Saturday, December 5, 2009

136kHz ideas

Some considerations to generation of frequencies in the region of the long wave band using counters and cheap crystals. The first number is the resulting qrg in Hz, the second number is the crystal frequency in MHz and the third number is the divider/counter.
Additionally, there are some approaches mixing different frequencies, I will not go into this in the present note.

The trick is to end the chain of dividers with a division by two, creating a 50% duty cycle.

I would like to point your interest to some frequencies for which ceramic resonators are available. Those could be nicely pulled, given the ratios, the stability of a ceramic resonators oscillator seems OK-ish to give some results still. Assume 1kHz drift @ 5.5MHz. This would resulting in a 25Hz drift @ 136kHz, not desirable, would allow for first tests however. It is clear that care should be taken to avoid drift all together.
For crystals, one could consider moderate super-VXOs.

At the end of this message, a band plan is attached. Some frequencies I listed are actually outside the band, consider this as a hint to SDR-receivers, in particular when the last division could be by 4.

There are two candidates for QRSS marked in red. However, both require a division by 13 :-(

Simple solution "ripple counters"

  • 138550 = 4.433619 / 32 (=8x4=2x2x2x2x2)
  • 138550 = 8.867238 / 64 (=8x2x4=2x2x2x2x2x2)

One decade counter + ripple counter or flipflops
  • 136533 = 9.8304 / 72 (=9x2x2x2)
  • 137500 = 22.000 / 160 (=10x8x2)
  • 138240 = 22.1184 / 160 (=10x4x4=10x4x2x2)
  • 136533 = 4.9152 / 36 (=9x2x2)
  • 138888 = 5.000 / 36 (=9x4=9x2x2)
  • 138888 = 10.000 / 72 (=9x2x2x2)
  • 144444 = 5.200 / 36 (=9x4=9x2x2)
  • 136533 = 6.5536 / 48 (=6x2x2x2)
  • 136533 = 7.3728 / 54 (=9x3x2)
  • 136533 = 14.7456 / 108 (=9x3x2x2)
  • 136533 = 16.384 / 120 (=10x3x2x2)
  • 136550 = 2.4579 / 18 (=9x2)
  • 136533 = 24.576 / 180 (=10x9x2)
  • 136533 = 3.2768 / 24 (=6x2x2)
  • 136533 = 3.6864 / 27 (=9x3)
  • 136533 = 4.096 / 30 (=5x3x2)

Two decade counters + ripple counter or flipflops
  • 136364 = 3 / 22 (=11x2)
  • 136364 = 6.000 / 44 (=11x2x2)
  • 137675 = 3.579545 / 26 (=13x2)
  • 137675 = 14.31818 / 104 (13x2x2x2)
  • 137255 = 14.000 / 102 (=17x3x2)
  • 136364 = 15.000 / 110 (=11x5x2)
  • 136364 = 18.000 / 132 (=11x3x2x2)

Ceramic resonators
  • 137500 = 5.50 / 40 (=10x2x2)
  • 138889 = 5.00 / 36 (=9x4x2)
  • 138889 = 10.00 / 72 (=9x8x2)
  • 136389 = 4.91 / 36 (9x2x2)


Now, what to select, taking into account the band plan:
135.7 - 136.0 kHz
Station Tests and transatlantic reception window
136.0 - 137.4 kHz
Telegraphy
137.4 - 137.6 kHz
Non-Telegraphy digital modes
137.6 - 137.8 kHz
Very slow telegraphy centred on 137.7 kHz

No comments:

Post a Comment