1. I don't know why you say US hams cannot experiment on HF unless our regs are changed. We currently have minimal bandwidth regulations. Someone is certainly welcome to correct me, but I don't know of any HF modem that tries to use 2 tones at 300 baud or higher. They all use multiple tone modems and modulate individual pairs at a substantially lower baud rate. Like 12 tone pairs, each at a rate of 60 baud which give an equivalent rate of 720 baud, substantially over the 300 baud regulation.
2. The very conditions you speak of is why multiple tone modems are used at HF. By the way they are also used in the UHF systems. 3. Don't know why you think vhf/uhf is channelized. Are you confusing memory locations with actual channels. All of my 2m rigs have 'vfo' mode. In fact, thats how you choose what goes in what memory location. Granted, the tuning steps are discrete and not continuous but they are pretty small increments. HF rigs with 2m let you spin the dial on 2m just like on 80/75m so they are from from channelized. 4. There is nothing to say you can't make a "high-noise" preamp for your 2m receiver. Most folks shoot for low-noise amps but you don't have to for test bed purposes. There is a lot of weak signal work done on vhf/uhf where low S/N ratios are the norm. QRM would be more difficult but that can be generated from a recorder playing through another rig on a dummy load. There just isn't any condition on HF that can't be simulated on 2m. 5. What does this have to do with the choices you make in the design process? If you want to experiment with a 3 kHz DV protocol on 2m, there is nothing to prevent it. If you design it to stay within a 300 baud limit on 2m there is nothing to prevent you from doing so. The whole point made in previous posts was that you can do the HF design/test process on vhf/uhf. No one is saying the ultimate test doesn't have to be done on HF with a lot of folks. However, the development work can be done on 2m right in your own shack. I sincerely doubt there are very many protocols in use today that didn't start out being designed and tested right on a test bench using dummy loads, attenuators, etc. Ultimately, you haven't provided any HF regulation that limits US hams from the experimentation being done elsewhere in the world. I'll try to state the problem with DV vs SSB in a more consise manner. Analog SSB pretty much sets the standard for spectrum efficiency, technical efficiency, and economic efficiency. Any DV implementation must meet or exceed these in order to be widely accepted and for it to replace SSB. The spectrum efficiency of SSB and the laws of physics (see Nyquist and Shannon) limits items like baud rate, bit rate, and bandwidth that you can use in a DV signal on HF and still be as spectrum efficient as SSB. I am sorry about that, but it is a fact. No one will accept a DV implementation where you say, hey my DV sounds as good and works as good as SSB but it takes 7 kHz of bandwidth. Before you can move on to TDM systems like you mentioned, there first has to be an implementation of a single user mode that competes on level ground with SSB in all the efficiency catagories. I am not aware of any HF DV implementations, here or overseas that comes close meeting all the different catagories of efficiency of SSB. I suspect it will require a revolutionary DSP design to do so. This DSP can certainly be invented here and then experimented with on the vhf/uhf bands. Until a DV implementation comes along that can meet all these criteria, overhauling the FCC regulations based upon a phantom idea seems premature at best. Sorry about being a bandwidth hog. Jim WA0LYK --- In digitalradio@yahoogroups.com, "Dr. Howard S. White" <[EMAIL PROTECTED]> wrote: > > Good question... > > Several Answers.. > 1. The rest of the world can already experiment on HF.. and will do so..whether we change our regs or not... > 2. HF has very different propagation characteristics that necessitate different DV solutions than those on VHF and UHF. > 3. HF is much more crowded and not channelized - which will necessitate different DV solutions than those on VHF/UHF > 4. HF DV has to be able to work in QRM and very low S/N ratios... not usual conditions on VHF/UHF. > 5. HF space is much smaller... necessitating DV solutions that fit the much smaller bandwidths... > > So while you might be able to design something at VHF/UHF... you need to be able to test it on HF...and the best way to test it is for many people to become Beta testers....hence the need to change the rules.... > __________________________________________________________ > Howard S. White Ph.D. P. Eng., VE3GFW/K6 ex-AE6SM KY6LA > Website: www.ky6la.com > "No Good Deed Goes Unpunished" > "Ham Antennas Save Lives - Katrina, 2003 San Diego Fires, 911" Need a Digital mode QSO? Connect to Telnet://cluster.dynalias.org Other areas of interest: The MixW Reflector : http://groups.yahoo.com/group/themixwgroup/ DigiPol: http://groups.yahoo.com/group/Digipol (band plan policy discussion) Yahoo! Groups Links <*> To visit your group on the web, go to: http://groups.yahoo.com/group/digitalradio/ <*> To unsubscribe from this group, send an email to: [EMAIL PROTECTED] <*> Your use of Yahoo! Groups is subject to: http://docs.yahoo.com/info/terms/
