View Full Version : Smallest most compact RF modulator?


Trekintosh
08-23-2017, 01:57 PM
Hi guys, I'm new here. I've got a passion for ~5" portable color tubes with AV inputs, but recently was gifted a lovely 13" Sharp Linytron Plus and was thinking about sticking my spare unused Chromecast inside to make an all-in-one package.

However to get there obviously I need to uncase several components and make the smallest device I possibly can inside the TV. So what's the smallest RF modulator I can find to stick inside some spare space? Getting HDMI to composite is easy and cheap, tiny active converters are common for $10, and they run on USB power so it's easy to tap into whatever power supply I find for the Chromecast, however most RF modulators I've seen are fairly clunky.

Electronic M
08-23-2017, 02:40 PM
Most off the shelf stuff is the same size (~1"X4"x3").
Only way I can think of to go smaller is to pull the shielded RF modulator module out of a VCR or sat box, google the data sheet and rig it to accept A/V and power inputs....I don't know your skill level, but this can vary from easy (I've got one out of an 80's cable box or VCR that has 4 input pins A,V,B+,Gnd), to complex (I have a REALLY tiny UHF agile multi-standard modulator out of a sat box that needs I^2C protocol from a micro-controller to set the channel, broadcast standard etc.*).

*That one I had to write code for an Arduino Uno board to control.

Personally (unless a set is rather beat up/undesirable, and the owner is motivated) I'm not a fan of modifying/hacking things up. If the mod becomes undesirable and is not easy to completely reverse, then the set takes on a crappy feel in any application after the mod falls out of use.

One thing that might be worth your consideration is not to modify the TV but find space elsewhere for a modulator and the chromecast. If the set is being used where you can't locate the modulator close and don't want to run cable, a good solution is to get a Blonder Tongue AM60, BAVMz or AM40 series modulator...While bigger than consumer offerings they (when working properly*) will provide superior picture and sound performance, and have enough RF power that with a good TX and RX antenna you can transmit wirelessly for a good block radius.
If you just want the chromecast/HDMI converter hidden for a classic look, perhaps you could hide those inside an old VCR (the VCR will have an RF modulator built in).

Electronic M
08-23-2017, 02:46 PM
One smaller modulator I just remembered was the outboard accessory ones sold for some LaserDisc players and some older camcorders. They had standard mono audio and video male RCA jacks and a male 1/16" phones plug between the RCA jacks, and would plug into a trio of matching connectors on the devices made to work with them. Those were IIRC ~2" in their biggest dimension.

Trekintosh
08-23-2017, 04:25 PM
Most off the shelf stuff is the same size (~1"X4"x3").
Only way I can think of to go smaller is to pull the shielded RF modulator module out of a VCR or sat box, google the data sheet and rig it to accept A/V and power inputs....I don't know your skill level, but this can vary from easy (I've got one out of an 80's cable box or VCR that has 4 input pins A,V,B+,Gnd), to complex (I have a REALLY tiny UHF agile multi-standard modulator out of a sat box that needs I^2C protocol from a micro-controller to set the channel, broadcast standard etc.*).

*That one I had to write code for an Arduino Uno board to control.

Personally (unless a set is rather beat up/undesirable, and the owner is motivated) I'm not a fan of modifying/hacking things up. If the mod becomes undesirable and is not easy to completely reverse, then the set takes on a crappy feel in any application after the mod falls out of use.

One thing that might be worth your consideration is not to modify the TV but find space elsewhere for a modulator and the chromecast. If the set is being used where you can't locate the modulator close and don't want to run cable, a good solution is to get a Blonder Tongue AM60, BAVMz or AM40 series modulator...While bigger than consumer offerings they (when working properly*) will provide superior picture and sound performance, and have enough RF power that with a good TX and RX antenna you can transmit wirelessly for a good block radius.
If you just want the chromecast/HDMI converter hidden for a classic look, perhaps you could hide those inside an old VCR (the VCR will have an RF modulator built in).

