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).

2. Thermionic converters & magneto-hydrodynamic generators:

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?) covers these somewhat fantastic devices in
its chapter on "Energy Conversion Phenomena". The thermionic converter
is especially intriguing, as it seems a fairly efficient (20%) direct
conversion from heat to electricity. I seem to remember seeing a program
on PBS about something like magnetohydrodynamics being developed for
deep-space exploration propulsion.

Are either of these devices being seriously researched or used nowadays?
Keep in mind that *this* book was written in 1966.


--
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.

In article
,
kens says...
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).

2. Thermionic converters & magneto-hydrodynamic generators:

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?) covers these somewhat fantastic devices in
its chapter on "Energy Conversion Phenomena". The thermionic converter
is especially intriguing, as it seems a fairly efficient (20%) direct
conversion from heat to electricity. I seem to remember seeing a program
on PBS about something like magnetohydrodynamics being developed for
deep-space exploration propulsion.

Are either of these devices being seriously researched or used nowadays?
Keep in mind that *this* book was written in 1966.

Did you mean deep-ocean exploration? IIRC, the
Russian sub in Hunt for Red October used a
MHD stealth drive.

Couldn't say if anyone's actually using it for
real...

On Sat, 15 Jan 2011 19:47:23 -0800, David Nebenzahl
wrote:

Talk about off topic... sigh.

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).

Yes, but it's not obvious or really TRF. The reason superheterodyne
receivers were invented was that decent narrow band LC or crystal IF
bandpass filters were not tuneable and didn't work well at higher RF
frequencies. About 45MHz was as high as they went before going exotic
with SAW devices.

These daze, dramatically improved semiconductor technology has
produced chips that work at almost any useful RF frequency. No more
need to downconvert when the IF filtering is done by a DSP (digital
signal processor). Instead of TRF, it's now called "direct
conversion". There's no local oscillator, no mixer, for fixed IF
filter, and probably no LC devices anywhere. Just a ceramic bandpass
filter (or duplexer) some gain, an A/D converter, and a DSP for
demodulation. Most GPS, Wi-Fi, and cellular chipsets work this way.
http://en.wikipedia.org/wiki/Direct-conversion_receiver

There are some rather simple TRF devices still around. A freqency
selective voltmeter is sometimes a TRF device. So are some field
strength measurement instruments, and remotes (car alarm, TV remote,
etc).

2. Thermionic converters & magneto-hydrodynamic generators:

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?) covers these somewhat fantastic devices in
its chapter on "Energy Conversion Phenomena". The thermionic converter
is especially intriguing, as it seems a fairly efficient (20%) direct
conversion from heat to electricity. I seem to remember seeing a program
on PBS about something like magnetohydrodynamics being developed for
deep-space exploration propulsion.

Are either of these devices being seriously researched or used nowadays?
Keep in mind that *this* book was written in 1966.

Yep. Just about anything that has to do with plasma research involves
MHD. However, the generator part is effectively dead because of lousy
efficiency. I think the best it can do is about 20% thermal
efficiency. Light reading:
http://en.wikipedia.org/wiki/MHD_generator
The only hope for commercial use of MHD technology is generating
electricity (and some cooling) from waste heat, such as nuclear
reactor coolant.


--
Jeff Liebermann
150 Felker St #D http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann AE6KS 831-336-2558

"Jeff Liebermann"


Yes, but it's not obvious or really TRF. The reason superheterodyne
receivers were invented was that decent narrow band LC or crystal IF
bandpass filters were not tuneable and didn't work well at higher RF
frequencies.

** Total hogwash.

That has got nothing to do with the invention and wide adoption of superhet
radios.


These daze, dramatically improved semiconductor technology has
produced chips that work at almost any useful RF frequency. No more
need to downconvert when the IF filtering is done by a DSP (digital
signal processor). Instead of TRF, it's now called "direct
conversion".

** TRF and "direct conversion" are separate techniques.


There's no local oscillator, no mixer, for fixed IF
filter, and probably no LC devices anywhere. Just a ceramic bandpass
filter (or duplexer) some gain, an A/D converter, and a DSP for
demodulation. Most GPS, Wi-Fi, and cellular chipsets work this way.


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


** How hysterically funny.

The bull****ting fool has posted a Wiki link that completely contradicts his
fabricated thesis.

" 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. "




...... Phil

David Nebenzahl wrote in message
.com...
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).

2. Thermionic converters & magneto-hydrodynamic generators:

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?) covers these somewhat fantastic devices in
its chapter on "Energy Conversion Phenomena". The thermionic converter
is especially intriguing, as it seems a fairly efficient (20%) direct
conversion from heat to electricity. I seem to remember seeing a program
on PBS about something like magnetohydrodynamics being developed for
deep-space exploration propulsion.

Are either of these devices being seriously researched or used nowadays?
Keep in mind that *this* book was written in 1966.


--
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.


Infra long-wave timecode receivers , eg Rugby and Darmstat, are usually TRF.

