Electronic curiosities

[Geoffrey S. Mendelson]

William Sommerwerck wrote:

What does this have to do with the perceived need
for an RF stage at the receiver?

Read the rest of the posting, it explains why.

I did. It was even more confusing.

Ok, maybe this will make more sense.

Hams either use resonant antennas or antenna tuners.

Resonant antennas by virtue of the fact they are resonant in-band, are not
resonant out of band and therefore reduce out of band signals.

Antenna tuners (for reception) act as preselectors which reduce out of band
signals. In practice and design, they are TRF stages.

So if you buy a ham radio with an antenna tuner, it may not have a tuned
front end as specfied, but in reality it does.

Geoff.

--
Geoffrey S. Mendelson N3OWJ/4X1GM
Those who cannot remember the past are condemned to misquote it.

 

[Meat Plow]

On Sun, 16 Jan 2011 03:38:51 -0800, William Sommerwerck wrote:

Another book (which I frankly don't like as much since it's so
math-heavy: wouldn't electronics be so easy to learn if all that
goddamn math didn't get in the way?)...

I hope you're joking, because without that math, you can't begin to
truly /understand/ electronics. Mathematics is used to model the
physical world. When you understand the math, you have a much better
comprehension of the physics involved.

Math in basic electricity is fundamental learning. You can't begin to
understand electronic circuits with inductance/impedance/reactant/etc..
Things like low pass high pass filters, simple RC circuits, tuned circuits
oscillators. These are the very basics. Understanding trigonometry and
algebra are also a must.



--
Live Fast, Die Young and Leave a Pretty Corpse

 

[William Sommerwerck]

"Geoffrey S. Mendelson" <gsm@mendelson.com> wrote in message
news:slrnij6e69.p2d.gsm@cable.mendelson.com...

William Sommerwerck wrote:

What does this have to do with the perceived need
for an RF stage at the receiver?

Read the rest of the posting, it explains why.

I did. It was even more confusing.

Ok, maybe this will make more sense.

Hams either use resonant antennas or antenna tuners.
Resonant antennas by virtue of the fact they are resonant in-band, are not
resonant out of band and therefore reduce out of band signals.
Antenna tuners (for reception) act as preselectors which reduce out of
band
signals. In practice and design, they are TRF stages.
So if you buy a ham radio with an antenna tuner, it may not have a tuned
front end as specfied, but in reality it does.

I'm not sure that's correct. My Yaesu ("joy of ham's desiring") has a
switchable antenna tuner and switchable RF stage, and they're not
interlocked in any way. No engineer would design a ham transceiver that
depended on an antenna to provide adequate selectivity.

Besides, the RF stage is also there to improve sensitivity (when needed). As
for selectivity... image rejection is more-important than selectivity, and
this is a triple-conversion receiver.

 

[William Sommerwerck]

No engineer would design a ham transceiver that
depended on an antenna to provide adequate selectivity.

Whoops.

No engineer would design a ham transceiver that
depended on an antenna tuner to provide adequate
selectivity.

 

[Baron]

Jeff Liebermann Inscribed thus:

On Sun, 16 Jan 2011 00:38:07 -0800, David Nebenzahl
nobody@but.us.chickens> wrote:

On 1/15/2011 10:14 PM Jeff Liebermann spake thus:
http://en.wikipedia.org/wiki/Direct-conversion_receiver

Before I blunder onward, permit me to say that I've locked horns with
the censors on Wikipedia (actually Wikibooks) and got a first hand
taste of why some of the articles are rather marginal. However, it's
still the best reference around for obtaining general information
about almost any topic and tends to be more understandable than
someone peer reviewed research paper or marginally reviewed book
extract. In topics that I am familiar, I can usually find something
in the article that could use improvement. I usually include a
Wikipedia reference primarily so that those unfamiliar with the topic
can get a general understanding.

OK, so this is why I absolutely *hate* Wikipedia.

Nothing is perfect. Finding errors is not sufficient grounds for
hatred. A lawyer friend has a similar problem with the various laws
and legal decisions. All of them could use improvement and almost any
written law can be misread and misinterpreted. Unlike Wikipedia,
readers are unable to repair the written legal system. Despite
chronic deficiencies, the legal system is still functional, and there
are few attorneys that *hate* the written law simply because there are
mistakes. Some tolerance would be helpful here.

