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'[EE] Crystal capacitance'
2006\01\08@052100 by Shawn Wilton

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I've never had to specify the loading capacitance for a crystal before, so I
need to ask for some help on reading the data sheet.  This is the link to
the DS on Mouser:  <
http://www.mouser.com/index.cfm?handler=displayproduct&lstdispproductid=563316
>

The part specifies B2 capacitance for the 50Mhz crystal, and a B2F for the
25Mhz I need.  Both are from the same company and have the same data sheet.
Any help?  What is the B for?  Does the two mean I need twice the cap. of
the crystals value?
--


Shawn Wilton (b9 Systems)
http://black9.com

2006\01\08@110607 by David VanHorn

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>
> The part specifies B2 capacitance for the 50Mhz crystal, and a B2F for the
> 25Mhz I need.  Both are from the same company and have the same data
> sheet.
> Any help?  What is the B for?  Does the two mean I need twice the cap. of
> the crystals value?



The part number mouser calls out dosen't match the system used in the
ordering options in the data sheet.
You can always call them and ask..
I'd expect to see a part number like: AB-50.000-18-R15-B-2-X-F
There's a note at the bottom that says "left blank if standard",  but I
don't see how they show you what's "standard" here.
I'd call abracon in the morning and ask.

Now.. The load capacitance number is not the value of the caps to use.
The two caps are in series from the crystal's point of view.
Basically, double that, and subtract 5 pF (as a first guess) for parasitic
capacitance in the circuit.
That gives you 31pF and the closest value without going over would be 27pF.
Try that, check operating frequency and oscillation margin, and then adjust
if you need to.

2006\01\08@112734 by Mike Hagen

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face
Many moons ago I used International Crystal in Ok. for ham radio crystals.
They have a pretty good website and used to be real helpful on the phone?
They made me several crystals at nearly $15 each 30 years ago! Ouch!

http://www.icmfg.com/microprocessor_crystals.html

Mike
Crestline, Ca.

2006\01\08@114247 by David VanHorn

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On 1/8/06, Mike Hagen <spam_OUTpicdogTakeThisOuTspamdslextreme.com> wrote:
>
> Many moons ago I used International Crystal in Ok. for ham radio crystals.
> They have a pretty good website and used to be real helpful on the phone?
> They made me several crystals at nearly $15 each 30 years ago! Ouch!


Cal Crystal Labs made me some one afternoon. Talk about rush, I was in Santa
Ana at the time, and before I could drive up there, they had them built.  No
guarantees on aging though, but that was a given.  At the moment I'm using
West in BC Canada, because they know how to make the crystals for the
Daniels repeater gear that I'm putting on the air here.

Basically, when you're specifying things (rather than selecting a crystal)
the tradeoff in shunt capacitance is stability and startup time.  Lighter
cap values start faster, but also are more subject to variability.  The
parasitic value in your circuit isn't something you can control all that
well, so the larger C values make that number less important.

2006\01\08@121244 by Mike Hagen

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face
Small world David, I was in Costa Mesa (3 miles from Santa Ana, still have a
house there) and converted an OLD Motorola 80D Edison radio (1950's?) to a 2
channel 2M ham radio for repeater access.  Johnstone Peak  (.22-.82) 146???
Then .94 simplex to talk to my lifetime ham buddy.
I heard of Cal Crystal, but allways read that Int Crystal was the "hams"
friend.  I still have this radio out side there waiting to go to the dump!
Crystals and Crystal Ovens too!  I was run with a dynamotor or vibrator off
6V?  I put a TV power transformer in it for 110VAC.  I weights about 50 Lbs!


Mike, WA6ISP

{Original Message removed}

2006\01\08@122305 by David VanHorn

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On 1/8/06, Mike Hagen <.....picdogKILLspamspam@spam@dslextreme.com> wrote:
>
> Small world David, I was in Costa Mesa (3 miles from Santa Ana, still have
> a
> house there) and converted an OLD Motorola 80D Edison radio (1950's?) to a
> 2
> channel 2M ham radio for repeater access.  Johnstone Peak  (.22-.82)
> 146???
> Then .94 simplex to talk to my lifetime ham buddy.
> I heard of Cal Crystal, but allways read that Int Crystal was the "hams"
> friend.


This was for a work project, a modem chip that needed a rather odd xtal
freq.

I still have this radio out side there waiting to go to the dump!
> Crystals and Crystal Ovens too!  I was run with a dynamotor or vibrator
> off
> 6V?  I put a TV power transformer in it for 110VAC.  I weights about 50
> Lbs!


:)  They don't call them "boat anchors" for nothing!
If you look on the repeaterbuilders site, you'll see my article on the
Daniels gear.
http://www.danelec.com shows their current stuff.  The MT-2 series that I'm working
with was recently obsoleted, but still is fine for us.

2006\01\08@162146 by Shawn Wilton

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OK, so it is the Load Cap value I'm looking at then (with the consideration
that's for two caps in series, plus parasitics)?

On 1/8/06, David VanHorn <dvanhornspamKILLspammicrobrix.com> wrote:
{Quote hidden}

> -

2006\01\08@165733 by David VanHorn

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On 1/8/06, Shawn Wilton <.....black9KILLspamspam.....gmail.com> wrote:
>
> OK, so it is the Load Cap value I'm looking at then (with the
> consideration
> that's for two caps in series, plus parasitics)?


Yes.

It's likely that this part number means 18pF, but I'd say it's unclear
without a call.

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