What Is The Story On Digital Tuners?

[admin]

I continue to prefer analog tuners that allow you to dial in just the right channel. On more occasions that I can recall the digital tuner has been too far above or below the channel I am seeking. In the old days we could just dial it in. Do I just have digital junk or has any one else eperienced this?

[jps]

I used to have an '80s Sony digital tuner that I thought was okay but once I replaced it with my Kenwood Model 600T FM tuner, I found radio bliss!

[paologregorio]

I thought you were talking about guitar/bass tuners.

[kiramdear]

I was led to a more fanciful misinterpretation.



Sorry, Peter, I couldn't help myself. But in a feeble attempt to get back on track, I will offer that I too prefer to dial in rather than punch in. The one exception is my Grundig Yacht Boy 400 portable digital multi-band receiver. If I had only one tuner, that would be it.

[cjj]

I assume you're talking about FM receivers, right? And when you say that with analog tuners you can tune in just the right frequency, are you talking about being able to tune in a particular station operating on the "same" frequency as other stations?

If so, this makes sense due to the way that both FM and digital tuners work. In theory, all radio stations operating on a particular frequency are actually transmitting on exactly the same frequency. But, due to the nature of FM, Frequency Modulation, the actual frequency being transmitted changes with the material being transmitted. There are other atmospheric effects, etc. that can cause slight frequency shifts as well.

So, in order to receive this jumping frequency, the receiver has to have a fairly wide bandwidth that it's looking at in order to find the signal. In general, this is done with a circuit called a "phase locked loop" or PLL. This circuit "looks" for a signal to lock on to within a small range set by the tuner controls and when it finds something, it "locks" on to that signal and that's the one you get. Obviously, if there are multiple signals in the same range, it may have trouble locking on to just one and may jump from one station to another depending on the relative signal strength and several other factors.

Well then, why should a digital tuner be worse at this than an analog one? The receiver has to have its own internal frequency reference that is used to change where the PLL is looking. with an analog tuner, you adjust this reference manually with the tuning knob so you can fine tune it to where you want. This means the PLL lock range can be designed fairly small since you can make small adjustments to how it is tuned. In the digital tuner, it is set to a theoretically "perfect" frequency, such as 94.7MHz. Well, as we discussed above, this may not be quite right and, the more likely thing, the frequency reference in the receiver may not be very accurate. High accuracy frequency references are very expensive because this type of circuit tends to drift with varying temperature, etc., so, to keep your tuner's price below $10,000, they use circuits that just aren't that great. Now, since you have all this inaccuracy going in, you need to design a PLL with a wider lock range in order to make up for the fact that you can't really get that close to the perfect frequency you want.

That is a HUGE oversimplification of what's going on, but I think it should get the idea across without having to write several hundred pages and requiring an advanced degree to understand...

[admin]

Thanks for the short answer which was informative even if brief. You mean there is more?

[cjj]

Oh yeah! Us techno-nerds can go on for HOURS!

[rictified]

Digital readout tuners tune onto the exact frequency that the stations are transmitting on in discrete steps, 91.3, 91.5 FM or 1200, 1210 AM etc. so in theory they should be easier for the average non-technical person to use. Analog tuners tune continuously from the bottom of the band to the top on both AM and FM. I much prefer analog tuners myself and use a late 70's Marantz analog receiver, I would never trade it for a modern digital receiver. Now if you're talking about digital radios that receive digital transmissions called HD, (it does not mean high definition) run fast and far away from those, they are expensive and just plain don't work and don't sound all that better than analog if it is properly broadcast.

FM modulates the sound onto the carrier signal radio wave and the the carrier wave frequency moves the frequency up and down depending on the frequency of the sound being transmitted. An FM signal modulated with a 1000 CPS tone will vary the carrier wave 500 cps above and 500 cps below the center 1000 times per second. The carrier wave never varies in strength it varies up and down in frequency in relation to whatever sound is being broadcast which is why FM is so clear.
AM varies the carrier wave in amplitude or in other words in strength, if a 1000 cycle tone is modulated onto a AM carrier wave the carrier wave goes from 0%-100% 1000 times a second, this is why it allows noise, because it is at 0 half the time, these are simplified explanations.