Adding to the air variable capacitor collection

While exploring the component bins, I came across a couple of air variable capacitors, one of which was still in the box and didn’t look like it had ever been used. A Hammarlund APC-50-B air padding capacitor, complete with knob. Capacitance range is 3.9-50 pF. Looks in really good condition and turns pretty smoothly.

Hammarlund air variable capacitor
Hammarlund air variable capacitor
Hammarlund air variable capacitor
Hammarlund air variable capacitor

The other air variable capacitor I found is a little more anonymous but also looked like it hadn’t been used before. One of the rotor plates at the very back was slightly bent causing it to make contact with a stator plate. Aside from that it seems in good condition and turns pretty well.

Air variable capacitor
Air variable capacitor

I’ll have to see if I can straighten out that one plate. Would be cool to use it in something.

Component gold mine

I had the fortune of acquiring a veritable gold mine of electrical components tonight. 5 parts bins worth of resistors, capacitors, transistors, switches, ICs and other miscellaneous parts. Most everything is pretty organized so there’s really no sorting that needs to be done. Most of the components were pretty easily identifiable, but there were others that I had never seen before and have no idea what they do.

Components!
Components!

A lot of items are pretty old, but have never been used. One whole parts bin is just resistors, containing regular carbon film resistors, a few big power resistors and some carbon composition resistors, which you don’t see a whole lot of these days.

Resistor bins
Resistor bins

The next bin contains transistors and a few other miscellaneous parts. Some of the are unidentifiable other than their form factor and others have never been used.

Transistors
Transistors

The third bin is kind of a mish-mash of parts – pre-wound coils, resistors, things that looked like variable capacitors. Quite a few components in this bin that I have never seen before.

Miscellaneous parts
Miscellaneous parts

The capacitors bin contains some interesting capacitors. Lots of electrolytic caps, and some really big caps in the mF range that I guess could be used for power filtering.

Capacitor bin
Capacitor bin

The fifth bin contained all sorts of ICs and EEPROMS. I’m not sure how much of what’s in here will be useful, but I’ll need to try to identify them first. There are even a bunch of Z80 CPU chips in here. I wonder if I could do anything with them.

ICs and EEPROMS
ICs and EEPROMS

I’m going to need more shelf space.

Reworking the sound card interface

Now that the sound card interface finally seems to be working ok, I’m contemplating the merits of tearing it apart and playing with the component layout to make things more compact. It’s not exactly sprawling across the perfboard, but the component spacing can be reduced and there are a few places where I see that I can compress things a little more by changing the arrangement of some of the components. It’s certainly functional the way it is, but the mildly obssessive tweaker in me wants to keep optimizing the component placement for minimum size.

I should probably spend some more time playing with it before I take it apart.

Sound card interface success!

After some troubleshooting and help from Jason/NT7S and Robert/AK6L, the problem turned out to be the transformers. Apparently they were step up/step down transformers and not the 1:1 transformers I really needed. Ordered some new transformers from Mouser and put them on when they arrived.

Still ran into problems getting the radio to transmit a signal, but after a closer examination of the board, I discovered I had connected one of my ground wires to the wrong spot so the audio signal to the radio ended up going to ground instead of the radio. Duh.

Fixed that, connected everything up and was able to make my first digimode QSO using the new interface with KC8MGD up in Michigan. From where he was, I had a good signal and wasn’t splattering across the band, so that’s a good sign.

So excited that I got this working! Now I can work on either coming up with an enclosure for this prototype board or build v0.3 and try to make it more compact. I have two more transformers that I can use to build a second interface, which I might save for later once I’m finished messing with this prototype board. I think I’ll try to find some PS2/mini-DIN6 sockets so that I can plug/unplug cables to it and get a little more flexibility about what I can plug into the board.

A QRP dummy load

Every ham needs a dummy load, right? I’ve been wanting to build a small little dummy load for QRP for a while so it became one of my day-off projects today. The dummy load kit from Hendricks QRP Kits served as my model for this build.

I emptied my inventory of 1kΩ 1/2W resistors and scrounged up 5 more 1kΩ 1/4W resistors out of the bag of goodies from Jason/NT7S (saved me a trip to Radio Shack). A total of 20 resistors went into the dummy load: 15 1/2W and 5 1/4W for a total theoretical power dissipation of 8.25W.

The platform for my dummy load is an Adafruit quarter size Perma-Proto board which I’ve really enjoyed working with. Here it is with half of the resistors placed on the board, but not soldered in yet.

Dummy load half complete
Dummy load half complete

Just under 100Ω with half the resistors in, so my layout is working.

Almost 100 ohms!
Almost 100 ohms!

It was a bit of a squeeze to get those 1/2W resistors in, but it worked. The 1/4W resistors fit easier into each row.

Tight fit
Tight fit

With everything soldered into place, I measure just under 50Ω. Pretty good.

Pretty close to 50 ohms
Pretty close to 50 ohms

The Hendricks dummy load also lets you use measure power output using a volt meter so I added that part in as well. A 1N5711 diode (again from the bag of goodies from Jason), a 10 nF cap and some header pins finishes the dummy load.

Completed dummy load
Completed dummy load

The two pins at the lower right of the board are for the connection to the radio, and the single pin on the left side is the voltage/power measurement point. All that remains now is to find an enclosure to put it in and add a convenient way to connect to the radio and access the measuring points.