Il 28/04/2016 12:28, Attila Kinali ha scritto:
On Thu, 28 Apr 2016 10:07:56 +0200
Ilia Platone <i...@iliaplatone.com> wrote:
Please note that not all the frequencies will be utilizable, here only
433MHz is free-for-all and at low power: only under 50mA transmitting power.
Does this mean you don't have an amateur radio license?
Then it would be a good time to get one :-)
:) yes, maybe...
BTW: you also have the 868MHz SRD and the 2.4GHz range available,
with similar power constraints though.
There are some very cheap FSK transmitters that can output at a maximum
rate of 9600bps: a 1KHz quad signal on these carriers, can drive a GPSDO
like the 10KHz output of some GPS receivers? The clock being compared to
this would be 10MHz downscaled by some decade counters.
this would be much simpler to implement.
I don't get exactly what you mean, but these FSK transmitters for sub-GHz
radios will not work. Their only purpose is low power radio transmissions
over a couple of 10m. Yes, you can use them to send data. Yes, you can
lock to that. But you will not get the control over phase/frequency you
need to implement a good frequency transfer or time transfer system.
Building your own 70cm is not difficult. There are plenty of amateur
radio books from the 70s and 80s around that explain how to build
one with minimal effort. The QRP community has also quite a few designs
that are very simple to build (and a bit more modern).
All you actually need for a CW transmitter is some oscillator, ie a VCO,
that you can either build yourself (L-C tank with a varactor)
or buy as a chip. Use some simple PLL to lock it to your reference
(ADF4002 or similar are a decent choice). Add a simple amplifier
to get the signal to a decent level and a piece of wire as antenna.
The receiver is a bit more involved. There you need to downmix
the received signal to a frequency that is not higher than your
OCXO's frequency, feed that to an amplifier and from there to
a PLL that steers the OCXO. The downmixing LO needs to be derived
from the OCXO as well.
The PLL of the receiver can be an analog design as with the transmitter
or a digital design where you digitze the signal and process it in
an FPGA that produces an output for a DAC that then steers the OCXO.
But all this depends on quite a bit of knowledge on how to design
analog circuits. If you have never done that, it would be a good
idea to find a companion where you live that helps you with the
project.
Attila Kinali
Thanks Attila, I know how to build a transmitter and a receiver, and now
is more clear the system you designed. But as I will propose this system
to an astro club, and in this astro club there's the possibility that
not all would have a radio license, I need something "free-to-play", if
it concern.
I was wondering if it would be more convenient to lock to a signal from
an AM broadcasting station, if available to a multiple of the OCXO. What
do you think about?
--
Ilia Platone
via Ferrara 54
47841
Cattolica (RN), Italy
Cell +39 349 1075999
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