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. 

Friday, November 27, 2020

Improving the Shack Desk

Finished, standing against wall.
Thirty-five years ago, I asked my father-in-law to be for advice on lumber for an operating desk. He suggested I find a solid core door. I bought an 80x30" door and have used as my operating desk since. It has held up very well, surviving two moves, and three re-finishings. 

Originally, I bought the door and two small two-drawer filing cabinets. With the cabinets on either side of the door, the result was a very stable platform, strong enough for me to stand on. 

However, it wasn't the most perfect arrangement, as I wrote four years ago. Adding a 1/4" radius edge to the front, was a  dramatic improvement, mainly because the operating surface was just too tall. 

This year during Contest University,  Doug Grant K1DG gave a talk on Optimizing Your Station For Contest Operations. One of the salient points in his talk was that the operating desk needed to be at the right height for the operator. 

The door across the filing cabinets was 30 7/8" off the floor. Doug's talk indicates that the optimum for my height should be closer to 28 1/2". The micro-shack desk was about 30", and the luncheon table that serves as my workbench on the other side of the shack is 29" off the floor. What I needed were shorter supports. 

Box frame.
It is not possible to make the filing cabinets shorter, so I needed something else. It had to be strong -- the door itself is heavy, and the linear amplifier and other bits of equipment add up. I also needed to be able to get it through the door to my 6x15 foot room that is the shack. 

What I came up with is a set of box frames aligned by some cross members. The box frame is a "U" shape made out of 2x4s, capped with a 30" 1x4. A couple of 1x4s act as a shear web to keep the box frame square. It's held together with glue and screws. Three 58" 1x4s serve as the cross members. The cross members are each in a different plane, and give plenty of room for a chair to roll underneath.

Finished stand.
It's sufficiently strong that I can easily sit or stand on it.

And, here's the best part. It's on six castors, so I can move it away from the wall to get behind the desk to wire things. No more having to do my rig wiring blind!

I was worried that the tile floor might make it hard to roll the desk, but it's actually pretty easy. 

This design is pretty simple, and it came together quickly. The 30" 1x4s on top have a single wood screw on each end into the door, so the surface can't slide around. And the cross members are held on only with screws, so they can be removed when in order to get the whole assembly out of the shack.

Voila! Away from wall.
The door already has a couple of power strips mounted on the underside, which makes plugging in equipment that much easier. 

Based on what I was thinking four years ago, the next improvement will be the equipment hutch that goes on the desk. That's also a relic from 30+ years ago. I've already purchased the lumber for that project....

Monday, November 23, 2020

KK1L 2x6 Antenna Switch

Completed relay unit.
I've been meaning to incorporate an automatic antenna switch in my shack for years. Indeed, I bought 20 RTB14012F relays 11 years ago just for such a project (and they were $2 each back then!). But, I'd never gotten around to designing and building one.

Somehow, I ran across a link to KK1L's 2x6 Antenna Switch board, and looked at the Relay Unit. I loved the elegance of the design, and the board was a beauty. I wrote to Ron asking him about the pricing for the board, and if my RTB14012F relays would fit.

Ron answered me promptly. He quoted me a price of $33 for each board, and he could mail up to five in a priority envelope for $7.15. He also informed me that my relays wouldn't fit -- that the pin spacing was incorrect. I was disappointed and set aside the idea for a couple of months. 

Board top.

While I was working on another order on, I couldn't get the KK1L relay unit board out of my mind, and checked out adding eighteen RTD14012 relays to my order. I decided I couldn't possibly do any better than Ron's design, so I wrote him back and ordered a board. I also used Ron's project, which included parts like the screw terminals, chassis, diodes, capacitors and resistors.

Electrically, this is a very simple design. There are six switching cells each with three relays, two diodes, two capacitors and one resistor. The "A" ports activate two relays, the "B" ports activate only one. 

Board bottom.

I had a lot of parts already. Besides the board, I ordered the relays, chassis, and screw terminals. I already had the SO-239 connectors, diodes, capacitors and some 1/2 watt 50-ohm resistors. 

[ UPDATE: I recommend using the 50 watt resistors specified by KK1L instead ]

Building the board was easy. The diodes and capacitors go in first, because they are under the relays. I used some 0.1 uF multi-layer ceramic caps I had on hand. These were smaller than the diodes and laid flat against the board. Relays went in next, and the screw terminals. I put the resistors in last. Then I had to remove them and put them in again, because I ran them through the wrong side of the board.

Now came the hard step - drilling the chassis. I'll be the first to admit I'm not a master machinist. I have a drill press, which helps. Precisely aligning all the holes necessary for the eight SO-239 jacks to pass perfectly through that beautiful circuit board was intimidating. I decided I only needed two screws on each jack to pass through the board. That limited the project to 24 holes, plus a couple of mounting holes, and a cable hole - 27 in all. 

