As you say...a high feed point (more than 1/4 wavelenght and I suspect more than 17% of a wavelength) does not produce the best NVIS radiation and as a result as the F0F2 layers combine after dusk (actually when the sun is just 10-15 deg above the horizan), the NVIS radiation pattern needs to put all the signal you can get up above 75 deg in the radiation pattern. I have seen many times seen a 75M signal from stations from 10-100 miles away go from a Q5 to unreadable during a short transmission.
There is no doubt that NVIS operation on 80-40M at night is quite a problem...and in the military (and MARS) it is worse because you normally don't have any frequencies between 3 and 4MHz. The Texas State Guard used to have some frequencies in the 160M range (actually unused marine frequencies) and also operated 160M. Mobiles used a 3 ft "extension" 160M MasterMobile coil and an 5-6 ft whip. Transmitters were a 6SN7 oscillator and 807 final. Modulation was a 6SN7 and 6L6. Much like the old commercial Collins AM HF rig. The receiver was a Gonset converter feeding the car's broadcast radio. Base stations ran the military equivalent of the Collins commercial AM HF radio. (If you want the URL to the radio, contact me off liet.) The antenna was GENERALLY a long wire (50-200 ft) fed with an antenna tuner. Some stations ran 50-90 ft verticals. The stations at Peacock Military Academy had a 50ft vertical and inverted L at 50ft and a total length of 200 ft. They also ran a BC-610. Hi Hi. The "Guard" had communications between most mobiles and bases all over the state...and the hams also enjoyed 160M. In college (1960-64) and while teaching at Peacock Military Academy (1964-1965) I ran 6M am (mainly 50.1-50.5MHz) at 2-15 wattes with an antenna at 20 ft and could easily talk 20 miles. My 2M (144.8) AM was 10 watts and I could talk about 15 miles with an antenna at 20 ft. As I have said, each situation is different. 73, Walt/K5YFW -----Original Message----- From: [email protected] [mailto:[EMAIL PROTECTED] Behalf Of KV9U Sent: Friday, October 27, 2006 9:37 AM To: [email protected] Subject: Re: [digitalradio] local HF net successes John, NVIS only works on the lower bands, and even 80 meters can go "long" in the later evening after 8 or 9 pm local. You need to monitor the FoF2 to get a feel for the highest frequency possible for NVIS operation. The other night, one of the stations who has a "high" dipole of about 70 feet for 80/160 went from way over S9 +40 to nearly inaudible later on. I use a NVIS 80 meter inverted vee at 35 feet apex but most can not do this. Also, the competition is quite difficult on 80 at times but that should lessen with the new phone band expansion. I would like to see more activity on 160 for this kind of work since you don't have much competition as compared to 80. You often can expect more QRN than 80 as conditions lengthen, but not always, since there are times that 80 is bringing in QRN from much farther distances, especially early in the evening. 160 has better ground wave coverage than 80, but I don't personally know how much difference there is since very few stations can get on 160 in my area. Maybe three of us at most out of a potential group of a dozen. Are there any OT folks here who operated 160 mobile back in the 50's or 60's before repeaters became popular and can tell us about how well it worked (or didn't compared to simplex VHF? I had a Novice and then Technician class license back in the early 60's, so later on only operated 2 meter AM simplex which was the main "local" band then. But that did not include people very far from the city area. I now live about 35-40 miles out so am not part of the core area. Some others who would like to participate live even further out though. If you don't operate NVIS, then the only other choice is ground wave/direct wave or whatever the mixture comes to. We tried 15 meters again and it was not as successful as the previous weeks net and so we all moved back to 10 later in the evening because 80 got too long and signals dropped out once you were out of ground wave coverage. It seems to me that NVIS is not working that well when the band goes long, even though it is supposed to work 24/7 as long as we don't have some kind of CME/ionospheric disturbance. Since most of the operators are running vertical omnidirectional antennas on 10, it seems that for those of us who are way outside the core area, we would have to run some gain antennas in order to participate more fully. I run a full 100 watts but do not have anything more. Making a beam (vertically polarized) just for this activity is probably not something I really want to do. We have shown that 10 meters does work better than 6 meters with unity gain verticals that are ground mounted, but I expect that at least part of that is the difference in capture area of the antennas. Yesterday, one of the hams more "local" to me was testing his new mobile 10 meter rig. We frequently work each other via 2 meter repeater and it was quite interesting how different the propagation is on 10 meter simplex. In most cases, I could copy him much more consistently on 10 meters. I should mention that we live in the "Driftless Area" of Wisconsin which is a portion of the state along with neighboring Iowa and Minnesota that did not have the glaciers shear off the land 10's of thousands of years ago so we have basically the remnants of the old sea floor of a billion or more years and deep valleys from other erosive forces of nature. You can even find enormous numbers of brachiopod fossils in quarries. These are some of the oldest forms of life in the Paleozoic. From a radio wave perspective this means we have a challenging environment with deep valleys and high hills. My elevation on my ridge farm is around 1250 and the Mississippi River is around 620 feet ASL. Many of the city stations are barely above the river elevation. Terrain can change drastically over only a few miles. That is why NVIS operation is so useful. But when most of the operators can not use it, you try other avenues. But try as I might, I can not get even one of the net members to try digital modes on any of the bands:( And because of that, digital is disfunctional for most emergency operation that I happen to be interested in. This is completely different than only 15 or 20 years ago when a great number of active hams at least had 2 meter packet capability. But no more. 73, Rick, KV9U John Champa wrote: >Antenna are important here, guys! > >Are you using NVIS antennas, e.g., a dipole NMT 1/4 wave high, etc. > >John - K8OCL > > > > >>>By the way, since I moved about 30-40 miles away from my former QTH >>>which was centrally located to our club's Wednesday night chat net, we >>>have tried many different HF frequencies to see what works the best for >>>voice. We initially started on 28.400 for the last year or two but the >>>reason for selecting 10 meter phone was so that the Tech + and Novices >>>could be part of the group. Guess what? At no time have we ever had any >>>of them come to the well publicized net. So recently we have been trying >>>other bands, and 80 tends to go long and you get too many distant >>>stations wanting to contact us, 40 and 20 are outside the NVIS range and >>>have a weaker ground wave. Unfortunately same for 6 meters:( We thought >>>that might work OK for direct/skywave, but very mediocre results with >>>our mediocre antennas. >>> >>>The bands that really work the best are: >>> >>>160 if the other stations are willing to install an antenna ... and ... >>>15 meters was the best "ground"/direct wave of all the bands we tried. >>>Even with Butternut and R7 type verticals. I still can not quite figure >>>out the reason. >>> >>>I sure wish I could get some of the stations to try digital, especially >>>on 6 meters and 160 meters, but it seems nearly impossible out of 150 + >>>hams in the greater area, we have very few that will even try digital >>>modes at all:( >>> >>> >> >> >> >> 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 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! 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