Here's the lead
paragraph in the article:

In telecommunication, a direct-conversion receiver (DCR), also
known as homodyne, synchrodyne, or zero-IF receiver, is a radio
receiver design that demodulates the incoming signal by mixing it
with a local oscillator signal synchronized in frequency to the
carrier of the wanted signal. The wanted modulation signal is
obtained immediately by low-pass filtering the mixer output,
without requiring further detection. Thus a direct-conversion
receiver requires only a single stage of detection and filtering,
as opposed to the more common superheterodyne receiver design,
which converts the carrier frequency to an intermediate frequency
first before extracting the modulation, and thus requires two
stages of detection and filtering.

Now, class, how many things are wrong here? (And please correct *me*
if I'm incorrect):

o First of all, superhet receivers have only one stage of detection
and filtering, not two, after the last IF stage, right? (I suppose
there may be some filtering in or around the mixer stage, but I don't
think that's what they're claiming, which I assume is filtering out
the carrier.) So where do they get "two stages of detection and
filtering"?

The original paragraph is poorly written and you managed to
misinterpret it. I'll try to do better.

A direct conversion receiver usually uses only a single stage for both
detection and filtering. In any receiver, there is only one stage of
detection. The articles reference to
"...and thus requires two stages of detection and filtering"
should read
"...and thus requires separate stages of detection and filtering". Is
that better?

o Is their explanation of how DCR works even correct?

Yes, it's correct. Mixing with a local oscillator (or reference
signal) on the operating frequency, as in a homodyne receiver, is
considered direct conversion. That includes extracting the carrier
from the receive signal, and subsequently mixing the carrier with the
receive signal to extract the modulation (such as in an I-Q
demodulator). Mixing with a signal that is NOT on the operating
frequency, is heterodyne conversion. Note that it doesn't matter
where the signal is mixed in a (super)heterodyne receiver. One active
stage can do everything as in an autodyne receiver.
http://en.wikipedia.org/wiki/Autodyne

I don't understand
the business of mixing the signal with a LO signal: why would you do
that?

The mixing is to extract the modulation. It's called a product
detector for AM and SSB.
http://en.wikipedia.org/wiki/Product_detector
http://www.google.com/images?q=product+detector
If you extract the carrier signal from the receive signal, mix these
together, and low pass the result, you get demodulated AM or SSB. With
slope detection, you can also demodulate FM. Extracting the carrier
is simply lots of amplification so that the amplitude modulation is
clipped (limited) and thus removed. For SSB, a PLL is often helpful
for weak signals, but not really necessary as just IF noise will
usually suffice to produce a usable carrier component.

They're a little vague: does "synchronized in frequency to the
carrier" mean *exactly* the same frequency as the carrier (???),

Yes. Exactly the same frequency. In order for a product detector or
direct conversion receiver to work, it needs to multiply (mix) the
carrier (with no modulation components present) with the receive
signal. What's left is the modulation.

or some
other frequency to produce a sum or difference frequency? (In which
case, we're back to IF, aren't we, so what's "direct conversion" about
this?

No. The distinction is that direct conversion uses a mixing signal
that is exactly the same as the receive signal. If the signal was
offset, it would be consider (super)heterodyne conversion.

If I were in front of a firing squad and had to try to describe DCR
without actually knowing what it is, I'd guess(tm)(R) that it's a
bunch of tuned RF stages followed by a detector.

Sure. The detector is allowed to use the received signal to perform
the demodulation, it's still direct conversion. Think of TRF (tuned
RF) type of receiver as a special case of direct conversion, where the
demodulator is rather simplistic.

Anyhow, I think I've shown that even if I'm way off base, Wikipedia
articles tend to be extremely badly written,

There's plenty of room for improvement. There may be mistakes but
they are NOT badly written.

if not outright full of
doubtful information.

They make an effort to reduce errors. Where it become difficult is
that there are so many areas of technology where there are multiple
points of view with large areas of overlap and controversy. As long
as the source of such "doubtful" information is specified, multiple
points of view are presented, and the author is fairly neutral, I
don't have any problem with presenting controversial information.

What else would one expect of the "encyclopedia"
that any PlayStation-playing, junk-food wolfing pimple-faced
junior-high-school student can edit?

The next time you research a topic, instead of using Google or
Wikipedia, try using Google Scholar instead.
http://scholar.google.com
This should give you a wide selection of papers and articles written
by qualified experts who probably don't own a Playstation. Some of
the papers have been peer reviewed and are thus deemed correct and
often even authoritative.

