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PostPosted: Tue Dec 08, 2015 7:31 pm 
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While RF is no great shakes when it comes to quality for any system, I have noticed that my NES's RF has significantly superior video quality to my Famicom's RF. Jailbars from the Famicom aside, the HVC-CPU-07's Famicom's picture is either softer or grittier than the NES-CPU-10 NES's picture.

Since I live in the US, the NES's RF modulator is fixed to US TV channels 3 and 4 (60MHz and 66MHz, respectively). Back in the days of analog TV broadcasting, I typically always kept my consoles set to channel 3 because nothing in my area used it outside the cable box. Channel 4 was assigned to the local NBC or CBS affiliate. The choice was there for people who found a better signal from the other channel. Now use digital TV broadcasting, I do not perceive a quality difference at either channel. Digital TV transmission, even though it uses the same frequencies, does not appear to interfere with the signal sent by the NES to any substantial degree.

As we all know, the Famicom's RF modulator is fixed to Japanese TV channels 1 and 2 (90MHz and 96Mhz). In the US, these are used by FM radio stations. US TVs did not used to support these frequencies, and apparently they were assigned to cable boxes but were infrequently used due to the overlap with FM radio. Within the 6MHz band required by a TV signal, you get 30 FM radio channel frequency assignments. Instead of one digital frequency, you can get bombarded by multiple analog frequencies. Some are more powerful than others, but between the RF modulator and the TV's demoulation circuitry there must be some extra interference coming from the more familiar analog signal of the radio stations. Does this make sense?

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PostPosted: Tue Dec 08, 2015 10:33 pm 
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It seems more likely to me that the famicom RF modulator modulates its video at a lower amplitude, producing a worse SNR.

It's pretty easy to turn off the NES/famicom and—as long as your TV doesn't decide to show blue instead of static—see what the received FM radio looks like. IME, I didn't really notice anything from trying to decode FM as NTSC, much in the same way that ATSC's 8VSB doesn't look like much when decoded as NTSC.


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PostPosted: Wed Dec 09, 2015 8:53 am 
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lidnariq wrote:
It seems more likely to me that the famicom RF modulator modulates its video at a lower amplitude, producing a worse SNR.

It's pretty easy to turn off the NES/famicom and—as long as your TV doesn't decide to show blue instead of static—see what the received FM radio looks like. IME, I didn't really notice anything from trying to decode FM as NTSC, much in the same way that ATSC's 8VSB doesn't look like much when decoded as NTSC.


My TVs show static on 95 and 96, but they mute the volume. Suppose an older TV exists that does not mute the volume and could be coaxed to display these channels (or you simply import a Japanese TV). I know that the audio accompanying an NTSC video transmission is carried over the as an FM signal 250kHz below the upper end of the 6MHz spectrum used. So could one conceivably hear the station at 95.7MHz or 101.7MHz depending on the TV channel in this instance?

Could one reason why a NES RF modulator may be using a higher amplitude is to allow the autoswitching RF switch to work? I understood that Atari 2600 (which also has a wavy artifact pattern on my TV) and older consoles could not with an autoswitching RF switch, they need a manual TV/GAME switch. The Famicom has its TV/GAME switch on the back of the console an used a simple switching box.

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PostPosted: Wed Dec 09, 2015 2:10 pm 
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Great Hierophant wrote:
Suppose an older TV exists that does not mute the volume and could be coaxed to display these channels [...]So could one conceivably hear the station at 95.7MHz or 101.7MHz depending on the TV channel in this instance?
Yup.

Some older televisions have enough range in their fine tune knob to get into the FM band anyway, by tuning to channels 6 or 7 and just adjusting it.

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Could one reason why a NES RF modulator may be using a higher amplitude is to allow the autoswitching RF switch to work?
That would make perfect sense. Note that the NES RF modulator adds a significant DC bias to power the autoswitch.
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The Famicom has its TV/GAME switch on the back of the console an used a simple switching box.
However, that's weird to me. If there's no switch on the RF modulator itself, the only thing this could be doing is removing power (and possibly the video signal also) from the external autoswitch.


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PostPosted: Wed Dec 09, 2015 4:01 pm 
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lidnariq wrote:
Great Hierophant wrote:
Suppose an older TV exists that does not mute the volume and could be coaxed to display these channels [...]So could one conceivably hear the station at 95.7MHz or 101.7MHz depending on the TV channel in this instance?
Yup.

Some older televisions have enough range in their fine tune knob to get into the FM band anyway, by tuning to channels 6 or 7 and just adjusting it.

Quote:
Could one reason why a NES RF modulator may be using a higher amplitude is to allow the autoswitching RF switch to work?
That would make perfect sense. Note that the NES RF modulator adds a significant DC bias to power the autoswitch.
Quote:
The Famicom has its TV/GAME switch on the back of the console an used a simple switching box.
However, that's weird to me. If there's no switch on the RF modulator itself, the only thing this could be doing is removing power (and possibly the video signal also) from the external autoswitch.


Wikipedia states that analog TV broadcast audio on channel 6 could have been heard by radio receivers by tuning the receiver to 87.75MHz (as low as the dial can go), so that makes sense cponsidering the overlap between FM radio and TV. Presumably it may be possible to hear the station at 87.9MHz on TV channel 6 now that analog broadcasts have ceased, but that frequency is only used by two stations in the US and nowhere near where I reside.

That Famicom switch is a strange duck : http://livedoor.blogimg.jp/ika_fam/imgs ... 343f0d.jpg
The thicker cord goes to the TV, the thin cord goes to the Famicom, and there are four ways the cord can end with #3 being the default.

I understand then that the DC offset is providing phantom power to the switchbox not unlike a condenser microphone. Does that then mean that audio coming from the NES's RF modulator is going to going to sound poorer than the Famicom's?

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PostPosted: Wed Dec 09, 2015 5:03 pm 
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Great Hierophant wrote:
That Famicom switch is a strange duck : http://livedoor.blogimg.jp/ika_fam/imgs ... 343f0d.jpg
The thicker cord goes to the TV, the thin cord goes to the Famicom, and there are four ways the cord can end with #3 being the default.
That looks like a fairly standard abstract RF kit. ① is a 300Ω twinlead to 75Ω F-type adapter on a piece of 300Ω twinlead. ② is is 300Ω twinlead (actually, it's the output of a 75Ω-to-300Ω RF transformer). ③ is bare 75Ω coax, probably RG59. ④ is an F-type connector on 75Ω cable.

So the famicom adapter looks like it's just got one of the 300Ω-to-75Ω adapters inside of it, that you can optionally bypass.

Older US televisions all used 300Ω twinlead. Newer ones (usually "CATV ready") used 75Ω F-type connectors.

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I understand then that the DC offset is providing phantom power to the switchbox not unlike a condenser microphone.
That's almost a perfect metaphor.
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Does that then mean that audio coming from the NES's RF modulator is going to going to sound poorer than the Famicom's?
Why would that be true?


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