> On Mon, 18 Apr 2005 10:08:50 -0400, Jerry Avins <jya@ieee.org> wrote:
>
>
>>We used 5 MHz crystals exposed to the vapor stream to measure film
>>thickness when evaporating metals and insulators in a vacuum system. The
>>change in frequency is a measure of the deposited mass. The sensitivity
>>can be changed by varying the size of the hole open to the vapor. We
>>converted frequency shift to voltage, differentiated that, and closed a
>>loop around the heater current to maintain constant deposition rate.
>
>
> Dude! I hope you didn't have to calibrate this, but there's one thing
> to be said about the wonderful digital clean world of the future: it
> ain't here yet.
>
> And I'm astonished at such an elegant solution. Hats, gentlemen,
Calibration isn't difficult. For each material, one test sample. (It's
established that delta-f is linear with mass, hence thickness. The
evaporation is sustained until the frequency is shifted some standard
amount -- approximate, but the exact value recorded -- and the film
thickness measured interferometrically. (A Fabry-Perot interferometer is
simple: a semitransparent reflecting film on a glass slide, laid over
the step edge of the evaporated film ans illuminated with collimated
light of known wavelength. The displacement of the interference fringes
gives the height in half-wave steps, with quarter-wave or better easily
estimated.) I have the means to measure the film thickness at home.
Jerry
--
Engineering is the art of making what you want from things you can get.
�����������������������������������������������������������������������
Reply by Chris Hornbeck●April 19, 20052005-04-19
On Mon, 18 Apr 2005 10:08:50 -0400, Jerry Avins <jya@ieee.org> wrote:
>We used 5 MHz crystals exposed to the vapor stream to measure film
>thickness when evaporating metals and insulators in a vacuum system. The
>change in frequency is a measure of the deposited mass. The sensitivity
>can be changed by varying the size of the hole open to the vapor. We
>converted frequency shift to voltage, differentiated that, and closed a
>loop around the heater current to maintain constant deposition rate.
Dude! I hope you didn't have to calibrate this, but there's one thing
to be said about the wonderful digital clean world of the future: it
ain't here yet.
And I'm astonished at such an elegant solution. Hats, gentlemen,
Chris Hornbeck
"Hum is more than just not knowing the words." -ha
Reply by john●April 19, 20052005-04-19
Tim Wescott wrote:
> Chris Hornbeck wrote:
>
> > On Sun, 17 Apr 2005 15:55:23 -0400, robert bristow-johnson
> > <rbj@audioimagination.com> wrote:
> >
> >
> >>Heathkit "Hot Water" HW-100, the cheapest 5-band SSB a kid could
afford).
> >>although there were a lot of tubes, and 2 or 3 transistors in the
VFO, there
> >>were no all-pass filters nor direct Hilbert transformers in that
box. the
> >>SSB was generated the old fashioned way with AM (at some IF
frequency that i
> >>forget) and an nasty sharp crystal-lattice filter that was 2.1 kHz
wide.
> >
> >
> > Wouldn't those have had to be DSB modulators, and to have just
> > stripped the unwanted sideband? Wouldn't the carrier from an
> > AM modulator have been too large as a filter residual?
> > 'Course, times have changed!
> >
> The SB-102 is supposed to be the same circuit as the HW-100 but with
a
> better oscillator and fancier case. It had a balanced modulator with
> carrier suppression, as does just about any other SSB scheme I've
seen.
>
> In my '50s and '60s ARRL handbooks the phasing method and the filter
> method (ala HW-100) ran neck and neck. The filter method wins out
for
> production radios because crystal filters are hard to engineer but
> (relatively) easy to build once you get the recipe right. The
phasing
> method was (and is) often easier for home brew because it didn't take
as
> much engineering but _did_ take more fussing.
>
> Nowadays you take have I-Q demodulators straight from the GHz down to
> baseband and into a DSP -- and if you want to demodulate SSB it'd
Yes, but watch out for DC offsets! It is often better to mix down to an
IF that can be sampled by a two channel ADC and perform the final
downconversion in DSP.
John
Reply by Mark●April 19, 20052005-04-19
QRZ...
