conventional 136kc/s TX VFO
List of other pages
A. German WWII Radio communication equipment
C. Amateur radio experiments
L. VLF, MF and 136kHz equipment ideas
M. Measuring instruments
n18 Oscillator constructions
Based on some thoughts LA8OJ and I did some time ago I am sort of planning to build an xtal controlled (VXO) source
for 136kHz based on the xtal synthesizer principle, but it is unlikely that I need more than one xtal.
Have many xtals around 6520kHz and this is the reason for choosing this set frequencies. They are all JAN-crystals bought
35 years ago but I cannot remember which project they were for, probably a 2m xtal synthesizer. Found some xtals with 1090kHz
difference and also a par with 2180kHz difference, have many thousands xtals and it was a real task to sort through and
calculate the difference frequency of suspect objects.
The output from mixer is 4x (136-136.5kHz) ..somewhat near 540kHz. Suppose filtering is rather easy task so I would use a 455kHz IF
transformer.Experience from VHF says the coupling shall be inductive. possibly I could make a bandpassfilter of two IFT's an
LPF if anybody tell med that I am going to do something really stupid
Need comments whether it is a very bad mixer
(this is the second version of the simplified circuit diagram
It is important to have maximum signal out, but mixer products are supposed to be far away from this frequency, so
I just wonder if it is neccessary to make it more complicated? A 40673 mixer is another possibility,
it has very high gain on such low frequencies, but I would rather prefer bipolars if it is no reason for choosing something else.
IC's are no problem, but why use it if it is just foolish?
My friend LA7MI Stein didn't agree that it was a good solution when i spoke to him on the phone today, he was eager constructing
a variable xtal filter on 4MHz using some patented HP negative resistance amplifier, and had built a 3x10" pcb with SMD
components, he could choose continious bandwidth from 300-30kHz in 3 bands using varicap tuning, but back to the circuit
He suggested using a 20kHz VFO which locks a
135kHz VCO. Using a surplus 3x450pF tuning capacitor it seems to
possible. I have some 15625kHz time base inductors with slug tuning, so they may seem an idea to try. True VFO is not
really neccessary since you shall only agree on a frequency and use it for many QSO's, but the possibility to move it around
is sometimes useful.
2176-2208kHz clapp-type variable oscillator . It was intended to be used with a divide-by-16 divider to cover
136-138kHz band, so it is no problem concerned with using a clapp oscillator with varying output level