Does anyone have an 18.895 MHz crystal in HC6/U
gathering dust and wish to sell or swap?
Any assistance would be greatly appreciated.

In article ,
"Ray Joham" wrote:

Does anyone have an 18.895 MHz crystal in HC6/U
gathering dust and wish to sell or swap?
Any assistance would be greatly appreciated.

Ray-

I'm guessing that frequency could be used to convert one of the bands on
a Heathkit SB or HW 100 series transceiver to 10 MHz.

If you're willing to accept a dial error, a crystal might work if it is
as much as 350 KHz lower in frequency. I think that would move the
tuning range from 10.0 to 10.5 MHz down to 9.65 to 10.15 MHz. Or a
crystal up to 100 KHz higher would move the range to 10.10 to 10.60 MHz.

Otherwise you will need to order a custom crystal. The major crystal
companies should have data on the Heath heterodyne crystals if you
explain what you want to do.

Fred
K4DII

Many thanks Fred, as you so rightly deduced,
I want to use the crystal to convert the 10.100-10.150Mhz
band down to within the 500Khz tunable range of 8.835-8.395Mhz,
It will be used in a bank of other ex-Heathkit crystals in a multiband
converter running into a homebrew receiver.
I will see what some crystal manufacturers have to offer.

Hate to hijack a thread …

On Dec 6, 2:55*am, highlandham wrote:
With your tuneable range ,for 10.100-10.150 MHz you can use any crystal
in the 18.495 to 18.985 MHz range ,probably even a low cost
microprocessor type.

Out of curiosity, what's the difference between the "microprocessor"
type crystals and other crystals? Is it just frequency stability or
is there something more fundamental?

On Sun, 12 Dec 2010, Stuart Longland VK4MSL wrote:

Hate to hijack a thread …

On Dec 6, 2:55*am, highlandham wrote:
With your tuneable range ,for 10.100-10.150 MHz you can use any crystal
in the 18.495 to 18.985 MHz range ,probably even a low cost
microprocessor type.

Out of curiosity, what's the difference between the "microprocessor"
type crystals and other crystals? Is it just frequency stability or
is there something more fundamental?

Crystals traditionally were not commodity items. They were ground
on demand. Rare exceptions would be frequencies so common that
it wouldn't be a waste to make them ahead of time, so 100KHz
crystals were pretty standard.

WWII kind of spoiled people, because there was so much surplus
afterwards that for a long time, one could get a crystal "off the shelf"
because it existed as military surplus. You'd either live with a crystal
"close enough" or open it up and grind it so it fit. All those surplus
crystals allowed for people to make crystal filters when single sideband
became popular in the fifties, a lot of VHF work was able to use surplus
crystals in the 8 or 6MHz range (when the transmitters would be a string
of multipliers to get up to the desired frequency), there was even
enough that worked on the HF ham bands.

When 2M FM came along, that was a shock. Suddenly "close enough" wasn't,
since it was channelized, so there was an illusion that one suddenly
needed to have crystals ground to frequency, when that had been the
case all along. It didn't take many years before that got old, which is
when frequency synthesizers really took off in amateur radio.

An odd exception seemed to be CB crystals, where you often could buy off
the shelf, or at least on a very short wait. But they too were ground
just like all the rest, only the cb set's manufacturer saw there'd be
demand so they built up stock.

It was the rise of digital circuits that caused the growth of commodity
crystals. ICs would be designed to use a specific frequency, that often
looked pretty odd until you divided it down, and these ICs were used
enough that the crystals became available off the shelf. Some companies
tried to make use of existing commodity crystals, such as the very common
color subcarrier frequency 3.58MHz, but that didn't always work.
Initially it was a fairly small set of commodity crystals, but more than
the 100KHz and a few other frequencies seen before. "Microprocesser
crystal" is probably a misnomer, since they could often use whatever
frequency was available, but other things needed very specific things.
The variety of crystals multiplied as new ICs and gadgets came along,
until there was quite a few.

Commodity crystals likely are lower spec'd, certainly you have to make
the circuit work with the crystal rather than have a circuit and spend
the money to have a crystal ground to fit that circuit.