WB2WHC
Mark
Reply by Tim Wescott●April 19, 20052005-04-19
Chris Hornbeck wrote:
> On Sun, 17 Apr 2005 15:55:23 -0400, robert bristow-johnson
> <rbj@audioimagination.com> wrote:
>
>
>>Heathkit "Hot Water" HW-100, the cheapest 5-band SSB a kid could afford).
>>although there were a lot of tubes, and 2 or 3 transistors in the VFO, there
>>were no all-pass filters nor direct Hilbert transformers in that box. the
>>SSB was generated the old fashioned way with AM (at some IF frequency that i
>>forget) and an nasty sharp crystal-lattice filter that was 2.1 kHz wide.
>
>
> Wouldn't those have had to be DSB modulators, and to have just
> stripped the unwanted sideband? Wouldn't the carrier from an
> AM modulator have been too large as a filter residual?
> 'Course, times have changed!
>
The SB-102 is supposed to be the same circuit as the HW-100 but with a
better oscillator and fancier case. It had a balanced modulator with
carrier suppression, as does just about any other SSB scheme I've seen.
In my '50s and '60s ARRL handbooks the phasing method and the filter
method (ala HW-100) ran neck and neck. The filter method wins out for
production radios because crystal filters are hard to engineer but
(relatively) easy to build once you get the recipe right. The phasing
method was (and is) often easier for home brew because it didn't take as
much engineering but _did_ take more fussing.
Nowadays you take have I-Q demodulators straight from the GHz down to
baseband and into a DSP -- and if you want to demodulate SSB it'd better
be with phasing!
--
Tim Wescott
Wescott Design Services
http://www.wescottdesign.com
Reply by Jerry Avins●April 18, 20052005-04-18
Chris Hornbeck wrote:
> On Mon, 18 Apr 2005 00:37:54 -0400, robert bristow-johnson
> <rbj@audioimagination.com> wrote:
>
>
>> it would still need a good and
>>sharp filter. i remember that the crystal lattice filter was a component
>>mounted off of the circuit boards and 2 cables connected to it.
>
>
> And in those days the filter was PFM ( pure ... magic ) although some
> intrepid souls made their own, largely by (literally) cut-and-try,
> by filing on quartz crystals and inserting them into some hoped-for
> band pass filter.
>
> In that era the Collins LC (? is my memory correct?) filters at
> 455 kHz were considered to be "The Shit" because they had some
> really deep slopes.
>
> Probably nobody worried too much about residual carrier anyway;
> a small beat somewhere wasn't the end of the world.
>
> Thanks,
>
> Chris Hornbeck
> 6x9=42 April 29
Tuning a crystal up is easy: just thin it a little with fine emery
paper. Down was thought to be impossible by some, but I once tuned a
crystal down by writing "down" on it with a pencil, much to the
amazement of my buddy who thought it was a joke. Of course, any scribble
would have worked. The extra weight of the "lead" changed the frequency.
We used 5 MHz crystals exposed to the vapor stream to measure film
thickness when evaporating metals and insulators in a vacuum system. The
change in frequency is a measure of the deposited mass. The sensitivity
can be changed by varying the size of the hole open to the vapor. We
converted frequency shift to voltage, differentiated that, and closed a
loop around the heater current to maintain constant deposition rate. All
analog: in 1964, there was no other practical way. Believe me: digital
is simpler, once you get the hang of it.
Jerry
--
Engineering is the art of making what you want from things you can get.
�����������������������������������������������������������������������
Reply by Jerry Avins●April 18, 20052005-04-18
Chris Hornbeck wrote:
> On Sun, 17 Apr 2005 15:55:23 -0400, robert bristow-johnson
> <rbj@audioimagination.com> wrote:
>
>
>>Heathkit "Hot Water" HW-100, the cheapest 5-band SSB a kid could afford).
>>although there were a lot of tubes, and 2 or 3 transistors in the VFO, there
>>were no all-pass filters nor direct Hilbert transformers in that box. the
>>SSB was generated the old fashioned way with AM (at some IF frequency that i
>>forget) and an nasty sharp crystal-lattice filter that was 2.1 kHz wide.
