[OKDXA] Cheap Video Tricks...

[Nelson Derks]

Let's say you're interested in tinkering with ATV on the cheap.

(of course it's on the cheap, you're a Ham, aren't you?)

While making my final lap through the aisles of Ham Holiday as the last
stragglers were packing up their goods, I spied a TeleCaption II decoder box
with an asking price of $5.00... These set-top boxes enabled closed
captioning in the days before (1990) decoders became a standard 'new TV'
feature. The three-digit LED display with up/down tuning buttons and
TV/Cable switch on the back panel (along with a full complement of audio &
video I/O jacks) piqued my interest. I wonder how frequency-agile this
little rascal is? Three dollars later, the deal was made.

Turns out these boxes are becoming obsolete as the captioning standard for
2002 includes features this box, made in 1986, can't decode. No matter...
It's a 125 channel cable tuner and 69 channel off-air device that tunes
everything from 54 through 806 MHz. Peeking inside, we see the standard NTSC
TV building blocks like a voltage-tuned front end and a good-looking
demodulator board. The IF is most likely 45 MHz and the design had to be
fairly robust if they hoped to decode Line 21 reliably. The designers were
also kind enough to include scan tuning with fine tuning buttons and a
channel 3/4 modulator. Nice job.

You say... "So What?"

Although this little gem won't tune directly to the 913.25 MHz ATV repeater
downlink in Tulsa that I'm interested in, a fairly cheap downconverter kit
from North Country Radio will get me there. Plus, all the pretty parts like
the box, power supply and demodulator were done at the factory. It's
modification-friendly. Sure... I could go with a straight downconverter on
the TV and call it done, but having a dedicated baseband output I can record
or re-modulate to every TV in the house has its advantages. If you're
looking for a cheap TV demodulator, you'll find these on eBay for less than
$10.00 plus freight. The TeleCaption 2000, 3000 and 4000 models are newer,
but similar in capabilities. Bide your time and bid low. They're sensitive,
stable, and make a good picture comparable to what you'd see from a
'professional' demod. Look inside a Videotek and you'll see very similar
parts. If I hadn't seen one at Ham Holiday, I'd have never guessed they're
prime fodder for ATV use... What A Deal!

- AC5UP

PS: It does captions, too, and if I were really clever if could become a
video ID keyer, but I have a hunch I'm not that good... Or at least, not
yet.

(?)