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Is RF shielding really necessary?


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I've done extensive mods to my NES and finally tossed out the shields because they didn't fit. I tried to Dremel cut the bottom one to fit around my CopyNES and trashed it. Then I just tossed the top shield after I installed the Blinky Light Win. I haven't noticed any additional noise on the A/V or other symptoms. Is RF shielding really necessary for proper operation of retro consoles, or is it mainly just to satisfy the FCC regulations to prevent the infinitesimal possibility that it causes interference to some unknown device in a worst case scenario? I've noticed later generations of video game consoles seemed to use less shielding as time went on despite running higher and higher clocks.

Edited by stardust4ever
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In many cass, RF shieldings are only for US systems. The Famicom doesn't have shielding.

Some French-marketed Intellivision lack shielding too - tho I found one with, and one without, I'm not sure if they trashed the shielding when modifying the systems for PAL/SECAM, or if Mattel started to save money by shipping Euro models without shielding.

I think the Colecovision I have doesn't have any shielding at all as well.

 

On some systems the shielding is part of the cooling system, and sometime double as grounding (Bally Astrocade, Commodore C128) so you might want to look on internet if it is safe to do so.

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On some systems the shielding is part of the cooling system, and sometime double as grounding (Bally Astrocade, Commodore C128) so you might want to look on internet if it is safe to do so.

Well on the NES that is not the case. The 7805 is connected to a meaty sink adjacent to the shielded RF box. The RF box is like an impenetrable fort. I left that one alone. I just pulled off the top and bottom thin sheet metal shielding because it interfered with the various mods I have performed.

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Indeed, on the NES it is neither grounding or cooling system, and in fact you might liek to remove them to offer some cooling to the system.

On the other hand, the shielding on the RF is necessary if you might want to use that, because the tuning coils inside are VERY sensitive to any electromagnetic field... on RF emitters, the shielding both protect the outside from paratitic emissions, and also protect the tuning system from outside parasites.

If you can pop one RF tuner on one of your systems, one day, poke your finger in (there is no high voltage, it's safe to do) and look what a mess you'll do on the TV. In fact, just removing the RF cover might have a noticeable effect already on the picture.

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Yes... tho I think they are more here so you can retune them if they get out of tune, and keep the sound and picture interval at the correct frequencies.

 

It probably would'nt allow you to tune from channel 4 to channel 6 for example, but more from channel 4.0 to channel 4.2 :P

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Yes... tho I think they are more here so you can retune them if they get out of tune, and keep the sound and picture interval at the correct frequencies.

 

It probably would'nt allow you to tune from channel 4 to channel 6 for example, but more from channel 4.0 to channel 4.2 :P

You know, someone posted in another forum about their Famicom working flawlessly on channel 3 & 4 RF with US TV. Famicom tunes to Channel 1 or 2 (US FM radio band, 90-96Mhz and 96-102Mhz). Do you think it would be possible to detune Famicom channel 1 down to US NTSC channel 6 (82-88Mhz)? That's only about an 8Mhz drop in frequency. Larger jumps (like converting a Famicom to run on NTSC channel 3 & 4) would likely be possible by using the tuning pot/choke in combination with a swapped out capacitor or resistor.

 

I'm just glad mine's the AV model so I don't have to worry about Japanese RF bullsh**.

 

EDIT:

 

Care then to explain to me how my Famicom works just fine on channel 3 or 4 on a US television (using the gray RF box that's for a NES)? That would indicate the Famicom itself isn't outputting anything at some specific frequency range, but rather the RF box is whats doing the signal-to-frequency conversion bit. If you don't believe me I'm happy to make a video. Otherwise what am I missing?

http://forums.nesdev.com/viewtopic.php?f=5&t=9474&sid=0b44ec2446e2476eeef37152ad68cfff#p102688

Edited by stardust4ever
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On the other hand, the shielding on the RF is necessary if you might want to use that, because the tuning coils inside are VERY sensitive to any electromagnetic field... on RF emitters, the shielding both protect the outside from paratitic emissions, and also protect the tuning system from outside parasites.

If you can pop one RF tuner on one of your systems, one day, poke your finger in (there is no high voltage, it's safe to do) and look what a mess you'll do on the TV. In fact, just removing the RF cover might have a noticeable effect already on the picture.

 

I was kind of thinking something similar. While a console like the NES or Famicom could probably do just fine without its shielding when pumping through composite output, I've seen my VCS' output look like a snow globe if I run it without shielding via RF out. I haven't done it, but I'd be curious to see what the effect would be on an NES to operate shieldless through RF. Maybe nothing, but I have to imagine it'd be more noticeable than via the composite jack.

