In article ,
fred wrote:
Surely 'rectified frequency' is DC? Although with some ripple on it
unless smoothed?

Not if it's the output of a diode detector for an AM transmission it's
not . . . oh how quickly we forget :-D.

Surely you mean the cat's whisker? ;-)

--
*Toilet stolen from police station. Cops have nothing to go on.

Dave Plowman London SW
To e-mail, change noise into sound.

On 2005-07-14, Dave Plowman (News) wrote:
In article ,
fred wrote:
Surely 'rectified frequency' is DC? Although with some ripple on it
unless smoothed?

Not if it's the output of a diode detector for an AM transmission it's
not . . . oh how quickly we forget :-D.

Surely you mean the cat's whisker? ;-)

I had one of those as a kid which I won't forget anytime soon. With round
bakelite end-cheeks separated by a glass tube. Galena crystal in a holder
screwed through one cheek and adjustable phosphor-bronze spring/whisker
assembly screwed through the other. A big coil former with DCC wire round
it, an enormous multi-vane airspaced tuning capacitor, mains plug earth
(not sure now about the safety) and a long wire aerial.

Bootstrapping the receiver was an issue. I can't now remember precisely
how I got the whole thing set up from the initial conditions:

- a tuned circuit tuned to some near-random frequency that probably
didn't correspond to any radio station; and

- a diode detector which probably wouldn't detect without some tweaking.

I assume I (1) tweaked the whisker/crystal contact, then (2) scanned the
tuning, repeating steps 1 and 2 until something (anything!) came in.
Then I assume it was a matter of optimization of the tuning and the
crystal. The job was then to ensure the crystal remained unjogged.

Remarkably, the set with its rather uncomfortable 600-Ohm BT surplus
headset proved very useful over quite a time. I guess I was easier to
please then.

--
John Phillips

In article , John Phillips
writes
On 2005-07-14, Dave Plowman (News) wrote:
In article ,
fred wrote:
Surely 'rectified frequency' is DC? Although with some ripple on it
unless smoothed?

Not if it's the output of a diode detector for an AM transmission it's
not . . . oh how quickly we forget :-D.

Surely you mean the cat's whisker? ;-)

I had one of those as a kid which I won't forget anytime soon. With round
bakelite end-cheeks separated by a glass tube. Galena crystal in a holder
screwed through one cheek and adjustable phosphor-bronze spring/whisker
assembly screwed through the other. A big coil former with DCC wire round
it, an enormous multi-vane airspaced tuning capacitor, mains plug earth
(not sure now about the safety) and a long wire aerial.

Bootstrapping the receiver was an issue. I can't now remember precisely
how I got the whole thing set up from the initial conditions:

- a tuned circuit tuned to some near-random frequency that probably
didn't correspond to any radio station; and

- a diode detector which probably wouldn't detect without some tweaking.

I assume I (1) tweaked the whisker/crystal contact, then (2) scanned the
tuning, repeating steps 1 and 2 until something (anything!) came in.
Then I assume it was a matter of optimization of the tuning and the
crystal. The job was then to ensure the crystal remained unjogged.

Remarkably, the set with its rather uncomfortable 600-Ohm BT surplus
headset proved very useful over quite a time. I guess I was easier to
please then.

Aaaarg, aaaaarg, no more reminiscences pleeeeeeease . . . . . :-)
--
fred

On Thu, 14 Jul 2005 15:10:28 +0100, "Dave Plowman (News)"
wrote:

| Surely you mean the cat's whisker? ;-)

That brings back memories! I listened to the Queens coronation on a
cat's whisker set I made myself.
--
Dave Fawthrop dave hyphenologist co uk In Case of Emergency
Store the word "ICE" in your mobile phone address book, and
against it enter the number of the person you would want to be
contacted "In Case of Emergency". http://tinyurl.com/79lz9

http://www.soc.napier.ac.uk/module.p...reid=16 89263

It's simply a mistake, isn't it? An 'RF Modulator' is ALWAYS a 'radio
frequency modulator'.

There is simply no such thing as a 'rectified frequency modulator'. It's a
brain glitch on the part of the author, which the reviewers didn't pick up.

Staiger

yeah, but crystal sets are "powered" only by the received radio waves,
so you need a pretty damn long aerial to hear anything!

In article , Staiger
wrote:

http://www.soc.napier.ac.uk/module.p...reid=16 89263

It's simply a mistake, isn't it?

