Digital voice transmission on Ham frequencies?
I know nothing about the digital modes (JT65, BPSK, etc), but I know they
are transmitted like single-side band (½ of AM, LOL!). But, sitting here,
thinking, how about digital FM? As I understand it D-Star transmits FM
with P-25 technology. Could this be adapted to HF frequencies? To me,
it would be of great help to use this on HF as a long-distance Skywarn
Net. Information about the storm(s) could be sent out nd given enough
leeway, save lives.
Lately it seems that a storm will start, go down on the ground for a period
then lift back up to form just a rain cloud, then travel several hundred
miles before reforming in the middle of the night, and drop down again,
suddenly, and without warning and folks are killed. Using long-range FM
Should a tornado or severe storm be in an area, using FM would mean no
QRN or QRM, you'd just need to go to a antenna closer to the ground to
take away possible lightning strikes, LOL!
What is y' all's thoughts on this?
It's good to see that you're thinking! I'm not sure I see how DSTAR on HF would be of help, but I think there are other techniques out there that certainly might.
DSTAR is not P25 over FM. It's GMSK modulation, and doesn't use the P25 codex for the digital audio. You can do DSTAR on HF - you can buy boards to add the DSTAR protocol to your own radio - and it need not be on VHF. Some folks are using the Kenwood TS2000 to do DSTAR on HF.
However, I don't think the currently available hardware will support simultaneous data and voice, and if it did, I think you'd run afoul of FCC regulations. For that matter, I question the legality of GMSK on HF, even though it's only 6 kHz wide.
I've wanted to see a way to easily transmit video of radar displays to the SKYWARN people in the field. A 2.3 GHz. mesh network should make this practical in most flat country. But actually, we're pretty close to having it now. A local AC0ID has a neat Android phone app that shows the radar displays, and overlays APRS information on top of it. As long as your cellphone is working, you can see where you in relation to the cells, and where the other spotters are. It's VERY handy. I'd like to see a way to send that without using the cellphone network. It would also be nice to be able to send live video of suspicious looking things.
EchoLink, IRLP, Allstar and DSTAR linking - adding interest to repeaters worldwide 24X7
Digital transmissions are set up to be just about noise free. It doesn't matter if you're using AM, SSB or FM the signals are supposted to be just like they are standing next to you. This hold true as long as the signal has a S/N ratio so it can be decoded. Once a signal falls below the detection threshold you get either beeps and bloops or you get nothing. In our current status you cannot use digital with voice and data on the HF bands. You can on 160 meters and it's still a toss up if you can do that with the new rules concerning the 60 meter band.
There are some folks running experiments with digital of the HF bands and there is a manufacturer that sells a unit the will covert a SSB rig to digital voice.
Hope this helps
I don't know squat about P-25 or D-Star for that matter, I was just
trying to think of a transmission mode that could be used in disaster
IMHO, since the F.C.C. 'stole' the bottom VHF TV channels, they could
allocate, say Channel 2 to send out the NOAA's radar. If you lived
within the recption area, you could see the radar screen without having
to have cable or satellite.
You can already download the NOAA weather radar images.. Of course they arent on the ham bands..
There is some digital voice activity on HF:
I have not used that particular software, but I have received its broadcast counterpart. And I was not too impressed. Lots of dropouts on signal fades. By the time the signal becomes strong enough to eliminate the dropouts, it is probably about strong enough to sound perfectly clear in analog mode anyway.
But as you mentioned, it can be good for transmitting digital images without the degradation that occurs with analog reception. Here is a link to digital SSTV program for HF:
Does require a fairly strong signal for reliable copy though.
One of the things I have been wondering about is what happens when multiple stations transmit at the same time on the same frequency. The doubling on SSB isn't much of a problem and you can usually hear everybody that is transmitting. On digital you would most likely not be able to copy anybody when that happens. I would think the advent of this system would be a jammers delight.
Time will tell.
This can not happen because its against the Part 97 rules, and for good reason. FM is FAR to wide for this. Take 18Mhz for example. You would take out the majority of the band with that single FM transmission. Its just WAY to wide. You will hear at some point some yahoo saying "Part 97 does not restrict FM on HF below 10M". They would be right! But it DOES forbid any signal that wide. Secondly, FM does not propagate the same as SSB, CW, and other Digital modes. You would not get the realistic long-haul communication on FM that you would on these other modes even if you could.
Also there are ways to run digital voice in the bandwidth as allotted using sound card mode digital voice. See the following projects..