Tuesday, December 29, 2020

KK1L Antenna Switch Installed

Antenna selection panel at eye level in station.
Last month, I built the KK1L 2x6 Antenna switch. But to use it in my station, I needed to be able to select the right antennas.

I found a small metal box and a 1 pole-7 way switch in my junk box. A couple of switches, an LED and a 15 volt DC wall-wart, and I was done.

On the right is a power switch with an LED. The center switch selects the antenna relay, or none at all (it has seven selections, and there are only six relays). 

The small switch on the left controls the shunt feed matching network

It works great, and has completely replaced the 6-position B&W switch I've been using for years. In fact, I had to remove the old B&W switch from the operating position because of the habit of looking at it. 

Monday, December 28, 2020

A3S/A743 Refurbished - Rotating Once Again

A3S/A743 QRV @ 15m
Since I took it down back in October, the A3S/A743 is once again proudly back at the top of my tower. It's been something of a long ordeal.

Refurbishing the antenna was delayed when I had to wait eight weeks to get traps out of MFJ -- they, like many companies have been greatly affected by the Coronavirus. Indeed, their biggest problem is getting parts from their suppliers, who are likewise affected.

Even after getting the parts, I had a lot of trouble tuning the A3S somewhere close to the bands. That required a lot of jockeying on the tower. It did give me a lot of time at the top of the tower, something that is always a confidence-builder.

I had a little trouble with the rotator yesterday -- one of the connector lugs came off the pigtail. This meant that while the rotator was in place, it wouldn't turn. I was tired from the long climb yesterday, and fixed it today. 

The good news is the antenna seems to be working correctly. I haven't worked a lot with it, but I'm sure I'll get a chance during the RTTY Roundup this next weekend. 

Hopefully, this antenna should serve me well for many years to come -- the initial installation worked for over fifteen years. Fifteen more would be fine by me.

Next project will be to fix the WARC trap dipole and put it back up.


Sunday, December 27, 2020

Re-writing the K9AY Controller

 I was quite happy earlier this month to get the K9AY Loop Controller working. After using it in the ARRL 160m contest, I decided I needed to make some changes to the firmware.

That presented a problem. You see, while Microchip has made some excellent developer tools available for their PIC series of microcontrollers, like all software, it is updated from time to time, and things change.

When I used MPLAB X three years ago to write the controller firmware, I used the PIC assembly language tool MPASM. That was with version 3 of MPLAB X. I recently updated to version 5 of MPLAB X, and MPASM was no longer supported. Instead the new assembly tool was called pic-as. And, of course, it was syntactically different than the old MPASM.

I made an attempt to edit my existing code into something acceptable to pic-as. While I got it to build, I found it didn't run correctly. Rather than try to debug, I figured it might be easier to start over.

Microchip has a good C compiler. I decided to start there. I'm well experienced with C, but this left open a lot of questions. The PIC has a number of configuration registers that must be set at startup. How does one do that with C? 

This actually turned out to be very easy. Microchip has a tool called the MPLAB Code Configurator (MCC). It provides a number of graphical tools and wizards that specify the chip configuration, down to the pin assignments and interrupts. MCC then generates the appropriate C code. This is a good thing. One of the hard parts of working with the PIC is figuring out how to set all the internal registers. MCC does this part for you.

My second question had to do with interrupts. How do we process interrupts in a C program? This also turned out to be easy, because MCC generates code to handle interrupts, too. When properly configured in MCC, one need only write a simple void function to process the interrupt. My controller uses a timer interrupt every 2 ms to check the state of all the buttons and update the LEDs and relays appropriately.

Re-writing the controller program in C ended up taking less time than figuring out the assembler syntax changes between MPASM and pic-as. 

And the best part is, it worked! 

Saturday, December 19, 2020

Tuning the A3S/A743

Adjusted A3S/A743, ready for rotator.
After adjusting the A3S/A743 on the ground and getting it back on the tower, I was very disappointed to find the SWR dips for each of 10, 15, 20 and 40m were all outside the band. They were all too low. This surprised me. When I measured the antenna with the beam facing upward, the dips were very close to the band. Now that the antenna was on the tower, it was going to be more difficult to adjust.

Rick Dougherty, NQ4I, gave me an important tip. Always measure horizontal antennas horizontally. Don't attempt to make measurements with the antenna vertical. With the antenna 6-8 feet off the ground, you can get a good sense of the measurements, knowing that the antenna will rise in frequency as it moves away from the ground. Generally by about 100-300 kHz at the 30 or 40 foot level. As you move further from the ground, the effect lessons. 

Rick knows his stuff -- he built a superstation in Griffin, GA, and has experienced this phenomena putting up dozens of antennas. 

OK, I didn't follow Rick's belated but sage advice - what should I do now? I didn't want to take the antenna off the tower again, it was a lot of trouble to get it up there in the first place. I decided I could make adjustments similar to how I added the A743 option originally - by tipping the Driven Element (DE) vertically and climbing down the tower.

On the tower adjusting
the now vertical DE.
One the first climb to make adjustments, I could already see part of the problem - some of the DE joints had slipped outward while the antenna was waiting to be installed pointed vertically. The extra weight of the A743 parts probably had something to do with this. 

Loosening the U-bolts for the DE and the support mast, the DE tipped over easily and I was able to climb down the tower and adjust. I had to make some of the adjustments somewhat blind, since I could not easily put a measuring tape against the elements. 

I ended up with the 10m traps out about 83.5" (A), the 10 and 15m traps spaced as 6" (B), and the 15 and 20m traps at 18.75" (C) -- this was the lower limit, since the tubing ends were contacting each other inside the support tube. the 40m portion I extended to about 66". These measurements are for each side of the DE.

