[time-nuts] Need advice for multilateration setup

Jim Lux jimlux at earthlink.net
Tue Apr 7 18:46:43 EDT 2015


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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