On 20/11/2018 21:05, mrdynalink wrote:
So ... back from experimenting. What I did:
1.) I connected a very strongl regulated powersupply with thick
wires direct to the U3S mainboard. Hmm ... there was no visible
change at all. I played with the supply-voltage, reducing the
voltage to 4.8V changed the frequency only for 10Hz. But at start
of transmission the "chirp" seems to come from "infinity"...
2.) When I put my finger on the crystal I see the frequency
jumping for 100Hz or more. It seems to be very
temperature-critical. Somewhere I read that it is a good idea to
put a heatsink to the crystal to make the temperature-changing
lazy. So I soldered a 2 Cent coin direct on the crystal. But
again, no influence to the chirp at the beginning of transmission.
3.) Now I tried to measure the 27 MHz Carrier from the crystal. I
connected my Perseus antenna-input direct with the 2 Cent coin and
I found the crystal oscillating at 27.005 MHz. Then I tuned the
Perseus into the wspr window and made a recording with Argo. This
was very interesting:
During the pause between the transmissions the crystal frequency
makes a big jump. But the crystal should oscillate accurate on one
fixed frequency! What is the reason for this behaviour ? Currently
I have no idea and have to think about it. Possibly somebody else
has an idea for the reason ?
However ... I think it`s a good idea to order the oven-controlled
version ... not primary for
the oven but for the decoupled 27 MHz oscilator.
Perhaps if you take the OXCO route as you have
documented characteristics for the Si5351 kit at VHF, it would be
a useful half way step to repeat the testing with the OCXO
but with the heater unpowered to
purely to observe the improvement brought about by alternative Osc
circuit.Before employing the heater
Alternatively as others have stated the cheap
TCXO's generally have a robust output not to be affected by
The FOX has being used in the past, if you
search the complete forum thread, another device characterised is
The page title is for the ProgRock, but
in actual fact the improvements are made solely to the Si5351
module and is applicable to all QRP-Labs kits using the Si5351
It's smaller than the Fox alternative, but may
be worth consideration if you can work with the device?