If that is insufficiently accurate, try searching for terms using
Google patent search.
http://www.google.com/patents
If you think Wikipedia is full of inaccurate information, wait until
you read some of the hogwash found in some patents. Try searching for
"perpetual motion" for a good start.

Good Grief ! If William started a search for "perpetual motion" he'd

dissappear under a mountain of hits.

--
Best Regards:
Baron.

 

[David Nebenzahl]

On 1/16/2011 3:38 AM William Sommerwerck spake thus:

[me said:]

Another book (which I frankly don't like as much since
it's so math-heavy: wouldn't electronics be so easy to
learn if all that goddamn math didn't get in the way?)...

I hope you're joking, because without that math, you can't begin to truly
/understand/ electronics. Mathematics is used to model the physical world.
When you understand the math, you have a much better comprehension of the
physics involved.

Hint: I don't use smiley faces.

Of course math is essential to understanding electronics. I'm OK with
algebra and trig, but have problems with calculus, even though I have a
basic understanding of it (differentiation, integration, etc.).

Maybe in the next lifetime ...


--
Comment on quaint Usenet customs, from Usenet:

To me, the *plonk...* reminds me of the old man at the public hearing
who stands to make his point, then removes his hearing aid as a sign
that he is not going to hear any rebuttals.

 

[Phil Allison]

"David Nebenzahl"

http://en.wikipedia.org/wiki/Direct-conversion_receiver

OK, so this is why I absolutely *hate* Wikipedia. Here's the lead
paragraph in the article:

In telecommunication, a direct-conversion receiver (DCR), also known as
homodyne, synchrodyne, or zero-IF receiver, is a radio receiver design
that demodulates the incoming signal by mixing it with a local
oscillator signal synchronized in frequency to the carrier of the wanted
signal. The wanted modulation signal is obtained immediately by low-pass
filtering the mixer output, without requiring further detection. Thus a
direct-conversion receiver requires only a single stage of detection and
filtering, as opposed to the more common superheterodyne receiver
design, which converts the carrier frequency to an intermediate
frequency first before extracting the modulation, and thus requires two
stages of detection and filtering.

Now, class, how many things are wrong here? (And please correct *me* if
I'm incorrect):

** Only one error.

A basic superhet has two stages of filtering ( RF and IF) followed by one
stage of detection.

o Is their explanation of how DCR works even correct? I don't understand
the business of mixing the signal with a LO signal: why would you do that?

** To shift the modulation down to base band - silly.

They're a little vague: does "synchronized in frequency to the carrier"
mean *exactly* the same frequency as the carrier (???),

** Yep - that is exactly how it works.

In the case of an AM receiver, the original carrier can be extracted and
then mixed with the original AM signal to recover the modulation. Some
hi-fi AM tuners worked this way.

If I were in front of a firing squad and had to try to describe DCR
without actually knowing what it is, I'd guess(tm)(R) that it's a bunch of
tuned RF stages followed by a detector.

** The you would be justifiably shot.

Cos that describes a TRF receiver.

Anyhow, I think I've shown that even if I'm way off base, Wikipedia
articles tend to be extremely badly written, if not outright full of
doubtful information.

** Bob Dylan wrote a song about people like you.



...... Phil

 

[Phil Allison]

"David Nebenzahl"

It occurred to me that maybe they (the Wikipedia article) are referring to
FM, not AM, DCR (it doesn't say)?

** Don't think DCR works with FM.



...... Phil

 

[William Sommerwerck]

Another book (which I frankly don't like as much since
it's so math-heavy: wouldn't electronics be so easy to
learn if all that goddamn math didn't get in the way?)...

I hope you're joking, because without that math, you can't
begin to truly /understand/ electronics. Mathematics is used
to model the physical world. When you understand the math,
you have a much better comprehension of the physics involved.

Hint: I don't use smiley faces.

Hint: I don't generally assume they're there, unless I see them. As an
extremely sarcastic person, I rarely fail to see sarcasm when it's present.
Don't complain that I missed something that wasn't there.

Of course math is essential to understanding electronics.
I'm OK with algebra and trig, but have problems with calculus,
even though I have a basic understanding of it (differentiation,
integration, etc).

Calculus is pretty simple -- if you have a good book. I can't recommend any,
because I don't know any off the top of my head. (Recommendations, anyone?)

I took calculus in high school 45 years ago, at a time when very, very few
high schools in the US offered it. We were given a book to study over the
summer, which carefully walked the reader through the basics of the
differential calculus. When we got to class in the fall, we a preliminary
understanding under our belts.

