On Tue, 18 Feb 2014, gareth wrote:

There was a time, back inthe 1920s and 1930s, that any active device
(valves in them thar days, tubes for the leftpondians) would cost nearly
a week's wages for the average working man, and so it was good economical
sense to try and use it as many ways as possible simultaneously.

Times have changes, and active devices with performance into the tens
of MegaHertz are now ten-a-penny, so what is achieved by competitions
such as the "Two Transistor Challenge" where it is the costs of switching
(manual, relays) which would be the major outlay?

Not carping, just curious.

There have always been "contests" like that, though sometimes they were
about "build a whole receiver using the same transistor type", or "build a
receiver without any ICs" after ICs had come around.

SOme of the time it's not about design, but the building, so one can just
copy what existed.

In some cases, this is just about getting people to build something, so a
two transistor whatever is simple and might attract more people.

But in suggesting a problem, people may come up with interesting
solutions. I remember a bit years ago where a bipolar transistor was used
to generate two different crystal controlled frequencies, the frequency
chosen by how polarity was applied. I forget the details, but it relied
ont he transistor having some amplification in an unexpected area.

If people don't have to be frugal, then such things never get found.

Or think about in the thirties. People had little money, so yes, a simple
transceiver would be a great thing. Someone decided to build that, in
effect a tube that was a superrenerative receiver and on transmit a
modulated oscillator. It helped get people on 10metres (I think) and
56MHz, and 112MHz and so on. It would generate activity on an otherwise
unused band because it was cheap and simple, so people built them. The
cost of the switch was less than the cost of the tubes. And every so
often, such a thing would be banned, as rules for more stability came into
effect, and usually by then that band was populated. So the concept moved
to a higher frequency, until it was deemed to unstable for there too, and
up to the next band. They even existed in the 420MHz band, and while
generally nobody built them, at 1296MHz people often got a start with
APX/6 surplus that amounted to simple equipment. 20 to 30 years ago,
23,000MHz got a boost with surplus door openers. SImple equipment gets
more people onto a band than complicated equipment, and some will move on
to fancier equipment.

That same sort of thing, an active element switched between a superregen
receiver and a modulated oscillator still existed till at least 30 years
ago, in license free walkie talkies, first in the 27MHz range and then in
the 49MHz range. Even then the cost of the switch was seen as simpler than
more transistors.

It can also teach something. You can reuse the transistor for two
functions, by switching the three leads of the transistor, which means
much more complication. But if people see that, they may learn that
design can become simpler by more complication. More transistors seem to
complicate things, but if it does away with switching, it may simplify the
design overall.

Michael