[TenTec] More Omni VI alignment/functioning questions...

[John Clifford]

Well, I've gotten LSB and USB aligned.  CW is proving to be a bear.

The original padding cap had a value of 56pF.  That allowed me to get the
freq down to 9.001900 Hz (needs to be 9.000400 Hz).  I added an extra 56pF
cap and got it to 9.001400 Hz +/-.  I then pulled both caps, and added a
220pF cap... and got it to 9.001380 Hz.  Seems like this crystal has swung
about as far as it can... at least by adding capacitance.

A test CW QSO showed me to be about 900 Hz off... coincidentally (?... I
think not!) about the same freq difference between where the CW BFO is and
where it should be.

I did not check the CW BFO freq before I pulled the original Ten-Tec
9.003300 Mhz crystal.  I am wondering that one side-effect of a crystal that
is more thermally stable might also be that it is harder to swing (higher
Q?).  I don't understand otherwise how less capacitance let a crystal with a
higher resonant frequency swing to a lower BFO frequency.  I am also
wondering if perhaps this 9.003000 Mhz crystal is actually not at that
frequency... it is higher (I had to have about 30pF of capacitance for the
USB circuit to get a BFO freq of 9.003000 Mhz, the nominal crystal
frequency... if I had to add capacitance isn't the crystal's resonant
frequency higher than 9.003000 Mhz?  Can a crystal oscillate at a HIGHER
frequency?)

How can you add negative capacitance to a crystal?  Inductance?  The FSK
trimmers have inductors, while the CW trimmer has a resistor... could I
decrease the value of the resistor and thereby lower the base frequency of
the crystal for that mode?

Anyone know of a simple circuit that I can build on a breadboard to
check/verify crystal frequency?

 - jgc

John Clifford KD7KGX

Heathkit HW-9 WARC/HFT-9/HM-9
Elecraft K2 #1678 /KSB2/KIO2/KBT2/KAT2/KNB2/KAF2/KPA100
Ten-Tec Omni VI/Opt1

email: kd7kgx@arrl.net