My mini head end -- a report

[Doug E.]

I've just completed a project that's been in the back of my mind for years...a way to achieve the following:

--use the channel selectors on my vintage TV's instead of being stuck on channel 3 or 4;

--obtain more technically correct NTSC video (modulation levels, vestigial sideband, etc.) than is usually possible with a consumer-grade RF modulator;

--do the necessary sound processing to achieve appropriate audio for TV's from the 60's, which entails dynamic range compression, equalization, & volume normalization;

--be able to set up more varied & flexible "programs" for TV viewing, combining multiple DVD's, MP4 & other video files, & YouTube videos that are in 4:3 aspect ratio;

--have the flexibility to support two cable lines, one for each TV, in separate rooms;

--have the capability of transmitting over the air using a simple dipole antenna, with enough signal strength to cover my apartment (but not too much);

--have all the equipment in a compact cabinet without messy wiring;

--have easy access to the necessary adjustments.

I think I've achieved it all in the "head end" that I designed. A friend who is a talented cabinetmaker made the case for me. I'm so pleased with it that I feel like showing it off :-) The picture doesn't do it justice, but it sits inside an aquarium cabinet so the light isn't that great.
Here's what's in it:
--2 Sony DVD players
--a Behringer mini 9-band equalizer
--3 Blonder Tongue mini agile modulators (2 AMCM-860D's & an AMCM-806) & a Blonder Tongue MIPS4 power supply
--3 Radio Shack variable attenuators that give up to 20dB attenuation
--a 3-way splitter used "backwards" as a combiner for the 3 coax outputs
--a 2-way splitter
--a coax antenna switch connected between the third modulator output & its attenuator, allowing me to switch that output (full signal strength) to a dipole for over-the-air transmission
--a CB/ham radio filter just for the heck of it, because it came with one of the attenuators & has just the right length of coax to connect the combiner to the splitter;
--an outlet strip in the lower compartment with storage space for all the power cords.

The third modulator is connected to a laptop computer with its HDMI output going to an HDMI-to-composite video converter. I'm using SMPlayer as the video player & Pulseeffects for audio processing.

Each of the 3 video sources gets the benefit of dynamic range compression (either through the DVD player or the laptop computer audio software), equalization (through the Behringer or the computer's audio software) & volume normalization (2 of the modulators have built-in volume normalization & Pulseeffects provides it for the laptop).

Anyhow, I just wanted to share...

Doug E.

[kf4rca]

So, how many channels are you running total? Have you seen any of those UHF modulators that are out there?

[DavGoodlin]

Very impressive! The power strip with switches and pilot lamps tops it out for me.

Many of the UHF channels are actually in the "hyper band" cable channels above 450 mc.

I think the one BT mod I got that was to cover a high numbered cable channel, which is marked on the output filter, IE "70" corresponds to channel 18 UHF and "101" is 45 UHF. It is just enough to cover 50 feet between my garage and house, even in the basement

[Doug E.]

Originally Posted by kf4rca

So, how many channels are you running total? Have you seen any of those UHF modulators that are out there?

Just 3 channels. I don't really have need for any more at this point. All the modulators are agile so I can switch them around occasionally to use all the channels on the tuner. The third channel was going to be more of an experiment to see whether I could get decent NTSC video from a laptop, playing mp4's or YouTube videos as well as using it as another DVD source. But...before I knew it, I had "proof of concept" & now I use the laptop more often than the 2 DVD players. It's fun to make up my own program schedule, including test patterns, commercials, bumpers & promos, & keep it running continuously during the day. You wouldn't believe what you can snarf off the internet, or maybe you would... :-)

The Blonder Tongue mini-modulators can do any UHF channel up to 69, I believe, as well as those cable channels that are sometimes in between the broadcast frequencies.

Doug E.

[kf4rca]

Those BT modulators are great. I've got 2 fixed tuned BT's that I got for free. The older laptops often have composite out. But you can get a vga to ntsc scan converter real cheap these days. I've even seen them at thrift stores. The first one I ever bought was $99. It was made by ADS and was an 8-bit ISA card for a computer. It would only do 640x480. There was a program out there called showjpg.exe that I used to display test patterns. These days most scan converters that I see, are external units.

[Doug E.]

Originally Posted by kf4rca

Those BT modulators are great. I've got 2 fixed tuned BT's that I got for free. The older laptops often have composite out. But you can get a vga to ntsc scan converter real cheap these days. I've even seen them at thrift stores. The first one I ever bought was $99. It was made by ADS and was an 8-bit ISA card for a computer. It would only do 640x480. There was a program out there called showjpg.exe that I used to display test patterns. These days most scan converters that I see, are external units.

