[sci.electronics] tv tuner ?

tds32845@uxa.cso.uiuc.edu (09/22/90)

	I would like to know just how complicated a tv tuner is.  Does the
tuner use any special components?

	I would appreciate any comments.

--tony
--tonys@uiuc.edu

whit@milton.u.washington.edu (John Whitmore) (09/23/90)

In article <44900012@uxa.cso.uiuc.edu> tds32845@uxa.cso.uiuc.edu writes:
>
>	I would like to know just how complicated a tv tuner is.  Does the
>tuner use any special components?
>
	Modern tuners (part of remote-control systems) are almost always
assemblies of voltage-controlled filters (one for VHF, one for UHF),
voltage-controlled oscillators (one for UHF, one for low VHF, one for
high VHF), and just enough RF amplification to drive a mixer without
degrading the signal (the mixer's insertion loss plus maybe 20 dB of
gain).
	The only special components are the UHF mixer/oscillator/amplifier,
which is almost always an Esaki diode (tunnel diode).  One two-terminal
device does all three functions, and does it at near 1 GHz.  Tuning
this sort of gizmo is very difficult with general-purpose equipment,
because the tunnel diode will oscillate simultaneously at dozens of
different frequencies if given any encouragement to do so.
	For the rest, the most important components are simple coils
of wire, high-Q capacitors, and the occasional voltage-controlled
capacitor (varactor diode, epicap diode, tuning diode).  All these are
inexpensive (this is a KEY requirement) and easy to design with.
The problems in aligning tuners (getting all the filter stages
working together instead of fighting each other) are severe enough
that most tuners are made in specialty manufacturing facilities and
installed as pre-aligned units into mass-produced TVs.  
	Making a tuner is a very challenging project, if you want
full UHF coverage.  Buying one, as a built module, is relatively
easy (that's how a TV service shop fixes 'em).

	If it matters, the stage following the 'tuner' is the IF amplifier
(with its own automatic gain control), IF filter (often a simple looking
ceramic filter) and sound separator/FM sound demodulator/SSB video
demodulator/color decoder.  The tuner output is 45 MHz (kind of like
a Channel 0 television signal) and has the exact same encoding of
sound/color/brightness as the original TV transmission.  The tuner
output, thus, cannot just be piped into a video monitor or speaker,
but must have a lot of processing first.

                               John Whitmore

markz@ssc.UUCP (Mark Zenier) (09/24/90)

> In article <44900012@uxa.cso.uiuc.edu> tds32845@uxa.cso.uiuc.edu writes:
> >
> >	I would like to know just how complicated a tv tuner is.  Does the
> >tuner use any special components?
> >

Some of the newer "cable ready" tuners use a 610 Mhz SAW filter
as the the first IF and upconvert.  And then mix down to low VHF.
PIN diode attenuators for AGC, 1 GHz prescalers.  A lot of new
stuff.

See the article on building your own spectrum monitor in the
September 1989 Radio-Electronics.

markz@ssc.uucp