From the tone of the letter it sounds like the bank cancelled line of credit,

Which is stupid given that much of their line is military which is getting a huge boost in spending

On 3/11/17 4:30 PM, Scott McGrath wrote:

Or, he wants to retire and nobody wants to carry it on.  His dad started
it in 1950, the son picked it up in 1970.  It's 47 years later.

Plenty of other crystal and oscillator manufacturers around.

There's also a change in what kinds of crystals are needed.  I suspect
most things being built and designed today use the crystal as a "master
oscillator" that is used to drive some sort of synthesis chain. The need
for "I have to have a 12.345,324 Hz crystal" is going away.

Hi

International’s main business  was re-channeling non-synthesized radios and replacing
broken crystals in various pieces of com gear. It’s been a lot of years since the last of the
non-synthesized radios came out. The business probably has been dropping off pretty steadily
for many years …

Bob

Hi,

On 03/11/2017 10:56 PM, Bryan _ wrote:

At the bottom is a 1964 U.S. Air Force training film:

https://www.youtube.com/watch?v=dUZFxMTEss0

Haven't seen that one before. Enjoy.

I could use that to toss at my amateur radio students that wants to
learn more about crystals than I cover in my lecture for them.

I don't like how higher Q is confused with higher frequency stability.
As most here should know, it is a bit of a mix-up of two different
stability aspects.

Cheers,
Magnus

On 3/12/17 5:53 AM, Magnus Danielson wrote:

That is indeed a "time-nuts" vs "frequency-nuts" level distinction.

Hi Jim,

On 03/12/2017 10:39 PM, jimlux wrote:

Well, Q does have it's influence on phase-noise and thus ADEV, but
doesn't really say much about frequency in regard to temperature
stability or drift.

Yeah, I'm a bit picky about details like that, and I think others should
learn it right.

Cheers,
Magnus

I got a job in 1975 to design Konel's first synthesized radio, which
was to obsolete their crystal controlled radios.  That's over 40 years
ago.  The other trend (not mentioned) is that since 20 years ago or
so, complete oscillator sales have vastly outnumbered sales of loose
crystals.

Rick N6RK

On 3/11/2017 8:51 PM, Bob Camp wrote:

sorry, what do you mean by "complete oscillator" have outnumbered loose crystals?

-=Bryan=-

From: time-nuts time-nuts-bounces@febo.com on behalf of Richard (Rick) Karlquist richard@karlquist.com
Sent: March 12, 2017 4:38 PM
To: Discussion of precise time and frequency measurement
Subject: Re: [time-nuts] Bye-Bye Crystals

I got a job in 1975 to design Konel's first synthesized radio, which
was to obsolete their crystal controlled radios.  That's over 40 years
ago.  The other trend (not mentioned) is that since 20 years ago or
so, complete oscillator sales have vastly outnumbered sales of loose
crystals.

Rick N6RK

On 3/11/2017 8:51 PM, Bob Camp wrote:

[https://www.bing.com/th?id=OVF.LElrlkkbByR3K%2f6qfaeHjg&pid=Api]http://hackaday.com/2017/03/11/so-long-and-thanks-for-all-the-crystals/

So Long, and Thanks for all the Crystalshttp://hackaday.com/2017/03/11/so-long-and-thanks-for-all-the-crystals/
hackaday.com
There was a time when anyone involved with radio transmitting -- ham operators, CB'ers, scanner enthusiasts, or remote control model fans -- had a collection of ...

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Hi

There also was an intermediate phase between channel frequency -> crystal frequency -> you buy a crystal and synthesizers.
My early fun and games at Motorola involved designing TCXO’s and OCXO’s that had non-replicable crystals in them. We shipped
them as a fully sealed unit. The compensation on them was very specific to the crystal involved. The assembly was such that
replacing the crystal likely broke the part in some way. At the very least it required you to re-weld the case on the TCXO’s.

So yes, in this context (as opposed to the market in general) radios based on complete oscillators dominated a long time ago.

Bob

The article mentions that the business started in his father's garage.

What minimal equipment would you need to make your own crystals ?

On Mon, Mar 13, 2017 at 2:11 PM, Van Horn, David <
david.vanhorn@backcountryaccess.com> wrote:

A complete oscillator consists of the crystal integrated with the
electronics.  A loose crystal is just a resonator, and the buyer has to
supply his own electronics.  You rarely see the latter any more in
applications other  than oven oscillators.  The same thing happened in
SAW resonators.  About all you can buy now are SAW oscillators.

Rick N6RK

On 3/13/2017 12:07 AM, Bryan _ wrote:

I don't think it's as much the manufacturing process as it is procuring the

raw material.

73, Dick, W1KSZ

Sent from Outlookhttp://aka.ms/weboutlook

From: time-nuts time-nuts-bounces@febo.com on behalf of Adrian Godwin artgodwin@gmail.com
Sent: Monday, March 13, 2017 8:01:39 AM
To: Discussion of precise time and frequency measurement
Subject: Re: [time-nuts] Bye-Bye Crystals

The article mentions that the business started in his father's garage.

What minimal equipment would you need to make your own crystals ?

On Mon, Mar 13, 2017 at 2:11 PM, Van Horn, David <
david.vanhorn@backcountryaccess.com> wrote:

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and follow the instructions there.

With a chunk of raw crystal material and a lapidary saw, blanks can be cut.

Typical FT-243/U crystal construction technology up through the 1950's:

http://www.rfcafe.com/references/popular-electronics/after-class-Quartz-Crystals-january-1957-popular-electronics.htm

It was very common for hams to regrind crystals for other nearby
frequencies at home:
http://www.bliley.net/XTAL/docs/misc/XTAL_grinding/grinding.html

I have a large assortment of 50's/60's/early 70's FT-243 crystals and they
are uniformly crummy from a Q or frequency accuracy perspective. Sometimes
opening the holder and cleaning the electrodes and crystal helps a bit -
there's some attempt at sealing, like a rubber grommet, in some of the
FT-243 holders but mostly there's no attempt at sealing. It's possible the
rubber grommets just made things worse through outgassing.

Tim N3QE

On Mon, Mar 13, 2017 at 11:01 AM, Adrian Godwin artgodwin@gmail.com wrote:

I work for a company that builds electronics products, low volume,
highly complex units.

It used to be that you bought a crystal and then made an oscillator
that would use that crystal.  Or you had a single chip micro that used
a crystal for the time base, in the early days you might have to fight
with that oscillator to make it work acceptably.

Now for under a dollar one can have an oscillator without the hassle.
If the oscillator is a (very) small part of the unit cost, one can
spend the engineering effort on more complex parts of the design.

You can chose the parameters you want to optimize cost, phase noise,
stability etc.

On Mon, 13 Mar 2017 10:09:39 -0700
"Richard (Rick) Karlquist" richard@karlquist.com wrote:

On Mon, 13 Mar 2017 15:01:39 +0000
Adrian Godwin artgodwin@gmail.com wrote:

The equipment is quite minimal:

• A diamond precision saw to cut the crystals
• Some tool to check the accuracy of the cut (orientation and thicknes)
• a lapping/grinding machine
• an electroplating machine (usually sputtering) for the electrodes.
• either some machine to produce the crystal holder yourself or buy them
• vacuum system to evacuate the crystal holder and to bake everything
• something to (cold) weld the case close

All of this can be put in a (relatively) small workshop.
The difficulty is also not producing quartz crystals
in holders. The difficulty controlling the whole process
to such an degree that you get high quality crystals
at the frequency you want.

If you managed to do that, you can further improve
your system by using a BVA[1,2] like geometry, where
the electrodes are not on the resonator itself but
on the surrounding crystal, which acts at the same
time as holder.
But be warned, many attempted to re-create the BVAs
but few succeeded... and none but Oscilloquartz ever
managed to produce a economically viable product.

		Attila Kinali

[1] http://www.nature.com/articles/srep02132/figures/1
[2] http://www.nature.com/articles/srep02132/figures/2

--
It is upon moral qualities that a society is ultimately founded. All
the prosperity and technological sophistication in the world is of no
use without that foundation.
-- Miss Matheson, The Diamond Age, Neil Stephenson

On 3/13/17 8:01 AM, Adrian Godwin wrote:

Lapping compound and a hunk of glass/polished granite?
You can probably buy blanks that are approximately the right size and
with the correct cut.
If not, you'll need the appropriate saw and jigs and a source of quartz

A supply of crystal holders, and the technology to seal them (welding
these days, I would imagine)

the actual mechanics is probably less of a challenge than establishing
the supply chains.

