GPS sensitivity
Hi, is there any difference in GPS sensitivity between KiwiSDR1 and KiwiSDR2 ? I have one of each and the GPS antennas are on exactly the same spot.
kiwiSDR1:
kiwiSDR2:
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Comments
It's a completely new GPS front-end chip with Kiwi-2 since the old one in Kiwi-1 is now out of production.
Is that using the same GPS antenna through a splitter feeding both Kiwis? Or is it the GPS antenna delivered with the Kiwi-2? Because we made a change with Kiwi-2 and used antennas with a 5m rg174 cable instead of 3m as with Kiwi-1.
So that extra 2m of cable at 1.6 GHz is definitely going to impact the sensitivity. But people have long complained about the 3m cable being too short. So we compromised.
For SDR clock compensation having only 4 sats is fine in most cases. The scheme is not a GPSDO after all..
Now the other thing is that the new GPS chip (MAX2769B) has more ADC output bits. This means that potentially greater sensitivity could be achieved by widening the GPS data path in the FPGA (Christoph suggested this possibility). But this would take a fair amount of work. And we are already very tight on FPGA space. So it's not clear when something like that might be attempted.
I'm using the delivered antennas. Not one antenna and a splitter. Yes I recognized that the cable is longer which is good. It's not a problem. I was just curious but then I know that the implementation is new.
@SM6MUY regardless of antenna/kiwi, I note that you are in a location with the dip in your northern footprint. I wonder where your antenna is relative to things that might block your GPS antenna's southern view?
I just checked with my KiWi V1 & V2, which are both fed from the same external GPS antenna using an active splitter.
The performance is pretty much identical, but the system noise figure and sensitivity in this case is being defined by the GPS antenna and splitter. But it does indicate that there is no major difference in performance.
However, it is not the best indicator of how well the KiWi GPS receivers would perform when using a marginal antenna.
Swapping the antennas over, to see if any degradation in performance remains with one antenna or receiver, may be a better test method.
Regards,
Martin