Reply by glen herrmannsfeldt●July 20, 20052005-07-20
Joel Kolstad wrote:
(snip)
> Hmm... I'm not so sure... Faroudja was pushing his so-called "super NTSC" some
> 20+ years ago already, and it never caught on, despite the fact that it would
> have remained compatible with "regular" NTSC receivers.
I am not sure what super NTSC is, but only relatively recently did
anyone build a proper NTSC demodulator.
NTSC, as designed in 1954, uses two chroma signals called I and Q,
which don't correspond to R, G, or B but linear combinations of them.
I has more bandwidth than Q, as the eye has more spatial resolution
for those colors. The color burst, though, is phased to make it easy
to decode along the R and B axis, ignoring the extra resolution.
About the time that HDTV started to get interesting, some made EDTV
receivers which could finally decode this information, about 40 years
after it was added to the standard.
> As far as I can tell, even today the average consumer is often much more
> interested in picture size and brightness than in picture detail. I've been
> surprised just how well some of the image processing found in modern projector
> TVs with screens in the 60+" realm manage to do in terms of keeping the
> picture looking relatively "sharp" given the signal they have to work with.
-- glen
Reply by Dave Coffey●July 19, 20052005-07-19
Steve Underwood wrote:
> I believe the world's first colour TV where the only thermionic device
> was the picture tube was the Thorn 2000 (sold and rented under various
> names). This had a class D amp capable of very good results. You didn't
> need to mess around with an external IF and audio amp. If you just
> disconnected the internal speaker and connected a good external one is
> sounded pretty good.
>
> The current fad for class D amps as the shiny new way to get the size of
> home theatre boxes down amuses me. They seem to be nearly 40 years late. :-)
>
> Regards,
> Steve
Wow.
The Thorn 2000. What an addled youth I had working on
those beasts. The sound was the least of the problems there.
It also had as I remember, the first Switch Mode PSU with the
PSU and the line oscillator forming and integrated unit, discrete
transistor PAL decoder and a colour convergence board almost as big
as the CRT. Those were the days.
I can also sympathise with Jerry's tweaking propensity as I worked
for a company who imported TVs from Germany to Ireland and my job
then was to re-tune the sound I.F. from 5.5MHz to 6MHz and re-align
the PAL decoders etc. I fondly remember that despite the excellent
level of elegance in the German design, I had to add a hand wound
coil to the collector of the video amp to 'square up' the teletext
pulses.
I digress...
Dave.
Reply by Steve Underwood●July 18, 20052005-07-18
Jerry Avins wrote:
> glen herrmannsfeldt wrote:
>
>> Jerry Avins wrote:
>>
>> (snip)
>>
>>>>> Not really. If you have a single frequency and you know what it
>>>>> is, then
>>>>> you can do it. That's rather uninteresting. Think about what happens
>>>>> when you start with a band of frequencies. For one thing, how
>>>>> would you
>>>>> multiply?
>>>>
>>
>>
>> Slightly different, but I have heard of optical systems with
>> frequency multipliers, such as a red laser through a non-linear
>> material and then separating the third harmonic of the source
>> beam. That is to get short wavelengths where there aren't any
>> laser materials.
>>
>> For a modulated source it would be more complicated, but it seems
>> that it could still work.
>
>
> Sure it works. That's what's behind heterodyning. The modulated signal
> is, of course, narrow band at the original frequency. The intercarrier
> TV sound carrier is at 4.5 MHz. I brought it out of one set into a
> push-push diode frequency doubler (aka full-wave rectifier) and into
> the retuned IF (10.7 MHz to 9) of a broadcast FM tuner. Listeners were
> surprised to hear how good the actually broadcast sound was. In
> service like that, the intermodulation products are easily removed by
> minimally selective filters.
I believe the world's first colour TV where the only thermionic device
was the picture tube was the Thorn 2000 (sold and rented under various
names). This had a class D amp capable of very good results. You didn't
need to mess around with an external IF and audio amp. If you just
disconnected the internal speaker and connected a good external one is
sounded pretty good.
