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Wednesday, January 28, 2009

My ET-1 / FETer (Transceiver Made with One FET)

Magnificent, don't you think? This is my version of the ET-1 or FETer. It is an HF transceiver using only one active device -- a single MPF-102 Field Effect Transistor. I didn't have a 4 pole Double Throw switch in the junkbox, but I did have a 4PDT relay, so I used the relay. So far I have only built the receiver. It is working nicely. I was listening to German and Polish stations on 80 meter CW this morning.

I had always wanted to build W2UW's ET-1... I've been reading in "Empire of the Air" the inspiring account of Armstrong's invention of the regen receiver... Then, along came SPRAT 137 and G3XBM's FETer. I could no longer resist. Solder was melted.

It is great fun to listen to 80 meters and realize that the only thing between you and the ether is one small FET (you can see mine standing proudly atop the relay!) . Its a lot like using a crystal receiver. That one FET is serving simultaneously as an RF amplifier, mixer and BFO!

On to the transmitter! Thanks to OM Armstrong, to Glen (W2UW), and to Roger (G3XBM).

Monday, January 26, 2009

Minimalist Radio: The ET-1 and the FETer

SPRAT # 137 (Winter 2008-2009) has a number of great articles on minimalist radio -- very simple rigs with low parts counts. Roger G3XBM has a very nice re-make of the ET-1, first introduced by Glen Yingling W2UW in SPRAT 108. I remembered Glen's article -- I always wanted to try it. The ET-1 has just one active device: an MPF-102 FET. And it is a transceiver.
The schematic of the ET-1 appears above. I started building mine yesterday. Got the receiver done and --- WOW! -- heard some 80 meter signals this morning. More to follow...

Sunday, January 25, 2009

The SolderSmoke Store: T-shirts, Caps, Mugs, Bumper Stickers, MORE!


A while back, a SolderSmoke listener suggested that we open up a T-shirt store. That was a good idea. Here it is! The SolderSmoke Store at CafePress. We design the items, CafePress does most of the work, and a portion of the revenue will help keep the podcast and blog going.

Right now we have T-shirts, sweatshirts, mugs, hats, and some bumper stickers.

We are open to suggestions: If there is something SolderSmoke or homebrew or QRP-related that you would like see on a T-shirt, coffee mug, hat, etc., drop me a line and we will see if we can fit it in with our fine line of Knack-wear!

Here is the link to the store:
http://www.cafepress.com/SolderSmoke

Saturday, January 24, 2009

My Frequency Counter. FIXED!

I mentioned my broken frequency counter... Tony Fishpool, G4WIF, of G-QRP sent me a replacement CMOS chip. The counter is now counting beautifully. It was a real chore to get the bad chip off the double-sided board, then I doubled my work by putting Tony's chip in upside down. It doesn't work very well that way. I did another chip extraction. By this time I had all kinds of lifted pads, broken traces, pins on the verge of breaking. I felt sure that all the heating and de-soldering had destroyed the CMOS. But no! It lives!

This was a very satisfying troubleshoot and repair. I feel like Dr. House. The whole thing was made even nicer by the fact that the repair part came from the junkbox of a friend. Thanks Tony!

Looks like the old counter is still well-calibrated. It has my QRSS sig at 10140070. ON5EX's grabber puts me at 10140050. So the counter is 20 Hz high. Not bad for flea market junk.

A. Frederick Collins - Radio Pioneer from my Hometown

I've been reading "Empire of the Air" by Tom Lewis, and I've been struck by how much radio history took place in the Hudson Valley. I have a special interest in this, because I grew up there. As I was reading about Lee de Forest (BOOO! HISS!) I started wondering if the lake near my parents' house was named for him. I grew up near Lake de Forest. Surprisingly, Google and Wiki did not provide the answer (anybody know?), but in the course of my Googling, I discovered something that really surprised me: my little town was the summer home of radio pioneer Archie Frederick Collins (what a great name!). Collins was one of the pioneers of radio telephone, using arc transmitters to send his voice out over the airwaves. Some of the experiments took place right in dear old Congers, N.Y. Collins seems to have been a great guy -- in addition to his pioneering work in radio, he was prolific author, writing for the Knack victims of the day.

Here's a 1908 Scientific American article about his radio work:
http://earlyradiohistory.us/1908col.htm
Here's a good Wiki article on him:
http://en.wikipedia.org/wiki/Archie_Frederick_Collins

One quote from the Wiki: He wrote scientific adventure series novels such as "Jack Heaton, Wireless Operator(1919)" which told of the training and adventures of a 15 year old wireless amateur. Many of his books, such as "The Boy Scientist," (1925) had lots of illustrations and few equations, with an emphasis on "hands-on" experimentation, at a level intended for high school students. After discussing the "Einstein Theory," Collins tells his readers how to build a spectroscope, a radio, and a x-ray machine for home experimentation. Collins encouraged his readers to use their home-built x-ray machine to examine their own bone structure with a fluoroscope.

Friday, January 23, 2009

Degenerative Feedback and Distortion Reduction

Continuing on negative feedback, on SolderSmoke I recently asked for help in understanding why negative feedback is said to "reduce distortion." Let me know if you think I'm on the right track. Thanks to all who sent e-mails.

Following Fourier’s advice, let’s think of distortion as an additional waveform riding along with our desired signal. In the diagram we have a 5X voltage amplifier with 20 mV at the input, let’s say that it produces a complex distorted waveform that consists of our desired 100 mV sine wave, along with an ugly 10 mV distortion signal.

The feedback network takes 10 percent of both signals and feeds them back to the input (with a 180 phase shift). At the input, for the desired signal, the 10 mV of feedback meets up with 30 mV of input signal (as in TM 11-455, I’ll keep outputs the same, but increase inputs); we end up with 20mV at the input to the amplifier device. This then goes through the 5X amp and we get our 100 mV output.

But look what happens to the ugly distortion signal: It arises IN the device. When the feedback portion of this distortion gets to the input, it does NOT meet up with an input signal. It just goes back through the amp. So the feedback network takes 10% of the 10 mV distortion, introduces a 180 phase shift and sends this 1 mV waveform through the 5X amp. At the output of the amp we can think of the original 10 mV of distortion combining with what is now a 5mV out of phase signal. In this case, half of the distortion signal is canceled. We can say that compared with the no-feedback amplifier, distortion has been reduced from 10% to 5%. We can say that this circuit discriminates against distortion signals that arise inside the device. The desired signal meets up with the input signal, cancels a portion of it, but then the remaining signal goes through the amp producing the desired amplified signal. But the distortion signal has nothing to meet at the input. It just goes through the amp and then cancels a portion of distortion signal at the output. More desired signal, less distortion.

Thursday, January 22, 2009

Busted... By the FCC

When I was a kid, I lived in fear that one day men in black suits from the Federal Government would appear on the front steps of our house in Congers, NY. I worried that they would discover some harmonic from my Heath HW-32A doing something awful to air traffic control comms.... or perhaps they would want to check my log book (that would have definitely resulted in jail time).

George, K8VU, sent along this link to an article about a kid who DID get a visit from the FCC:
http://www.rwonline.com/article/72138

The Radio World site seems to have a very nice collection of articles. Thanks George.
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