On 25/02/15 06:45, rickman wrote:
On 2/24/2015 7:32 PM, Brian Reay wrote:
rickman wrote:
On 2/24/2015 6:35 PM, gareth wrote:
"rickman" wrote in message
...
On 2/24/2015 12:37 PM, gareth wrote:
"Spike" wrote in message
...
Get a CW signal peaked on the 20 c/s nose of the HRO crystal filter,
with
the phasing notching out any nearby signal, and you realise that DSP
just
isn't necessary due to the quality of the 80-year-old technology
employed.

WHS.

The Eddystone EA12 does not have a phasing control as that part of
the
cct
is fixed-tuned, but it does have a tunable notch in the 100kHz IF to
achieve the same effect.

Mind you, there seems to be a diminishing band of people who know
how to
do this, so the simplistic approach of using someone else's
ever-upgraded
software to do something less effective is about as far as the
tick-box
Amateur seems to go. Heavens - they even buy ready-made wire
aerials!

And going from previous threads, there are even fewer who
understand that
setting up for single-signal reception means that the notional
carrier
frequency has
to lie half-way between the peak of the Xtal and the notch of the
phasing
control.

We should not forget that he who sneers loud and long about
others' grasp
of
the mathematics of DSP maintains that changing the direction of a
rotating
vector
(A Phasor, and not related to the weapons of Star Trek!) causes it to
decrease in sixe.

What is "sixe"???

Typo - adjacent key - size

I thought it might be that, but it still makes no sense to me. Who or
how does changing the direction of rotation of a rotating vector change
its "size". Are you defining size as the rotation so that going from
a +
to a - is like reversing the direction of a vector? I think most people
would consider the "size" of a vector to be the magnitude which is
independent of phase angle and so rotation, no?

Perhaps you can explain this with a little math?


He is (deliberately) misrepresenting the discussion. The point was made
that the phasor was rotating clockwise, thus the angle decreasing, ie
becoming negative.

This has been repeatedly explained to him but he continues to churn
out his
bilge.

His maths (or math) isn't up to it, it is too complex for him (pun
intended).

If you look in the archives you will see him referring to 'negative
frequency', not to mention questioning basic DSP theory, the use of the
Dirac Delta, .....

Best just to ignore him, he is simply trying to start a row.

Maybe I don't understand the issue. Isn't that a valid example of a
negative frequency? There are some DSP experts in comp.dsp who talk
about negative frequency often.


I went over this at the time, although in connection with another of his
wild claims (he claimed that you couldn't divide complex numbers).

Basically, the mathematical concept, which wasn't Evans' point, of
negative frequency arises from Euler's Identities for sin (theta) and
cos (theta) which leads to the result that a simple, real, sinusoid, is
the sum (using Euler's Identities) of positive and negative terms. In
DSP circles, the negative terms, are generally referred to the 'negative
frequency terms' (or some variation, depending on local usage). These
are generally removed, or filtered (numerically) to simplify the overall
processing task.


If you dig into the archive to the time when Evans first raised this,
you will see he was clearly not referring to 'negative frequency' in
terms of the above. I pointed out his error, although I did under
estimate his lack of understanding and/or ability to twist facts. This
is one of the topics he drags up after a drubbing and he promptly gets
another one.