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<Hack> Reuse "old" TV tuners

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Conundrum

Fri Jun 11 2010, 10:23PM

Registered Member #96 Joined: Thu Feb 09 2006, 05:37PM
Location: CI, Earth
Posts: 4062

Hi all.
I worked out how to repurpose those now-useless analogue TV tuners which are unusable after November.

seems that with a bit of careful butchery you can use a diode ladder on the varicap tuner input to set them at 20MHz intervals and then connect five to a spare satellite LNB in order to use it without a "dodgybox" for the purposes of amateur 10.250GHz.

the lnbs aren't really designed to work this low but they should work, and using this method allows 100MHz bandwidth.

as a bonus you can also use this method to resurrect defunct Sky boxes that have broken tuners but otherwise work.
comments?

-A

803

Fri Jun 11 2010, 10:34PM

Registered Member #2807 Joined: Fri Apr 16 2010, 08:10PM
Location:
Posts: 191

you use them in antique tv!!!!!!! I repair then as a hobby. if you see a tv on the side of the road, if it is old, don't ruin it!!!!!!!

Conundrum

Sat Jun 12 2010, 10:17AM

Registered Member #96 Joined: Thu Feb 09 2006, 05:37PM
Location: CI, Earth
Posts: 4062

hmm..
the modern "junk" sets often all use the same tuner, and they are pretty small these days.

Interesting, I didn't realise anyone here repaired antique stuff..

-A

radiotech

Sat Jun 12 2010, 06:13PM

Registered Member #2463 Joined: Wed Nov 11 2009, 03:49AM
Location:
Posts: 1546

When the analog TV stations clear off perhaps use the tuners to carefully listen for might have be hiding between the combs.

For the past 40 years TV stations have been locked to a master clock everywhere, meaning that most of the energy was clumped around multiples of 15734 in the channel groups .-- in the US.

Steve Conner

Sat Jun 12 2010, 09:58PM

Registered Member #30 Joined: Fri Feb 03 2006, 10:52AM
Location: Glasgow, Scotland
Posts: 6706

When they turn the analog TV off, they'll sell the extra spectrum before you know it, it's worth a lot of money.

How does five tuners add up to a 100MHz bandwidth? That's like saying that you can beat the land speed record by gluing together 15 Minis.

There are lots of interesting projects you can make with TV tuners. Some of them are entirely analog and tuned by a high voltage that you apply to a varicap diode. You can make a ghetto spectrum analyzer from one of these quite easily, by applying a sawtooth wave to the tuning voltage input.

Others have a PLL chip that accepts tuning commands over I2C and locks to an accurate frequency. You can make a nice radio receiver out of one of these.

Plans for both of the above are available with a quick Google search.

Tuners for digital TV are very similar to the ones in the newest analog TVs. The difference between an analog TV set and a digital one is really just in the demodulation.

Not all antique stuff is worth fixing. I've done three tube amps and a Grundig table radio, but anything with transistors in it, I'd leave in the dumpster

Conundrum

Sun Jun 13 2010, 09:07AM

Registered Member #96 Joined: Thu Feb 09 2006, 05:37PM
Location: CI, Earth
Posts: 4062

same sort of idea as the "ghetto spectrum analyser".

the plan here is to set them up with zero overlap then recombine the signals electronically.

I might need to increase the number of tuners as the response does fall off rapidly past 6 MHz and even with amplification you'd be fightning noise..

the beauty of this hack is that the main component is available for free

In my "box o'junk" i have a broken citizen 08TA B/W LCD TV where the screen's ITO contacts all degraded but the tuner works fine.
Was made in the mid 1980's IIRC, probably cost something like Â£300 (!)
Thanks to Mike Reeves for hanging onto this beast for nearly 20 years...

Another source for cheap tuner modules is those DVB-T sticks that are useless without the (buggy, crash prone) software- the chipset shouldn't be too hard to repurpose for decoding an LNB's signal.

contrary to popular belief satellite TV is not always encrypted, so you could use a PC as the decoder.

-A

currently trying to build a VISOR.. so far I have the infrared portion working..

Steve Conner

Sun Jun 13 2010, 06:42PM

Registered Member #30 Joined: Fri Feb 03 2006, 10:52AM
Location: Glasgow, Scotland
Posts: 6706

Conundrum wrote ...

contrary to popular belief satellite TV is not always encrypted, so you could use a PC as the decoder.

Contrary to popular belief? I know lots of people who watch Freesat. :P

radiotech

Sun Jun 13 2010, 09:53PM

Registered Member #2463 Joined: Wed Nov 11 2009, 03:49AM
Location:
Posts: 1546

Some "tv tuners" are complete receivers outputting both video and audio via a pair of link-jacks on the back. They were intended to be connected to various cable or MTS demodulators provided by the cable company in the early days of pay-tv. They are sold by flea markets for pennies.

Those are more adaptable to make an AM-FM spectum analyser
and also some have an FM AFC loop from the demod section back to the main tuner section.

NTSC TV FM is 25 kHz wide and the pre-emphasis is 75 uSec.
(This can hacked in the receiver.) The AM video part is 3.5 mHz wide.
which means the tuner's local oscilator would make a dandy very low powered transmitter.(evil doers spent endless hours tripping repeaters by just using picked off RF from portable scanners.)

This shows that flea power RF does travel considerable distance and could be put to some use like finding what F works best in tunnels or caves.

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