on occasion less than 100 miles on VHF and sometimes as little as 30 miles on 80M HF
I disagree with the assumption that for Emcomms we only need span 100 miles. That may be true in higher population areas, and where the state is broken down into counties. Up here we will be working into provincial EOC's, which could be up to 500km away (300 Miles), too far for VHF point to point. Furthermore we don't have the density of hams in the rural areas which we allow for relay points. We have good cellular coverage along our highways, but once off the major roads rural cellular service is very spotty. Internet access via cellular to pass text messages cannot be relied upon, so that throws us back to HF as the most likely link (besides sat Phone) I really don't understand the restrictions that you have in the USA on baud rate and mode restrictions. Your mode works well but would be wonderful a little faster. RFSM 8000 works well, but is wide, and am still not sure how it will work under poor HF conditions. ALE400 works well into the weeds, and it would be great to see you and Patrick team up to combine NBEMS and Ale400 in one package. John VE5MU From: digitalradio@yahoogroups.com [mailto:[EMAIL PROTECTED] On Behalf Of kh6ty Sent: Sunday, March 02, 2008 9:13 PM To: digitalradio@yahoogroups.com Subject: Re: [digitalradio] Re: Keeping NBEMS in mind John, Over what distance are you getting flutter or Doppler on VHF? I only get the flutter (usually all the time!) when I try to work Charlotte, NC from Charleston, SC on 70 cm, which is 173 miles away, but I am not far enough north for Aurora. For emcomm, we only need to span up to 100 miles. I am interested to know if you also find flutter on VHF within 100 miles. Skip KH6TY ----- Original Message ----- From: "John Bradley" <[EMAIL PROTECTED] <mailto:jbradley%40sasktel.net> > To: <digitalradio@yahoogroups.com <mailto:digitalradio%40yahoogroups.com> > Sent: Sunday, March 02, 2008 9:30 PM Subject: RE: [digitalradio] Re: Keeping NBEMS in mind > This may be true at lower latitudes, but up here at 50 degrees north, we > get > sustained aurora flutter or Doppler on HF and VHF. Sometimes the audio has > a > distinct echo. PSK125 and 250 are worse. > > we do have days where we have strong signals but cannot decode anything. > > it would be nice to have something a little faster than regular MFSK for a > robust mode > > John > VE5MU > > > -----Original Message----- > From: digitalradio@yahoogroups.com <mailto:digitalradio%40yahoogroups.com> [mailto:digitalradio@yahoogroups.com <mailto:digitalradio%40yahoogroups.com> ] > On > Behalf Of kh6ty > Sent: Sunday, March 02, 2008 4:18 PM > To: digitalradio@yahoogroups.com <mailto:digitalradio%40yahoogroups.com> > Subject: Re: [digitalradio] Re: Keeping NBEMS in mind > > >> >> I have seen some multiipath, especially when I have tested PSK31 on VHF, >> but much of that was from aircraft. I am not sure how I can discern >> multipath when on HF. Is there any clue in the waterfall or do you go by >> the sound? >> >> 73, >> >> Rick, KV9U > > You will see three kinds of multipath on VHF, which you can see on the > waterfall. > > One is reflections from airplanes, which tends to look like a ghost signal > accelerating across the main signal. When it coincides with the main > signal, > > all copy will be momentarily lost, no matter how strong the signal. > > The second correlates with wind conditions, and the ghost signal moves > slightly in and out of the main signal during wind gusts, especially when > a > weather front is moving through. > > The third is reflections from fixed objects, and the ghost signal tends to > stay a fixed distance away from the main signal. > > PSK63 is less affected by multipath reflections than PSK31 is on VHF, and > PSK125 even less so. When cancellation does occur, if you are using ARQ, > that frame is just resent and the transfer is delayed by that much. Of > course, only ARQ is going to guarantee error-free copy. FEC only helps, > but > does not insure no errors. > > QRN seems to be the biggest problem on HF and QSB second. During a period > of > > thunderstorm activity, as we often have in South Carolina, and more > especially in Florida, PSK125 is greatly disturbed and PSK250 so much that > it is unusable, but PSK63 not nearly as much. All the decoders seem to > have > this problem, and there may be a way to improve that cascaded loss of sync > in the faster modes, due to QRN, but we have not yet tackled this problem. > Fortunately, for our 100 mile emcomm uses, QRN and QSB are not problems on > VHF, and ARQ takes care of the multipath reflection problem. > > 73, Skip KH6TY > > > > > > > Announce your digital presence via our Interactive Sked Page at > http://www.obriensweb.com/sked > > Check our other Yahoo Groups.... > http://groups.yahoo.com/group/dxlist/ > http://groups.yahoo.com/group/contesting > http://groups.yahoo.com/group/themixwgroup > > Yahoo! Groups Links > > > > > > -- > No virus found in this incoming message. > Checked by AVG Free Edition. > Version: 7.5.516 / Virus Database: 269.21.3/1306 - Release Date: 3/1/2008 > 5:41 PM > > ---------------------------------------------------------- No virus found in this incoming message. Checked by AVG Free Edition. Version: 7.5.516 / Virus Database: 269.21.3/1306 - Release Date: 3/1/2008 5:41 PM
