Friday, November 20, 2015

Mark V Shunt Feed Matching Network (80m)

Inside of the Mark V matching network. Notice the larger
capacitor in the back upper right, and the new inductor,
both for 80m.
I wrote earlier that I was having trouble with my 80m shunt-feed matching network. I managed to identify the problem using an enormous variable capacitor, but that was only temporary. As it was, the Bread-slicer obtained several spots of rust for the week I left it outside. I needed a permanent solution.

Having nothing in my junk box that was suitable, I found a 80 pF variable cap with reasonable (4 kV) plate spacing on eBay. It would fit into my NEMA box, but just barely.

In my earlier hunt for the 80m issue, I had already re-wound the 80m inductor on a T200-2 core with insulated wire.

While I was doing this, I realized I had no more T200-2 cores. I was giving idle thought to going to 2 T200-2 cores, as I had for the 160m inductor. Double cores would allow me to use fewer turns, so I could use a larger gauge wire, increasing the inductor Q.

T200A-2 core in center, cover in
fiberglass tape on left, and a
finished 80m coil on a T200-2 core
for comparison on right.
While I was shopping on-line, I came across a new product from Amidon. It is variously labelled T200A-2 or T200-2B, but it is essentially a T200-2 core that is 1 inch thick -- the same as stacking two cores together. Needless to say, I bought two.

New 80m inductor.
Using the larger core, I went from 38 turns on the T200-2 to only 28 turns on the T200A-2 core. The most difficult part of this exercise was finding suitable wire in the junk box. I ended up using a bright orange 16 gauge wire that had much thicker insulating than I needed -- but it is what I had. The resulting coil was a bit difficult to wind, and I used a couple of wire ties to keep the ends from unravelling.

New cap and inductor for 80m.
Shoehorning the capacitor and the larger inductor into the NEMA box took some doing. I had to move the relay just to get the capacitor in the box. And the wiring had to be re-done.

I used two 100 pF 6 kV disc ceramic caps in parallel with the 80 pF variable to get enough capacitance to match.

All assembled, it tunes up nicely around 3800 kHz with a 1.1:1 SWR. And the SWR doesn't change at all when going to 100 watts. Perhaps with the new cap and inductor, I could put a few hundred watts through it with no problems. I'll have to wait to fix the AL-80A before I can test that.

Next step will be to get the 160m network to tune better, it's a little off lately, I think I need more capacitance.

Wednesday, November 11, 2015

Enter the Bread-slicer

Dual 300 pF variable capacitor. Plate spacing is about 1/2".
That's a half-dollar coin on the workbench. This sucker
is BIG. Breakdown voltage is probably around 14 kV.
I've been having trouble with my 80m shunt-feed matching network. Since I moved from Floyd County, I found that the SWR shifts when I transmit more than about 20-25 watts. The Elecraft K3 will work just fine at it's tuning level of 5 watts and find a perfect match. But, when more than about 25 watts is applied, the SWR shifts.

This has made the shunt-fed tower unusable on 80m. This is especially bad, since the tower is my only 80m antenna at the moment in Gwinnett County. I've written about my pursuit of 5-band DXCC. I need an 80m antenna.

The question in this case -- what causes the shift? No doubt it is due to arcing. Initially, I thought the 80m network had the same problem as I had on 160m -- that the inductor was arcing between turns. I originally used enameled wire to wind both inductors. Over time, with the heating and cooling of the coils caused the windings to rub against another, which eventually caused the 160m inductor to arc between turns.

I re-wound the 160m inductor with insulated wire back in 2006, right at the start of the ARRL 160m contest. I haven't had any trouble with arcing. It was behaving much like the 80m network was.  Re-winding the 80m inductor was easy. Unfortunately, it didn't solve the problem.

There's not much else to the matching network. It's a simple L network with a series inductor and a shunt capacitor. It might be the capacitor, it might be some part of the switching network. How to find out?

What I needed was a capacitor with greater breakdown voltage. The variable capacitor I used on 80m is a 15-250 pF unit that was the plate-tuning cap in a DX-40. A survey of likely substitutes found nothing that suitable in my junk box. I'd need to buy a replacement. But first, I needed to know if the capacitor was the problem.

I did have one part in my junk box that I might use. The Bread-slicer. You see, when my friend Mike (now W1YM) moved away from Atlanta, he gave me a whole bunch of ham-related stuff, with instructions to sell off what I couldn't use and fund my tower project. And that's exactly what I did. Among the items he gave me were a couple of very large variable capacitors.

