Fixing A Noise Problem on an Astron RS-35M

Ground Noise on Astron Power Supplies

Not too long after acquiring an Elecraft KX3 and the PX3 panadapter,  I experienced how useful having a real-time spectrum display was in tracking down noise problems.   It's interesting that several local noise problems revealed were ones that for the most part were not audible, particularly on an HF band with expected atmospheric noise levels masking a good bit -- but seeing is believing.

Astron RS-35M -- 1990's

One particular issue I ran into was low frequency (audio range 0-300 hertz) noise / spikes showing up on the PX3 when powering it from a 1990's vintage Astron RS-35M power supply -- one that has served me well for a long time for a number of purposes.

Running the Elecraft from either a battery, a Bioenno Power Pack, or a Pro Audio Engineering power supply eliminated the problem -- with everything else in the setup not changed.   It seemed either a ground loop of some sort or a failing component in the supply was likely the root cause.

Jim Brown, K9YC, published a white paper around an issue that sounded very similar to what I was seeing -- although he was initially validating that a transmit audio issue was being caused by a ground issue on the V- of some Astron supplies.  Repeater-Builder.com has also compiled much information on this subject as well and can be found here.

To net it out, particular Astron supplies manufactured at certain times have bonded the V-  (the negative/ black lead) output of the supply to the chassis, along with the "green wire" third pin on the standard AC plug.  In other words, the supply as manufactured this way is not a floating DC supply -- and anything on the AC safety ground will make its way to the V- feeding your rig and accessories, potentially causing noise current to flow through things you'd rather it not flow through.  Putting an ohmmeter from V- to the chassis will tell the story -- if there is something close to zero ohms, it is not floating.

RS-35M with Negative Bonded to Chassis

In my case, checking the resistance revealed .006 ohms between the chassis and the negative terminal, so I cracked open the case to see how this was achieved.   Simply, a black 16 gauge lead ran from the circuit board "ground" to a screw with star washers on the bottom of the chassis -- this was in parallel to another wire that went from the same solder pad to the V- terminal on the rear. (It is interesting that the V- terminal is actually insulated from the chassis, go figure)   I disconnected the chassis wire, heat shrink wrapped the now disconnected terminal (if for some reason I wanted to reconnect later), and put the cover back together.   Plugged it in, tested the voltage, powered up the KX3 / PX3 and -- No Noise.

Maybe this workhorse will be around the shack another 10 years!

Liquidambar Styraciflua Needs An Antenna

There are a LOT of trees on my property.  And that is both a blessing and a curse for antenna work.  I tend to be an optimist, so focusing on the blessing part works better for me...

Given where we are in the sunspot cycle, I've been considering ways to bolster W4QA's DX performance on the lower bands.  Specifically, 80 meters has always been a weak point in my antennas situation for the usual reasons:  you need room, you need elevation.     If maximum efficiency is desired, there's just little substitute for size -- and that goes for both horizontal and vertical antennas (including the radial / GP system).

So in that context, this tree in my backyard -- about 125' from the house and maybe 90' high, is begging to be a useful support for 'something'; for now, that 'something' is going to be a full-sized, 1/4 wave, 80 meter wire vertical with elevated radials.  This tree (Liquidambar Styraciflua), what we call a "Sweet Gum" tree in the Carolinas,  aren't that useful for much other than firewood, and, well antenna supports. (The seed pods are a devil to deal with in your yard...but that's another topic.)

In general, the vertical element will be made out of 13 gauge stranded / insulated copper wire and the radials from 18 gauge stranded / insulated copper wire -- all from The Wire Man (no affiliation).   The feedpoint will incorporate a choke/unun and depending on the Z measurements, I may design some type of simple matching (possibly a shunt inductor at the base (?)) to raise the input impedance closer to 50 ohms. 

Look for more posts as this develops and I welcome comments....

73, Rush

Critters and Coax

Having run across a few round-tuits recently with a less intense work-travel schedule, tower and antenna maintenance is finally making its way onto the agenda.  It's been neglected, and that really bugs me.   Things have held up pretty well over the past decade (except for the tree mounted wire antennas, which I seem to get maybe 5 years of life before something breaks), but the Telrex tribander has suffered from metal fatigue on the big reflector, which made its way to earth unfortunately -- so a full inspection is needed.

SWR / directional wattmeters of various types are handy (I really prefer my Bird 43 for a simple, accurate, reliable meter) -- but they only give part of the picture about what's going on in your antenna system.  For really granular tasks, nothing beats a Vector Network Analyzer to spell out the real and imaginary components of impedance, resonance points (which don't always correspond to low-SWR points), faults in feedlines, etc.    A quick scan of my 7/8" Heliax and then the LMR-600 (which feeds the 30/17/12m antenna) revealed issues.   The Andrews hardline looked great (thank goodness...it is way too expensive in today's copper market to contemplate a new run) -- but the LMR looked awful, with significant reflections appearing on the VNA TDR at different distances from the shack.


Turns out, that about 25' feet from the shack, the LMR-600 is exposed for a brief distance before it goes underground out to the tower.   What did I find at the first fault?  Teeth marks in the outer jacket... some critter had attempted to make a dinner out of my coax, and it looked like the jacket had been penetrated -- if ever so slightly.   That section of coax needed to be replaced if there was any way to salvage the run.   You can see (to the right) what the shield and dielectric looked like -- moisture had entered the coax and had slowly contaminated / oxidized the braid; normally both the foil and outer braid would be a nice, bright, shiny silver color.  And here's the thing..the tiny holes allowed enough moisture to enter that it wicked in both directions from the damage about 4'  -- so almost 8' of coax was ruined.  No telling over what period of time this was allowed to happen -- but it was on the order of years.  This contamination does nothing to DC -- but looks almost like a short to RF.  Be warned.

