Archive for September, 2010

Pin 1 and a Pound of Ferrite

September 19th, 2010

The commonly-held wisdom goes that an “ounce of prevention is worth a pound of cure.”  As things typically go around the K8GU station, 50% of problems are solved by prevention and 50% by cure.  Today, it was a cure.  Readers of the blog are no doubt aware that I have a recently-discovered problem with QRM between my radios when they were on the 20- and 40-meter bands.  (I didn’t notice this problem until I got both of the TS-930’s up and going again; so, it’s probably the result of the “new” station location and arrangement.)

I pulled the 20- and 40-meter W3NQN filters out of the circuit and measured them.  They benefited from a little tweaking, but nothing that would have caused the problem.  I put them back in and was rewarded with much lower VSWR in across both bands.

It didn’t matter which of the radios was on 20 and which was on 40, the interference, a popping hash that followed the leading edge of my keying, was there.  The next step was to put a dummy load on the output of one radio, then both radios.  Even when transmitting into the dummy load, the interference remained.  This suggested to me that the problem was very close by.  All of my gear is bonded together with heavy straps.  So, I wasn’t too worried that it would be difficult to find.  I noticed that the 40-meter LED flickered on my KK1L band decoder box following my keying.  It became the prime suspect.

I found some split beads that AD8P and I bought from AA1K in the Dayton flea market a few years ago.  I’m not sure what mix they are, probably 43 or possibly 77.  Winding a few turns of the band data lines from each radio through the beads knocked down the interference a good bit.  I slapped some more on the audio lines going to the Heil HCS that I use for SO2R audio and the interference disappeared.  But, I was using the dummy load on one of the radios.  As soon as I went back to the external antennas, the inteference came back.

Next, I dug out a couple of the 2.4-inch diamater mix-31 toroids that I purchased in the first K9YC “group buy” of these parts back in 2005 or 2006.  I wrapped the DC power supply line to the KK1L box and the AC supply to the HCS.  And, the problems pretty much disappeared.  At least one of these is due to what K9YC calles “the pin 1 problem.”  Basically, if the shield is brought through the metal enclosure to the circuit board, it conducts (noise) current that’s riding on it into the enclosure.  So, I need to dissect the HCS and KK1L boxes to see if I can find a deeper fix than just slapping ferrite on the outside.

But, there’s hope for SO2R in this week’s NSL!

VHF/UHF firepower

September 16th, 2010

As if I don’t have enough projects already, I recently obtained these two surplus FAA AM-6155 amplifiers on, as usual, very attractive terms.  I don’t have the equipment to properly test them at this point.  But, that is coming.  The FAA specified these to do 50 watts continuous duty AM.  With modification, they will do about 300-400 clean watts with 10 watts of drive on 144, 222, and 432 MHz.  Once I get the first two working (on 222 and 432), I plan to find two more of them and use them on 50 and 144 MHz.  For 50 MHz, I plan to remove the VHF/UHF cavity and components and install an RF deck using the same Amperex DX393 or Eimac 8930 tube.  Comments and ideas welcome.  They’re a lot cheaper than bricks!  One of my units appears to be at least partially converted already, but I’ve only had it open for a few minutes with my brother Seth, who got all of the mechanical aptitude in the family.

Note:  Thanks to WY3X for catching my error on the tube type.  He also notes that 300 watts would be a conservative maximum on 432.  I plan to run the amps with very low drive after tuning so I can compete in the ARRL’s low power category at 100 watts on 222 and 432.

QRL for Sprint and September VHF

September 16th, 2010

As I mentioned previously, I was planning to make the NCJ North American Sprint and the ARRL September VHF contests my kick-off to the Fall/Winter contest season.  When a work trip was scheduled for that weekend, I assembled my portable station.  But, Sarah convinced me not to take it since carrying the ham gear always complicates travel a little bit.  Since the work trip was radio-related, I thought I’d share a couple of pictures and stories.

One of the projects in which I participate is the middle-latitude expansion of SuperDARN (Super Dual Auroral Radar Network).  SuperDARN is a global HF radar network that is used to monitor plasma processes in the polar ionosphere/magnetosphere.  It was recently highlighted on  Last year, we built a pair of radars near Hays, KS.  This year, two radars are under construction in central Oregon.  I went out to assist with the initial phases of the build.

The radars are installed on an old HF over-the-horizon-backscatter (OTH-B) radar transmitting site in Christmas Valley, OR.

Two of these radars were constructed for the U.S. Air Force as an early-warning system for aircraft, one in Maine and one in Oregon/California.  The western portion of the radar was only turned on briefly for testing before being relegated to “warm storage” and then decommissioning.  Typical.  None of the antennas or transmitters are still on site and a lot of the copper wiring has been looted.  Everything left inside the building, including the backup generator, was in essentially mint condition.  As an aside, the transmitters from the Maine site were recently installed at Arecibo Observatory.  I have no idea what happened to the transmitters from this site.  Despite the fact that the antennas and transmitters were missing, there were a number of interesting things to see.

This OTH-B radar was a megawatt class (output, not ERP) system split into three segments/sectors, facing NW, W, and SW, each fed by four transmitters.  Each sector had a separate, dedicated 3-phase power line that came from a substation some 50 miles away—I found it on the way home.  You could follow the poles straight to it if you knew what you were looking for.   Each of the transmitting arrays was surrounded by a fence, for obvious reasons.  The fence was made entirely of wood.  Furthermore, almost all of the washers were a fiber material, not galvanized steel like the bolts.

At first, I thought that the washers might have been an electromagnetic consideration, like the wooden fence, which might have distorted the antenna pattern in the best of cases or simply melted in the worst.  But, I suspect now that it was a mechanical consideration to deal with dramatic changes in temperature and humidity in central Orgeon’s Great Sandy Desert.

The actual construction of the SuperDARN radar is not that exciting at this point, but here are some of the 72 aluminum poles we dressed with cables for the two radars.  Each radar has a 16-element phased-array of folded dipoles mounted in a corner reflector.  I installed a lot of N connectors on LMR-600 and a lot of Preformed end-grips on Phillystran, in addition to some more cerebral tasks.

The site has good optical conditions, too.  So, I’m looking forward to trying some of my optical instruments out there.  Here’s a quick star-trail exposure I took with the camera propped up on a picnic table in the motel parking lot.

So, that’s what I was doing instead of Sprinting and grid hunting!  I should be QRV in the NS Ladder tonight.


September 16th, 2010

NS Ladder (3 September 2010)

September 2nd, 2010

Definitely unprepared this week and the score has gone down appropriately.  I’ve been slowly working to combat RF gremlins in the station.  80 and 40 are now 100% clean for SO2R, but I still have problems on 20 and 40 (both ways).  I think the 20-meter feedline is picking up (radiating) garbage.  I had a number of SO2R QLF moments.  The QRN was pretty nasty here (probably on account of the approach of Hurricane Earl) and I had to work hard to concentrate on the main radio.  I ended up just going to one radio after I went for three minutes without a QSO.

For next week’s NS and the NA Sprint, I plan to be QRV from a different QTH.  More on this when it happens.

NCCC Sprint Ladder - Sep 3

Call: K8GU
Operator(s): K8GU
Station: K8GU

Class: Single Op LP
Operating Time (hrs): 0.5
Radios: SO2R

 Band  QSOs  Mults
  160:   0      0
   80:   8      5
   40:  12      9
   20:  10      6
Total:  30     21  Total Score = 630

Club: Potomac Valley Radio Club