One of them was far to small to work -- only about 15 pF max. The other, however, was perfect. It's a dual 300 pF cap with a plate game around 1/4 inch. Breakdown voltage for this cap is over 10 kV. I call it the Bread-slicer, since it looks large enough to slice an entire loaf of bread at once. It would be perfect for a test.

The Bread-slicer in position at the base of
the tower. Note that I don't even have a
knob large enough to fit on the shaft.
The problem with this cap is that it is huge. It's literally bigger than a breadbox. No way it would fit in the 6" cube of the NEMA box that houses the 160m and 80m matching networks. But, it would prove to me if the variable cap I was using was the failing part.

So, one very damp evening this week, I put the matching network back on the tower without the 80m capacitor and jumped the Bread-slicer in the circuit. Lacking any knobs large enough to fit on the shaft of this enormous capacitor, I used a pair of vice-grips.

With some quick work with the MFJ-259 antenna analyzer, I found a 1:1 match right around 3800 kHz - just as expected. Hooking up the coax and stepping back inside, I tuned the K3 to the 80m shunt-feed, and gave it a quick full-power test.

No SWR shifts. Yes, it's definitely the variable capacitor that was arcing. Since I can't use the Bread-slicer on a permanent basis, I've already ordered another part. It's only 80 pF, but has a 4 kV breakdown voltage. And, it should fit in the NEMA box. Once I get it, we'll see how well it works.

Thursday, October 15, 2015

The Last One Hundred (Plus Nine)

Back in 2007, after uploading logs to Logbook of the World for three and a half years, I qualified for DXCC. I'd been licensed as a ham 32 years earlier, and had worked nearly 200 entities, but didn't get the confirmations until 2007.

I mentioned this on the SEDXC email-reflector, and got many positive replies. David Johnson K4SSU wrote me and said that he envied the enjoyment I would have working and confirming the next 200+ entities.

Now, eight years later, I have been at 231 current entities for a few months now. It dawned on me that I have only 100 more to go to reach the honor roll. I'm now working up that steeper slope that David Johnson mentioned, where the thrill of working a new one comes only after much waiting.

I haven't been idle. I'm inching closer to 5BDXCC, and trying to work the DXpeditions as they pop up -- especially those that aren't on the air but once a decade.

Still, there's a lot of DX, even easy DX that has eluded me. I still haven't gotten the hang of postal QSLs -- still depending far too much on LoTW. That's probably something I need to fix. There's probably a bunch of DX I've already worked that can't be confirmed any other way.

Friday, September 18, 2015

The Venerable TS-430S

The Venerable TS-430S with AT-250 antenna tuner.
I realized earlier this week that my backup rig, the Kenwood TS-430S, turns 30 years old this month. Yup, I bought that rig back in September of 1985. For the next 16+ years, it would be my only HF rig.   I held on to that rig so long, by 1995, I was already calling it "venerable."

How I got to that point is an interesting story. My original Novice setup was an SB-301/SB-401 combo. In my second or third year of college, I sold my SB-401 to my brother Ben (now NJ8J). I still had the SB-301, and eventually I set it up in one of my college apartments. But I lacked a transmitter.

One summer, I attempted to rebuild my Novice transmitter using a 6GK6 and 6146 design published in the ARRL handbook. I added a lot of extras, like a built-in VFO and a KOX (key-operated-switch), with automatic T/R switching. (the VFO and KOX board were salvaged from a home-brew 40m QRP rig project that I assembled, but never could get to work) I never could get any output from that 6146 rig, and it chirped pretty badly.

Shortly after I finished college and moved into an apartment, I borrowed a friends FT-101E. The rig worked great. Because of my crummy antenna situation, I had a lot of trouble making contacts. Eventually my friend asked for his FT-101E back.

Since he bought the SB-401, my brother wasn't using a Heathkit DX-60B he had, so I borrowed it. I pulled the VFO out of the Novice transmitter, mounted it in a box with the KOX circuit board, a power supply and connectors for the DX-60B. This actually worked! I made a handful of contacts, but again the antenna situation really limited me.

In the summer of 1985, I moved to a new apartment much closer to work. It was two stories tall, and there were a number of trees about 30 feet away from the back. I took a couple of 100 foot spools of #26 wire wrap wire and strung them into the trees from my second-floor shack window, fed from the back of a crappy MFJ tuner with a balun. This formed a crude doublet.

For an operating table, I bought a door, placed it on two short two-drawer filing cabinets, and finished it with stain and polyurethane. I did a good job, because this door is still my operating table to this day in Gwinnett county.

I still needed a rig. I decided I didn't want to fool with tube-type radios any more. (That urge would return later) I wanted something that was all solid-state, had a direct-reading frequency display, supported the new WARC bands, and didn't cost terribly much.

