Triggering the Radioberry at a precise time

[James Montgomery]

Hey everyone, we have a small science project at HF that we're considering using the Radioberry for. We need to put out a signal that starts at a precise time, eg within a microsecond of the commanded time.

With other hardware units (such as an Ettus radio or similar) there would be a 1PPS input that could be used to trigger the start of the signal on the rising edge from a GPS. I can discipline the Pi wall-clock time with a GPS and chrony, but my concern is that I won't be able to get very precise timing with the Radioberry as there is no explicit hardware trigger for the start. Can anyone comment on the ability to issue commands to the Radioberry at a precise time and if there's a way to reliably start a transmission at a specific UTC start time (within about a microsecond of variation)? Many thanks.

James

[pa3gsb]

Hi James,

With the setup using the rb directly connected to the rpi  using the driver and firmware the whole system uses the openhpsdr Protocol-1 (P-1)

In the firmware the control to switch to transmit is done :

- when PTT is clicked in a  SDR program this info is transferred to the firmware using P-1  and will inform the gateware.

- using external ptt control; here a poll mechanism of every 1/10th of a sec the gateware will be informed.

So even you have a well defined moment there is a not very well defined latency to go in transmit mode.

For more accurate start moments you need maybe an different setup. 

73 Johan

PA3GSB

Op zaterdag 10 september 2022 om 20:25:10 UTC+2 schreef James Montgomery:

[Paulh002]

The only thing I can think of is to operate the tx in duplex mode and modulate the input stream. You cannot use the normal interface as Johan described because of buffering and dependencies on tcp stack.

You have to use the driver directly. The fpga does some buffering, but sourcecode is available, so you can check.

73

Paul

Op za 10 sep. 2022 om 20:25 schreef James Montgomery <james.brian...@gmail.com>:

Hey everyone, we have a small science project at HF that we're considering using the Radioberry for. We need to put out a signal that starts at a precise time, eg within a microsecond of the commanded time.

With other hardware units (such as an Ettus radio or similar) there would be a 1PPS input that could be used to trigger the start of the signal on the rising edge from a GPS. I can discipline the Pi wall-clock time with a GPS and chrony, but my concern is that I won't be able to get very precise timing with the Radioberry as there is no explicit hardware trigger for the start. Can anyone comment on the ability to issue commands to the Radioberry at a precise time and if there's a way to reliably start a transmission at a specific UTC start time (within about a microsecond of variation)? Many thanks.

James

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