Click on the image for a better view
The timing (1895) and the context (railroad telegraphy) seem about right. But other etymologies are out there. Lexicographer Steve Silverman KB3SII is on the case. What do you guys think? Are the roots of "ham" radio in railroad telegraphy?
Thank God for the Wayback machine. For a moment I feared that this article about Farhan's DC-40 receiver had been lost. (Phonestack is now some Vietnamese vendor. ) But the WayBack Machine archive came through for us.
https://web.archive.org/web/20171109081542/http://www.phonestack.com/farhan/dc40.html
Farhan's receiver has been covered on this blog before, but it is especially relevant for us now that we are immersed in our own direct conversion receiver project. Farhan was working with his niece, who was a student. We are working with high school students.
I really like Farhan's blow-by-blow description of the build. There are raw emotions here: He speaks of his hatred of LM-386s, and of how he thought of using the copper clad board as a projectile. His niece wonders about the possibility of evil spirits in the receiver. The battle against AM breakthrough is very familiar. (I like the RF choke idea.) You won't find candor like this in QST or QEX.
Farhan's DC-40 project was one of the inspirations for our high school effort. In fact, when we first went to the school, I left behind a direct conversion receiver that I had built. Taped onto the bottom of the receiver was a quote from the DC-40 article and a picture of the Wizard of Hyderabad. (See above, and click on the picture for a better look).
This week we will inject some more Farhan-ismo into our receiver. The time has come to build the mixer. Like Farhan, we will go with the diode ring. Winding the transformers would be very time consuming. I remembered that on his visit, Farhan had left me a box of trifilar toroids wound by the seamstresses of Hyderabad using FT37-43 cores. We will uses these in our build. They will add a lot of soul to the new machine.
Dean KK4DAS and I were at the high school on Thursday and Friday of this week for the construction (by the students) of the variable frequency oscillator stage of their analog, discrete, direct-conversion receivers for 40 meters. Most of the students have already obtained their Technician Class licenses, so they are already radio amateurs. Both the licensing classes and the receiver build are being done with the assistance of the Vienna Wireless Society.
A week earlier Dean and I had demonstrated how to build the oscillator stage using the Manhattan technique (isolation pads super-glued to copper clad boards), but this week was the first time these students were actually building anything like this themselves.
We had parts for 15 receivers. But on the first day there were more than 60 students. So four students per project. On the first day we actually ran out of soldering stations.
We cautioned the students against dawdling. We told them to get on with it, and to "make haste slowly." We also injected an element of competition into the build by announcing that the first team to achieve oscillation would win. (Prize still TBD).
By the end of the Thursday session, many boards had been built but there were not yet any oscillations. We reconvened on Friday afternoon -- Dean and I set up support/troubleshooting stations.
Right off the bat, one of the students came up with a board that he wanted to test. After one quick correction (enamel still on the oscillator coil leads), my frequency counter showed that it was oscillating. I fired up my DX-390 receiver and we heard the loud tone. We had a winner!
In the following hour or so, Dean and I did troubleshooting on about 10 more boards. We found some of the problems that we would all expect (because we have all made these mistakes ourselves!):
-- There were cold soldering joints. We showed the students how to properly solder -- usually they just had to re-heat some cold-looking connections.
-- A few of the Zener diodes and transistors were wired in backwards (been there, done that).
-- A few of the feedback capacitors were of the wrong values. Dean and I had brought some good caps, so the students were able to quickly swap out the parts. This was another good lesson.
-- There were a few wiring errors -- these were quickly corrected.
It was exciting. One-by-one we would hear the whoop-whoop as the DX-390 confirmed that another oscillator was OSCILLATING! The students really liked to HEAR the oscillations that they had created. We reminded them at the beginning that they would be taking DC from a little square 9 volt battery and turning it into RF that could (if connected to an antenna) be heard around the world, or in our case be used to receive signals from around the world.
We got eight of the oscillators going. We think the students will be able -- without much help from us -- to get the remaining seven oscillators going.
They learned a lot. They learned about the ease, flexibility, and usefulness of the Manhattan technique, and we think they could see how this represents a basic kind of PC board design. Their soldering skills improved a lot. And they learned how to troubleshoot: Is the layout correct? Are any parts wired in backwards. Is the soldering OK? Are any of the parts bad (or of incorrect values)? Most importantly, they learned that they CAN build circuits themselves, and actually get them working.
The real payoff came each time oscillation was achieved. The students were really amazed and pleased. I could tell that some of them weren't really sure their little device was actually creating the signal they were hearing. So while we listened to the DX-390, I asked them to disconnect and reconnect the battery. Confirmed. Oscillation! Smiles. It was really great.
Soon, after finishing up some PTO odds and ends, we will move on to the other stages. We'll probably do the bandpass filter or the mixer next. Then the AF amp. Then put it all together into a full receiver. We think each stage will get easier and easier to build as the students learn and improve their homebrewing skills and their self-confidence.
Check out Hans's site about the circumnavigators:
