Hi Jim,
On 04/08/2015 12:46 AM, Jim Lux wrote:
On 4/7/15 11:33 AM, Magnus Danielson wrote:
Hi,
O
One might look at the available frequencies and see if there is a
telemetry band available which allows wider bandwidth. For the
application, I don't see that very much transmitted power is needed.
If the OP is a licensed amateur radio person, then choosing one of the
low microwave ham bands would be easy. Parts to generate a carrier and
BPSK at 2.39-2.45,3.3-3.5, 5.6-5.8 GHz are cheap and readily available.
You might be able to get away with a VCO and no crystal as the
transmitter, but even if you can't, there's tons of PLLs out there that
will nicely lock to a crystal and are cheap.
You might want to do a link budget and see how much power you need to
radiate, so that you get a decent SNR at the receiver.
free space path loss between isotropic antennas (in dB)
= 34 + 20 log10(freq in MHz) + 20 log10(distance in km).
1km at 3 GHz is 34+69 = 103 dB.
If you radiate 1 mW (0dBm) from an omni (a piece of wire), you'll see
-103 dBm at the input to your receiver, which is a fairly healthy
signal. A detection bandwidth of 10 Hz would have a noise floor of -164
dBm before taking into account the receiver noise, but even if the
receiver is terrible, you're still looking at tens of dB SNR with a very
simple transmitter.
Indeed. I realized that without doing the numbers, so I think the focus
could be in how to realize a simple and light transmitter. A small FPGA
will suffice for the code-generation. It will be essentially empty.
Re-cycling the GPS C/A codes should be trivial. It should not be too
hard to build the receiver side too. It's essentially the same as
building a GPS receiver.
That's a very good argument for higher chiping rates.
I expect that the launch is a bit challenging for the tracking loop.
If you're trying to track in real time, certainly. If you're doing post
processing, less so.
Fair enough. If you know you can track it in real time, then you know
you can do it in post-processing.
Cheers,
Magnus
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