[sdiy] ot: long wave radio reciever for time/frequency

[Czech Martin]

Thanx Tim and John and all.

Yesterday I hooked it up, used a jfet amplifier to decouple
the resonant circuit. First I thought how I could determine
the resonant frequency. I tryed to feed in a signal
via 100k resistor, but this is allready damping the circuit.
So I looked into my "diverse" box and pulled out an electro
magnet I got when I was 14 or so ("discover electronics set,
christmas present"). 

So be carefull when you throw away things!

This magnet coil was then connected to my old sine
generator. Works very good. Next I tuned the circuit to
77.5kHz. Did take some time, since I coulnd't find the right
capacitor in my big poly styrol box. 
And then.... voila, the carrier was clearly there with 50mV
amplitude. Of course, very noisy. No, it is no self oscillation
because I could clearly see the 1s amplitude modulation.
The signal falls to -6dB if I get 1kHz away from center.
So Q is about 30 or so. I do not know why it is so
low, perhaps I use the wrong definition for Q.
Not bad in this long wave range with about 250 km away
from the station (I know, the U.S. people on this list will
laugh about that kind of distance).
I could clearly see the horizontal polarisation, and that the
ferrite rod must point east - west.
I'm really asking me how many of these radio clocks merily
run in OPEN LOOP mode because their antenna get's no signal?


Next thing will be to get some more gain. I guess I will use
transistor amplifier stages, and may be AGC.
I do not know if I need further parallel resonant LC
circuits to filter more of the signal.

If I'm using a PLL, it has to use a LC tank, otherwise the jitter
will eat up all the performance. This is a problem with the
4046 RC VCO.


Of course there is a lot of noise, also phase noise.
But I think if I average the signal via division or 
PLL, I should be o.k.

m.c.