I totally understand the sentiment of not wanting to modify a perfectly good set. This unit is rather tired, of the "sat in the garage and had stuff on top of it" variety. That said, I'm not going to be doing any irreversible mods. At most I would tap into the AC input for the converters/chromecast, and the antenna input for the output of the RF modulator. Possibly hot snot a couple of microswitches if for some reason I wanted the adapters inside to turn off when the TV is off. I'm not going to be cutting or chopping anything physical if I can possibly avoid it.

As for an agile modulator, that is something I considered, but I really like the idea of a pick up and go set, and I tend to take my old TVs (and their corresponding adapter chains) with me to friends' houses or work, so the idea of just having an all-in-one machine that can play or stream content is very appealing. I'll be eventually getting a Blonder Tongue for my other sets. This one is more experimental for me, as it's not a size or type of TV I normally collect.

I'm not really up to making a whole Arduino board to control a modulator. Preferably looking for near plug n play devices, though obviously minor soldering won't be a big bother. I'll definitely take a look at those accessory modulators. That sounds like a perfect setup to me, as they have normal RCA jacks making it easier to set things up.

lnx64
08-23-2017, 04:32 PM
If you want a super small RF modulator, get an old model 1 Sega Genesis. I'm not kidding, they have super tiny RF modulators in them, and have the most simplest pinout: Ground, 5v, video, audio. (Not in that particular order).

http://retrorgb.com/images/GenesisRGBBypass02.jpg

Trekintosh
08-23-2017, 05:00 PM
If you want a super small RF modulator, get an old model 1 Sega Genesis. I'm not kidding, they have super tiny RF modulators in them, and have the most simplest pinout: Ground, 5v, video, audio. (Not in that particular order).

http://retrorgb.com/images/GenesisRGBBypass02.jpg

That's the can at the back, right? That'd be super useful. I assume that's composite video in the pinout? If that's the case this'd probably be the easiest to source tiny RF modulator. Easy to find cheap untested bare consoles on eBay.

lnx64
08-23-2017, 05:02 PM
Correct, the little metal box in the back (and yes it's composite video..). In fact, I have a Genesis system here where I don't use the RF, and would be willing to remove it to send for you. I'll test the RF out to make sure it works, and if the picture looks good enough, I'd be happy to sell it to you.

Mine is from the US, so it's NTSC with channel 3 and 4 selection. I'll post pictures of the RF out quality from it.

Trekintosh
08-23-2017, 05:09 PM
Correct, the little metal box in the back. In fact, I have a Genesis system here where I don't use the RF, and would be willing to remove it to send for you. I'll test the RF out to make sure it works, and if the picture looks good enough, I'd be happy to sell it to you.

Hey, works for me! Even if I don't end up using it in this project I have been wanting to make a tiny TV test box and the RF can would be useful for that, too.

lnx64
08-23-2017, 05:17 PM
Here's pics of the quality of the small RF modulator in these machines.

https://imgur.com/a/s7BlV

lnx64
08-23-2017, 05:19 PM
Hey, works for me! Even if I don't end up using it in this project I have been wanting to make a tiny TV test box and the RF can would be useful for that, too.

Cool, shoot me a PM and I'll see what we can work out. I'm modifying my Genesis for RGB video, and with how I'm trying to get the best picture and sound out of it (even replaced the sound chip with something better--but compatible), I have been wanting to get rid of the RF modulator in it, to remove any noise it may be injecting back on the system.

Findm-Keepm
08-23-2017, 09:09 PM
I have some Astec modulators from old 70s and 80s stuff, but my favorite is the little Alps modulators used in later VCRs and DVDs. 2X1x1/2 inch or so. You can find larger VCR, Cable and Satellite box modulators for 2 bucks each new, so I no longer scrounge. They even have RF pass through, so I use them on my daily driver with my DTT900 to test video units.

Worst modulator? Some of the early game units (we're not talking Atari, Nintendo, or Sega, but the cheaper/California all-in-one start-up stuff) - all discrete components, and drift like you wouldn't believe.