The lesson here of course is to not put off maintenance; it really should be a routine part of running your station.  Things will decay.  Things will break. Mother nature will absolutely have her day.  And putting off fixes only compounds the problems -- if I had caught this earlier, I could have saved a lot of time, effort, and $$ on the fix.  And, good engineering can avoid problems.... in this case, limiting exposure to the coax (not laying it on the ground in a flower bed) would have prevented this.

Oh, just about forgot.  The other fault found in the LMR was located at the base of the tower about 5' from the ground where the coax emerged from underground.   The problem?  A pellet from an air rifle.  Yep.  Unlikely but true...  it had penetrated the jacket in two places, and became lodged on the far side of the coax as it tried to exit.   I'll see if I can find a picture and post it.   Same result as the other fault, except for the water migration was primarily down from the break in the jacket about 5 feet.

Given where these faults were located-- I'm likely going to just replace the entire run and salvage the remainder into a couple of 100' pieces which will get used on some future project.

Dayton 2019

Finally after 42 years of hearing about it, I'm making the trip to the Dayton Hamvention today!  It is a bit of a drive, but the weather is looking pretty fair and the journey up will take me through some really beautiful parts of North Carolina, Virginia, and West Virginia.   DMR and 2m FM will accompany me and I hope to connect with others making the trek!

Besides attending a few of the forums, my shopping list includes a few things that are needed around here, such as: 1) new remote antenna switch, 2) Vector Network Analyzer, 3) various 'tweenie' connectors....and we'll see what other things jump into the shopping cart.  (Not sure Array Solutions is going to be attending this year -- guess we'll find out soon enough...)   A new main HF transceiver is on the longer term wish list, so spending time in the various manufacturer's booths kicking tires is certainly on the agenda.   If things go as planned, I'll also attend the FlexRadio banquet on Friday night to see what's new in the Software Defined Radio world.

Look for a post or two from Ohio over the next several days!  (edit: A few pictures added below...)

We Can All Agree.

Begali Keys: Wonderful People and Morse Art

20 Minutes Before 2019 Hamvention

Feedline at the VOA Bethany Relay Station:  GIANT

WSPR with an RSPduo SDR

This is WSJT-x running WSPR mode (RX only) along with the software for the SDRduo software defined radio on Windows 10 with the RSPduo SDR.  The trickiest part for me was 1) routing the audio signals with Virtual Audio Cables software, and 2) adjusting audio levels in what seems like too many places to get a decent decode.  It's probably cockpit error on my part, but the audio adjustments seem to be very sensitive and at times almost arbitrary.   At times I could hear the audio in parallel to the decode, and then others, it seemed to decide not to route audio to my external speakers....  More fiddling is needed.

The fun part was decoding Australia this morning a bit after my sunrise and watching propagation change throughout the day; currently I'm seeing Europe pound in and N. America has been open pretty much full time.

The 30m antenna here is a rotatable dipole at about 120' --- probably the most effective antenna I have for a given band, so this is a good place to experiment with WSPR.   This is a keeper...lots of fun.

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!  

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....

Antenna projects dampened...

My sincere apologies for the Dad-humor-esque pun.  Couldn't stop myself.

Fall and winter in the Charlotte, NC region can be a great time for outdoor projects -- and my antenna farm is sorely in need of maintenance and upgrades.  However, rain storms and antenna work don't go well together, at least in my book.   I remarked to my wife the other day that it seems like it's been months since we've had a nice, clear, typical Carolina weekend to get outside; I've felt like I should be working on Ark plans.   This has been the rainiest season in recollection...

Was I the only one thinking that?  Looking up the historic rainfall averages and comparing those to what the actuals have been shows it's not just my imagination. We are over 19" ahead of the historic totals since July 2018.   That's a lot of water.

Any of you with some excess sunshine...please box some up and send our way.

73,
Rush

Radio + Digitization = Fun

I had the opportunity to attend the BayCon 2019 conference in San Jose, CA recently with my work colleague Ben, N6XPD -- who is just starting out in Amateur Radio.   It was a really fun experience and motivating to be among a group of Silicon Valley hams that are on the leading edge of a number of innovations within the hobby.  Ben was so motivated by one of the talks on SOTA, he's now learning code and made some new Elmer friends while there...  Love to see that...

One of the conference forums was a primer on DMR by Reilly, K6YAP.  (Great job Reilly!)  (more on that here: https://www.ke6mt.us/2019/02/baycon-2019-presentation-successful-sota-strategies/)  He was able to answer so many of the questions around digital trunked radio, its roots, its applications, and how to get started -- that it motivated me to take the plunge and get started.  So very glad I did!

2m FM was a real novelty to me back in my Novice days in the 70's (a motivator to upgrade to General) -- the clarity, the "local" nature of the coverage, the squelch tails, the autopatch -- it was really cool.   The first few days of using DMR has rekindled that same kind of reaction -- just amazed at the quality of the audio, the flexibility of using Talkgroups and the ability to meld RF and the Internet in a truly useful and fun way -- pretty much regardless of where you are.  My 3rd contact was with Fawaz, 9A2AA in Bahrain -- sunspots not required.    No repeater?   No problem -- just link your HT to the internet via a DMR modem.  What a hoot.

Today -- I'm trying the new Alinco dual band DJ-MD5 coupled with the OpenSpot2 "hotspot" connected via WiFi to my home network or my iPhone WiFi connection.  Both methods are working great...   The learning curve is a bit steep, coming out of almost a pure analog experience, but it is a healthy and stimulating process....

If you haven't tried DMR -- do it....  you'll be surprised at how little you have to invest vs. the capabilities and fun you'll have!

73,
Rush, W4QA