One is cost, but it turns out that channel 4 is where the 5th harmonic of the digital video bit clock (13.5MHz) ends up in. Making herringbone interference patterns in channel 4. Channel 3 doesn't have this problem. I installed in a DVD player an RF modulator I salvaged out of a dead VCR, so this is how I know... :D

A nice feature of this modulator I salvaged out of a Sharp brand VCR is that it will pass TV channels with the power off. Many VCR TV modulators need the power to be on always, and an additional control line to pass or modulate. Which means I don't have to have power on in the DVD player all the time.

Channel 4 never worked as well as 3, even in VCRs. Some DVD players did have modulators, although most that did were VCR combos.

As this modulator has differing spacing of the antenna input and the modulator output F connectors the old one I had in there before, I decided to just mount the new modulator in an empty space inside the player. And run coax connectors from the modulator to new F connectors mounted where the old modulator used to be. The channel 3 or 4 selector is now buried inside the player, but that's okay. It's on channel 3, for the previous mentioned reasons.

And my Admiral TV's tuner needs a cleaning. When I get ambitious enough...

Wouldn't another reason be that the svhs or componenant outputs provide more resolution and in a flat screen world rf inputs are useless unless running off some antenna?

Wouldn't another reason be that the svhs or componenant outputs provide more resolution and in a flat screen world rf inputs are useless unless running off some antenna?

According to Wikipedia the DVD format came to be in 1995....Assuming it hit shelves by 1996 it had about 10-12 years of existence before flat panels dominated the new set market. So it does not make much sense to argue no RF was to accommodate flat pannels.

by 1995-6 new sets all had video inputs, older sets with only rf were not common anymore, and gave the store something else to sell - a new Tv, or a modulator box.

They probably don't have built-in modulators for the simple reason that it costs more money to add the additional circuitry that would rarely be needed when buying any TV of the current era when they came out.

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Although VHS/DVD/tuner combo's from that same era had them, and I don't recall ever seeing this ch 4 interference when using the DVD player with the RF feeding the TV

My Samsung VHS/DVD combo has an RF modulator and there is no interference problem so there must some shielding issues in your conversion.

Or power supply decoupling.

...must some shielding issues in your conversion.
Rerouting the wires feeding the modulator's power helped a lot. Still not prefect, still some sparkles left to reduce.

Sparklies increased when I put the metal top cover on... :( I eventually found that it was a piece of metal mounting bracket not grounded except thru the cover. Seems to be picking up noise off the front control board. Ran ground wires to ground it to the chassis, helped some more. Changed the shielded wire I used to coax, to send the video and the audio to the modulator, helped a little. More power supply decoupling helped a lot. Used a bigger value coil right at the modulator's power input.

Signal to noise is almost acceptable now...

Got it better, I gave the modulator its own 7805 regulator (fed by 12V), mounted right at the modulator. no sparklies now. It's now decent. :)

One last tweak: Had to tune the modulator's 4.5MHz FM sound subcarrier frequency. It was a little off, which caused visible beats with the chroma subcarrier (I made it switchable: color or B&W). Now it works well. :banana: Looks like the best improvemsnts came from using a dedicated voltage regulator, tuning the subcarrier, using well shielded audio and video lines.

One last tweak: Had to tune the modulator's 4.5MHz FM sound subcarrier frequency. It was a little off, which caused visible beats with the chroma subcarrier (I made it switchable: color or B&W). Now it works well. :banana: Looks like the best improvemsnts came from using a dedicated voltage regulator, tuning the subcarrier, using well shielded audio and video lines.

Can you elaborate on how you made it switchable: color or B&W?

How did you manage to get around macrovision ?

Can you elaborate on how you made it switchable: color or B&W?

He probably mixes the two S-video lines and has a switch in the color line to disconnect it....Many here have been getting pure monochrome by disconnecting the chroma line on S-video connectors.

He probably mixes the two S-video lines and has a switch in the color line to disconnect it.

That's essentially it, though here I created a low pass luma filter, a bandpass chroma filter and merged these to create a composite video signal that would look good on older color TV sets (the one that use a notch filter). I switch that and an unfiltered luma only signal.

http://www.wa2ise.com/radios/admTVdvd.jpg

Thanks for sharing this. And what type of rf modulator are you using that runs on 5 volts?

Thanks for sharing this. And what type of rf modulator are you using that runs on 5 volts?

I dunno, so I asked Google:

http://www.talonix.com/shop/item.aspx?itemid=10044

2 bucks.

Hey, those are cute.

My DVD recorder/player RF output can be tuned to any UHF channel from 21 to 68 for older TV's. No English TV's made since 1969/70 were fitted with VHF tuners as VHF TV was phased out & we became a UHF only Country. Early video recorders were factory preset to channel 36 RF output as that has never been used for TV broadcasting, but you could adjust the output between channels 30 & 40 with a screwdriver, later ones could tune 21 to 68. Channels 35,36,37 & 38 were not used until the channel 5 network started broadcasting on ch 37 in 1997, then on ch 35 in 1998, this could cause adjacent channel interference & ch 5 had to send re-tuning engineers to affected areas FREE of charge to viewers. It cost them millions of pounds. Of course it's all digital now so problem no longer exists..

Hey, those are cute.

Naw, these are cute - and small - looks to be matchbox sized, and also 2 bux.

http://www.talonix.com/shop/item.aspx?itemid=10045