[amsat-bb] AIDC 3733 Crystal Information

[K5GNA@xxxxxxx]

 >From K5GNA:

People have been asking me about the crystals.  I originally tried the 60 
degree cut crystals for the PTC thermistors and did not like the results.  I 
ordered the ambient temperature cut crystals and that is what I am offering.

PROBLEMS WITH THE PTC THERMISTOR + CRYSTAL. 

1. The closeness of the spacing in the downconverter meant that the crystal 
and terminator were in contact with the case and thus it was trying to 
thermally stabilize the whole downconverter case. It did reach some thermal 
equilibrium, but not as good as expected.  Then, I cut my case up and put 
Styrofoam over the crystal (now mounted vertically) and it helped, but this 
would not be feasible for everyone to do.  I am back to using an unmodified 
one.

2.  Even though the crystal was trembly stabile with the PTA thermistor 
attached in heatshrink and Styrofoam, components on the circuit board (I 
suspect the trimmer) caused some slight short time thermal drift.  The same 
amount of drift was measured in an unmodified one using the same test.

CONCLUSIONS: 

1. The downconverter will reach some thermal equilibrium by itself if it is 
left on continously and will be suitable for AO-40.

2.The 60 degree crystal and PTC thermistor helped, but is not for everyone.

3. Insulating the downconverter on the dish will aide the thermal stability.

TNX & 73,

Bob Seydler
K5GNA

----
Via the amsat-bb mailing list at AMSAT.ORG courtesy of AMSAT-NA.
To unsubscribe, send "unsubscribe amsat-bb" to Majordomo@amsat.org