I've now had a chance to look at the above...

Yes, it looks to me to be a plain error on the part of the person who wrote
the document. Indeed, the document seems to contain a number of statements
which seem to me to be either ambiguous, misleading, or simply incorrect.

Couple of other examples.

1)

"HDTV (High Density) is a new medium allowing 16:9 ratios instead of
4:3..."

IIUC HDTV means High Definition TV, not 'High Density'. Also, since
standard definition TV can also convey 16:9 images the statement seems to
me to be misleading as it implies this is only possible if we use HDTV.

2)

Note at the bottom of page 2. This seems to not clearly understand or
explain U/V, and claims "Green signals can be approximated by the
combination..."

IIUC U and V are colour diffs with Y. (This concept seems not to be
explained at all) and the recovery of green is not an "approximation"
except in the sense that any computation with finite accuracy or precision
may not be absolutely accurate.

There are various other places where what us written is dubious, but can be
interpreted either correctly or incorrectly.

An 'RF Modulator' is ALWAYS a 'radio frequency modulator'.

So far as I know, that is the case. There may be exceptions which I am
unaware of. However in the context of the above document it looks to me to
simply be an error.

There is simply no such thing as a 'rectified frequency modulator'.
It's a brain glitch on the part of the author, which the reviewers
didn't pick up.

What reviewers? My impression is that this is a set of course notes put
together in a hurry, and not checked. Notes like these are - in my
experience - written by the lecturer/demonstrators, and the only checking
is when they are presented. Other staff won't have the time, and many won't
have a clue about the topics they aren't teaching/researching themselves.

Alas, it is easy enough to make simple errors like this, particularly if
in a hurry. I've done it countless times. :-) However I usually realised
I'd written twaddle when I stood in front of students and tried to explain
the nonsense I'd written in the notes, or someone asked a question that
skewered the error. ;-

Slainte,

Jim

--
Electronics http://www.st-and.ac.uk/~www_pa/Scot...o/electron.htm
Audio Misc http://www.st-and.demon.co.uk/AudioMisc/index.html
Armstrong Audio http://www.st-and.demon.co.uk/Audio/armstrong.html
Barbirolli Soc. http://www.st-and.demon.co.uk/JBSoc/JBSoc.html

Jim Lesurf wrote:

Alas, it is easy enough to make simple errors like this,
particularly if in a hurry. I've done it countless times. :-)
However I usually realised I'd written twaddle when I stood in front
of students and tried to explain the nonsense I'd written in the
notes, or someone asked a question that skewered the error. ;-

Thought lecturers did that on purpose, to see who was thinking and who
was just writing down anything the lecturer said.

--
yours S

Nihil curo de ista tua stulta superstitione

In article , soup
wrote:
Jim Lesurf wrote:

Alas, it is easy enough to make simple errors like this, particularly
if in a hurry. I've done it countless times. :-) However I usually
realised I'd written twaddle when I stood in front of students and
tried to explain the nonsense I'd written in the notes, or someone
asked a question that skewered the error. ;-

Thought lecturers did that on purpose, to see who was thinking and who
was just writing down anything the lecturer said.

I've tried that excuse, but I don't have a good poker-face. My
congratulations to those who can make it convincing... :-)

The way I use to check if students are listeing is to tell occasional
'jokes' sic. Those who wince or groan are listening. Those who laugh are
hoping for a good exam mark. Those who do not react are in auto-write-mode
or sleeping off last night.

Anyway, most experienced lecturers know full well that students who write
things down usually aren't thinking about the content. Mind you, nor is a
failure to write things down a sign that they are, either. ;-

TBH Having to teach something is an excellent way to discover that you
*don't* actually understand it, despite having assumed that you did! The
snag is that you may need time to allow the realisation to dawn that what
you have just written down (or said) is twaddle. Alas, 'modern' teaching
and lecturing often has to be done in too much of a rush to allow time for
this.

Slainte,

Jim

--
Electronics http://www.st-and.ac.uk/~www_pa/Scot...o/electron.htm
Audio Misc http://www.st-and.demon.co.uk/AudioMisc/index.html
Armstrong Audio http://www.st-and.demon.co.uk/Audio/armstrong.html
Barbirolli Soc. http://www.st-and.demon.co.uk/JBSoc/JBSoc.html