Saturation and Class C Amplfier Efficiency

Originally posted on Gadgeteer News: 10 December 2006

FIRST LTSPICE VIDEOCAST

I made a 5 minute video using a video screen-capture program and the circuit simulator LTSpice. In addition to showing how LTSpice can
be used, the video looks at how saturation affects the efficiency of Class C amplifiers. I put the file on YouTube, but the video quality is poor when viewed through that service (it is difficult to see the graph lines in the YouTube version). So I have also uploaded the 26 meg file (.wmv)
to the http://www.gadgeteer.us web site.

Click here for the direct download of the .wmv file

Click here for the YouTube (lower quality) version

Thoughts on Minimalist Radio

I had a lot of good articles on the old web-page version of this blog. I want to get them into the index, and the only way I can think of to do this is by posting them again. I don't think this is a problem: many readers will have never seen them, and even for those who have, many of these are so good they deserve a second look. This 2006 piece by KK7B is a good example (The picture is from Roger, KA7EXM's FDIM 2007 photo collection and shows KK7B winning a toroid winding contest):

A FEW THOUGHTS ON MINIMALIST RADIO FROM KK7B
(Originally posted on the EMRFD Yahoo group)

If you really want to do minimalist radio, you may want to step way
back and take a look at some very early history. The Pixie circuit
has many more components than an early CW station from the era
immediately after spark.

Rather than starting with the Pixie and trying to figure out what to
eliminate, maybe a better approach is to start from zero and decide
what you need. Combining transmit and receive functions is the last
thing to think about.

Starting with the receiver.... The first thing you need is wire up
in the air. The more, the better. If you have the real estate for a
full sized dipole on 80 meters, you can collect enough signal energy
to hear on a crystal set when conditions are good. I've copied CW
signals on 40 meters with just a dipole, transmatch, a 1N34 diode, a
good pair of headphones, and a one transistor Pierce oscillator
running on the bench. The leakage from the crystal oscillator picked
up by the antenna beats against the incoming signals. I didn't power
the oscillator with lemon juice, but I could have (see Bob Culter and
Wes Hayward, "Lemonized QSO" in March 1992 QST.)

Then for the transmitter, just heat-sink the Pierce oscillator and
key the connection to the load. The shift in load impedance will
offset the crystal oscillator frequency.

A dual pi-net transmatch configuration would take care of the
harmonics and allow maximum energy transfer between the antenna and
diode--but I'd analyze it to make sure the harmonic suppression is
more than legal.

So far I count 5 components for the dual Pi-Net transmatch, a 1N34
diode, 6 components for the one-transistor Pierce oscillator. A
dozen parts, plus headphones, a key, and battery--or some electrodes
to push into a lemon.

That would make contacts, but Wes and I have discussed a basic rule
for radios, which is that a station should be able to work an
identical station over a distance of a few miles. It could probably
be done with the above station, but a single transistor audio
amplifier running at maximum gain between the 1N34 and headphones
would make it possible to extract many more signals from the 80 meter
dipole. That's another 5 or 6 parts. So now I'm up to about 20.

For a more serious station, I'd probably add two more transistors and
a diode, so I could have a separate PA, a balanced mixer, and two
audio stages. The receiver would end up looking a bit like EMRFD
figure 8.7 with a PA tacked on. That would have about 35 parts, but
it would be able to work DX off the ionosphere...about the same
complexity and performance as many other variations on the theme. A
previous version of the Pixie from the 1970s was called "The
Optimist."

Unlike Muntz--instead of starting with someone else's circuit and
trying to eliminate parts until I had something that just barely
works, I'd start from scratch, study EMRFD (and other references too--
but in EMRFD all the circuits have been designed and tested) for
circuit ideas, and then start experimenting on the bench, one stage
and one component at a time. Since one of the joys of minimalist
radios is that they can be understood all the way down to the device
physics, I avoid ICs. (I particularly avoid cell-phone ICs, which I
designed for a number of years. It's like working in a sausage
factory--you are much happier if you don't know what's inside.)