Findm-Keepm
08-23-2017, 09:14 PM
Cool, shoot me a PM and I'll see what we can work out. I'm modifying my Genesis for RGB video, and with how I'm trying to get the best picture and sound out of it (even replaced the sound chip with something better--but compatible), I have been wanting to get rid of the RF modulator in it, to remove any noise it may be injecting back on the system.

With the Saw-resonator based modulators (last 15 years or so from Alps, Matsushita, Murata, and Toshiba), they lock dead on, with zero harmonics - any noise is typically a ground loop or RF leakage. I like HVAC tin foil tape for RF leakage issues, although the last I've really experienced was with the old OAK and SciAtlanta Cable boxes. Once they went addressable, we no longer could repair them.

lnx64
08-23-2017, 09:20 PM
With the Saw-resonator based modulators (last 15 years or so from Alps, Matsushita, Murata, and Toshiba), they lock dead on, with zero harmonics - any noise is typically a ground loop or RF leakage. I like HVAC tin foil tape for RF leakage issues, although the last I've really experienced was with the old OAK and SciAtlanta Cable boxes. Once they went addressable, we no longer could repair them.

Shouldn't be any RF leakage, but I think it's ground loop issues. On the Sega Genesis, it's VERY sensitive with these RF modulators (Sega was certainly reluctant to put adequate filtering on it). The modulator works great otherwise, even as simple as it is. Since removing it to prepare possibly sending it to OP, as expected, RGB video cleaned up and lost the jailbars I was seeing before.

This is what this tiny little RF modulator has inside: http://i.imgur.com/zY5KfdD.jpg

No idea what the POT does, I'm guessing output power, but I have no plans to mess with it.

Electronic M
08-24-2017, 09:51 AM
No idea what the POT does, I'm guessing output power, but I have no plans to mess with it.

Neat to get a look inside that.

That adjustment is NOT a pot, it is a ferrite tuned inductor or transformer. It likely tunes the frequency of the modulator, or some filtering for the system. I agree, you don't want to mess with it casually.

Findm-Keepm
08-24-2017, 12:21 PM
Neat to get a look inside that.

That adjustment is NOT a pot, it is a ferrite tuned inductor or transformer. It likely tunes the frequency of the modulator, or some filtering for the system. I agree, you don't want to mess with it casually.

The saw resonator sets the Output frequency - the adjustable coil sets the Audio modulation center frequency, for the 4.5MHz offset.

I've got several hundred brand new SAW resonators for a later Toshiba chip - useless these days, as the chip is about 3 bucks, and a whole modulator is a buck less. :sigh:

Trekintosh
08-25-2017, 11:27 AM
Thanks to lnx64, Looks like I've found my modulator for this project. Finally got the matching transformer I was missing to hook up my normal modulator to the TV and I found that there was a *lot* of crawling snow in the signal. Underneath the interference it looked fine, but the interference was really problematic, made viewing a pain. I live in a very EMI noisy home. There's an AC and fan that are running 24/7(the fan is plugged into the same socket as the TV/modulator are), there's wifi running all the time, and there's neighbors' wifi running too. How best can I isolate the TV and modulator to clean up the signal? Will just snapping a few ferrite chokes around the coax and power cables be enough?

kf4rca
08-25-2017, 12:38 PM
I built a video only modulator once. It used only half a dozen components. It was a clone of the modulator in the Heathkit IG5240 bar/dot generator. It uses an FET and a channel 3 crystal, which might be hard to find these days. I got my crystal at a hamfest. The guy had a whole bin of them.

Findm-Keepm
08-25-2017, 01:46 PM
Thanks to lnx64, Looks like I've found my modulator for this project. Finally got the matching transformer I was missing to hook up my normal modulator to the TV and I found that there was a *lot* of crawling snow in the signal. Underneath the interference it looked fine, but the interference was really problematic, made viewing a pain. I live in a very EMI noisy home. There's an AC and fan that are running 24/7(the fan is plugged into the same socket as the TV/modulator are), there's wifi running all the time, and there's neighbors' wifi running too. How best can I isolate the TV and modulator to clean up the signal? Will just snapping a few ferrite chokes around the coax and power cables be enough?

