On Sun, 30 Oct 2005 21:49:08 -0800, Richard Clark
Hi Richard,

In general, no rf stage is needed (or desired).

In general, no rf stage has been designed into a receiver for a
quarter century. Hence touting it as a hallmark is rather pedestrian.


True, but few of the inexpensive receivers that operate without rf
stages perform very well. And I don't know any commercial application
that uses regenerative feedback to gain selectivity in a real world
receiver application. Typically, receivers that perform well have many
(post detector) poles of modest Q filter stages to prevent undesirable
features such as ringing. This uses alot of hardware, especially
precision resistors and capacitors.

Yes, scaf filters are relatively clean, but it's still a multichip
solution needing quite a few R's and C's.

But, recovering the audio without DSP based software (usually
a sound card) is very difficult, needing large amounts of selective
audio filters slowly tailor the audio response to an appropriate
selectivity.

Even there, bi-quad active filters have been doing this for those same
25 - 30 years, and quite smartly too.

You need to return to basics a la Robert Pease who does a lot of
informational multimedia for National Semi these days. He properly
offers that so much that has been handed over to binary twiddling is
such a step backwards to accomplishing a job better handled in the
linear domain.


There's room for both. KK7P's single chip digital solution to
processing the I and Q from the detector to the speaker is quite
attractive. It offers the potential of high performance while freeing
us from the sound card/computer leash (and the big three Japanese
corportions that dominate the ham radio transceiver industry) that
currently restrains us. It's the missing link that makes high
performance digital solutions into a 'free standing' piece of
hardware.

It appears to me that DSP uses a great deal of power to do the job
though. In practical terms, what we save in portability and bulk with
a single chip digital solution might be minimal because we have to
carry bigger batteries to make it happen in a portable environment.

Like I said, there's room for both...and small changes in hardware
availability constantly move the equation regarding 'what's best for
me' in varying directions.

I prefer to know both digital and analog worlds though instead of
limiting myself by only knowing 1 possible option.

Since the original responder wrote about regenerative methods however,
I will keep my eye peeled for a practical means to implement it with
modern technology components. If it was implemented in the post
detector audio processing, it might minimize hardware needed to
achieve high selectivity with clean sounding audio. I thank him for
the reality check regarding this possibly useful method.

Regards,

T