Minimalist radio is one of the more interesting design games that we
play using the methods of EMRFD. It's cheap, it's interesting...and
as we dig in, we discover that the details can be every bit as
challenging for a radio project with 30 parts as one with 30,000.

Have fun.

Best Regards,

Rick kk7b

In Rotterdam

I'm up here with Billy on a violin gig. Beautiful place! Will descrbe
on next podcast. 73

Radio Signals from Jupiter and Io on 17 Meters

Jupiter and Io montage captured by the New horizons spacecraft.
The Jupiter image is false-color near IR data obtained with the LEISA instrument, built at GSFC.

I try to always read the QRP-L postings of NA5N -- Paul always has something interesting in his messages. Today I found this:
Jupiter emissions peak around 18-22MHz; they are a function of when the moon Io crosses certain longitudes of the relatively fast spinning Jupiter. There used to be a couple of calculators online (haven't checked lately) as to when the L-bursts should occur. The timing is quite predictable; detecting them on every predicted occurrence is not. You have to have an antenna with a little bit of gain. The signals are generally weaker (that is, near the atmospheric noise level) than can be detected with a dipole. With a fairly decent setup, the Jovian L-bursts sounds like ocean waves crashing on a distant beach, just barely above the noise level. The S-bursts sounds like random pulse type static in short bursts. These are harder to detect than the L-bursts.

I had known about the Jovian radio emissions, but I didn't know that the moon Io was involved. For me, Io's involvement somehow makes this even more interesting. Jupiter and its moons (including Io) are some of the few celestial objects I can regularly see from central Rome.

Here is a good description of Jupiter's radio signals, and Io's role in transmitting them:
http://radiojove.gsfc.nasa.gov/library/sci_briefs/decametric.htm

And here is an interesting article about the discovery (50 years ago) of these signals:
http://radiojove.gsfc.nasa.gov/library/sci_briefs/discovery.html

SolderSmoke Podcast #108

http://www.soldersmoke.com

In SolderSmoke 108:

May 24, 2009
Hubble Space Telescope Repair Mission
WSPR: W3PM sees my sigs, back to visual (briefly), on to Slow Hell.
Ubuntu ham radio software
Time nuts
Jean Shepherd gets his Class A license
"SolderSmoke -- The Book" Good for summer vacation reading.
SPECIAL REPORT FROM DAYTON - FDIM BY BOB W8SX
MAILBAG

CHECK OUT THE BOOK: (First chapter preview available)

http://www.lulu.com/content/paperback-book/soldersmoke/6743576



73 from Rome

Tech Details on ET's "Phone Home" Beacon Rig

Mark "MOJ" Johnson, W8MOJ, sent me a really amazing 73 Magazine article. It is from the APRIL 1983 issue. (The month of publication set off my April-fool alert alarm, but this is for real.) When Steven Spielberg was making ET, the producers contacted Bell Labs and asked for help in designing the rig that ET would use to phone home. A ham, Henry Feinberg, K2SSQ, got the job. In the article, Henry wrote: "What Spielberg wanted was a beacon transmitter, something to say, 'Here I am, Come and get me!' I reasoned that three main parts wee needed for a basic beacon: a means of producing a message, a programmer to repeat the message, and a way of transmitting the signal into outer space."

Later, in describing the keying device, Henry wrote: " The surface of the saw blade was coated with several layers of spray paint, which served as insulation, preventing the bobby pins from contacting the metal blade. The message was programmed on the blade by carefully etching through the paint. "

OK, that does it. Time for me to go back to the Trastevere flea market to pick up some more cheap clock drives... and maybe some circular saw blades. I need to get going on my mechanical QRSS one-transistor becaon project.

REAL Hams Make Their Own Crystals....

