Sunday, October 4, 2020

A3S/A743 On The Ground

A3S/A743 on the ground

I've known for some time now that my A3S/A743 has problems. Back in March 2019, I noticed that one of the 20m traps was arcing. Then a couple of months ago, I could see that several of the trap end caps were either missing or damaged. 

It's taken me several tower climbs to bring this antenna to the ground, but this weekend, we were finally able to successfully lower it down without incident.

My daughter Lauren acted as my ground crew and did an excellent job. I couldn't have done it without her.

Antenna mounted on tripod

Once the had the A3S/A743 on the ground, the next process was to carefully mark, measure and inspect the antenna. I didn't want the antenna lying on the ground. I had a roof tripod I'd picked up somewhere along the way, and with a short piece of mast, it allowed me to work on the antenna horizontal at ground level.

As soon as we had the antenna on the tripod, I marked all the traps. The original Cushcraft trap markings weather off rather easily. I used a sharpie to indicate the element, trap band, and an arrow pointing toward the boom. It will be important to reassemble the antenna with the traps in the correct direction.

DE traps showing disintegrating
end caps.

Next step was to mark all the element distances. This just required a quick sharpie mark at each tubing junction. 

After this, I got out a clipboard and a measuring tape, and took measurements of all element segment lengths for all three elements. I wanted to see how the antenna measurements matched up with my records. As it turns out, even after 19 years in the weather, the director and reflector elements were spot on. The driven element was a little asymmetric -- that likely happened when I added the A743 kit in 2005. 

DE support rope covered 
in lichen.

With the marking and measuring done, it was time to inspect the antenna. Overall, all of the aluminum tubing appears to be in fine shape -- nothing bent, warped or cracked. The traps were a concern. All of the trap end caps were either missing, damaged, cracked or weathered. Three of the element tips were missing, even the boom end caps bad broken. 

My daughter Lauren noticed the lichen growing on the antenna. Lichen covered a few trap end caps as well as the entire DE support rope.

I was surprised to find the bead balun in such good shape after 19 years. The feed line it surrounded seemed rather weathered, and it is my intention to replace it.

Next, I disassembled the antenna. Because I used No-Al-Ox 19 years ago, separating the sections was easy. Once a clamp was loose, they slid right off. I removed the traps and outer sections, leaving the center part of the elements intact. The outer sections I stored in my basement, and the traps went to the workbench. The boom and center part of the elements, I lashed to my back porch for now. 

With the outside work done, it was time to inspect the traps. I pulled all twenty-eight end caps off. Maybe four or five were intact, but even those are heavily weathered. I blew all traps out with compressed air, finding surprisingly little material come out, which I took as a good sign.

The two 20m (TK) traps were a concern. These traps I saw glowing back in March 2019. One of the end caps had melted. With the end caps off, I could see the outer end insulator on both traps had melted.

Only a little char on this one.
To know how bad it was, I had to disassemble the 20m traps. Disassembling these traps is a difficult proposition. The outer end of the trap cover is dented inward in four places to hold on to the end insulator. Because of this, it can only slide outward. The inner end of the trap cover has a double-z bend to make connection to the element tubing. If you undo the bend, the cover will slide off outward. But undoing the bend will likely break the aluminum. 

A lot of char on this one...

For the 20m traps, the outer insulators were toast anyway, so I didn't have any trouble sliding the trap cover inward. I just had to remove the screw at the double-z bend first. 

What I saw inside was not pretty. Both traps were damaged due to arcing and will need to be replaced. 

I also disassembled one of the 15m DE traps. Of course I broke the double-z bend in doing so. However, the inside of the trap looked clean, and, unlike the 20m trap, the coil windings were protected with resin. I didn't think it was worth disassembling any more traps and breaking more double-z bends.

I believe the 20m traps may have suffered from too much droop on the elements and collected a lot of moisture inside the trap. Once fired up with RF, it arced and toasted the traps. 

Some of the traps had corrosion evident around the hold-down screw on the trap covers. I removed the screw and put a thin layer of No-Al-Ox between the z-bend and the trap element tubing. This should limit further corrosion in this joint.

Monday, September 21, 2020

80/40/20m Trap Dipole

80/40/20m dipole strung from tower.
I've had good experience with trap antennas. I built an 80/40m trap dipole a decade ago, and it served me well at four different locations. That is, until it met an untimely demise when a rope was cut and the mowers encountered the antenna on the ground.

Wanting to build a three-band dipole, I did some experiments with computer modeling. I found that there was a lot of interaction between the values used for the traps and the wire lengths used. I fussed around with a model for a while. Eventually, I decide it would be simpler to just build one.

I started with the traps. They are made from short sections of 3" schedule 20 PVC. (Having an outer diameter of about 3.25") The exactly frequency of resonance doesn't matter terribly much, just so the traps are identical.

For the 40m traps, I used 9.75 turns of #12 wire with a 56 pF 6 kV disc ceramic cap. This resonates at about 6.88 MHz, just below the band. I started out with 10 turns, but they resonated around 6.5 MHz, which was too low.

On 20m, 6 turns of #12 wire with a 27 pF 6 kV disc ceramic cap. Resonating at about 13.84 MHz, right below the band.

Early version of traps, showing construction.

I then put it together to form a dipole with the following segment lengths on each side:

20m: 17 feet
40m: 17 feet
80m: 20 feet

This made the whole antenna nearly108 feet long. The ends of the 80m segment are looped back on themselves by about a foot and twisted to anchor to the end insulator. I strung it between the tower and some trees in the back yard. It's roughly 10m high. 

The dipole is fed with good quality RG-8X using 16 Fair-Rite #43 1/2" ferrite beads as a current balun. 

Then began the tedious process of trimming to resonance. I started with the 20m segments, then worked out to 40m and finally to 80m. Patience is warranted here, because it is too easy to cut too much off.

I ended up with these segment dimensions, resonance points and SWR:

20m: 16' 4" - 14.125 - 1.45:1
40m: 10' 4 - 7.165 - 1.2: 1
80m: 21' 8" - 3.76 - 1.1:1

And, yes, I added 20" to the end of each 80m segment. The resulting antenna is about 96 feet long. It covers all of 20m and much of 40m with a 2:1 or better SWR. 80m, by comparison is very narrow. I didn't have much of a chance to use the antenna, but it appears to hear very well. 

I've got a second one I've cobbled together for the Fulton County QTH. I'll need to wait until the tree lose their leaves so I can get it up to operating height for final trim. 

Sunday, August 16, 2020

Bringing Comfort to the Heil Proset

Heil Proset with Brainwavz earpads

I've owned a Heil Proset for several years. While I love the headset -- it sounds great, and has the HC-4 mic element, which, inexplicably, Heil no longer sells -- it has one shortcoming. After about an hour, it gets very uncomfortable -- less like a headset and more like a head vise.

The stock ear pads are the problem. They are not even 1/2" thick. Plus, the cloth covering that goes over the ear pad tends to press the outer ear (the pinna) against the head. For 30 minutes or so, this is tolerable. After an hour, your ears start to hurt. After wearing them for 30-plus hours during a long contest weekend, your ears won't feel right for days.

I'd largely given up on the Proset for long contest use, opting to use the more comfortable Koss SB-45 or Yamaha CB500 headsets (or even a pair of old Sony headphones, if I don't need the mic). But the Koss or Yamaha headsets are designed for good fidelity, not for communications. The Proset is more listenable.

I read some old threads on the CQ-Contest mailing list about a company called Brainwavz that makes replacement ear pads for the video gaming industry. Many gamers wear a headset for hours while playing multi-player games. Perfect. Bob WA1FCN recommended them to me in a private email. 

Brainwavz, unfortunately, doesn't make a product specifically to fit the Heil Proset. I measured the earpieces of the Proset and found them to be 4" (101mm) tall and 3.5" (88.5mm) wide in a rounded triangle shape.

Comparison of thickness with
the stock earpads

Brainwavz replacements are designed for oval earpieces. I worried a little about the fit, since the Proset earpieces are triangular. It seemed worth a try. WA1FCN recommended ear pads designed for certain models of ATH headsets, their dimensions being 110mm x 90mm. I ordered them off Amazon for less than $25.

Removing the old ear pads was easy - they pull off with a little tug. A plastic retainer ring fits under the ear pad edge and snaps into a plastic ring on the inside of the ear pads. Then the whole assembly snaps on to the headset. Given the size of the Brainwavz ear pad edges, the plastic retainer wouldn't be able to hold them. And I couldn't remove the plastic ring from the original ear pads without destroying them. I opted to remove the plastic retainer from the ear pad and place it on the headset, then fit the Brainwavz ear pads over the entire earpiece body.

That took a bit of struggle. I started at the wide end (the top) and worked the edges of the earpads around with my fingers. The material does not stretch much, but it was enough to fit around the earpiece body. Once in place, I did not worry about it coming off. Just work slowly and use minimal tension to get the job done.

Brainwavz pads offer over 3/4" of room

These ear pads give the headset a different look -- much more cushiony.  But do they work?

The headset rests comfortably around the ear. It's slightly nicer than either the Koss or Yamaha headsets.  I gave them a trial run during the NAQP CW. I operated about six hours, and felt no discomfort at any time using the larger ear pads. 

Definitely a worthy modification. 

Sunday, August 2, 2020

OK, That's Not Good

Noticed today while I was mowing grass that two of the traps on the A3S/A743 -- the 15m trap on the director and the 20m trap on the driven element -- both have end caps that have come off the traps. 

This means the traps are exposed to the weather, insects and what not. 

That's not good. 

Indeed, from the ground, this antenna isn't operating correctly, either. The SWR is over 2 to 1 on 15 and 10m, and the antenna doesn't seem to be that effective on those bands, either. Only a little bit better on 20 and 40m.

The A3S has been up since 2001. I added the A743 in 2005. That's been 15 to 19 years exposed to the elements. It's not surprising this antenna needs maintenance.

I've got the gin pole on the tower, just need a couple of days at the Gwinnett QTH with a little help to get that antenna on the ground.

Sunday, February 16, 2020

SoundBlaster X G1

I'm always on the lookout for good USB sound cards. I've found a few. Some were expensive, like the M-Audio Transit. Others were cheaper, like the Startech ICUSBAUDIOMH. Both of these are 96 kHz, 24-bit, stereo input and output sound cards.

And neither of them work any more. You see, these devices, although the hardware is perfectly capable, are no longer supported with current drivers. As such, they no longer function with the latest operating systems. It's a very disappointing situation.

So, I continue my search to find good sound cards. I look for 48 or 96 kHz, 24-bit devices, preferably with stereo input. Sadly, this last function is hard to find.

The SoundBlaster X G1 seemed promising. It was advertised as 96 kHz, 24-bit, stereo device. It was only about $30, so it fit my criteria as inexpensive. I received one at Christmas time and checked it out.

The SoundBlaster X G1 comes with a TRRS mini phone jack, which should have been a clue that it didn't have stereo input. It comes with an adapter that exposes the connections as a separate headphone and microphone jack. The microphone input is connected to the ring terminal, the tip having no connection. This is apparently pretty standard for PC microphones.

When I first tested the device, I was disappointed that it only had 44.1 kHz, 16-bit input and output. At least, that's the only function it would perform out of the box. While the input appeared on the computer as stereo, both channels are hooked to the single input channel -- giving you two copies of the same input signal.

Turns out, the SoundBlaster people have created a device that has multiple "profiles" and can appear as a device with different capabilities. The default profile is intended to be compatible with the Sony Playstation, and has minimal capabilities. Using a special Windows program, I reconfigured the profile to the Generic profile.

On the Generic profile, the device conforms more closely to it's specifications. 96 kHz operation is restricted to output-only. Input maxes out at 48 kHz. But both input and output are 24-bit.

Once configured, the SoundBlaster X G1 makes a decent sound card, although it is restricted to a single input signal.

SoundBlaster also makes the SoundBlaster Play!, which appears to have similar capabilities 96/48 kHz, 24-bit, stereo out, mono in. The Play! is about 20% cheaper, but both are inexpensive.

Friday, January 10, 2020

Ingenious Fan Holder for K2/100

Binder clip. I should have thought of this earlier!
The K2/100 is a nice little radio, but when running RTTY or other full-duty cycle modes, it lacks sufficient cooling. I couldn't run more than about 30-35 watts without the KPA100 amplifier heat sink becoming alarmingly hot.