For a "one off", it would be pretty easy.

On 3/13/17 10:09 AM, Richard (Rick) Karlquist wrote:

what about cheap crystals for microcontrollers.. I think the Arduino,
for instance, uses a crystal (and the oscillator electronics are inside
the Atmel part)

The Arduino Ethernet I have sitting in front of me has a fairly large
can labeled T25.000 that looks an awful lot like a crystal, rather than
an oscillator.
The published Arduino Uno schematic shows a crystal.

On 3/13/17 11:29 AM, Tim Shoppa wrote:

"Grinding your own crystals can be lots of fun, and you can have the
freedom of a v.f.o. without the danger of a pink ticket."

why, it's as simple as spinning the knob on the VFO<grin>

On 3/13/2017 11:05 AM, Richard Solomon wrote:

Here you go.

actually the process started as Statek started to etch the crystals
http://www.statek.com/corporateoverview.php in 1970 and produces high
quality crystal since than

73

KJ6UHN

On 3/13/2017 11:05 AM, Richard Solomon wrote:

.....and some micro-soldering kit to attach the plated unit to the lead
frame. Our factory used homemade hot air jets, I have no idea what the
solder was prob LMP.

Lapping a single blank is difficult, one tends to get rounded edges(even
with the best machine) which affect the activity. See the video, they are
lapping several at the same time. The unplated blanks are put into a skelton
holder and measured and the most promising one proceded with. First an
evaporated contact to fix the blank to the lead frame. Then electrode
evaporation which brings the frequency down, so the final stage evaporates
electrode while measuring the mounted crystal frequency. Allowances need to
be made for the can.

I doubt most small modern firms would have a X-ray goniometer (?) The one I
saw in the 60s would never pass H&S criteria now. They probably buy cut
blanks in bulk, I think they are relatively cheap this way. My supplier in
the 90s did this.
The whole job is quite labour intensive, making a single crystal might
easily eat $1000 worth of manhours for an amateur, not even allowing for the
occasional "oops".
:-))
Alan
G3NYK
----- Original Message -----
From: "Attila Kinali" attila@kinali.ch
To: "Discussion of precise time and frequency measurement"
time-nuts@febo.com
Sent: Monday, March 13, 2017 7:56 PM
Subject: Re: [time-nuts] Bye-Bye Crystals

On Mon, Mar 13, 2017 at 4:53 PM, jimlux jimlux@earthlink.net wrote:

You're right. Some of the Arduino boards, the Leonardo for example, use
ceramic resonators, which make them truly awful for timekeeping
applications.

--

--Jim Harman

Hi

…. ummm …. errr … Add to that:

X-ray gear to work out the orientation of the (possibly natural) bar you are sawing
Lapping gear to get the blanks flat (as optically flat)
Automated / sorting X-ray gear to figure out what’s what after they are lapped
Rounding equipment to turn the square ones into round ones without damaging them
Contouring gear to put the proper shape on one or both sides (or pipes)
Polishing gear to finish the shaping process
Etching baths to get the surface to it’s final condition
High vacuum cleaning to get all the crud off of all the parts before you do much of anything with themA base plater to put on the initial electrodes
Mounting fixtures to get the crystal into the holder
Cement curing (generally vacuum based) gear
Plate to frequency gear

That’s a short list, there actually is a bit more on a full list. The cleaning gear can get pretty extensive depending on the end application.

Bob

actually the process  started as Statek started to etch the crystals
http://www.statek.com/corporateoverview.php in 1970, and produces high
quality crystal since than.

73
Alex
KJ6UHN

On 3/13/2017 11:05 AM, Richard Solomon wrote:

On Mon, Mar 13, 2017 at 6:05 PM, Jim Harman j99harman@gmail.com wrote:

Sorry, the Leonardo does have a crystal. The original Uno had a resonator.

--

--Jim Harman

On 3/13/17 2:59 PM, Alan Melia wrote:

But you would wind up with some nice "artisanally hand crafted" crystals
to plug into a retro radio.
Definitely good for one-upsmanship at the local craft brewery.

I put this in the same sort of bucket as grinding your own telescope
mirrors - maybe something to try once.

Not all crystals are plated, either. I recall pulling crystals out of
holders and using toothpaste to raise their frequency, and a pencil to
lower it. (I will not claim high quality or stability or anything good
about it).

On 3/13/17 3:19 PM, Bob Camp wrote:

Just get the Kurt J. Lesker catalog out and start ordering<grin>

Making a finished crystal, especially a high-Q one of a target frequency far
removed from the 8-10 Mhz sweet spot, is definitely one of those projects
that is a lot harder than you would think it is.  I was down at ICM a few
years back when we were building some high-Q 70 Mhz VHF crystals for a
filter project and it was amazing the amount of stuff they had there.

73/jeff/ac0c
www.ac0c.com
alpha-charlie-zero-charlie

-----Original Message-----
From: Bob Camp
Sent: Monday, March 13, 2017 5:19 PM
To: Discussion of precise time and frequency measurement
Subject: Re: [time-nuts] Bye-Bye Crystals

Hi

…. ummm …. errr … Add to that:

X-ray gear to work out the orientation of the (possibly natural) bar you are
sawing
Lapping gear to get the blanks flat (as optically flat)
Automated / sorting X-ray gear to figure out what’s what after they are
lapped
Rounding equipment to turn the square ones into round ones without damaging
them
Contouring gear to put the proper shape on one or both sides (or pipes)
Polishing gear to finish the shaping process
Etching baths to get the surface to it’s final condition
High vacuum cleaning to get all the crud off of all the parts before you do
much of anything with themA base plater to put on the initial electrodes
Mounting fixtures to get the crystal into the holder
Cement curing (generally vacuum based) gear
Plate to frequency gear

That’s a short list, there actually is a bit more on a full list. The
cleaning gear can get pretty extensive depending on the end application.

Bob

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Hi

… since a lot of it goes into a single “never break vacuum” enclosure, it gets complicated fast. Toss in the
fact that you want a good vacuum and there’s a lot of stainless steel all over the place.

Bob

On Mon, 13 Mar 2017 15:01:39 +0000, you wrote:

There was a WWII era "how they spend your war bonds" film that showed the
process pretty well.  Diamond saws to cut the raw quartz, X-ray diffraction
to find the proper axes prior to cutting out blanks, assorted
polishing/lapping stuff, etching with truly nasty stuff.  ISTR that if you
put a piece of foil under the plate glass you're grinding on, you can hear
a noise peak on a receiver at the approximate frequency.
I once raised a cheapo surplus crystal 60Kc plus to put it into the
40-meter CW band; worked fine!

IOW, not a trivial thing.

--
Gary Woods AKA K2AHC- PGP key on request, or at home.earthlink.net/~garygarlic
Zone 5/4 in upstate New York, 1420' elevation. NY WO G

This email has been checked for viruses by AVG.
http://www.avg.com

Hi

…. ummm …… errr ….. 10 MHz sweet spot is a fiction.

Roughly speaking the Q of a crystal is inversely proportional to the frequency. Drop the frequency 2:1 and the Q doubles. That
assumes you don’t run into size constraints. If your package is a bit larger, the sweet spot is 2.5 MHz. If it’s a bit smaller the sweet
spot is 30 MHz. As package size has gotten smaller and smaller over the last 70 years, the idea of the “ideal frequency” has gone
up. This of course leads to the interesting question of reversing package size history …. If anybody has a few million dollars to toss
around, it’s an interesting thing to dig into.

Bob

I think what he means is that the typical device sold today has four
terminals not two.  It looks like a crystal because it is inside a
little silver can but has four lead wires Power, ground and "output"
and the fourth lead might not be used.  It is an "XO" not an "X".

But I argue that every one of these device has a crystal inside.  So
they still make crystals, just you don't see them

On Mon, Mar 13, 2017 at 12:07 AM, Bryan _ bpl521@outlook.com wrote:

--

Chris Albertson
Redondo Beach, California

Hi

These days, they may well have a MEMS resonator in them. No quartz and
no crystal. Good luck on the close in noise if that’s what they are doing ….

Bob

On 3/14/17 12:19 AM, Chris Albertson wrote:

A lot of those have micromachined silicon as the resonator, though

http://www.silabs.com/products/timing/oscillators/xo-silicon

Hi,

Some claims that MEMS will kill crystals. It will surely eat a good
market share, but I think there is applications where MEMS is not mature
enough compared to crystals.

Another aspect is that various forms of synthesis technologies now
exists, so that a high frequency CMOS oscillator is locked and divided
down. Works sufficiently well for a whole bunch of applications.

Again, your milage may vary and there is applications where you need the
real deal or the right stuff.

Cheers,
Magnus

On 03/14/2017 01:06 PM, Bob Camp wrote:

Hi

Some (but not all) of the resonant structures in the MEMS parts are effectively multi
resonator / multi peak structures. Because of this the phase noise has multiple major
bumps in it as you get into the region of all the peaks. Thats not going to give you
great close in phase noise or ADEV. Since the manufacturers are often a bit unclear
on “what’s inside” you need be a bit careful as you sort through the different parts out
there. Even after sorting, you still run the risk of an “improved” design suddenly
replacing the one you decided on.

So much fun !!!

Bob

On Tue, 14 Mar 2017 13:39:02 +0100
Magnus Danielson magnus@rubidium.dyndns.org wrote:

MEMS is quite mature, it's just that it is playing a different game.
While with quartz (and other piezoelectric crystals) we know how
to design a crystal to frequency, things aren't so simple for MEMS.
Simply scaling the design doesn't work apparently.

What they instead do is to use the MEMS oscillator as a reference
for a PLL locked VCO. As the whole thing is going to be a few mm^2
of silicon anyways, reserving some µm^2 for the PLL and VCO don't
cost much. And it gives the ability to "tune" the oscillator
for the frequency needed after production (the same technique is used
with "programmable" crystal oscillators). Of course, having a PLL,
mostly a fractional-N PLL, causes a lot of spurs in the output,
which can cause problems, depending on the application.

The big promise of MEMS oscillators was, that they'd be cheaper (due to
integration in silicon) and used less power. As far as I am aware,
neither promise could be upheld. MEMS need a quite different production
process than normal digital electronics, hence it's usually more economic
to have the oscillator on a different die than the digital chip. As for
power consumption, the low power MEMS are about at the same level as the
low power 32kHz crystal oscillators (and also in the same frequency).
One place where MEMS are exceedingly good is temperature characteristics.
Silabs demonstrated an oscillator, which, prior to any compensation,
exhibited only <5ppm shift over the full temperature range.

As for the demise of single quartz crystal units, I think that is not
going to happen any soon. It is rather that the economics shift. Most
of the single crystals are used as reference oscillators for digital
and analog/RF chips. Ie most these chips have an internal oscillator
that uses an external crystal to drive their internall VCO+PLL.
As the crystal frequency is dictated by the frequencies these chips
have to generate, there is a kind of standardization going on due to
the limited number of protocols that need special frequencies. Two very
common frequencies are 12MHz, for USB, and 25MHz, for Ethernet.
16MHz is base for CAN, some Wifi chipsets and USB as well. Then there
are a couple of frequencies that are related to GSM, UMTS and the various
other telephone standards. There are maybe a handfull of these frequencies,
which "everyone" needs (ie are used in many high volume products). These are
the crystals we will be able around for the forseeable future. There are
other frequencies that are less used, which you will still get, but need
to pay more or are made to order. Frequencies for protocols that are
not used much anymore, or can be easily generated from another frequency
that is more common, are bound to die out (as has happend with all those
UART crystals, which are only used in legacy systems or for historical reasons).

For specialized applications, where the crystal is not directly interfaced
to a chip that provides the oscillator, it is more convenient for the
designer to just use a complete oscillator than to design his own oscillator
with all the problems that it involves. Getting such a device reliable to
work in production volumes is nothing an average engineer without prior
experience in can just pull off. Heck, I design my stuff to use oscialltors
instead of crystals, because that's one thing less I have to care about.
But even with these oscillators, there is only a limited number of frequencies
that are easy to get. Those are again the standard frequencies from above,
and a couple of round numbers (like multiples of 10MHz)

		Attila Kinali

--
It is upon moral qualities that a society is ultimately founded. All
the prosperity and technological sophistication in the world is of no
use without that foundation.
-- Miss Matheson, The Diamond Age, Neil Stephenson

For other common crystal frequencies, let's not forget
3.579545 MHz and 4x that - NTSC TV color burst

and others listed here...
https://en.wikipedia.org/wiki/Crystal_oscillator_frequencies

On Tue, Mar 14, 2017 at 3:39 PM, Attila Kinali attila@kinali.ch wrote:

--

--Jim Harman

On 3/14/17 12:39 PM, Attila Kinali wrote:

Well, the SiLabs parts are quite attractive for places where they are
appropriate. They're cost competitive in small quantities with the
"XO+PLL" modules, and physically much smaller.