The current fad for class D amps as the shiny new way to get the size of
home theatre boxes down amuses me. They seem to be nearly 40 years late. :-)
Regards,
Steve
Reply by Jerry Avins●July 18, 20052005-07-18
Joel Kolstad wrote:
> "glen herrmannsfeldt" <gah@ugcs.caltech.edu> wrote in message
> news:B6idnYHSROwJrkXfRVn-2w@comcast.com...
>
>>At about the same time the public was getting more interested in
>>better quality TV and especially better sound.
>
>
> Hmm... I'm not so sure... Faroudja was pushing his so-called "super NTSC" some
> 20+ years ago already, and it never caught on, despite the fact that it would
> have remained compatible with "regular" NTSC receivers.
>
> As far as I can tell, even today the average consumer is often much more
> interested in picture size and brightness than in picture detail. I've been
> surprised just how well some of the image processing found in modern projector
> TVs with screens in the 60+" realm manage to do in terms of keeping the
> picture looking relatively "sharp" given the signal they have to work with.
Back when TV receivers needed manual fine tuning, few viewers bothered
to use it. To promote its use, makers eventually put a separate
fine-tuning capacitor for each channel, so that once tuned, it stayed
that way. Since the carrier is tuned on a 6 dB/octave slope, fine tuning
made a big difference. It could even create a negative image and unless
intercarrier sound was implemented, being off tune would pass the
vertical rate through to the audio.
I would visit someone watching the tube, and automatically walk over to
the set and adjust the tuning. (Presumptuous, I know. I was young.) My
hosts kindly humored me, but usually sent a clear message: why bother?
Jerry
--
Engineering is the art of making what you want from things you can get.
�����������������������������������������������������������������������
Reply by Joel Kolstad●July 18, 20052005-07-18
"glen herrmannsfeldt" <gah@ugcs.caltech.edu> wrote in message
news:B6idnYHSROwJrkXfRVn-2w@comcast.com...
> At about the same time the public was getting more interested in
> better quality TV and especially better sound.
Hmm... I'm not so sure... Faroudja was pushing his so-called "super NTSC" some
20+ years ago already, and it never caught on, despite the fact that it would
have remained compatible with "regular" NTSC receivers.
As far as I can tell, even today the average consumer is often much more
interested in picture size and brightness than in picture detail. I've been
surprised just how well some of the image processing found in modern projector
TVs with screens in the 60+" realm manage to do in terms of keeping the
picture looking relatively "sharp" given the signal they have to work with.
---Joel Kolstad
Reply by Jerry Avins●July 15, 20052005-07-15
glen herrmannsfeldt wrote:
> Jerry Avins wrote:
> (snip)
>
>> Sure it works. That's what's behind heterodyning. The modulated signal
>> is, of course, narrow band at the original frequency. The intercarrier
>> TV sound carrier is at 4.5 MHz. I brought it out of one set into a
>> push-push diode frequency doubler (aka full-wave rectifier) and into
>> the retuned IF (10.7 MHz to 9) of a broadcast FM tuner. Listeners were
>> surprised to hear how good the actually broadcast sound was. In
>> service like that, the intermodulation products are easily removed by
>> minimally selective filters.
>
>
> As I understand it until about 1980, TV sound was sent through telephone
> lines while the video went through microwave links. Around then the
That surprises me. The sound subcarrier fits well within the 6 MHz
allotted to a TV channel. and an ordinary phone channel doesn't have the
bandwidth customary for broadcast. I wonder it that's just a myth.
> At about the same time the public was getting more interested in
> better quality TV and especially better sound. Pioneer produced
> a HiFi quality TV audio tuner, the standard for stereo and SAP
> for TV audio was developed, and other improvements in the audio
> section of available TV sets such as line level outputs were
> available. Thus more incentive for broadcasters to transmit
> high quality audio.
High-fidelity TV tuners imply high-fidelity broadcast sound. It was
there even before stereo, certainly before 1059 as an FCC requirement.
Jerry
--
Engineering is the art of making what you want from things you can get.
�����������������������������������������������������������������������
Reply by glen herrmannsfeldt●July 15, 20052005-07-15
Jerry Avins wrote:
(snip)
> Sure it works. That's what's behind heterodyning. The modulated signal
> is, of course, narrow band at the original frequency. The intercarrier
> TV sound carrier is at 4.5 MHz. I brought it out of one set into a
> push-push diode frequency doubler (aka full-wave rectifier) and into the
> retuned IF (10.7 MHz to 9) of a broadcast FM tuner. Listeners were
> surprised to hear how good the actually broadcast sound was. In service
> like that, the intermodulation products are easily removed by minimally
> selective filters.