I solved this problem a years ago with a small muffin fan on top of the heat sink. The fan is mounted on tiny rubber feet. It blows air upward, resulting in airflow across the fins. Placed just above the finals, it does a good job of keeping everything cool.

This fan is noisy at full speed, so I used a small resistor in series. The resulting half speed airflow is more than sufficient.

This worked great at my Gwinnett QTH for years, where the radio was raised above the desk a couple of inches by a shelf. The K2/100 sat almost flat, and the fan stayed in place. However, when I moved the K2/100 to the parsonage QTH, the radio rested on the desk, and I used the KAT100 tilt bail. Because of the tilt, the fan had a tendency to drift to the back. Every once in a while, it would fall off.

While I was readying the K2/100 for the 2020 ARRL RTTY Roundup, I wanted to make sure the fan stayed put. I came up with a very inexpensive solution. A small binder clip attaches easily to the heat sink fins. The ears of the clip rest against the fan body and prevent it from drifting.

Worked about eight hours over two days in the RTTY Roundup, and the fan never budged. I really wish I had thought of it sooner!

Saturday, December 21, 2019

Replacing the AL-80A Bandswitch

The AL-80B bandswitch, compared to the existing switch shaft.
With my wallet being $115 lighter, the AL-80B bandswitch arrived within a week. Now, it isn't the same as the original AL-80A bandswitch.

There are two key differences. First, as you can see from the picture, the shaft layout is different. In the original AL-80A bandswitch has the input network switch wafter in front of the bandswitch, whereas the AL-80B has it behind the bandswitch.

This means you can't just replace the AL-80A switch with the AL-80B switch. The best you can do is to unstack the wafers and put them on the original AL-80A switch shaft.

AL-80B switch with AL-80A wafers.
The second difference has to do with the switch wafers. Electrically, they are identical. The AL-80B switch has the 160m padder cap and the Pi-L network wafers reverse. Since we're going to re-stack the wafers anyway, this doesn't matter.

The Pi-L wafer is positioned differently. The contacts are two positions counter clockwise (as viewed from the front of the shaft) from the AL-80A. This means that a bit of re-wiring is necessary to make the connections.

Wafer-less switch.
Removing the switch wafers isn't a big deal, since I have done this earlier. The rear wafer comes off with all the coils attached, and the padding caps unscrewed, there being only one wire that needs to be unsoldered, and it slips off. The middle wafer has a similar wire to be unsoldered, and it comes off as well. The front wafer has one wire to the padder cap, and it comes off as well.

With all the wafers off, the new switch wafers are stacked on. Because the Pi-L wafer has contacts rotated two positions, they are a little harder to access between the switch and the loading capacitor.

New wafers in place.
Once all the wafters are on and screwed down, the next step is to re-solder all of the connections. I took lots of pictures before unsoldering the old wafers, so I had a pretty good idea of what goes where.

Front switch wafer anchors the coax shield, and adds the 160m padder cap. The Pi-L switch wafer was the only one that gave me trouble. Since the contacts are rotated from the original, this required a bit of extra wire to make the required connections. The rear switch wafter has five connections tot he coil assembly. It took a bit of work to unsolder. This sort of thing is best not rushed and done with great care, to avoid damaging the coils. Everything goes in the same place on this last switch wafer, which was easy once I got all the coil wires into the right positions in the narrow switch contact lugs.
The finished product. Reassembled with new switch wafers.

Sounds easy, eh? But realistically, it was nearly three hours on the workbench.

Moved it back to the operating desk and tested for full output into a dummy load on all bands. No problem on 160, 80, 40, 20, 15 and 10m.

For 17m and 12m, I proceeded more cautiously. The AL-80A is designed to operate on 12m using the 10m switch position. It works on 17m using the 20m switch position. But it has often been on 17 or 12m that I've had the most issues with arcing in the PA circuit.

For this reason, I've decided to reduce drive to about 30 watts for 17 and 12m. It's a little less output power, but also less of a chance of burning up a $115 bandswitch.

With the testing done, it was time to button up the amp. Took me about 20 minutes to find 10 of the 13 screws that hold the cabinet top on. I had removed them a year and a half before, but finally found them in a neat pile on the workbench.

The AL-80A is back up and running on all bands!