Norway to be first to go all digital FM

[Hank Thompson K6HUH]

In the Amateur service some rig manufacturers have already started digital radio.  I own 2 digital radios from Yaesu myself. Now, Norway is digitizing it's entire FM public network.  I wonder how digital radio would affect the Amateur service as we know it.......They did this here for Television, and most people I know just have cable TV, or TV via the local exchange carrier (Like AT&T Uverse or Verizon FIOS):

http://www.npr.org/sections/thetwo-way/2017/01/06/508501366/norway-will-be-first-country-to-shut-down-fm-network-go-all-digital

Any commments?  Remember, we used to be primairily AM on all frequencies, then SSB which bought us more bandwidth.  That may have been good, but I wonder how digital radio would propagate for dx?
I can see a future where a contest would be WAC, for worked all cities.....  Or how about this, we just go back to 100% code.  That's digital!

One thing about it, QRM would be a thing of the past -
Comments??

Hank
K6HUH

[KP4MD]

I've tried FreeDV digital voice on HF and my experience was similar to https://n9sja.com/2013/02/04/freedv-digital-voice-for-hf-bands/ With current technology the human ear and brain decode voice better than digital can in the presence of QRM and weak signals in noise. This is due to digital voice mode's "cliff threshold" effect where you either hear all or nothing when the signal reception is marginal. On the other hand, the human ear and brain power can often fill in missed syllables and words using analog voice modes under those conditions. That is not an issue for those high power clear channel broadcast stations in Norway.

73, Carol KP4MD

[Hank Thompson K6HUH]

In the YouTube demo of this mode, I could clearly hear the difference between digital and analog modes.  The SSB mode, although rife with background noise, was to me much clearer.  I wonder what the A-D sample rate is for the digital mode? I'm thinking that if it were as high as lossless audio, or high sample rate DVD then maybe it might sound better?.

A couple of weeks ago, I was listening to a network of guys using AM transmission, and I gotta say, both ends of the conversations (One in Southern California, the other in Texas) was as clear as a local AM commercial station.

Does the digital voice mode use less bandwidth than SSB? How would digital be for DX?  Comments?


BTW, Does anyone else out there have a digital radio like the FTM-400DR? I would like to converse OTA and do a comparison if you do, please contact me.

Hank
K6HUH

[Hank Thompson K6HUH]

Well, I'm not really answering myself, but this forum is new to me, and I don't know how to just add a comment:

I was looking around for more on digital voice modes, and found this on the ARRL web site:

"...........Digital Voice is a new technique built around analog to digital converters and codecs that sample a voice signal, compress it, and transmit it as a bit stream. Like other digital media, digital voice offers interference free communications if the radio signal is strong enough to overcome the general noise and interference level".
Now, I'm really on the hunt for the sample values used for the A-D conversion in ham radios.

I first became aware of digital communications in the early 1960's , when I worked T-Carrier for Ma Bell.  Original T-1 had a sampling rate of 8K per channel, and a 1.544 MHZ T-1/d1 system was comprised of 24 channels, each with this sample rate.  This form of digital signal processing was originally used for trunks between central offices.  24 analog conversations would normally use up 24 pairs of wires, where T-1 only used 4 pair of wires, 2 wires for transmit, and 2 wires for receive.  Because the typical phone line only passed frequencies in the range of 204 hz to 3004 hz, 8K sample rates were deemed wide enough. In the T-1 system, repeaters at about 3KF were used to help the digital signal maintain a certain level, in order to maintain S/N ratios.  T-1 communications could not be used on loaded cable pairs, only bare copper was used. Inductance would destroy the digital signal.  When the internet became available in my neighborhood, and customer farther from the central office than 6,000 feet would probably not get good service.  Now, the neighborhood has UVERSE, where fiber cable is terminated in a neighborhood "box", then converted to a wire interface, and then to the customer.  This super wide bandwidth permits me to have 59,403kbs available to my gateway, for phone, internet, and TV.  How times change!

HANK
k6huh

Now, in the ARRL note above, it states that " interference free communications if the radio signal is strong enough to overcome the general noise and interference level".  Sounds to me like more RF power.  I wonder,how much more power to improve the S/N ?

[Kevin Hooke KK6DCT]

I think the point about "interference free communications if the radio signal is strong enough to overcome the general noise and interference level" is talking about the characteristic of digital voice where you're receiving a digital stream of data - if you receive enough of the data to successfully decode from digital back to an analog waveform, then you can reproduce the sampled audio exactly as it was captured from the sender, therefore, 'interference free'.

The point where you can no longer receive enough of the datastream to successfully decode though, then you have nothing. No audio, or extremely garbled audio. It's more of an 'all or nothing' compromise. It's what Carol described as the 'cliff threshold', once you go past the point where you're not receiving enough of the signal data, you have nothing, you drop off the cliff. 

Given that HF DX is prone to signal fading and QRM from many sources, my guess is that current approaches for digital voice are much better suited for local communication. I would be interested to find out if there's any studies for how a digital voice signal could be transmitted to account for the typical fading and interference you get with propagation. I'm sure there must have been studies on this already. 

Kevin KK6DCT

[Kevin Hooke KK6DCT]

Re. sample rates, the FreeDV site says they sample at 44.1 or 48kHz.

Kevin

[Hank Thompson K6HUH]

With a sampling rate as high as you state above, I wonder how much is bound to be sampled noise? And if that is the case, how quieter really is digital communications?
Does that web site say anything about compression? how many dB?
hank
K6HUH