Ferrites might work, but it's best to run whatever displays the interference on an EMI filter. The common mode chokes in most sets ain't enough. Ferrites don't work on TV coax well, if at all. A coaxial line isolator (See a good CATV supplier, or check eBay..) might work - but only with RF interference - they were used with Satellite systems back in the 90s/2000s

Best options:

1) Get yourself an AC line conditioner ($$$$) I use a Sola, but mostly for line regulation (132V at my outlets.....yes, too high, right off the tranny outside.) It filters out everything but >400msec surges. Pricey items - got mine surplus for pennies.

2) Build your own EMI filter ($) Use an IEC EMI input filter, and a wall outlet output. I made one back in 2002ish for a Navy need. Be sure to carry the ground to a common point.
IEC filter:
https://www.google.com/search?q=emi+filter+iec&num=40&source=lnms&tbm=isch&sa=X&ved=0ahUKEwic5o299fLVAhVLilQKHZLlCnYQ_AUICigB&biw=1280&bih=834

3) Buy a TDK or Murata (may be sold under KEC as well) EMI Filter - used ($), new ($$). We used the TDKs on computers - the dot matrix machines we had (22" platen) would generate all sorts of noise on one phase of the line. The TDKs are only rated for 6 or 8 amps, plenty for a TV. The Muratas are larger and harder to find anymore. Schaffner may make some standalones like the TDKs.

The X10 Home control system also offered one - it used to be available at RadioShack, good for 5A, and $20 or so. Check eBay.

Other tips - use quality coax from Belden/Alpha or Channel Master. Most of the discount store stuff is cheapo 40% coverage - you want >90% coverage, which is braid AND shield foil.

Try plugging the TV into an outlet that is off a different leg than the other items. Tough to figure out if you don't have the means to trace the circuit from the panel to the outlet.

Trekintosh
08-25-2017, 06:09 PM
Ferrites might work, but it's best to run whatever displays the interference on an EMI filter. The common mode chokes in most sets ain't enough. Ferrites don't work on TV coax well, if at all. A coaxial line isolator (See a good CATV supplier, or check eBay..) might work - but only with RF interference - they were used with Satellite systems back in the 90s/2000s

Best options:

1) Get yourself an AC line conditioner ($$$$) I use a Sola, but mostly for line regulation (132V at my outlets.....yes, too high, right off the tranny outside.) It filters out everything but >400msec surges. Pricey items - got mine surplus for pennies.

2) Build your own EMI filter ($) Use an IEC EMI input filter, and a wall outlet output. I made one back in 2002ish for a Navy need. Be sure to carry the ground to a common point.
IEC filter:
https://www.google.com/search?q=emi+filter+iec&num=40&source=lnms&tbm=isch&sa=X&ved=0ahUKEwic5o299fLVAhVLilQKHZLlCnYQ_AUICigB&biw=1280&bih=834

3) Buy a TDK or Murata (may be sold under KEC as well) EMI Filter - used ($), new ($$). We used the TDKs on computers - the dot matrix machines we had (22" platen) would generate all sorts of noise on one phase of the line. The TDKs are only rated for 6 or 8 amps, plenty for a TV. The Muratas are larger and harder to find anymore. Schaffner may make some standalones like the TDKs.

The X10 Home control system also offered one - it used to be available at RadioShack, good for 5A, and $20 or so. Check eBay.

Other tips - use quality coax from Belden/Alpha or Channel Master. Most of the discount store stuff is cheapo 40% coverage - you want >90% coverage, which is braid AND shield foil.

Try plugging the TV into an outlet that is off a different leg than the other items. Tough to figure out if you don't have the means to trace the circuit from the panel to the outlet.

Seems like we have a winner here.

Unfortunately, the entire home is on one circuit, except the air conditioner which is on a circuit with the other aircons in the building. It's super hard to find a place where I wouldn't have interference. Might get a choke too, just to see what happens.