But the real reason they are cheap is they are mass-produced, because
the demand is there. So long as you can make do with what other people
want or need, then you can get cheap crystals. It's not unlike the
decades after WWII when there were all those surplus crystals, you lived
with what there was (but there were so many, it often wasn't a hardship).

Michael VE2BVW

In article
,
Stuart Longland VK4MSL wrote:

Out of curiosity, what's the difference between the "microprocessor"
type crystals and other crystals? Is it just frequency stability or
is there something more fundamental?

Stuart-

Michael's explanation brought back memories of my teenage years and
home-brew crystal controlled rigs.

A shorter answer is that a microprocessor crystal frequency may not be
critical while a radio crystal frequency may be.

It would be critical if you needed your transmitter to be on an exact
frequency. In your computer, it wouldn't matter much because no one is
listening! The only time it would matter is if the crystal frequency is
used to keep the computer's clock accurate.

Fred
K4DII

On Dec 13, 2:16*pm, Fred McKenzie wrote:
In article
,
*Stuart Longland VK4MSL wrote:

Out of curiosity, what's the difference between the "microprocessor"
type crystals and other crystals? *Is it just frequency stability or
is there something more fundamental?

Stuart-

Michael's explanation brought back memories of my teenage years and
home-brew crystal controlled rigs.

A shorter answer is that a microprocessor crystal frequency may not be
critical while a radio crystal frequency may be.

It would be critical if you needed your transmitter to be on an exact
frequency. *In your computer, it wouldn't matter much because no one is
listening! *The only time it would matter is if the crystal frequency is
used to keep the computer's clock accurate.

Hi Michael & Fred,

Yep… economies of scale, I can grasp that. So I'm guessing the main
difference is that one is tuned to a frequency that's more suited to
RF applications (e.g. maybe 455kHz) whereas microcontrollers will be
whatever's convenient for the microcontroller in use.

I was thinking maybe the microcontrollers were somehow less accurate
with the frequency. Of course the fact that they are mass produced
would make them cheaper, but I thought maybe they had taken shortcuts
since microcontrollers are less critical. (For timing purposes, a lot
use a 32.768kHz crystal.)

Thanks for the informative post however. Guess I'm spoiled having
never lived through this earlier time. ;-)

Regards,
Stuart Longland

On 12/12/2010 11:16 PM, Fred McKenzie wrote:
In article
,
Stuart Longland wrote:

Out of curiosity, what's the difference between the "microprocessor"
type crystals and other crystals? Is it just frequency stability or
is there something more fundamental?

Stuart-

Michael's explanation brought back memories of my teenage years and
home-brew crystal controlled rigs.

A shorter answer is that a microprocessor crystal frequency may not be
critical while a radio crystal frequency may be.

It would be critical if you needed your transmitter to be on an exact
frequency. In your computer, it wouldn't matter much because no one is
listening! The only time it would matter is if the crystal frequency is
used to keep the computer's clock accurate.

Fred
K4DII
There is nothing wrong with microprocessor crystals, they are often made
to good tolerances, often 10ppm or better. There are only a few common
frequencies (not surprising many are a power of two, or a multiple
thereof), and the crystals are manufactured in huge numbers so they are
cheap (often around 50 cents each or less in small lots). Many hams
have built good IF ladder filters out of these rocks. You do have to
buy a few of them to find a matched set for the filter, but the total
cost will be a fraction of what a new filter would cost. Another thing
about these crystals is that they are often found in very small SMT
packages. I'm not sure that the smallest sizes work well in a ladder
filter though. The same goes for the 'tuning fork' version that uses
laser timed metal elements with a very small amount of quartz (I've
heard that high quality quartz is getting scarce and crystal makers are
looking at ways to use less).

Kenneth Scharf wrote:
Another thing about these crystals is that they are often found in
very small SMT packages. I'm not sure that the smallest sizes work
well in a ladder filter though. The same goes for the 'tuning fork'
version that uses laser timed metal elements with a very small amount
of quartz (I've heard that high quality quartz is getting scarce and
crystal makers are looking at ways to use less).

I think the motivation is to simply make them smaller. Crystals have
been made from synthetic quartz for quite some time now.


--
David Griffith
--- Put my last name where it belongs