<a few popular frequencies available in large quantities from multiple sources>

I think the "individual crystal" market will remain, but it will be
expensive.  I fully expect that folks like  Bliley  and Croven (part of
Wenzel since 2006) will be around for a long long time.

What probably won't last much longer is companies like ICM that you
could send your "frequency control module" to and have them "recrystal"
it for a new frequency.

The low budget folks (ham radio) will go to little synthesizer board
retrofits of some sort or another - which they've already started doing,
since really nice 10 MHz GPSDOs became available, rather than using that
special oscillator at around 90 MHz (I can't remember the magic
frequency) that you could double and triple up to microwave frequencies
step by step while using your trusty 28 or 144 MHz transceiver as a back
end.

And some day, all those 1970s and 1980s FM repeaters still on the air 40
years later having been repurposed from land mobile radio service will
be replaced by something else.  My friends with a garage full of old
Moto and GE gear that they've been saving just in case will have to
dispose of it.

Hi,

Oh yes. I remember a certain design from a certain vendor. It was an
crystal oscillator, sort of. Available in many diverse frequencies
(hint). It was really a crystal oscillator and a PLL that could be
programmed relatively inexpensively. Solves many problems, so it's a
fine product, but it is a no-go for gigabit serial links, such as
fibre-channel, gigabit ethernet and the like, as the PLL caused some
serious systematics. This systematics along with the noise was scaled up
as the step-up PLL just did a wide-band step-up (as it should). The
combination causes excessive bit-errors rendering the link quite
unusefull. With the tools at my hand, a sub-sampling scope with some
cool histogram capabilities I used a resistive divider and a coax delay
so that I could measure the trigger point and also the 1 cycle jitter,
which is essentially what dominates for this kind of setup. I could see
the systematic jitter clearly this way, and I could also get numbers for
the random jitter. The vendors rep said "you can't measure that!" where
I insisted I could. We ended up using other products for that purpose. I
ended up measuring many oscillators to approve their jitter properties.

So well yes, you learn the hard way what those 4-leggers do when you
have a bit of requirements. Later I dug up the patent for the process,
which was focused more on the production of one standard product and
late setting the frequency for customer needs. For it's purpose a great
concept, not for all cases thought.

I know of MEMS issues. One MEMS I measured was tossed into a lock-loop,
but the noise of it made the scope-view completely smeared out, despite
being locked on average. I only showed the scope, pointiing out it was
locked and that was the end of that discussion.

There is nothing wrong with these devices for many purposes, but expect
that it may not solve everything, so measure and learn what
characteristics is important for that particular application.

Cheers,
Magnus

On 03/14/2017 04:02 PM, Bob Camp wrote:

Attila,

On 03/14/2017 08:39 PM, Attila Kinali wrote:

Actually, as I described in a post before, all this actually started
with crystal oscillators and was motivated by much simplified production
as a fixed crystal frequency could be manufactured and then
resynthesized to any of a large set of frequencies much later. When MEMS
came along, the whole pipe was already cleaned and "a minor
implementation detail" could be changed.

For many purposes, I see MEMS as a nice complementary technology.
The market cut and splices up a bit differently between them than it
used to be, but not very drastic.

In general, the miniatyrization of synthesis is a much greater change to
the scenery than MEMS. There is plenty of chips out there that allows
you to synthesize several frequencies. A re-occurring structure is a
high-frequency CMOS oscillator, possibly multi-phase, which is locked to
a reference (say 20 MHz or 26 MHz) and then output dividers provide
variants. Fractional synthesis is also in there for more uneven
frequency shifts. FPGAs also comes which multiple DLLs and lately PLLs
on chip that does essentially the same thing, but maybe not as elaborate
as the dedicated chips. DDS chips is another branch. In general, these
types of chips have become much much better in terms of jitter,
frequency range, control etc.

In this context, MEMS does much less to affect the market. The whole
synthesiz part have made huge difference for a whole range of products
already.

