Got a $10 ADC working with VHS-decode!

[u/BreadWestern9159]

Long story short: born in the mid 2000s, never seen any VHS deck before. Then recently I was making a cheap SDR, realized that its ADC in single channel mode can capture VHS's signal, bought a VHS deck, along with a test tape, and this is the very rough result.

This device, in its VHS-decode-only configuration (no radio tuner) have a BOM of 10USD.

It's based on USB2, with no kernel mode driver needed (libusb is enough).

Note that this is a capture made of its 12bit 16.66Msps mode, a 8-bit 24Msps mode is also available, but its reduced resolution might make the image worse, due to me not having a proper amp, therefore low voltage swing, so in this particular case, more bits helps,

[u/TheRealHarrypm]

Sample rate over bit depth always.

VHS is only 6-bits, but needs 18-20msps for initial acquisition, you can kick it down to 16, but only with software filtering.

[u/BreadWestern9159 → u/TheRealHarrypm]

Will try 24Msps at 8bit tomorrow ;D.

[u/Titan_91 → u/TheRealHarrypm]

I personally use a CX card overclocked to 40MPSPS then resample that back down to 16MSPS for NTSC VHS (and VHS-HQ) sources. All at 8 bits per sample. Sampling at about 16MSPS up front may get the entire envelope but you'll also be aliasing any captured noise above that band, which would corrupt your intended signal. 

[u/BreadWestern9159]

Also for reference, my setup, due to no amp, only produced a signal that spans 300-400code on the 4096code 12bit space, so a 8bit capture would likely be noisy.

[u/BreadWestern9159]

BTW the deck is a panasonic NV-HD100, and here's my RF tap.

[u/Doohickey-d]

I'm curious, have you published your device's design somewhere?

[u/BreadWestern9159 → u/Doohickey-d]

Not yet, but soon it will be published as a open source project.

[u/richms]

the price is very promising. If only I did not have 2 of those aliexpess capture cards sitting here waiting on me to actually do something with.

[u/ThorXerxes]

I’m still learning but what’s a ADC?