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I was kind of thinking something similar. While a console like the NES or Famicom could probably do just fine without its shielding when pumping through composite output, I've seen my VCS' output look like a snow globe if I run it without shielding via RF out. I haven't done it, but I'd be curious to see what the effect would be on an NES to operate shieldless through RF. Maybe nothing, but I have to imagine it'd be more noticeable than via the composite jack.

Funny you mention the Atari VCS. Back in 2012, I did a channel scan on my old CRT while hooked up to the Atari. This was mainly to eliminate the many cable presets present in the scan memory. And long past the digital transition, I received two local Christian stations still broadcasting on analog UHF channels 40 and 42. Mind you my Atari VCS was direct connected to the TV with a shielded coax running from the console to TV, and all stock shielding intact. BTW, my Atari is a 4-switcher.

 

All I am saying is if my TV somehow received enough signal to pick up a snowy UHF station while my Atari was plugged in and running, I can assume there was also a fair amount of leakage from the RF circuit on the motherboard. If some PCB traces make a decent UHF antenna, they probably radiate at least a little bit in the target VHF band. One fun thing to do now that the VHF band is completely blacked out in my area, would be to hook a pair of rabbit ears up to the VCS output and get one of those old portable 5" b/w tube TVs and see how far it can pick up the signal from across the room/house.

 

Who knows? My neighbors might get a kick of watching me play PONG on VHF channel 2... :P

Edited by stardust4ever
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Well, one reason why all radio and most sound systems use coaxial cable is because any lenght of wire can make an antenna both an emitting and receiving antenna.

Shielding and grounding the outer shell protect the core wire to emit and receive too much emissions, but if the emitter is close enough or happen to be a some frequency (radio and TV receivers use frequency multiplier and dividers circuits; because a variable capacitor really able to tune continuously from 80 to 800mhtz would be gigantic, it's more like a 8Mhtz capacitor with frequency multipliers of 10 and 100 - from what I understood of radio receivers) you'll receive the signal from any cable wired to the TV... in some lucky case, even just a stick of 110/220V copper wire at the back of our TV would do.

Or like people that lived between 3 and 10km from the French emitter of Allouis, emitting France Inter - they reported hearing the radio station on any of their sound items - the signal was creeping into everything through the wires, and even non radio based items like record players would let them listen to France Inter.

 

And your experiment would work indeed. You might even try color, at short distance ( >1m )you might get color even.

Edited by CatPix
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And your experiment would work indeed. You might even try color, at short distance ( >1m )you might get color even.

Yes. Any well designed receiving antenna will make an effective radiator with similar spread and coverage pattern. The fact that I got another analog UHF station through a shielded cable connected directly to the motherboard proved that there is RF leakage for this very reason. Even if I put a 75 ohm terminator on the coax output, the portion of the motherboard circuit receiving said UHF signal would still radiate a small portion of the VHF signal to the air. Granted the UHF channel 42 was probably an order of magnitude higher in frequency than VHF channel 2 the Atari used, so the signal leakage might have be significantly less in the VHF region.

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Brought down a plane you say??

 

I had an electronics kit when I was a kid. I built a spark gap transmitter off a 12V relay coil (by energizing the coil using the normally closed contact repeatedly breaking it's own connection, created a high pitched buzzing effect) and connected the coil to a makeshift antenna. AM, Shortwave, completely jammed. VHF TV showed horizontal white lines all over the picture. FM radio as well as TV audio was unaffected no thanks to my device creating broadband amplitude modulation interferance to which frequency modulation is immune. In my dad's car, I could still pick up the high pitched buzz on AM band about a quarter mile away... One bored weekend, I send out SOS distress calls for hours, then left it run all day until the batteries drained. Didn't really know morse code but I just kept hammering out ...---... over and over again. Nobody answered. Looking back, that was probably a good thing, as I would have got in an ass-load of trouble for my shenanigans. Still less than 2 miles from the airport, same as today... :o

Edited by stardust4ever
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Funny you mention the Atari VCS. Back in 2012, I did a channel scan on my old CRT while hooked up to the Atari. This was mainly to eliminate the many cable presets present in the scan memory. And long past the digital transition, I received two local Christian stations still broadcasting on analog UHF channels 40 and 42. Mind you my Atari VCS was direct connected to the TV with a shielded coax running from the console to TV, and all stock shielding intact. BTW, my Atari is a 4-switcher.

 

My 2600jr makes a decent DTV antenna. It can pick almost as many stations as my leaf antenna. If it ever dies I could always nail it to my roof and permanently re-purpose it. :)

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