappear, but are much less pronounced.

Unit #3 - perhaps only needs power input filtering?

This year -- you guess it -- I found another one for $5! This unit is a little different, as it has a large ferrite bead with both power leads run through it to the compression terminals. Perhaps it will only need a big of work on the power leads. We'll see when I can get it on the bench.

These are very capable little power supplies. They are easily able to power a 100 watt transceiver, and with a little work, they are quiet enough for MF and HF use.