Which reminds me - I used to use Teletext timecode for within 1 second
accuracy but that was analogue processing - gone now with "digital" delays
to TV . So bad , up to about 8 seconds delay , and variable , the digital
Teletext has only the minutes of time shown

On 1/15/2011 10:14 PM Jeff Liebermann spake thus:

On Sat, 15 Jan 2011 19:47:23 -0800, David Nebenzahl
wrote:

Talk about off topic... sigh.

Hey, at least it's about *electronics* ...

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).

Yes, but it's not obvious or really TRF. The reason superheterodyne
receivers were invented was that decent narrow band LC or crystal IF
bandpass filters were not tuneable and didn't work well at higher RF
frequencies. About 45MHz was as high as they went before going exotic
with SAW devices.

These daze, dramatically improved semiconductor technology has
produced chips that work at almost any useful RF frequency. No more
need to downconvert when the IF filtering is done by a DSP (digital
signal processor). Instead of TRF, it's now called "direct
conversion". There's no local oscillator, no mixer, for fixed IF
filter, and probably no LC devices anywhere. Just a ceramic bandpass
filter (or duplexer) some gain, an A/D converter, and a DSP for
demodulation. Most GPS, Wi-Fi, and cellular chipsets work this way.
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):

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"?

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

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.

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


--
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.

On 1/16/2011 12:38 AM David Nebenzahl spake thus:

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

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


--
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.

David Nebenzahl wrote:
On 1/15/2011 10:14 PM Jeff Liebermann spake thus:

On Sat, 15 Jan 2011 19:47:23 -0800, David Nebenzahl
wrote:

Talk about off topic... sigh.

Hey, at least it's about *electronics* ...

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).
Yes, but it's not obvious or really TRF. The reason superheterodyne
receivers were invented was that decent narrow band LC or crystal IF
bandpass filters were not tuneable and didn't work well at higher RF
frequencies. About 45MHz was as high as they went before going exotic
with SAW devices.

These daze, dramatically improved semiconductor technology has
produced chips that work at almost any useful RF frequency. No more
need to downconvert when the IF filtering is done by a DSP (digital
signal processor). Instead of TRF, it's now called "direct
conversion". There's no local oscillator, no mixer, for fixed IF
filter, and probably no LC devices anywhere. Just a ceramic bandpass
filter (or duplexer) some gain, an A/D converter, and a DSP for
demodulation. Most GPS, Wi-Fi, and cellular chipsets work this way.
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):

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"?

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

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.

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


The story above sounds like descibing a Single Sideband
receiver, where you indeed have to mix in a carrier to detect things.

David Nebenzahl wrote:
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"?

Not really. While there only needs to be one stage of filtering, it is
common in high end receivers (ham radio and millitary, not audiophile)
to have multiple stages of filtering. So for example, if you have a tripple
conversion receiver you often see filters at the final two.

They are cascaded, meaning you might have a 2.4kHz filter at the 2nd if, and
a 1.8kHz one at the third. Or a 600Hz at the second and a 250Hz at the third.

They are also used as "roofing" filters for DSP filters. If you have a
DSP filter capable of adjustable bandwidth from 6kHz to 100Hz, you may see
a roofing filter (6Hz) in front of it. Since up until a few years ago IF DSP
filters were limited to low frequencies, such as 455kHz, you would see the
roofing filter in the second IF, say 8.8mHz or 10.7mHz, and the DSP at 455kHz.

Now you see them in both places.

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

If you mix two signals, you get 4, the originals, plus the sum and the
difference. Sounds familar correct. Instead of mixing two signals 455kHz,
or 10.7 mHz, or whatever apart, a DC receiver mixes them with much closer
frequencies, for example, 800Hz for CW (morse code) or even for audio.

In that case you mix the locally generated signal and the distant one
put them through an audio filter and viola, you have a signal. The problem
with that is they are notoriously poorly selective, and if you are scanning
the ham bands in a large city, you may end up with Rush Limbaugh every few
kilohertz. :-(

Now they are most often used in cheap (and I mean cheap) ham radios usually
kits. Since mixer chips, if filters, etc are so easily and cheaply available,
most radios in the $100 plus range are single stage superhets instead.

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.

Rarely. No one bothers with the TRF stages. They tend to be expensive and
unless you have a junk box full of multistage capacitors too costly to make.

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

Actually the wikipedia is one of the better sources of information available
today. The paper version of the encyclopedia that used to be given away with
CD ROM drives in the mid 1990's (not Encarta, the other one) was worse.

It's just that it's uneven. Some articles are very well researched and
documented. Others are just an exposition of a (or conflicting) point of
view.

That led me, years ago to come up with Mendelson's Corollary to Godwin's
whatever. In it's simplest form replace "calling someone a NAZI" with quoteing
from the wikipedia. :-)

http://en.wikipedia.org/wiki/Godwin%27s_law


Meanwhile there are many good electronics books which have goneout of
copyright and are being preserved by people scanning them. Some are
available free for dowload, some are sold often for the cost of a blank
CD and shipping.

