EMRFD Message Archive 2611
Message Date From Subject 2611 2009-01-20 18:02:12 Steve Crystal resistance measurements
I have a 10.7MHz ITT model 024DD crystal that's about 30 years old. It
is rectangular in shape and has three pins on each end. One of the pins
on each end is common to the crystal case. The other pair of pins on
each end are both isolated from the case.
A friend suggested the isolated pins might indicate a transformer on
each port of the crystal. I measure 3.2uH across each pair of isolated
pins (with the other set of pins open).
Ohmmeter readings baffle me. I can understand a low resistance between
the pair isolated pins on each end of the crystal if there is indeed a
transformer in there. Those readings are less than half an ohm. But
further measurements with an ohmmeter provide me with readings of less
than half an ohm from any pin to any pin.
Does the inductance measurement support the idea of a transformer
internal to the crystal case on each port?
Do the very low resistance readings from any pin to any other pin sound
right? I wasn't expecting continuity between isolated pins and the case
nor between isolated pins on opposite ends of the crystal, yet it's there.
Help.
Thanks.
Steve K8JQ2612 2009-01-20 19:32:59 Wes Hayward Re: Crystal resistance measurements
Most interesting. I can't say that I have seen anything quite like
the thing that you described. I posted an item in the "files"
section with the title "Is this the crystal.jpg" which seems to fit
your description. That is, you would measure inductance between the
end terminals, yet all terminals are at DC common. If this sketch is
indeed a representati2613 2009-01-20 20:45:54 John Kolb Re: Crystal resistance measurements
Thus you would read from one of the isolated terminals at one end through the
grounded case to an isolated terminal at the other end. You can
verify a center
tapped coil by measuring the inductance from each of the isolated terminals to
the grounded pin.
It's hard to make low resistance readings with the usual digital
VOM's. The lead
resistance can be an appreciable part of the 1/2 ohm you see so it's
hard to tell
if the resistance from either isolated terminal to gnd is half that
of the isolated
terminal to isolated terminal reading. The old Simson or Triplet VOM's, with
a zero adjust pot would be better for this.
John
At 06:02 PM 1/20/2009, you wrote:
>I'm climbing the crystal filter learning curve and need some advice.--
>
>I have a 10.7MHz ITT model 024DD crystal that's about 30 years old. It
>is rectangular in shape and has three pins on each end. One of the pins
>on each end is common to the crystal case. The other pair of pins on
>each end are both isolated from the case.
>
>A friend suggested the isolated pins might indicate a transformer on
>each port of the crystal. I measure 3.2uH across each pair of isolated
>pins (with the other set of pins open).
>
>Ohmmeter readings baffle me. I can understand a low resistance between
>the pair isolated pins on each end of the crystal if there is indeed a
>transformer in there. Those readings are less than half an ohm. But
>further measurements with an ohmmeter provide me with readings of less
>than half an ohm from any pin to any pin.
>
>Does the inductance measurement support the idea of a transformer
>internal to the crystal case on each port?
>
>Do the very low resistance readings from any pin to any other pin sound
>right? I wasn't expecting continuity between isolated pins and the case
>nor between isolated pins on opposite ends of the crystal, yet it's there.
>
>Help.
>
>Thanks.
>
>Steve K8JQ
>
>------------------------------------
>
>Yahoo! Groups Links
>
>
>
>
>
>--
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>Version: 7.5.552 / Virus Database: 270.10.9/1900 - Release Date:
>1/18/2009 12:11 PM
>
>
>
>
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Version: 7.5.552 / Virus Database: 270.10.9/1900 - Release Date: 1/18/2009 12:11 PM2614 2009-01-20 22:08:17 Stephen Wandling Re: Crystal resistance measurements
It appears you have an:
ITT 024DD 10.7MHz ±3.75kHz 8-pole Crystal Filter
There are a couple of nice photos, and it shows the 3 pins on each end.
72
Stephen
VE7NSD
John Kolb wrote:
> Sounds like a transformer winding at each end which has a grounded center tap.--
> Thus you would read from one of the isolated terminals at one end through the
> grounded case to an isolated terminal at the other end. You can
> verify a center
> tapped coil by measuring the inductance from each of the isolated terminals to
> the grounded pin.
>
> It's hard to make low resistance readings with the usual digital
> VOM's. The lead
> resistance can be an appreciable part of the 1/2 ohm you see so it's
> hard to tell
> if the resistance from either isolated terminal to gnd is half that
> of the isolated
> terminal to isolated terminal reading. The old Simson or Triplet VOM's, with
> a zero adjust pot would be better for this.
>
> John
>
> At 06:02 PM 1/20/2009, you wrote:
>
>
>> I'm climbing the crystal filter learning curve and need some advice.
>>
>> I have a 10.7MHz ITT model 024DD crystal that's about 30 years old. It
>> is rectangular in shape and has three pins on each end. One of the pins
>> on each end is common to the crystal case. The other pair of pins on
>> each end are both isolated from the case.
>>
>> A friend suggested the isolated pins might indicate a transformer on
>> each port of the crystal. I measure 3.2uH across each pair of isolated
>> pins (with the other set of pins open).