As I understand it until about 1980, TV sound was sent through telephone
lines while the video went through microwave links. Around then the
technology changed such that the sound also went through microwave links.
At about the same time the public was getting more interested in
better quality TV and especially better sound. Pioneer produced
a HiFi quality TV audio tuner, the standard for stereo and SAP
for TV audio was developed, and other improvements in the audio
section of available TV sets such as line level outputs were
available. Thus more incentive for broadcasters to transmit
high quality audio.
-- glen
Reply by Jerry Avins●July 13, 20052005-07-13
Clay S. Turner wrote:
...
> One problem with freq. multiplication is the increase in phase noise. FM is
> tolerant of this, so many FM transmitters use freq. mult. However, in other
> areas, simply mixing is used to change frequencies.
Armstrong's quasi-commercial FM station at Alpine, NJ used a crystal
oscillator and phase modulated the buffered output, using an integrator
in the modulator chain to convert PM to FM. (The same thing can be done
by amplitude modulating a balanced modulator to suppress the carrier,
then injecting a large carrier component in quadrature with the
suppresses one.) At this point, the deviation -- more properly, the
modulation index -- is quite small. The signal qualifies as NBFM. To
increase the deviation the signal is tripled, then heterodyned down,
thus preserving the increased deviation. The process is repeated until
the desired deviation is attained. The heterodyning frequencies* are
chosen so that neither they nor their multiples combine to produce spurs
that survive the filtering.
Jerry
____________________________________
* Armstrong also invented the superheterodyne receiver.
--
Engineering is the art of making what you want from things you can get.
�����������������������������������������������������������������������
Reply by Jerry Avins●July 13, 20052005-07-13
glen herrmannsfeldt wrote:
> Jerry Avins wrote:
>
> (snip)
>
>>>> Not really. If you have a single frequency and you know what it is,
>>>> then
>>>> you can do it. That's rather uninteresting. Think about what happens
>>>> when you start with a band of frequencies. For one thing, how would you
>>>> multiply?
>
>
> Slightly different, but I have heard of optical systems with
> frequency multipliers, such as a red laser through a non-linear
> material and then separating the third harmonic of the source
> beam. That is to get short wavelengths where there aren't any
> laser materials.
>
> For a modulated source it would be more complicated, but it seems
> that it could still work.
Sure it works. That's what's behind heterodyning. The modulated signal
is, of course, narrow band at the original frequency. The intercarrier
TV sound carrier is at 4.5 MHz. I brought it out of one set into a
push-push diode frequency doubler (aka full-wave rectifier) and into the
retuned IF (10.7 MHz to 9) of a broadcast FM tuner. Listeners were
surprised to hear how good the actually broadcast sound was. In service
like that, the intermodulation products are easily removed by minimally
selective filters.
Jerry
--
Engineering is the art of making what you want from things you can get.
�����������������������������������������������������������������������
Reply by Joel Kolstad●July 13, 20052005-07-13
"glen herrmannsfeldt" <gah@ugcs.caltech.edu> wrote in message
news:mp6dnRrfSKSUfEnfRVn-sg@comcast.com...
> For a modulated source it would be more complicated, but it seems
> that it could still work.
Something that should have been obvious to me (my college professors would be
quite dismayed...) is that running a signal through a frequency multiplier
simply convolves the signal with itself in the frqeuency domain; hence you can
get a pretty good qualitative idea of what's going to happen with a shaped
pulse with a few quick sketches...
It is still somewhat surprising to me that frequency multipliers work as well
as they do for FM... for a cosine input, their Fourier spectra has all those
"Bessel function harmonics" as dictated by the modulation index, and running
that spectra through a frequency multiplier seems as though it's going to
produce a various changes in the output spectra other than just stretching.
I've been told that, in general, frequency multipliers are applicable to
pretty much any signalling standard that has a constant envelope... FM, PM,
FSK, perhaps even OQPSK.
---Joel