At that time, the top contenders were the Kenwood TS-430S and the Yaesu FT-757GX. Both had a reasonable feature set, and were similarly priced around $600. I don't know what tipped me toward the Kenwood. In retrospect, based on what I know today, the FT-757GX had more features -- it does full QSK and has a built-in keyer, as well as supporting computer control via the CAT system. Computer control would be something I would pine for a few years later when I got into contesting.

Back in 1985, I wanted to get the best deal on my TS-430S, and I must have called a dozen different dealers for a price quote. The deal I found was a TS-430S for about $630, including the optional FM board. I placed the order with my credit card -- and this was perhaps the first time I would go into debt for my hobby.

I didn't do a lot of operating from that apartment, but I did enjoy the TS-430S. The crude doublet actually worked pretty well. I spent a fair amount of time on 30m, which was a relatively new back then, but I also hung out around the Novice bands on 80, 40 and 15m.

I moved to a house in Stone Mountain, GA, and the TS-430S was my main rig. My antennas progressed from a 300 long wire to a loop skywire, to a 125 foot doublet, eventually complemented by a Butternut HF4B beam on a roof tower that eventually gave way to a Cushcraft A3S. I started contesting in 1986 with CW Sweepstakes. The TS-430S paved the way for a whole lot of radio experience for me.

As a rig, the TS-430S is not a bad performer. There are two key deficiencies that were fixed by it's successor, the TS-440S: a) computer control, b) 100% duty cycle. The TS-440S adds a host of other features (100 memories, internal antenna tuner, selectable filter bandwidths, FSK, selectable AGC) Ironically, the TS-440S would be introduced at Dayton in 1986, just a few months after I bought the TS-430S.

CW performance is reasonable, depending on your expectations. There is no QSK, but the VOX operation from the key is quick and reliable. You can at least listen between words. AGC action is fast. The 500 Hz CW filter is a must-have.

SSB works well. VOX is fully adjustable, and the speech processor produces reasonable results on air. Choosing LSB or USB, though selects the slow AGC, which is annoyingly sluggish.

FM is interesting. I played around with 10m FM in the late 80s. There used to be a few guys in the Atlanta area that would hang out there back then. I think it may have faded, along with a lot of 2m FM.

Receiver performance is pretty good considering the up-conversion design and the vintage. There's certainly some front-end IMD, which you hear as a "sparkle" sound, especially on 10m when it is open during a contest. Usually hitting the attenuator knocks that out. The notch filter is pretty good, provided you are only dealing with one carrier. Of course, you have to adjust it manually. Noise blanker is one of the better ones.

Some contesters would be displeased with the manually-centered RIT. Never bothered me. IF Shift can sometimes help fight QRM -- but not in really crowded conditions.

This rig has some features I have rarely used. General Coverage Receive is one of them. Program scan has got to be the most useless of all -- since you have to manually hold the scan if you hear a signal.

I have made a handful of mods to my TS-430S. I did the 10 Hz frequency readout right away. (Why they didn't ship it from the factory this way, I'll never understand) Back when I used transverters for 2m, I enabled all-frequency transmit. Oh, and I did a simple mod that allows the YK-88C 500 Hz CW filter to be used for SSB narrow. This is useless for Phone, but makes easy work for RTTY.

Running RTTY is a mixed blessing. With the 500 Hz filter and the IF Shift adjusted, it does respectably on receive. The slow AGC is a little bit of a problem. Transmitting, though, should be limited to about 50-75 watts. Be sure to turn off the speech processor.

This rig has been with me at five different QTHs, as well as a host of Field Day operations. Although I long ago bought an MB-430 mobile mount bracket, I have never mounted it in a mobile.

Considering all the rapid changes in electronic and radio equipment in the late 70s to mid-80s, what with the transition from tubes to transistors to integrated circuits, plus the addition of new amateur bands -- it is amazing this rig still holds its own. I certainly didn't expect to be using it 30 years later.

Wednesday, September 9, 2015

BAM! - AL-80A Broken Again

Well, crap. The AL-80A is broken again. Yup. I was on 17m chasing a bit of DX, when I decided I needed more than 100 watts. I hit the A->B button, then A/B, then tuned a bit away from the DX frequency (never tune up on DX - ever), dialed in 50 watts, switched the amp to operate and hit the Tune button.

Heard something go POP! as I turned the plate tuning knob, and immediately the grid current meter pegged. Not good.

A little diagnoses -- with no RF, keying the amplifier the grid current meter reads about 100 mA. Even with about 20 watts, the grid current meter pegs. Seeing the output meter peg, too.

