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Re: N310 phase sync issue with antenna array

From: Steve Hubbard
Subject: Re: N310 phase sync issue with antenna array
Date: Thu, 1 Jul 2021 18:53:31 +0930
User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:78.0) Gecko/20100101 Thunderbird/78.11.0

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

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