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