Electronic curiosities

[David Nebenzahl]

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.

 

[Randy Day]

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...

 

[Phil Allison]

"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 bullshitting 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

 

[N_Cook]

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

 

[David Nebenzahl]

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

Talk about off topic... sigh.

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

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.

 

[David Nebenzahl]

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.

 

[Sjouke Burry]

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


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.

 

[Geoffrey S. Mendelson]

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's_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.

 

[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.

 

[William Sommerwerck]

The reason superheterodyne receivers were invented was

** 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?

 

[William Sommerwerck]

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.

 

[William Sommerwerck]

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.

 

[William Sommerwerck]

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).

 

[Geoffrey S. Mendelson]

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.

 

[William Sommerwerck]

Many modern /high-performance/ receivers omit the RF stage

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?

 

[Geoffrey S. Mendelson]

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.

 

[William Sommerwerck]

What does this have to do with the perceived need

Read the rest of the posting, it explains why.

I did. It was even more confusing.

 

[Geoffrey S. Mendelson]

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.

 

[Meat Plow]

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.

 

[William Sommerwerck]

William Sommerwerck wrote:

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.