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.
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.
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