Motivation

Wanted to use vhsdecode (software defined VHS decoder)

https://github.com/oyvindln/vhs-decode

Typical vhshdecode hardware

Common hardware used are two clock-synchronized cxadc cards
Video capture cards based on CX2388x that can be used as general purpose ADC
- need PCI/PCIe-port
2x 40 MSPS @ 8 bit (FM audio, Video signal)

Mine hadn’t arrived yet…

Hantek PSO2020

FX2 oscilloscope block diagram

FX2 oscilloscope PCB

Source: https://sigrok.org/wiki/File:Hantek_6022bl_pcb_top.jpg

USB oscilloscopes

Supported oscilloscopes:

Hantek 6022BE
Hantek 6022BL
Hantek PSO2020
Instrustar ISDS205A
SainSmart DDS120
YiXingDianZi MDSO
LHT00SU1

FX2 GPIF

ADC is connected via GPIF (General Purpose Interface):

two 8 bit ports can be either used as 8 or 16 bit port
limitation for 2 channel scopes
either stream CH1 or CH1 + CH2
CH2 alone with full sample rate not posible!

FX2 GPIF clock modes

As a main clock for the interface you can select:

30 MHz
48 MHz (too fast for HS USB 2.0!)
or add delay cycles
IFCLK input

Clock modification

Sigrok

FX2-based oscilloscopes are supported by Sigrok
Use that to capture data stream?
- This specific model was not supported yet by fx2lafw ⇒ added that
- libsigrok only uses a single USB transfer for FX2 scopes…

libfx2adc

Small library that loads (patched) fx2lafw and streams from the device
Voltage divider (input gain) can be specified via commandline argument
Checks if Si5351 is present, can use that to generate clock
Uses AC coupling if present
Usual rtl-sdr like tools:
- fx2adc_file
- fx2adc_tcp
- fx2adc_test

VHS RF tap with USB oscilloscope

VHS RF spectrum

fx2adc + R820T

FX2-based logic analyzer with analog input

T100-b-v1.2.jpg

All chinese components, ~24 USD
Unfortunately ADC is connected to second 8 bit port, so 16 MSPS max

Listening to DAB with LHT00SU1 + R820T

Summary

FX2-based oscilloscopes can be used for:

extending bandwidth of rtl-sdr sticks
direct sampling HF receiver (add some external LPF, amp)
vhsdecode
maybe scopehal + ngscopeclient?

However:

need HW modification to get maximum sample rate
more than one device connected to a single host don’t work with 40 MSPS
- seems to be a limitation of USB 2.0 host controllers..

Can you spot the difference?

Can you spot the difference?

EOF

More information:
https://github.com/steve-m/fx2adc

Other resources: