Hi Larry,
I don't have experience with the N310 but I have used the X310 with a
TwinRx card. I had a Gnuradio flow setup to capture both channels into
files. 10Gbit network. Executing the Python script from Gnuradio
resulted in captures being stored as two INT16 IQ files. When I looked
at the results I found that there was a time offset between the
channels, perhaps about 18 us from memory but it varied between
captures. I assumed the script was starting one capture then the other
but that's just speculation. Obviously this amount of offset is much
more than you'd get from cables. But if you're getting the right result
with cables, perhaps this is not happening.
Perhaps you are seeing multipath effects. You don't mention the
frequency so it's hard visualise. At 5 feet the wave front may be a long
way from plane. Even in the open air you will have a ground reflection.
At shallow angles the reflection coefficient can approach unity, with a
180 degree phase change so you get up to 6 dB constructive interference
or almost complete destructive interference, depending on height and
distance until the point at which the path difference becomes less then
1/2 wavelength. Beyond that there's a 4th power law drop off.
https://en.wikipedia.org/wiki/Two-ray_ground-reflection_model
I hope this helps.
Steve Hubbard
