Crystal ESR - was Cricket musings


WA0ITP
 

GM John,

Thanks for the excellent post, good info, nothing better than having data.  Cricket users have discovered that some (most) HC49S crystals wont oscillate, but that the HC49U crystals will perform ok.  Actually some of those didn't oscillate reliably either, resulting in changes in R9 and R10 before going into production.  In an earlier post, NM0S also provided insight into higher ESR requiring more feedback. Thanks for mentioning 200p and 470p for C9 and C10.  The  Cricket is a very open design and several builders have  experimented with the feedback, and probably will continue to do so.

Thanks again.
72 WAØITP
I love this radio stuff. 
www.wa0itp.com
www.4sqrp.com
On 5/12/2017 10:09 PM, jwc123@... [4sqrp] wrote:

 

JAN is no longer making crystals either? Wow!

Last night and a little today I was home brewing and experimenting with part of the cricket while waiting for the official kit to arrive.

An ESR more than 100 may be a bit high for this circuit.  My HC49S (short case) 3.579's are measuring around 124 ohms and will not fire up without adding extra capacitance to C9 (200pF) and C10 (470pF).  It might take less but 470pF is a standard values I normally use for 80M so just popped in to test.  C9 at 100pF didn't fire up so maybe somewhere between 100-200pF.  The Rx/Tx shift is also low, around 300Hz replacing C15 with a gimmick.

For the HC49S (short case) 3535 3550 and 3560 the ESR measures around 70-80 ohms and most of the time fired up but it has failed a few times on the prototyping board.  Again adding a little extra to C10 cured the problem.


The above all have specs of a 150 ohm ESR maximum, 30ppm tolerance, and an 18pF load capacitance.  Measurements were with an old Saunders Crystal Impedance Meter.  I can't guarantee 4 digit accuracy but calibrations show it's close enough for government work.

Also played with an HC49U (tall case) 3.6864 from the junk box.  Putting it on the meter gave an ESR of 74 ohms and found out it was a series crystal.  Still worked.  Maybe I'll give a CQ to those Extra Phone guys one day.... hi hi  I have a small hand-full of these up for grabs. If anyone is interested in a couple give me a shout and I'll send them your way.

If you want a gang-buster output then find an old BIG (HC6/U?) TV colorburst crystal.  10 ohms ESR and the voltage output on the o-scope more than doubled.  I wonder if that will drive the MOSFET too hard once that part of the circuit is done?

Having too much fun but need to call it a night, will continue the fun when the kit arrives......

72 John kc9on


 


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