You also need to learn about Laplace transforms. They make it possible to
analyze circuits with simple algebra, rather than differential equations.
Very, very handy.

 

[Adrian C]

On 16/01/2011 21:58, David Nebenzahl wrote:

Of course math is essential to understanding electronics. I'm OK with
algebra and trig, but have problems with calculus, even though I have a
basic understanding of it (differentiation, integration, etc.).

Maybe in the next lifetime ...

Nah, plenty to read in this one

I wonder if you are aware of this collection of US Navy training
manuals. Looks pretty well written, and only written 13 years ago so
relatively recent.

http://www.rarmy.com/coleman/neets/index.html

--
Adrian C

 

[David Nebenzahl]

On 1/16/2011 3:14 PM William Sommerwerck spake thus:

[I wrote, which for some reason William failed to attribute:]

Of course math is essential to understanding electronics.
I'm OK with algebra and trig, but have problems with calculus,
even though I have a basic understanding of it (differentiation,
integration, etc).

Calculus is pretty simple -- if you have a good book. I can't recommend any,
because I don't know any off the top of my head. (Recommendations, anyone?)

I took calculus in high school 45 years ago, at a time when very, very few
high schools in the US offered it. We were given a book to study over the
summer, which carefully walked the reader through the basics of the
differential calculus. When we got to class in the fall, we a preliminary
understanding under our belts.

I took one semester of calculus back in college and still have the
textbook, a giant tome that's pretty good: /Calculus and Analytic
Geometry/, Edwards and Penney. Didn't do too badly in the course, but
that was a while ago ...

You also need to learn about Laplace transforms. They make it possible to
analyze circuits with simple algebra, rather than differential equations.
Very, very handy.

No doubt. Wouldn't hurt to know Fourier analysis either, and I'm sure a
bunch of other techniques.


--
Comment on quaint Usenet customs, from Usenet:

To me, the *plonk...* reminds me of the old man at the public hearing
who stands to make his point, then removes his hearing aid as a sign
that he is not going to hear any rebuttals.

 

[Tony Matt]

On 1/15/2011 10:47 PM, David Nebenzahl wrote:

Trying to teach myself electronics, I've been reading a few textbooks I
inherited on the subject. Tough going, as my math is in serious need of
repair.

Anyhow, found a couple of interesting things in these older books:

1. TRF:

In the section on modulation, demodulation and other radio-related stuff
one book brings up "the tuned radio-frequency receiver" before
discussing superhet, as one would expect. But they say;

During the evolution of radio, the tuned-radio-frequency (TRF)
receiver was used to receive AM signals. Today, a few special
applications still use TRF receivers.

Now, they go on to explain why TRF is inferior to superheterodyne. But
I'm curious: are there still any radios that use TRF? and why? (Keep in
mind this book was written in 1979).

The Realistic TRF (12-655) radio was sold into the (IIRC) mid-80s:
http://www.radiomuseum.org/r/radio_shac_realistic_long_range_trf.html
This link indicates that it was actually a superhet with an RF stage; I
was under the impression all these years that it was a solid state
analog to an AK-40 or similar. Oh well.

TM

 

[William Sommerwerck]

"David Nebenzahl" <nobody@but.us.chickens> wrote in message
news:4d33a563$0$2370$822641b3@news.adtechcomputers.com...

On 1/16/2011 3:14 PM William Sommerwerck spake thus:

You also need to learn about Laplace transforms. They make
it possible to analyze circuits with simple algebra, rather than
differential equations. Very, very handy.

No doubt. Wouldn't hurt to know Fourier analysis either, and I'm
sure a bunch of other techniques.

Fourier analysis is worth understanding on a theoretical level, but actually
performing the analysis is something that's commonly left to computers.

 

[hrhofmann@att.net]

On Jan 17, 7:14 am, "William Sommerwerck" <grizzledgee...@comcast.net>
wrote:

"David Nebenzahl" <nob...@but.us.chickens> wrote in message

news:4d33a563$0$2370$822641b3@news.adtechcomputers.com...

On 1/16/2011 3:14 PM William Sommerwerck spake thus:
You also need to learn about Laplace transforms. They make
it possible to analyze circuits with simple algebra, rather than
differential equations. Very, very handy.
No doubt. Wouldn't hurt to know Fourier analysis either, and I'm
sure a bunch of other techniques.

Fourier analysis is worth understanding on a theoretical level, but actually
performing the analysis is something that's commonly left to computers.

Thank God for computers!!