Dave Platt wrote:
In article ,
Thierry To answer me in private use http://www.astrosurf.com/lombry/post.htm wrote:

Hi,

For over 85 years now (Armstrong, 1918) the superheterodyne circuit is at
the base of all transceiver without exception I believe.

Your belief would be wrong, I think.

Superhets are certainly popular. However, there has been a very
significant increase in interest in direct-conversion transmitters and
receivers over the past few years, and a lot of such designs are now
being put into commercial use.

Most of the ones I've seen mentioned (in the commercial world at
least) are going into UHF and microwave systems - cellphones, 802.11
data radios of various sorts, and so forth.

But, among the "most" expert engineers of you, is there a way or does it
already exist somewhere some experiments to create a new model of
transceiver using another technology ?

Direct conversion (as noted above) is one variety. A lot of the
simpler QRP CW radios use direct conversion... hams have been building
tin-can-sized-or-smaller CW transceivers for years.

I've seen some interesting designs which handle sideband, by combining
direct-conversion RF front ends with phasing circuitry - an approach
used a fair bit back in the 1960s, recently revitalized by the
availability of affordable high-crunchpower DSP chips which can
implement the phasing method via digital techniques. Some HF radio
systems even work by sampling the RF directly, and doing pretty much
everything in the DSP... all of the fine tuning, and the various
modulations and demodulations are done digitally.

And the US Dept. of Defense is sponsoring research into _direct_ DC-
to-daylight receivers that sample the RF directly and do everything
digitally. This should prove _very_ interesting indeed, as the number
of signals handled by the receiver -- and what is done with them --
is pretty much limited only by the speed of the computers processing
the signals.

Now _there_'s some equipment I want to be able to buy -- preferably at
surplus prices, of course.

--
Mike Andrews

Tired old sysadmin