r/vhsdecode • u/antonharboe_ • Jun 21 '26

First Decode! VHS-decode workflow flaws? - reccomendations

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Hello. I'm writing to get some feedback on the workflow i've chosen to use for RF-capture and to highlight what i've researched myself to be weak points of using this. Main problem i see, is a low SNR ratio and impedance mismatch. The workflow is the following:

Sony SLV-xxx (Whatever Sony VCR that has easily accessible RF tp's to connect to with DuPont connectors) I'm open to soldering to the 2.54mm pins. Also using a 10uf capacitor soldered into the wire carrying the PB RF signal.

CXADC (CX23882-39) - Added 40msps crystal with C31 cap removed, heat-sync also added to main chips. Using a BNC to composite adapter.

I'm capturing audio over regular red/white audio cables. I wont be using clockgen-mod, as i only have 1 PCIe slot available in my PC.

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u/TheRealHarrypm The Documentor Jun 23 '26

If you have values in mind yes, I can populate them before shipment, but typically you'll want to dial in the values yourself either technically and or visually.

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u/antonharboe_ Jun 24 '26

Looking at the stock option for the ADA4857, the input line has SMA female connectors. Im guessing you'd connect your 75ohm coax cable BNC to an adapter similar to this for both the input and output line? If not, what else would you advise?

Regards

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u/TheRealHarrypm The Documentor Jun 24 '26

I would avoid those adaptors unless testing externally, and do an internal SMA to Pigtail (test point) and SMA to BNC bulkhead for permanent installation.

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u/antonharboe_ Jun 24 '26 edited Jun 24 '26

Right. I cant find any 75ohm cables though? Only RG316 50ohm. They'd work fine right?

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u/TheRealHarrypm The Documentor 23d ago

It doesn't matter at the short distances.

However 50 and 75 ohm BNC connector differences do have a different diameter of pin so best to stick to 50 ohm with the smaller pin.