FWIW I am currently working on measuring and sorting 500x 5 MHz HC-49S crystals into 10 bins based on Fs at 0 C and then sub-sort into 10 bins based on Fs at 50 C drawing the crystals from a water bath.
This is a prelude to building the 4th order 5 MHz example in EMRFD and then figuring out if I can tune it electrically +/- 200 Hz. If that works I'll build a 2nd one which would provide an 8th order response.
A Bessel is the maximally flat delay filter. As the orders get higher it converges to a Gaussian. With the low height of the HC-49S a pair of 4 crystal filters will fit in the same space as the NorCal 40A filter.
The NaN concept main features are:
Fully analog operation
5 MHz IF with dual tunable BP filters
direct connection of IF to antenna for WWV reception
noise diode at antenna input for self test
quadrature baseband mixer with IQ output
an analog audio section to convert IQ into binaural audio to highlight pitch and relative relationships
interface to separate module with waterfall, digital readout and recording to uSD using its own power
<250 mA receive drain analog section
The logic is that when you are setting up to keep a sked in portable mode, you need to look for a frequency that's open and start calling. But once the QSO starts you no longer need the waterfall or the frequency display. The Icom 705 does this, but the FPGA still eats a lot of power.
The premise underlying the effort is that I can make an analog version of a digital filter. I've done digital filters for 40 years.
Have Fun!
Reg
