[RX888 mk II / rx888_stream] Parameter tweaking

[Martin G8JNJ]

Hi Bas,

OK, thanks for that.

I was aware that Phantom didn't control the values. I just wondered if excessive gain, or poor gain distribution, was contributing to the AGC issues.

HDSDR has separate RF and IF gain controls for the RX888, and it seems to handle strong signals better.

I think there must be some issues with the RX888STREAM-driver, as the values don't seem to always work as expected.

Regards,

Martin

As for Phantom, Phantom doesn't control any of these values.

[John DF4UE]

Martin,

the "gain" in ./start-rx888mk2.sh is not the gain in dB but the "gain code". The "gain code" is explained in the data sheet of the VGA (AD8370).

73
John

[Martin G8JNJ]

Hi John,

OK, thanks for that. I'm used to configuring RTL type devices in websdr, where the gain parameter is specified in dB.

So values of 0 to 127 should set the gain, and the High / Low gain mode switch effectively sets the MSB.

https://www.alldatasheet.com/datasheet-pdf/view/549369/AD/AD8370.html

Page 1 shows graph of the gain vs. code.

This still doesn't explain why values below 10 seem to cause a problem.

Martin,

the "gain" in ./start-rx888mk2.sh is not the gain in dB but the "gain code". The "gain code" is explained in the data sheet of the VGA (AD8370).

73
John

[Martin G8JNJ]

For reference, my current settings are:-

rx888_stream -f ./rx888_stream/SDDC_FX3.img -s 82000000 -g 20 -m low -d --pga -o -

A gain setting of 20 (in theory just above 0dB) causes my noise floor to rise by approx 6dB at 30MHz when the antenna is connected.

6 to 10dB increase in noise floor, is the optimum value in terms of Signal to Noise Vs. dynamic range, but I'm not convinced that the current gain distribution is the best that can be achieved.

Regards,

Martin

[HB9RYZ]

I'm still using this command:

rx888_stream -f ./rx888_stream/SDDC_FX3.img -s 60000000 -g 40 -m low -r --pga -o - | build/spectrumserver --config config.toml

And it works fine, more than one week without any crash.

And I installed a Broadcast Blocker 88-108 MHz.
https://www.passion-radio.com/sdr-accessory/fm-band-reject-473.html

[9a7aof]

Autostart?

This work fine:

sudo su
crontab -e

Code Select Expand

# Edit this file to introduce tasks to be run by cron.
#-------------------
@reboot /bin/bash -lc 'cd /home/websdr/PhantomSDR-Plus/ && ./start-rx888mk2.sh'
#-------------------
#
# Each task to run has to be defined through a single line
# indicating with different fields when the task will be run
# and what command to run for the task
#

Good luck with the reboot,

Darko, 9a7aof

[Martin G8JNJ]

Hi Darko,

Thanks for the suggestion.

On running the crontab -e command I get back

# chrontab -e
Command 'chrontab' not found, did you mean:
  command 'crontab' from deb cron (3.0pl1-137ubuntu3)
  command 'crontab' from deb bcron (0.11-9)
  command 'crontab' from deb systemd-cron (1.15.18-1)
Try: apt install <deb name>

I assume it is the first option, but what's the best way to proceed ?

Regards,

Martin

Autostart?

This work fine:

sudo su
crontab -e

Code Select Expand

# Edit this file to introduce tasks to be run by cron.
#-------------------
@reboot /bin/bash -lc 'cd /home/websdr/PhantomSDR-Plus/ && ./start-rx888mk2.sh'
#-------------------
#
# Each task to run has to be defined through a single line
# indicating with different fields when the task will be run
# and what command to run for the task
#

Good luck with the reboot,

Darko, 9a7aof

[magicint1337]

To use pga you can try to use low gain mode, it only worked for me on low gain mode, the rx888 driver is not that well so you cant use every combination.

[magicint1337]

also for crontab you wrote "chrontab", crontab -e would be correct which lets you edit it with your editor (like nano)

https://www.adminschoice.com/crontab-quick-reference