Mad or plausible ? Videotape as RF-shielding material.

[DK6400Brian]

I'm in the midst of servicing my JVC HR-S5000EH S-VHS machine. The first S-VHS machine in Europe AFAIK.

Amongst the usual suspects, pinchroller, belts, idler tire, lubrication and electrical adjustments and alignments, my brain has come up with ideas for tweaking this machine if at all possible.

My estimation upon manufactoring this piece of equipment is, that a lot of engineering and manpower at JVC went into introducing the world to the next level of domestic videotaping, the S-VHS system.

But I was wondering. Standards were and are made in order to have at least a minimum of quality in production and development to provide the costumers a level of trust in order to sell their manufactored goods.

Now....that does also mean, that a manufactorer can decide to cut short and not to make their product better in order to avoid costs and loss of sales due to prices. Unless of course certain products are specifically made for higher quality and sales are made because certain customers will pay the price for this higher level of quality, like broadcasting equipment or equipment with military specifications.

And if I take a look inside my JVC HR-S5000EH, made for the consumer market, apart from the PSU, nothing is shielded at all. Every single PCB is placed inside naked and theoretically they're wide open for induced RF noise from other PCB and vice versa.

The Luma and Chroma noise levels have my attention. Of course the noise levels are made according to standard, but what is to be gained if it can be reduced in an innovative and cheap way ?

So I came up with the idea of shielding the video circuitry for a start.
For RF-shielding in the 0.5-7 MHz area, simple steelplate on top and bottom of the PCB is excellent. Copper is also excellent, but to keep the costs down, steelplate is fine.
I thought of stripping an old DVD-player for its top cover and have it made to fit.

But what about avoiding noise generated from some areas of circuitry on the PCB itself to other areas ? Is it possible to find a material, that will absorb emitted radiation from the components on the PCB, before they'll travel over to other parts of the circuitry ?
Well...here I thought of finding some RF-absorbent material and an internetsearch went on, only to find very expensive RF-absorbing foam used in microwave ovens, medical and military equipment.
The common denomianator was a material which was based on iron particles covered with carbon, so......it would be too costly and too much struggle just to lower the noisefloor on an almost 30-year old videomachine.

It was at that point my mediocre brain, God help me, came up with the idea of: How about having the videocircuitry covered in videotape ?
If anything, videotape is exactly RF-absorbant. It's its purpose.

Either put some double adhesive film inside the steelplate shield, and covering it with videotape ?

Or....take a piece of Mylar, add double adhesive film, then videotape, then another layer of adhesive film and then some (neoprene) foam, in order to push the layer of (the possibly) RF-absorbant videotape down amongst the components on the PCB, and then the steelplate shield on top.

One could experiment with several layers.....and go even further, add Carbon-33 into the mess.

Bottom line:
- Are anything to be gained from adding internal shielding to the PCB's inside a VCR ?
- Does the theory of videotape as RF-shielding hold true ?

Unfortunately, I'm not on drugs, but that doesn't rule out a fried brain.

[paulsherwin]

Even S-VHS is a relatively low resolution technology compared with broadcast standards. I don't think adding additional screening will give a significant improvement.

[DK6400Brian]

Thanks Paul.

One thing is to have ideas run wild. It's a wonderful thing in itself. Another thing if these are worth pursuing.
Your advice therefore came in handy and is much appreciated. I'm relieved from having a lot to do then