On 05/06/2024 08:43, David Raeman via USRP-users wrote:
Hello,
I'm having a difficult time getting consistent GPS fix behavior from a
set of USRP E320 radios. They are all using UHD 4.4 with the same
active GPS antenna (Siretta Tango 21, which has a 28dB LNA and short
~6" coax run).
When outside with a view of the sky and 6 radios sitting together,
10-15 minutes after power-on, some of the radios will have a lock and
others will not. For radios that get a lock, sometimes they will
briefly glitch into "unlocked" state briefly every 20-30 seconds
before reporting as locked again. If I let it sit another 10-15
minutes, nothing really changes. Looking at the output of 'gpsmon' on
the radio, the radios which never locked will see fewer satellites,
and the ones in common will have far different SNR levels.
I'm trying to find a solution for more consistent behavior, especially
since these are outside with a view of the sky. I confirmed the
radio's GPS ANT port has the +3.3V bias so I assume the antennas
receive power as expected.
Searching the mailing list, over the years this topic has come up a
couple times specifically with E320 radios. I know the same Jackson
Labs LTE-Lite SOM is also used in the newer X410 radios, though it's
configured a bit differently via strapping pins. I think:
* The X410 sets the module in 1Hz mode instead of 5Hz.
* The X410 uses it in "mobile" mode instead of auto-surveying
“stationary” mode.
* Curiously, the E320 seems to connect pin 1 (EFC) to pin 2 (NC),
though this doesn't make any sense based on the LTE-Lite public tech
manual. The X410 leaves them NC.
Does anybody know whether any of the changes (or others) represent
"lessons learned" that would improve GPS TTFF or disciplining
behavior? I don’t mind changing resistor populations if there is a
reason to. Or any other suggestions around this topic?
Thank you,
David Raeman
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IF you move the antennas further apart, what happens?
If they are all tightly packed together, there's an opportunity for
shadowing (small, but, maybe?).
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