This took two climbs, and ended up with the 10, 15 and 40m SWR curves well centered in the bands, and 20m right at the bottom of the band. This isn't perfect, but it is usable. Note I did not make any adjustments to the Reflector or Director, as they are well out of reach.

Next time I set up an A3S/A743, I think I will adjust the 10 and 15m portions to the MID-band settings, and split the MID and CW settings for 20 and 40m. That's roughly where I ended up anyway. 

I'll also consider replacing a lot of those stainless steel worm clamps. After being out in the weather for 30 years, a few of them would not tighten the way I would like. 

The A3S/A743 should be ready to go after one more climb to raise the antenna and install the rotator. I also plan to tweak the support mast a bit higher to keep water from accumulating in the 20m (TK) traps, since that's likely how they failed in the first place. 



Wednesday, December 16, 2020

4U1UN (and 4U75UN)

A little more than a year ago, I was looking at the Most Wanted list in ClubLog. I noticed that the United Nations HQ entity was number 30 on the list. In all my years of ham radio, I had never heard them on the air, much less worked them. I wondered if I'd ever have the opportunity to work them at all.

Well, the 4U1UN club has been busy, and late fall 2019, they finished their installation which allows them to remotely operate a transceiver near the top of the UN towers from a room on the ground floor of the building. Since that time, they have been sporadically active. 

I don't know what the rules are for operating 4U1UN, but the station has been active at least some time every month during the past year. They have gone from an entity you'd wonder if you'd ever work, to one that can easily be worked by anyone with a bit of determination.

Over the past year, I've kept a running DX Watch query going to see when they were on the air, and worked them any time I could hear them. They've been easy to work even with compromise antennas.

They confused me in September, as I thought they had gone silent. No, they just switched callsigns. They are celebrating 75 years of the UN with the call 4U75UN. There's a special certificate for working them. They should continue with that call until December 31st.

They'd be pretty easy from the USA on 160m, but I don't believe anyone has ever operated on that band. I doubt they have an antenna, and I head the noise level in NYC is extraordinarily high.

They QSL promptly through LoTW (be patient, it may take a week or two to be uploaded). I've gone from wondering if I'd ever work them to having them confirmed on nine bands (80m-6m) and three modes: CW, Phone and Digital. 

Keep an eye peeled on the spotting networks, and perhaps you can work a new one.

Wednesday, December 2, 2020

K9AY Controller and Antenna

K9AY Controller at operating position.
In 2007, I put up some K9AY loops. They were a little less than half-sized, about 33 feet in each loop. They worked pretty well on 80 and 40m, although they were a little weak on 160m. After about three years, they stopped working. At the time, I was using a rotary switch to change directions, but I really wanted a push-button controller.

In 2015, I designed a controlled based on a 74LS175 Quad D-type flip-flip. It was pretty simple in concept, but, it didn't work. The bounces from the switches changed directions rather randomly.

Which lead me to write this article, about a solution - using a PIC micro-controller to solve the bouncing switch problem. 

I built that prototype, and wrote about it three years ago. One problem was that the wiring appeared flaky, it wasn't always dependably switching. I figured I needed to design a PC board. 

While I've been working on that, I had a thought a couple of weeks ago -- maybe I could piggyback a second piece of perfboard to my prototype and keep the board from flexing, and that would avoid the flaky wiring. Easy enough to try.

Sure enough,  doubling up the perfboard helped. I determined that the wiring wasn't that flaky. Part of the problem was that the NW and SW switches and LEDs were reversed. Pressing the SW button sent the NW voltage, and vice versa. 

With that fixed, I couldn't find any reason not to put the K9AY back up. I used 42 feet of wire in each loop. This is a good compromise length for 160, 80 and 40m. 

Some on the air testing shows that it works pretty much as expected, and the push-buttons make it really easy to change directions. 


Monday, November 30, 2020

Schematic for the Little 40m Receiver

I'll admit that it has taken far too long for me to publish this schematic. I wrote the original article about a small solid state receiver in January of 2009. I promised a schematic, but I never published it. 

The original sketches of the schematic are too embarrassing to publish directly, so I had to re-draw the schematic neatly.  I started on it last summer, but I finally finished it very recently. 

Just click on the image to the right. 

A couple of notes on the schematic.

The IF Out label on the right side of the page connects to the IF Out label in the lower middle of the drawing. 

I didn't have a 7808, so I used a 7805 regulator with a stack of four 1N4001 diodes that gives about a 7.5 volt supply. You could use a 7808. In fact, I purchased one a while ago, but I've never modified the rig to use it.

You might have to adjust the values in the S-meter circuit if your meter movement isn't a 600-ohm 250 uA device like I used.

I don't have a block diagram, but the sections are straightforward:

  • SA612 Mixer / Oscillator
  • Crystal ladder filter
  • MC1350 IF Amplifier
  • SA612 Product Detector / Oscillator
  • LM 386 AF Amplifier
  • LM 358 AGC Amplifier / S-meter driver
  • 2N3906 Mute driver

I built the rig in stages, starting with the AF Amplifier, then the Product Detector, IF Amplifier, Crystal Ladder filter, Mixer. I then added the AGC Amplifier and the S-meter driver, and finally the mute driver. 

The Crystal Ladder filter is based on 4.915 MHz crystals. The Oscillator is 7 MHz above that, nominally tuning 11.915-12.065 MHz. I've been thinking about adding a switch with a different oscillator and bandpass coil to cover 30m.