At the worst, I may have fried my tube. I suspect I may have blown more of the metering circuitry.

This amplifier is very picky about 17m....

Monday, August 31, 2015

Pursuit of 5BDXCC III - 80m

I wrote of this dream first two years ago. Back then, I thought it would be an easy thing, perhaps to work (and confirm) nearly 30 countries on 80m in a single winter. Boy, was I naive. I only added six confirmations on 80m the entire year.
Can this shunt-fed tower put me over the top?
The next  year, I at least had the sense to understand the difficulty of the proposition. I enumerated things I might do that year. In the end, I only did a couple of them. I did not add more radials to the Inverted-L, I did not bring the amplifier up to Floyd county, I never did finish the new K9AY controller. 

However, I was there a lot. I spent a lot of time on 80m. As a result, I now stand at 89/88 confirmations - I added a dozen over the year. That's twice as productive as the previous year. 

If I can pull it off again this year with a dozen confirmations, I should be able to meet all the requirements of 5BDXCC.

It's going to be interesting. At the moment, the Inverted L, with over 30 lbs of radials, is sitting in a box. I'm still trying to figure out if I can put it somewhere where I can lay down those radials safely. My only 80m DX antenna is the shunt-fed tower in Gwinnett county. 

Wish me luck.

Wednesday, August 12, 2015

AL-80A Repairs

AL-80A back in the operating position
Hard to believe, but it has been 10 years since I purchased the AL-80A. Archie, K4GA owned it before me, and it has served me well since that time. I added a step-start circuit a few years ago, and it's been doing well until April 2014.

I wrote earlier this year that the AL-80A had a failure that I traced down to an open 1.5 ohm 3 watt resistor on the meter board.

I finally got a replacement part from a source in China. (Well, it was cheap, but not fast) Installing the resistor was the easy part. While I had the amplifier away from the operating position, I decided I needed to do a couple of other updates.

Back in 2009, I added a glitch resistor, but I installed it on the wrong side of the B- line. It was between the capacitor bank and the rectifier, where it wasn't doing any good. I moved it into the B- line between the capacitor bank and the meter board.

Glitch resistor on the rectifier board.
My AL-80A rectifier board had a number of unused lands (likely for full-wave rectifier bridges in other amplifier designs), two of which were perfect for the glitch resistor. If you look carefully at the photo, you'll see a darker brown wire going from the capacitor bank land near the middle back to up the board. This goes to the far end of the glitch resistor.

The near end is hooked up to the brown wire that disappears off the bottom of the capacitor board, heading to the meter board. 

This made for a neat installation, and now that is is on the right side, it will actually do some good.

The other issue I addressed was the meter lighting. Because of a bad trip to Barbados long ago, the two grain of wheat bulbs were not affixed to the grid meter. One of them had been destroyed, and one other bulb on the multi-meter had burned out.

Grain of wheat bulbs like this are nearly impossible to find these days, plus I didn't want to have to fool with changing them when they burn out. So, I took a tip from the internet and replaced them with white LEDs. The LEDs were ones I had bought some time ago from (Mouser part # 593-VAOL-5LWY4 - 4000 mcd standard white / clear LED -- these are still in stock, although you can get way brighter ones (35,000 mcd!) for less money) At 5mm (T 1-3/4) they were the perfect replacements for the old bulbs. 

The Grid Current meter did not have the holes drilled for the lamps. I held my breath and did this, using a very slow drill speed and working slowly. I didn't want to mess up the meters. Since the lamps are run from the internal 12 volts supply (actually about 13.5 volts), a 1.5 kiloohm resistor was wired in series to set the current at about 9 mA.

LEDs being glued in place on the meters.
The LEDs are glued to the back of the meter faces. Superglue would have been perfect, but unfortunately, I was out. I ended up using 30 minute epoxy, but this particular stuff is so old it was more like 240 minute epoxy.

I re-used the blue leads from the defunct grain of wheat bulb to wire in the negative terminal of the LEDs, and picked out some red wire for the positive side. I mounted the LEDs so the negative and positive corresponded to the terminals on the meter. Less chance of screwing something up.

Toughest part of this exercise was wrestling the meter board back into place. After buttoning it all up, it was time for the moment of truth.
Lighted meter faces.

Et voila, it works! The LEDs are not quite as diffuse a light as the grain of wheat bulbs, but they do a respectable job of indicating that the amplifier is turned on. 

It might be nice to get some more even illumination, but I'm pretty satisfied. Perhaps I might add some reflection inside the meters next time I need to open the box -- which hopefully, won't be for a while. Maybe in another five or six years.