>
>
> Wouldn't those have had to be DSB modulators, and to have just
> stripped the unwanted sideband? Wouldn't the carrier from an
> AM modulator have been too large as a filter residual?
> 'Course, times have changed!
>
> Chris Hornbeck
> 6x9=42 April 29
The residual was 40 t0 60 dB down. We used balanced modulators to
generate a double-sideband suppressed-carrier signal with about a 500 Hz
gap between upper and lower sidebands. After filtering out one sideband,
there was your signal. Without carrier, you need linear amplifiers in
subsequent stages. (Only a synchronous demodulator could recover the
signal while both sidebands were present.)
Jerry
--
Engineering is the art of making what you want from things you can get.
�����������������������������������������������������������������������
Reply by ●April 18, 20052005-04-18
I've worked on a broadband wireless system that generates a real
baseband signal, but uses a Hilbert transform to filter the negative
frequencies before digital modulation to the passband. In this case we
needed a good Hilbert filter, with passband coming right down to close
to 0Hz. In the end, this SSB scheme was implemented with a 41 tap FIR
Hilbert filter, using a truncated ideal Hilbert filter, and a Kaiser
smoothing window.
$0.02
Reply by Rune Allnor●April 18, 20052005-04-18
Rick Lyons wrote:
> Hi Guys,
>
> I have a question about Hilbert transformer applications.
> First, we can build Hilbert transformers using
> a tapped-delay line structure (like a tapped-delay
> line FIR filter.)
>
> An ideal Hilbert transformers (HT) would have a freq
> magnitude response that's flat over the HT's entire
> operating frequency range. However, practical HTs
> have a magnitude null at zero Hz and a freq mag response
> that slowly rises in magnitude as we go up in
> frequency. Like this:
>
>
> | ****************************
> | *
> | *
> | *
> | *
> | *
> |-*---------------------------------------
> 0 Freq -->
>
> Adding more taps (coefficients) to the HT's implementation
> allows us to increase the slope of the HT's mag response
> just above zero Hz. You guys know all of this.
>
> OK, here's my question: When would we want to increase
> the the slope of the HT's mag response?
> I know that increasing the slope widens the usable
> bandwidth of the HT, but I can't think of any applications
> where that's desirable. The only HTs I've designed
> operated on signals centered at Fs/4, so the HT's passband
> didn't have to be wide. To rephrase my question,
> for what applications (for what real-world signals)
> would we want an HT that operates very near zero Hz?
>
> I ask that question because a professor sent me
> a manuscript describing a "HT Implementation Trick"
> for building an HT whose usable passband extends down
> close to zero Hz. I haven't modeled his scheme yet to
> see if it actually works, but I'm just wondering if
> his idea is useful or not.
>
> Thanks for your opinions guys.
I would be most interested in such a HT. When dealing
with large volumes of broad-band data, one pushes the
limits of signal sampling, to save system/storage costs.
So even if the signal is centered at Fs/4, the bandwidth
may in some applications be as large as 0.05*Fs - 0.4*Fs.
To what extent I have used HTs with seismic data, I have
implemented it as an IFFT(FFT(X)[0:Fs/2])) transform,
which only works in off-line applications. Having a HT
that potentially could work in an on-line application
would be very interesting for "broadish-band" applications.
Rune
Reply by Chris Hornbeck●April 18, 20052005-04-18
On Mon, 18 Apr 2005 00:37:54 -0400, robert bristow-johnson
<rbj@audioimagination.com> wrote:
> it would still need a good and
>sharp filter. i remember that the crystal lattice filter was a component
>mounted off of the circuit boards and 2 cables connected to it.
And in those days the filter was PFM ( pure ... magic ) although some
intrepid souls made their own, largely by (literally) cut-and-try,
by filing on quartz crystals and inserting them into some hoped-for
band pass filter.
In that era the Collins LC (? is my memory correct?) filters at
455 kHz were considered to be "The Shit" because they had some
really deep slopes.
Probably nobody worried too much about residual carrier anyway;
a small beat somewhere wasn't the end of the world.
Thanks,
Chris Hornbeck
6x9=42 April 29