At 13:01 19/02/99 -0500, you wrote:
Peter, G3LDO mentioned his difficulties to build a reliable and stabile
exciter for LF and describes the solution developed by DJ1ZB.
I myself also had my difficulties to build a solution from scratch. After
experimenting with 5-6 MHz VFOs and frequency dividers, I came accross a
nice synthesizer kit. With a frequency range between 1 Hz (!) and 54 MHz
(!) it is a real overkill for the LF band, but the features contained in it
are excellent for what we are doing. The resolution is 1 Hz, the accuracy,
once calibrated is in the same range and long time stability is excellent
When I started on 136 I just used a simple VFO on 8.6-8.9MHz, divided that
by 64 and got a nice and stable 136kHz signal. Although it had a +/- 5Hz
shortterm and a +/- 50Hz longterm drif it was perfect suitable for normal CW.
When starting with slow CW this drift was not tolerable and I decided to
built a PLL VFO. I checked out for some special PLL IC's but either they
were hard to find or far to expensive, so I just took a handfull of
ordinary CMOS IC's (CD4000 series) a constructed a simple PLL VFO on 8.6MHz
in 64Hz steps. This signal was divided by 64 to get 136kHz in 1Hz steps.
Total cost was about 1000BFR (25 Euro), half of it spent on thumbwheel
I ended up with 9 CMOS IC's (OK, you can do it with a single specialized IC
but these CMOS are available in any electronics shop and alltogether
cheaper than a PLL IC). Everything fits on a 6 by 9 cm piece of 'testboard'.
I there is interest I will scan in the schematics and make it available.
But do not expect something special it is just a 'textbook' PLL system.
73, Rik ON7YD
Rik Strobbe ON7YD
Villadreef 14 B-3128 Baal BELGIUM (JO20IX)