[DSP-10] DSP-10 with external Frequency Control

[Lee Scott]

Doug,

I've considered the same here but I think you would have to do the following:

1. make an internal crystal osc at 10mhz separate from the PLL.  You would 
then have a switching diode pair (works the same way as the antenna switch 
diodes in the DSP-10) selecting the internal osc or external osc. This 
would give you a toggle switch selectable internal/external option. You 
would have to switch off the power to the internal osc and this voltage 
would also bias the diode for the internal signal.

I have a 432 transverter by Down East Microwave which does basically the 
same thing.  It has two crystal osc and a toggle switch to power/bias one 
or the other.  I'll be adding a third osc as an external one which is phase 
locked onto a 10mhz signal as soon as I can.  It will be basically the same 
as the osc in the DSP-10 and controlled by a PIC16F873 MicroChip 
controller.  This will be mounted on my tower with both the 10 meter IF and 
10MHz signals routed up to it.  If all works, I'll publish the results. Am 
working on the PC Board design now.

One other thought would be to have a small slide switch located at the 
crystal on the board and have a push/pull rod connected to it.  You have to 
keep the circuit for the crystal as short as possible so as not to effect 
the capacitance.

Lee Scott - AA1YN