I started with the printed template, but found that it didn't align perfectly with my board. I ended up using the board itself as a template and marked each hole on the chassis with a sharpie. 

The instructions say to use #6 hardware on the SO-239 jacks, but I have never seen a SO-239 that would pass #6 hardware. I used #4 hardware instead. I drilled all the holes with a #27 drill in any case, which gave me some leeway. The center holes were a little harder, I widened the pilot holes with two different drill sizes, then used a step drill to get to the final size. 

Chassis ready to install  board.
The instructions call for mounting the SO-239 jacks inside the chassis. I knew I had some hole alignment problems, so I opted to mount them outside the chassis. The disadvantage in doing this is that you can't remove the board from the chassis without unsoldering the antenna connections. But, it would hide all my ugly machining.

I used two short and two long screws for the SO-239s. For the longer screws, I used a jam nut and a couple of washers below the board, to give enough clearance from the chassis. I drilled the holes for the short screws after mounting the jacks and aligning to the board. I decided I only need two of the four mounting holes -- the two that were opposite the A and B connectors. The other end of the board is supported well by the three SO-239 jacks.

After everything was drilled and deburred, I took everything off the chassis and gave it a quick buffing with a wire wheel. This gives the chassis a little bit of sheen and hides any large scratches. The until will eventually be mounted on the wall as part of the single-point ground, so it didn't have to look too pretty.

Fully installed.
Once I had the board mounted, I realized I made a mistake. I mounted the screw terminals so the holes are facing the chassis (outside), which makes them difficult to access. Unsoldering would be a pain, so I decided I could live with the error. 

I did a little bit of testing. First test is to see that all antenna points read 50 ohms. Then I checked to see that all the relays activated correctly. Everything worked great. 

Next step will be to incorporate it into my station.

Sunday, November 8, 2020

K60XV - The Hard Way.

K60XV Built and Installed
Last September, I was somewhat distressed to learn that Elecraft was no longer offering the K60XV -- the 60m and transverter interface for the K2 transceiver. I had always planned to purchase this kit, because I intended to build a 6m transverter. 

According to Elecraft, the kit was discontinued because they no longer had a source for the bottom adjusting variable capacitors at C1 and C2. While I understood, I was still disappointed. 

While reading the Elecraft mailing list, I stumbled on a message from a fellow named Chuck. He said the managed to obtain the parts for a K60XV and put it together. I followed up with an e-mail, and Chuck indicated that he obtained the PC board, processor and a few other parts.

K60XV "Kit" - a collection of parts
I wrote to the Elecraft parts department, to check if certain parts were still available. I was delighted to find the K60XV PC Board and processed were still available in limited quantities. So, I put together an order:

  • E100193 - K60XV, PCB $24.93
  • E610018 - MCU, K60XV $6.60
  • E640001 - Relay DPDT LATCHING $2.60
  • E620005 - 8 pin FEMALE, 0.1LS $3.65
  • E620009 - 3 pin FEMALE, 0.1LS $2.08
  • E620076 - 8 pin MALE, 0.1LS, Elevated $2.49
  • E620077 - 3 pin MALE, 0.1LS, Elevated $0.92
  • E700090 - Nylon Stndff,3/16D,9/16L, Hex $1.18
These were all parts that were either exclusively from Elecraft, or those that I had trouble finding elsewhere.

I also ordered:
  • FWKAT100 - KAT100 F/W Upgrade to 1.05 $49.95
  • E700002 - TO220 Thermal Insulator, Adh $1.96
My KAT100 was older, and I needed the newer firmware for it to work on 60m. Installing the K60XV requires you to remove the heatsink panel, and I wanted to make sure I didn't destroy the thermal insulating pads.

For the rest of my parts, I combed through my junk box and also placed an order with Mouser. I didn't have any difficulty finding the rest of these parts. 

Board with parts in place.
The K60XV is not a complex option. If you've built the KSB2, this is piece of cake. The board goes together easily. I skipped installing C1 and C2. I had a couple of top adjusting 7-40 pF caps I planned to use. I waited to see what kind of clearance was available.

The main RF board requires a couple of modifications in order for the K60XV to function. This is probably the hardest part of installing this option.

If you were lucky enough to have a serial number of 3000 or higher, this job is much easier. For those of us with Rev A RF Boards, it's a little more difficult. 

D19 and D20 install.
The Rev A boards don't have a place for D19 or D20, so you have to mount them beneath the RF board. 

Hooking up the RF connection is a little picky as well. Take time when prepping the coaxial cable. Some folks have used heat shrink on both ends of the coax, but I didn't find that necessary.

