Goodbye FT8, Hello Olivia, The MAGIC Digital Mode For HF!

I dug up something K1JT said about this in the Yahoo group:

"Perhaps this is a good time to remind everyone that estimates of signal-to-noise ratios for very weak signals *always* have an associated (if unexpressed) uncertainty. When S/N is quoted in dB, this can have important consequences.

In a stochastic (noise-like) process, experimentally measured values will be scattered around the unknown "true" value; some will be pretty accurate, some too high, and some too low.

Suppose a signal's true S/N (in the detection bandwidth) is equal to 1.0. In a series of measurements of that signal, some of the estimated ("measured") values will be close to 1; some will be higher, maybe as high as 2 (or even more), and some will be as low as 0 (or even less). These are *linear* values of S/N: estimated ratios of signal power to noise power.

When the S/N is expressed in dB -- a logarithmic scale -- you quickly see the problem. A perfectly plausible estimated S/N=0.1 means that in dB, S/N_dB = -10 dB. At S/N=0 we get "minus infinity dB".

Some people think it's a big deal when they see a JT65 decode displayed with an estimated S/N_dB of, say, "-30 dB". This is nothing more than a statistical fluctuation of noise and an illustration of the nature of logarithms.

On the other side of the equation, some people think "everyone with +XX reports MUST be running HIGH POWER!" when power is only the tiniest fraction of the equation. Do you give out a lot of "+" reports? Then congratulations, you have a fairly low noise floor at your location. Not everyone is as lucky. Remember that the signal to noise reports are the signal strength relative to the local noise floor on the receive side. I, for example, give out a lot of + reports because I have a fairly low noise floor and it's hard to get "below" that noise floor. A mile down the road, it can be totally different. Just because someone has a "+" report does not necessarily mean that that person is running high power. It's worth remembering that the difference between 5 watts and 100 watts is only 16 dB and this is using an "ideal antenna in free space" - in real life applications, it's often much less and on the receive side, conditions can change from second to second. Signal reports are *directional* and not absolute.

 

Hmmm,

Beauty is in the eye of you-know-who,

Value is as value can do !

 

A lot of this thread is a distinction, looking for a difference.

 

And I won't disagree with any of what he said -- that's the nature of studying stochastic processes and statistical distributions.

But everything in that quote is independent of the additional practical consideration of minimum recoverable SNR of a particular modem design, which is the point at which HF operation rubber meets the road. It's the way that modem performance between modes is compared. There are all kinds of tables and diagrams showing how different modems rank against each other with respect to S/N and various signal-to-distortion recovery abilities. And until the JT modes, they all were complete demodulators that recovered both the signal state and its clock.

The practical minimum recoverable SNR has to do with how well the modem can recover the entire signal from the sum of signal, noise, and other distortions. If the modem doesn't recover the entire signal, it isn't possible to talk about how well that modem recovers a signal. When you talk about other modems, such as Olivia, RTTY, etc., those modem designs recover an entire signal, including both the data and clock. With JT, there is really no way to talk about the minimum recoverable SNR, since doing so would be to produce a figure that attempts to use the same units and terminology as the complete demodulator designs, but which inherently measures a completely different process with completely different goals, and is assisted in ways that are not included in any other measurement of a data demodulation process.

 

Sure -- that's how you meaningfully compare things to find the best one for your particular needs. You measure them all the same way using the same criteria, and then score them with a consistent metric. Someday we may even be able to do that with the JT modes.

 

You need to stick to your story that WSJT is somehow having recourse to some other CHANNEL in order to communicate. It doesn't. Out of band? Maybe out of my watch band. LOL

 

I don't disagree with you. I think you are overemphasizing clocking through this whole thing. While in radio and telecommunications it's normal to have to it recover clocking, calling it "half" the data is misleading at best and ignores the fact that a great many data systems use self or external clocking (like say TCP and this whole internet thing).

It's like saying well, ISDN uses out of band signaling, so it isn't really fair to compare the sound quality to a regular T1 that uses in-band signaling, because it gets use the whole bandwith of channel just because it moved all the pesky signaling off somewhere else. It's not fair I tell you....

 

Oooh, that's starting to sound awfully analogous to an old AM versus SSB argument, ie, no fair comparison can be made because that darn Donald Duck demod essentially inserts a carrier (clock) that didn't come over the air!

 

Why Olivia is not the most popular digital mode NOW?

 

Olivia will make contacts when few other modes can, but the difference between those few which also can is that Olivia is able to do more than make a logbook entry. Those who whine about it being slow have obviously never played with the settings.

 

Not too slow when conditions allow playing with the settings. And when condx don't allow, those using Olivia can close the band well after hams using most other modes are sitting in front of their TV set or computer as they mutter to themselves about how terrible the bands have been.

 

that statement is not correct , all the JT/FT modes send all the info over the radio , the internet connection is only used for getting the correct time set and , if you want it will report your receptions to the psk-reporter website.
ko6kL


...." FT8, because it (and all its brethren) only communicate half the data over the radio channel. Then again, they allow assistance in contests, so why not for FT8 awards.." kk5jy

 

The question, at least for me, is not the SNR number. It is the fact that with the JTx and FT8 modes I am able to communicate with stations around the globe with my limited power and antenna.
With modes like PSK, RTTY, Olivia , etc there is no chance for such contacts. Of course, the situation was different a few years ago when the propagation was much better.

 

I like to try as many modes as I can afford Hi Hi, Yes FT8 has grown in popularity,and during any major solar storm I can still play radio and make contacts with FT8. It is a inside joke with my family I say to them (Wow the bands are bad today but I know the FT8 gang will be there) and they are!

 

I'm late to this thread party, but since we're talking about clocks, you wrapped that up nicely and added a bow.

So far I've not seen anyone mention using GPS to sync a computer clock. Remote or "disconnected" JT / FT operations should be easy enough with an inexpensive USB-connected GPS receiver and software necessary to keep a computer clock in check. In distant locales and depending on your surroundings, GPS would definitely have a signal availability advantage over WWV/CHU.

Everyone should remember that GPS for time sync is very popular with the WSPR kit folks. We don't need no stinkin' internet!