There is a number of more or less odd-ball frequences that occur. For
instance, 25 MHz isn't used as much as 125 MHz these days for Ethernet,
as it matches the needs of GE. 148,5 MHz is another, in that range there
is a number of numbers that fit various gigabit-pipes divided by numbers
like 10, 16, 20, 32, 64, 66 and such. SAW oscillators is another
approach used there.

Cheers,
Magnus

On 3/14/17 3:17 PM, Magnus Danielson wrote:

actually, we use a lot of them in breadboards where you want to get
"cycle accurate" timing from FPGA logic at oddball clock rates when
developing software.

Historically, deep space radios have had a crystal that is related to
the assigned deep space channel number.  This would be referred to as
the f0 (f-naught) frequency and is around 9-10 MHz.

So if your assigned channel was 14, and your S-band downlink is at
2295.000000, you'd have a VCXO crystal cut for f0=9.5625 MHz (240xf0).
Your uplink frequency would be 2113.3125 or 221f0.  The receiver LO
would be 220f0, the IF at f0, and you'd set your VCXO PLL to lock to
the received IF.  If you work all the multipliers and such carefully,
all the drifts and noises mostly cancel out.

If you had a different channel assignment, you'd have a different crystal.

Same for X-band, except the ratio is 880/749

It took 2-3 years to get the crystal, but you're applying for your
frequency allocation years before anyway.  These days, the oscillator
runs at 4f0 or 8f0.

In any case, when we started using digital tracking loops, you'd run the
ADC and DAC at the same f0, and the FPGA at that same f0 (or some
multiple, like 76.5 MHz).

Similarly, for near earth comm, they use PN spreading codes at around 3
MHz where the chip rate is a integer fraction of the carrier frequency
(just like GPS), and it's convenient to have the DACs running at an
exact multiple of the chip rate, so you have an even number of samples/chip.

The GPS folks like a frequency that's something like 48.xxx MHz, because
sampling at that rate makes all the signals alias down to somewhere
convenient even at max negative Doppler.

Then you have a microprocessor that might be running at some other
convenient speed (like 66 MHz).  Since it takes years go get your
crystal (and what if you want to re-use the breadboard for another
mission on a different channel) it's handy to have a plug in oscillator
at the "right" frequency- yeah, it's got a lot of jitter, but at least
you can do things like test the logic behavior for all possible values
of register settings and stuff like that, which would be impractical
with the simulator which runs very, very slowly compared to real time.

The other reason we might run at something like 45 MHz is that it allows
us to use a converter rated at 50 MHz without having to explain why
we're running right at the rated speed with no design margin.

Woe to the poor guy or gal, though who starts to run bit error rate
tests on the RF generated from these convenient devices.

BTW, there are two spacecraft at Mars with the same channel number..
because one of them used the spare radio from the previous mission - if
you have dual redundancy, and a project with a nice budget, you buy
three radios.  Then, when you've launched, that spare can be adopted by
a subsequent mission, so you might wind up with a spacecraft with prime
and redundant on different channels (a pain in test and operationally),
and yet another channel in the testbed.

Our newer designs use DDS synthesis, so we're going to standard clock
frequencies like 50 or 80 or 100 MHz.

For missions doing radio science that carry a USO, all this same stuff
about getting the frequency right also counts (most of our radios have
an "ext ref" input for this purpose). ANd for the same "what if the
channel changes" reason, Applied Physics Lab (who make USOs) has a uso
design with a DDS in it.

Both we and APL (and I imagine anyone else in this limited business
area, like Thales) have spent some time working on DDS designs with
"good" spur behavior, but overall, having a radio that tunes the entire
band is a good thing.

Today, I'd build a radio with a reference oscillator at a "nice
frequency" (probably 100 MHz), multiply that up for a block converter,
then digitize the entire band (or maybe a chunk) (X-band is only 50 MHz
wide, Ka-band is 500 MHz wide) and do the carrier recovery and tracking
entirely in digital.

On 3/14/17 3:49 PM, Magnus Danielson wrote:

I would suggest we look to our Babylonian forebears and choose 360 as
the mother of all frequencies. Just because we have ten fingers and ten
toes is no reason to be slaves to frequencies like 10 or 100 MHz.  Cast
off the shackles deriving from Roman counting.