Bill: You say you buy your crystals from the electronics store? Real homebrewers grind their own crystals. See attachments. Russ

After reading this I was feeling like a complete APPLIANCE OPERATOR. But wait a second Russ -- that's a KIT! Real homebrewers don't need KITS to make their own crystals! And remember, you are talking to a guy who has used iron pyrite and a phosphor bronze to detect radio waves. That means I have homebrewed my own DIODES! ;-)

Thanks for the cool pictures Russ. Those were the days...

Seeing my WSPR signal

Graham, G3ZOD, sent me this WSPR screen-shot. He writes:

Hi Bill. Thought you might be interested in a screen grab of yourself. You're the near continuous signal along the centre of the waterfall just below 200 on the vertical axis.Not DX from Italy to England, but I'm using an indoor wire antenna and I usually receive you for short periods only - never seen such a consistent signal before. By the way: I think your computer clock may be a couple of seconds off according to the DT values; I have mine resync every 6 hours and my clock is generally within 150 milliseconds.
73 de Graham G3ZOD

Thanks Graham! The consistency of my signal is no doubt due to the fact that I have no receive system here yet, so on the WSPR software, in the "T/R Cycle" box I had "TX" checked. So I was "key down" most of the time. Your screen shot made me realize that this might not be the most neighborly thing to do -- someone else on the same freq might be QRMd by my 20 mW DSB sig. So I think I'll ratchet down the T/R cycle here.
My computer clock is erratic. I have to tweak it each day. I know there is a program out there that automates this -- haven't gotten to that yet. 73 From Rome

Shep's Class A License, Part II

I didn't mean to leave you guys in suspense. Here is the exciting conclusion.
EXCELSIOR!

Jean Shepherd Gets His Class A License

I was drifting off into Linux-land, but an e-mail from OM Gene, K8EE, brought me back. I'd thought that we had already unearthed all of the best ham radio episodes of the Jean Shepherd shows. WRONG! K8EE sent me YouTube recordings of the January 7, 1964 show on WOR New York. Gents, all I can say is that you should stop what you are doing, and listen to this. (And don't miss the exciting conclusion in part 2!)

"Mr. Rupp, what do you know about the Mu of an '807?" Indeed.

Ubuntu

As SolderSmoke listeners know, I'm not really a software guy. In fact, I'm only a marginally competent user of software. But I've taken a liking to Ubuntu Linux. It works, it is user friendly, and it seems to have developed a very cool African cultural thing around it. Check out the names of the various versions and you will see what I mean:

4.10 Warty Warthog
5.04 Hoary Hedgehog
5.10 Breezy Badger
6.06 Dapper Drake
6.10 Edgy Eft
7.04 Feisty Fawn
7.10 Gutsy Gibbon
8.04 Hardy Heron
8.10 Intrepid Ibex
9.04 Jaunty Jackalope
9.10 Karmic Koala (NEXT ONE) October 2009

OK, now back to the radios...

KO7M Suddenly Goes Manhattan

Perhaps he picked up the vibrations from Dayton and FDIM where they were conducting a Sudden Receiver build-a-thon... Jeff, KO7M, (aka the lucky guy with the Piper Cub) recently tried out Mahanttan-style construction -- he built an NE602-LM386 Sudden Receiver... and liked it.

Jeff writes:

Believe it or not, I have never built anything Manhattan style… So, I decided to give it a go and built a little 40m DC receiver designed by Rev. George Dobbs G3RJV consisting of a NE612 and LM386. I have included a shot of it below. I was very pleased with this building style and think I may adopt it going forward. In particular I like how easy it is to make changes. I just used tin snips to make the pads. For the 8 pin IC pads, I cut them 2 cm square and used a hacksaw to saw between the IC pins and up the middle to separate the pin pads electrically by removing the copper. Make sense? Very simple to then bend the IC pins 90 degrees and solder them down. Preaching to choir, I know… But it takes some us a little longer to get on board, eh? J I was very pleased with the outcome.

I like Jeff's technique for the IC pads. I will have to try that.

SolderSmoke 108 will feature an interview with George Dobbs in which he talks about the Sudden Build-a-thon.