I ended up being pretty happy with the RF board mods. 

RF line install finished.

These RF Board modifications require the heat sink panel to be removed. My early K2 (from 2002) didn't have the transverter holes on the heat sink panel, so I replaced it with the newer one. This requires the thermal insulating pads and the serial number sticker. I was actually a little nervous about this. I purchased spare pads, but I only had one shot at the sticker.

I shouldn't have been nervous. With a sharp knife, the sticker came off easily and transferred to the new panel with ease. The thermal insulating pads came off easily as well, and I had no trouble moving them.

I fitted the K60XV board and considered my options for installing C1 and C2. I considered installing my caps upside-down using short lengths of wire. However, there appeared to be plenty of clearance between the top of the K60XV board and the KPA100 shield. As I measured it, there was about 2mm of space between the top-mounted capacitors and the shield. So, I opted to mount them on top of the board. My caps were a perfect fit.

Rear view of the finished installation. Looks great.
Adjustment was easy. Set the D19 menu to Y, then adjust the C1 and C2 caps to peak 60m. 

Buttoning it all up again, I'm very pleased with the result. I don't know how long Elecraft's supply of parts will last, but if you really want a K60XV, you should inquire with Elecraft's parts department and see if they still have these parts available.

Sunday, November 1, 2020

Rebuilding the A3S/A743

I've had the A3S/A743 down for several weeks now. I've gotten it mostly rebuilt, but I'm waiting on parts. More about that in a moment. 

I wrote previously about my inspection of the traps. The 20m TK traps are completely toast. But the TA (10m), TB and TC (15m) traps appeared to be fine. All the plastic end caps, however, were toast.

This particular A3S/A743 has been up for a while. I originally purchases the A3S in 1991. It spent three years in the air at the old Stone Mountain QTH, then several years in my basement in Gwinnett. Then it spend a couple of years on W1YM's tower while he was waiting for his Skyhawk to be delivered. And nineteen years at the Gwinnett QTH. All told, that's twenty-four years exposed to the elements. The A743 40m option has only been up fifteen years. 

A few years ago, I bought another A3S at a hamfest for $100. Such a deal! This unit was manufactured in 2007 and does not appear to have been outside for any length of time. The plastic end caps on the traps look practically new.

During the rebuild, I decided to use the TA, TB, and TC traps from Cushcraft #2 on the Cushcraft #1 tubing and vice versa. Cushcraft #2 isn't going up any time soon (perhaps when I move to another QTH and can build a 70 foot / 35 foot stack). I figured I would use the least weathered traps on the antenna that I'll be using. 

I used No-Al-Ox liberally when I assembled the A3S nearly twenty years ago. After nineteen years in the weather, much of the original application had evaporated, but the sections came apart easily after unclamping. The traps from Cushcraft #2 had never seen a drop of No-Al-Ox, unfortunately. So, as I intermixed the parts, I made sure I applied some to every joint. 

I ordered all new trap end caps, boom and element end caps from MFJ, along with new TK traps. Laird communications sold off Cushcraft several years ago to MFJ. I was happy that parts were still available. However, the ordering system left much to be desired. MFJ is in the middle of a web site re-design, and there's no way at present to order individual parts. Their older web site would list parts on the same page as the product, and you could click through to the parts link to order each one. Why they would switch to a new web site that doesn't have this capability is beyond me. 

A call MFJ with all the proper part numbers, I ordered everything pretty easily. Then it got weird. The gentleman on the phone didn't tell me the total of my order, he just guessed it would be $130-140, which is about what I expected. He estimated my order would ship in two weeks, and that I should see an order confirmation email and another email when the order shipped. All good, I thought.

Then I noticed my credit card was charged $169.90 almost immediately after I got off the phone. I waited a few days, but I received neither a order confirmation or shipping confirmation email.

This is not right. Indeed, this may be illegal. You're not supposed to charge someone for an order unless their goods have shipped. That's how it is supposed to work. I called and asked about it, and they said they corrected my email address and I should get a confirmation. My order hadn't shipped yet, because the TK traps needed to be manufactured, and that would take at least two weeks. Fine. But, then I didn't receive any order confirmation emails. A week after my original order, I called again, had my email address corrected again, and asked that a confirmation email be sent. This time, I received it. At that time, I was told my order would ship in ten days. 

And, sure enough, ten days later, they shipped something. I was surprised when I received a very small box -- clearly not large enough to contain the two TK traps. Opening it, I found my entire order of plastic end caps. But no traps. 

It's now been four weeks since I placed my order, and no indication they are shipping the traps that take them two weeks to manufacture. There have been at least two good weekends for putting the tribander back on the tower, but without traps, I can't finish the assembly.

Keep your fingers crossed I actually see these traps sometime soon.