>>
>> Ohmmeter readings baffle me. I can understand a low resistance between
>> the pair isolated pins on each end of the crystal if there is indeed a
>> transformer in there. Those readings are less than half an ohm. But
>> further measurements with an ohmmeter provide me with readings of less
>> than half an ohm from any pin to any pin.
>>
>> Does the inductance measurement support the idea of a transformer
>> internal to the crystal case on each port?
>>
>> Do the very low resistance readings from any pin to any other pin sound
>> right? I wasn't expecting continuity between isolated pins and the case
>> nor between isolated pins on opposite ends of the crystal, yet it's there.
>>
>> Help.
>>
>> Thanks.
>>
>> Steve K8JQ
>>
>> ------------------------------------
>>
>> Yahoo! Groups Links
>>
>>
>>
>>
>>
>> --
>> No virus found in this incoming message.
>> Checked by AVG.
>> Version: 7.5.552 / Virus Database: 270.10.9/1900 - Release Date:
>> 1/18/2009 12:11 PM
>>
>>
>>
>>
>> --
>> No virus found in this incoming message.
>> Checked by AVG.
>> Version: 7.5.552 / Virus Database: 270.10.9/1900 - Release Date:
>> 1/18/2009 12:11 PM
>>
>
>
>
>
"You never change things by fighting the existing reality.
To change something, build a new model that makes the
existing model obsolete." -- Buckminster Fuller
"First they ignore you, then they ridicule you, then they
fight you, then you win" -- Gandhi2615 2009-01-21 05:47:51 steve65@suddenlin... Re: Crystal resistance measurements
Yes, the crystal below is the exact model that I have and I acquired it from that very eBay seller.
I did subtract the resistance of my DVM's shorted leads to arrive at the resistance values mentioned in my note.
I will make further inductance measurements in an attempt to determine if there is a center-tapped transformer on each port of the crystal.
I have an N2PK VNA with which I will also make some observations -- or at least make the attempt. This is a fairly sophisticated instrument that I have to date used mostly in reflection mode for antenna system measurements. Some learning curve will be involved on my part to provide meaningful data about this crystal.
Again, thanks to all for your most helpful responses and bear with me as I will probably be back with further questions. :)
Steve K8JQ
-2616 2009-01-21 09:57:19 WB6TPU Re: Crystal resistance measurements 2617 2009-01-21 11:39:57 pamunoz2001 Re: Crystal resistance measurements
isolated earth terminals". That means that terminals 2 and 4 are
internally connected to the case. So the input and output
transformers are not center-tapped, and the internal schematic must
be something similar to that posted by Wes (but with a 8 pole cristal
filter between the transformers).
I have a very similar filter (ITT 024BC 10.7MHz ±7.5KHz), that I
bought about 25 years ago2618 2009-01-21 11:43:19 joop_l Re: Crystal resistance measurements 2619 2009-01-21 13:10:35 Stephen Wandling Re: Crystal resistance measurements
While I didn't put it in my post, I thought that possibly contacting one
of the projects in the links on the eBay sellers page might result in
some clues? Also, there were some datasheets and performance info on
his page as well, but I gather that someone else has posted some to this
group.
But, maybe you are more interested in the educational benefits from
working out what's inside the box? I can relate to that. Good luck.
73
Stephen
VE7NSD
steve65@suddenlink.net wrote:
> Thanks all for the helpful comments.
>
> Yes, the crystal below is the exact model that I have and I acquired it from that very eBay seller.
>
> I did subtract the resistance of my DVM's shorted leads to arrive at the resistance values mentioned in my note.
>
> I will make further inductance measurements in an attempt to determine if there is a center-tapped transformer on each port of the crystal.
>
> I have an N2PK VNA with which I will also make some observations -- or at least make the attempt. This is a fairly sophisticated instrument that I have to date used mostly in reflection mode for antenna system measurements. Some learning curve will be involved on my part to provide meaningful data about this crystal.
>
> Again, thanks to all for your most helpful responses and bear with me as I will probably be back with further questions. :)
>
> Steve K8JQ
>
> -2620 2009-01-21 15:01:38 Paul VDP Re: Crystal resistance measurements
I have here a small pcb with a ITT 024DC filter on it. This one is the version with 'earth isolated' terminals, which I can confirm after unsoldering the filter. I guess ITT had the 2 versions available to also allow using the filter in a circuit where it must be 'floating' vs. ground-referenced. As Stephen says, in the 024DD pins#2 & #4 must be dead shorts to the ground-terminal (and case).
I have no information as to the internal circuit either. But for your information ; on the pbc here it is pin#3 that is used as input and pin#1 as output. More than probably the filter configuration inside is symetrical, also because in the datasheet no indicati2621 2009-01-22 08:17:19 Johan H. Bodin Re: Crystal resistance measurements
> You might want to match the impedance first before measuringOr put 860 ohms R (50+860 = 910) in series
> with your VNA. The VNA is probably 50 Ohm and the filter needs
> 910 Ohm//25pF. One option could be to make 4:17 winding
> transformer or a 4+13 autotransformer. One for each side of
> the filter.