Discovering those mini-modulators was what inspired me to do my head end project. I was familiar with units like the AM-60 but didn't have room for anything that filled a full rack space. The fixed BT modulators (MICM) are a lot more common. I've got one for use as a spare. The agile models can be found but they cost more. My head end uses 2 AMCM-860D's & 1 ACM-806 (an older model without LED display). I like the 860D's because they have built-in volume normalization, which gets rid of one of the major annoyances of digital program sources. We had 12-channel cable when I was a kid, going back to 1967, & I remember how you could set the volume on your TV & barely have to budge it when switching channels.

Doug E.

[kf4rca]

The BT's that I have are MAVM (9&13). 1RU each. I think they were the low end units.
I think you can still find that showjpg.exe program on line. You can take an old DOS box and set up the autoexec.bat and the computer will go into the program and display your test pattern upon bootup! No keyboard intervention necessary. You can turn it off and when you turn it back on the test pattern returns automatically. Of course you'll need a scan converter to get the VGA down to NTSC.

[Doug E.]

Originally Posted by kf4rca

I think you can still find that showjpg.exe program on line. You can take an old DOS box and set up the autoexec.bat and the computer will go into the program and display your test pattern upon bootup! No keyboard intervention necessary. You can turn it off and when you turn it back on the test pattern returns automatically. Of course you'll need a scan converter to get the VGA down to NTSC.

That .exe file sounds cool, but I'm using (I guess) a more hi-tech method. I found some test patterns online that are .mp4 files. They run for several minutes & you can play them in repeat mode on your video player. I had to re-size & trim some of them to get them to exact 4:3 ratio & remove borders.

Doug E.

[kf4rca]

The newer DVD players have a USB port on the front. You can play the test patterns as jpg files from the USB drive. They have a composite output so no scan conversion is necessary. Might have to use the remote to access the USB drive.

[Doug E.]

Originally Posted by kf4rca

The newer DVD players have a USB port on the front. You can play the test patterns as jpg files from the USB drive. They have a composite output so no scan conversion is necessary. Might have to use the remote to access the USB drive.

Wow, didn't know that. When planning this project, I purposely chose a cheap, basic Sony DVD player that's been in production for years. I think I'll pick up a few extras for replacement purposes.

As it is, I feel like a kid in a candy store, being able to store all kinds of video files on a laptop & play them in any order I want, plus streaming stuff like YouTube videos on my TVs. I know that's no great shakes nowadays but I'd never tried it before. It made my potential video library much bigger (& cheaper) than before. With a 500GB hard drive, you can store something like 1000 hours of entertainment. If I had it to do over again I'd also build in space for an external hard drive (8TB or more).

Doug E.

[Electronic M]

If you're using VLC media player on that laptop and you number the files you can build a 24Hr or longer Play list and put it on repeat so there's constant programming. Some computers support multiple graphics cards and some graphics cards supply multiple monitors. You can get USB audio adapters to have multiple independent audio outputs, CTRL+A in VLC toggles between different audio output devices, and you can run multiple instances of VLC simultaneously.... I've been wanting to use this to make my own single device 3-7 channel cable system with my Blonder Tongues.... Haven't gotten around to it yet but have basically all the components.

[Doug E.]

Originally Posted by Electronic M

If you're using VLC media player on that laptop and you number the files you can build a 24Hr or longer Play list and put it on repeat so there's constant programming. Some computers support multiple graphics cards and some graphics cards supply multiple monitors. You can get USB audio adapters to have multiple independent audio outputs, CTRL+A in VLC toggles between different audio output devices, and you can run multiple instances of VLC simultaneously.... I've been wanting to use this to make my own single device 3-7 channel cable system with my Blonder Tongues.... Haven't gotten around to it yet but have basically all the components.

That's great to know. I have VLC media player on that laptop, but I ran into a problem when I set up playlists...after 4 or 5 selections played, the audio of the next selection would start without the video coming on. I never found a solution & I switched to smplayer, which worked just fine. smplayer supports the same kinds of playlists, with repeat & shuffle modes.

I have space for a 4th mini-modulator & maybe someday I'll get a laptop that supports multiple graphics cards & video/audio outputs. But for now, 3 channels is enough for my needs. I love being able to set those channels adjacent to each other (usually on high-band VHF where there are no frequency gaps) & check the IF alignment & adjacent channel rejection on my RCA TV. If you grew up with a cable system & your TV had manual fine tuning, you became very familiar with tuning up & down from the proper setting & running into the interference from the next lower & higher channels. With RCA portables from the mid-60s, when you tuned up toward the higher channel there was usually a certain amount of "windshield wiper" from that channel's blanking bar (at least on high-band channels) but it disappeared completely when the fine tuning was dead on...or if it didn't, your TV was probably misaligned.

Doug E.