Loot from NEARfest

The power supplies at the right front are Tektronix type 125 and 128. They seem to function fine. I will be using them for my tube circuit experiments since they both provide nice B+ and filament voltages. The big one was $20. The small one was $15.

The radios in the rear of the picture are functional Heathkit AR-3 receivers. They have a little bit of hum. My plan was to part them out. If they’re common on eBay, I will part them out. Since they are from kit, the sockets aren’t riveted in, they’re screwed in. They both have nice transformers. The tuning and bandspread both have 5 to 1 gear reduction. I paid $40 for both. I think the parts inside may be worth more then I paid.

The odds and ends on the blue pad are some trimmer capacitors, some tube sockets, and a couple of banana plugs. I used one to fix my Signal Corps Frequency Meter which was missing one.

A friend of mine owns a Canada Marconi CP34 HF radio. It is capable of working from 2 to 18 mhz according to the data sheets I’ve seen.

The old beat-up pack the CP34 resides in

Nice looking radio eh?

My next project was a WWII Signal Corps Frequency Meter that I picked up at a local antique shop. I finally scraped together a power supply which was sufficient to test it. Amazingly, it works. It seems to have gone through a process called “tropicalization”. The inside looks like it came from the factory yesterday. The outside is a bit more beat up.

"Frequency Meter, 80-1000 Megacycles. 1 each."

Wow, the schematic is right inside!

The item badge

Really clean inside.

My last project was a one tube regenerative receiver. I’d present a schematic, but I sort of mashed several schematics I found on the web with the available parts I had in the junk box and came up with it. I attempted ugly construction with the tube socket, and it came out rather well. Basically, I cut out a square of PC board, scored the board to divide it up in eight equal sections, and soldered each pin of the tube socket to a section. It seems pretty sturdy. I scored the other PC board to make pads for the various connection points in the circuit. That worked out pretty well too. If I continue to make tube projects, I’ll probably build a tube breadboard to make it easier. The wiring of the coils matters a lot. If you build one and it fails to regenerate, switch the connections of one of the coils.

Labels are for the weak. The big knob is main tuning. Lower left is regeneration. Upper left is antenna tuning.

ugly, ugly construction. Note the pcb the tube is attached to.

The “power supply” consists of 10 9v batteries in series for the plate and 4 AA’s for the filament. This tube project was a lot of fun. The audio transformer doesn’t match to my headphones well. I may remove it and see how it sounds.

Butterworth Low Pass 2mhz

I used a tutorial to transform the schematic to a net list with gnetlist. The schematic includes all of the values needed to properly import into a net list. The command I used on the finished and saved schematic was:

gnetlist -g spice -o filter.net filter.sch

Then I called ngspice, “ngspice filter.net”

and from the ngspice command line, I setup a frequency sweep from 0.1 hz to 4 mhz (I can’t figure out the magic to do mhz in ngspice, so I used 4000 khz):

> ac lin 1000 0.1 4000khz
> plot n1

The result of the (voltage) plot is:

voltage plot of low pass filter

I then attempted a plot of power, which I am probably getting wrong. I’m using the formula v(at n1) / 50 (the termination resistance) * v (at n1 again). Below is the plot:

power plot of butterworth. Clearly wrong.

I’m doing something(s) wrong, but it’s a fun learning experience. Once I sort out my mistakes, I’ll add a post with some guidance on simulating a filter from a gschem schematic through the ngspice machinations.

The seal is broken.

Unboxed, sitting atop a sheet of copper clad.

It came with all of the basic cables and adaptors needed to hook up to the input and tracking generator. It also came with an antenna, and a long wire with alligator clips on both ends… *shrug*. I hooked up the reference oscillator in my frequency counter to the spectrum analyser:

Wow! Harmonics.

The center vertical line is 10 mhz. Each vertical division is 10 mhz. The harmonics on my reference oscillator are prominent. I checked the reference oscillator against the frequency counter to make sure something wasn’t wrong:

Well, the counter shows 10 mhz.

Then I checked the wave form on my ancient Tektronix 465 oscilloscope:

And that wave form explains the harmonics.

The analyser seems to be fairly accurate. I’ve never used a tracking generator before, so I figured I’d give that a go. I attached some probes to a crude low-pass and high pass filter made from one capacitor. One probe went to the tracking generator. The other went to the analyser input. Below are the results:

Low-pass

High-pass

The tracking generator is an oscillator which tracks the sweep of the spectrum analyser. This means we’re seeing a frequency response graph on the analyser. This is wicked nice. I didn’t have a tracking generator on my spectrum analyser when I was a Marine (fixing RADAR), or I would have used it more.