They make great reading and reference. However to keep it modern, the nook
does not display scanned PDF files well, it has too small a screen, and no
zoom and rotate. The iPad does it wonderfully. I can't comment on the color
nook or any form of the kindle, if someone else can, please do.

Geoff.

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

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.

The reason superheterodyne receivers were invented was
that decent narrow band LC or crystal IF bandpass filters
were not tuneable and didn't work well at higher RF
frequencies.

** Total hogwash.
That has nothing to do with the invention and wide adoption
of superhet radios.

That's not what the textbooks state. The stated advantages of superhet
receivers are obvious. Care to give another explanation?

First of all, superhet receivers have only one stage of detection
and filtering, not two, after the last IF stage, right?

Wrong. The conversion of the RF signal to the intermediate frequency is a
form of detection (ie, non-linear mixing). The IF stages provide filtering
that removes the unwanted components of the mixing process.


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?

Ever heard of a product detector?


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.

Badly written, yes. Some articles need a thorough re-write.

Doubtful information? I don't think so. In areas I'm knowledgeable about, I
find Wikipedia remarkably accurate.


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

What kind of useful criticism can we expect from someone who doesn't seem to
know much about receiver design?


By the way, the last "GE Transistor Manual" had a classic "direct
conversion" (???) FM tuner (p385) that had only one inductor and no bandpass
filters. (45 years later, I still don't understand how it works.) I'd wanted
to build it, but the transistors were expensive -- the parts came to close
to $100.

The story above sounds like descibing a single sideband
receiver, where you indeed have to mix in a carrier to detect things.

Product detectors can be used for AM reception. They have advantages over
envelope detection -- but I don't remember what they are.

Rarely. No one bothers with the TRF stages. They tend
to be expensive and unless you have a junk box full of
multistage capacitors too costly to make.

Many modern /high-performance/ receivers omit the RF stage (such as the Sony
DSP FM tuner), or allow you to bypass it (many ham receivers).

William Sommerwerck wrote:

Many modern /high-performance/ receivers omit the RF stage (such as the Sony
DSP FM tuner), or allow you to bypass it (many ham receivers).

Ham receivers omit it because most hams don't need or want it. Since you are
going to be transmitting into a ham antenna, it needs to be resonant or appear
to be resonant.

A resonant antenna, unless it is 100% a resistor, is not resonant on frequencies
you don't want, so they are signifcantly reduced in strength anyway.

If the antenna is not resonant, a device called a "tuner" is used to make it
appear resonant to the transmitter (it does not affect the actual antenna).
In the process of "tuning the antenna", as it were, it detune signals away from
the frequency desired, so in practice it acts as a TRF stage.

For reception only the device is called a pre-selector, although sometimes they
are also called tuners, because they contain the same circuity.

Early (pre WW-II and soon after) TV sets used TRF receivers because of both
the lack of competing signals and the very wide bandwidth needed. As the bands
became more crowded (signals receivable 1), more services used nearby
frequencies and receiver sophistication increased they moved to superhets.

Eventualy they went to digital sythesizers with mixers, filters and decoders
on a chip. Digital TV receivers are the same thing, except instead of the
"receiver" chip outputing a video signal and an audio signal, it outputs a
bit stream to a decoder chip.

Going back to the other discussion (ducks) that's the irony of DVB-T versus
ATSC. The RF part of the receiver is so generic and adjustable "on the fly",
that it can tune almost anything, the video stream for both is MPEG TS
(transport stream) data, it's the encoding of the bit stream in between.

ATSC was chosen specificaly NOT to be the same as DVB-T.

Someone already sells a chipset to laptop manufacturers to give them ATSC/DVB-T
reception capability, which gives you a TV set that will work almost anywhere.
The TS decoding is done by program in the CPU, so it can support any changes
that come down the line as it where.

Geoff.


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

Many modern /high-performance/ receivers omit the RF stage
(such as the Sony DSP FM tuner), or allow you to bypass it
(many ham receivers).

Ham receivers omit it because most hams don't need or want it.
Since you are going to be transmitting into a ham antenna, it
needs to be resonant or appear to be resonant.

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

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.

Geoff.


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

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.

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.

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

On Sun, 16 Jan 2011 00:38:07 -0800, David Nebenzahl
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.



--
Jeff Liebermann
150 Felker St #D http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann AE6KS 831-336-2558

"Geoffrey S. Mendelson" wrote in message
...
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.

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.

Jeff Liebermann Inscribed thus:

On Sun, 16 Jan 2011 00:38:07 -0800, David Nebenzahl
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.

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.

"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

"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

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.

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

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.

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_s...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

"David Nebenzahl" wrote in message
.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.

On Jan 17, 7:14*am, "William Sommerwerck"
wrote:
"David Nebenzahl" wrote in message

.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!!