On Monday, December 1, 2014 6:32:45 AM UTC-8, dave wrote:
Direct conversion is all the rage these days. Or Direct conversion to
I/Q quadrature directly into a DSP. A crystal radio is direct conversion
so I guess we are back where we started (except now we have the DSP).

How would you do quadrature at baseband? Two VCOs both digitally controlled and 90 degrees out of phase, or some witchcraft on the baseband signal itself?

-- ross


On 11/28/2014 11:42 PM, GCornelius wrote:
On 11/23/2014 09:37 AM, DhiaDuit wrote:
On Sunday, November 23, 2014 4:16:05 AM UTC-6, dxAce wrote:
DhiaDuit wrote:
Gift for Christmas used to be a transistor radio. See that article
at Headline News Stories 24/7 at www.rense.com

I recall my very first radio. It was some sort of crystal set shaped
like a rocket. No battery required. I got it when I was 3-4 years old
(and living in Ft. Wayne, IN). It was some sort of cereal promo as I
recall. That must have been 1956-57.

A few of my friends had them when I was in grade school. Alligator
clip for an antenna connection - I thought it weird that many would
clip it to a heating radiator - and an adjusting rod that must have
been attached to a ferrite core in the antenna coil.

Back in the 1950s my mom and dad gave myself and one of my sisters a
Motorola transistor radio. Those two radios were identical models of
radios. They had a big tuning knob on them and a carrying strap/shoulder
strap. A year or two before that I had ordered a little transistor radio
from a radio company in Kearney, Nebraska. That little radio (I think
it had two transistors in it) wasen't worth a durn for picking up long
distance radio stations. That little (Kearney, Nebraska) radio used to
be advertized in magazines such as Popular Mechanics and Popular Science
and Mechanix Illustrated and Science and Mechanics classifieds ads.
I believe a simple 'foxhole crystal radio would have worked much better.

Interesting that you mention it. I believe the name may have
been Western Radio (later Western Manufacturing).

Turns out, and I just recently found an article about it, that
a member of the Beshore family in Kearney started the operation -
I suppose in their basement or garage - and it grew from there.
It started with the "Tiny Tone" crystal radio in 1933. When
I was very young we lived a block west of the Beshores, probably
the family of one of the brothers mentioned in that article as
being involved in the operation.

If you go to this locatioon (a book index at the local
historical society site),

http://www.bchs.us/buffalo_tales.htm ,

there's a link - see Volume 13, Issue 10 of Buffalo Tales.

It was a few years after we moved away that I started
reading magazines like Popular Science and first saw the
ads, typically in the classified section at the very back.

George

On Mon, 1 Dec 2014, Ross Archer wrote:

On Monday, December 1, 2014 6:32:45 AM UTC-8, dave wrote:
Direct conversion is all the rage these days. Or Direct conversion to
I/Q quadrature directly into a DSP. A crystal radio is direct conversion
so I guess we are back where we started (except now we have the DSP).

How would you do quadrature at baseband? Two VCOs both digitally
controlled and 90 degrees out of phase, or some witchcraft on the
baseband signal itself?

I think his wording is throwing you off.

If they just convert to audio, there's now way to get rid of the audio
image. All the digital filtering in the world can't get rid of it,
because it's in the same area as the wanted signal.

If you convert with two mixers and an oscillator with two outputs, 90
degrees apart, you get two audio channels. The digital processing can
make use of that, and knock out the unwanted image.

It's just a more modern version of the phasing method of sideband
rejection (once upon a time common in SSB transmitters, and often used as
external devices to improve sideband reception on existing receivers when
SSB was new.

But instead of an audio phasing network after the two mixers (which is
what was used in all those sideband slicers in the fifties), digital audio
processing takes care of the audio phase network and can do a lot more.

What sometimes happens is they use the same scheme, but convert to a very
low IF. There, the two channels are used to get rid of the RF image, which
is relatively close to the signal since the IF is often below 100KHz, but
somewhere above audio.

Michael