What’s the verdict on this piece of equipment? Thumbs up at this point, especially with the tracking generator. If you’re a ham who likes RF electronics, you should consider saving your pennies and buying one. The AT6011 set me back about $1300 from a US seller on E-Bay. I could have gotten it for a lot less straight from China, but I would have had to wait longer, especially if there was some problem with customs.

For good measure, below is the package of toroids I got from the Toroid King:

Toroids! Woohoo!

ugly hartley but it works

One of my projects which is moving along very slowly is building a magnetic loop antenna. One of the problems is that the trombone capacitor I want to build is difficult to find parts for. I finally found some appropriate parts at the big home improvement center near by. What I really needed was a pipe which fits inside a dielectric which fits inside another pipe. The picture attempts to show some part numbers of the stuff I found in case someone else is having similar difficulties. The store sells 2 foot lengths of these items, so I don’t need to over-buy. The pipes are; 3/4 inch type M copper pipe, 1/2″ ID poly pipe (unidentified plastic), and 1/2″ type L copper pipe inside that. I have no idea what type of plastic “poly pipe” is, but it doesn’t appear to be PVC. I slid the pipes all together and the capacitance was about 370pf, so it must have a really good dielectric constant. I’ll have to find the strength next.

What is "poly pipe", anyway?

I found possibly the best appointed antique shop in my area called “Paul Martin Antiques” in Haverhill, MA. They have a huge warehouse with three floors of stuff. I bought an unidentified FADA Radio tube AM/shortwave there. After fixing some bad connections and replacing a capacitor, the thing works fine. It’s also a beautiful radio. My original plan was to part it out, but I can’t bring myself to wreck such a nice looking radio. This looks a lot like the Fada L67T but not quite. I believe it’s from around 1939 or 1940.

Art Deco... Nice.

Not so art deco, but still nice.

I realised recently that I never built a crystal radio as a kid, and not since then either. I remember my dad and grandfather talking about them a lot. It’s a simple project, so I built one this past weekend. The coil form was a piece of 2″ PVC pipe. The wire was 26 awg magnet wire. The diode was an old germanium diode I found among my grandfather’s parts, but a modern silicon diode may work fine too. The air variable capacitor is from an old TV tuner. It’s not needed, but can give you some extra flexibility in tuning. If you don’t have an air variable, you can steal the plastic variable cap from a cheap AM/FM radio. As a side note, I couldn’t get any kind of speaker to work, even the smallest peizo element didn’t produce any sound. A cheap ear phone worked fine though. The only station I could pick up was the spanish station a few miles away.

Layout. The other side of the board is a ground plane.

Schematic. I really need to get more symbols.

Alternative variable capacitor.

My last project was getting my G5RV lite antenna off the privacy fence and up higher in the air. My “delivery system” was a slingshot, a fishing pole, and some dacron cord. The transmission line goes up to the peak of the roof. The ends of the antenna go to nearby trees now. The improvement in reception is amazing. It is also much easier to tune the antenna. I just need to get up the gumption to transmit more then, “antenna test, AB1PX”.

antenna deployment system.

If you squint, you can almost see the wires of the antenna.

All of these sites, and other sites which involve antenna research recommend that you have an antenna analyser so you can measure the performance of your antenna. One of the simpler ones, called the ‘tenna dipper, uses a simple oscillator, an impedance bridge, and an LED to tell you what frequency the antenna is resonant at. If you’re willing to take on a more complex project, ZL2PD describes an analog and a digital version of an antenna analyser. The digital one uses an 87C552 micro-controller, which I’m not at all familiar with. If I attempt that project, I’ll probably try to convert it to something Atmel flavored.

This line of study lead me to start building oscillators again because I really would like to have a small signal generator. One of the more interesting ones for its simplicity is described by Ashhar Farhan. VU2ESE from India. His site is a wealth of information on homebrewing on a tight budget. He is the designer of the BITX 20 20 meter transceiver, which is popular in the QRP (low power) crowd. I made a modification or two to his signal generator design to match the parts I have and soldered it together, ugly style. Below is the result.

ugly Hartley based VFO

Depending on the inductor, I can get a fairly broad range of clean looking frequencies. I still have a couple of stages to complete, and I have to put in a switch to move from band to band, but it’s looking pretty good.  This may not even be my final stab at a general purpose signal generator, but it sure is a lot of fun building this stuff.