Sunday, March 31, 2019

Ground Issues....

I picked up an RSPduo from SDAplay recently via DX Engineering -- I had just put off too long putting my hands on a little 'black box' DC-to-daylight receiver to play with.   It's great -- amazing the capabilities in such a small inexpensive device.  This'll go with me on my travels in the future.   The only thing needed is the SDR, some type of antenna, and a laptop, and you're good to go to get your radio fix pretty much anywhere.

Not having been active on HF much recentl, and looking at my sad Telrex tribander on the tower with a broken reflector, maintenance was and is on the agenda to get W4QA QRO again.   The SDR came up nicely with a random wire about 15 feet in the air strung from the deck back into the woods.  But -- cruising through the bands -- a ton of noise was everywhere.  Birdies, hash, AC hum, spikes -- you name it.... enough to take a lot of the fun out of listening since only the very loudest of stations had a SNR good enough to be clear.

Adding a common mode choke to the AC inputs of the Windows PC and peripherals (two stacked #31 Mix toroids, and about 6 turns of the power cord) knocked a ton of it down -- but it was still there.  The beauty of the SDR and the waterfall display allows a visual confirmation of the noise in a few seconds across all the bands...  So, on to the next step.

The entrance panel into the basement shack is a single point for all the cables that come in via lightning arrestors, and it is bonded to an 8' copper rod with 2" copper strap thats about 2 feet away from the panel.  That rod is connected to the ground rod at the electric utility entrance at the meter on the other side of the house,  all connected via #4 gauge solid copper ground wire - about 125' away, buried a few inches.  This has been the grounding situation for about 15 years....so time for a check up.

After finding the antenna panel rod and cleaning it up and removing the clamp -- the measured resistance from the perimeter wire to "green wire ground" was an unacceptable 126 ohms (!) -- there was a good 2v of AC between these two points.  Not a great situation for both lightning protection and receive noise.  Just 10 Amps of lightning surge and there'd be 1.2kV (ouch) between those points...  On top of that one of the rod clamps wasn't completely tight.   (Cadweld OneShot is going to be the next project here -- I don't want to have to deal with this again down the road....)

Apparently, the perimeter wire had been damaged "somewhere" in the back yard during a project of some kind.   Not finding the break easily, replacement became the preferred option.   A trip to the big box store and three hours later, the perimeter wire was replaced,  and new clamps were put in place.  Measured resistance dropped to 0.3 Ohms...much, much better.  Much safer.  Quieter.

The result?  Noise levels, though not perfect, are now much more acceptable.  S/N improvement between fixing the ground and installing the common mode choke on the AC cords is at least 15 dB on 75 meters -- similar on other bands.   Its a good start getting the station back in fighting shape -- but there's a lot more work to do to track down the noisemakers in my house.   Killing the crazy switching power supply noises will be the next project -- it'll take some time, there's alot of them around!  


Sunday, March 10, 2019

Charlotte Hamfest 2019

Well, I got a chance to go by the Charlotte Hamfest this weekend.  It is always fun to see old friends and make a few new ones, browse the flea market, and see what's new with the onsite vendors.  I picked up a little stubby antenna for my new DMR radio and a few other small parts, but didn't walk away with any big purchases -- and that's just fine.

Bill, W4WNT has been a long time neighbor of mine, and he gave a really nice forum talk on FT8 to a room of folks that hadn't dabbled much in this mode.   I was astonished to hear that this has become one of, if not THE, most popular mode on the bands these days.   A combination of a sunspot cycle low, the continued integration of digital into the analog RF domain,  the increasingly difficult time folks are having putting up a decent HF antenna, and the increase in typical noise floors all contribute to the rise it FT8's popularity.   I'm putting it on the list....