One more comment (and not contrary to what Bob is saying): For us at far north latitudes, ISS never rises very high (about 11-deg. max), so using a high gain vertical works well with ISS which is always near the horizon. I worked Bill MacArthur in 2005 using my 9-dB cushcraft 17-foot base whip running only 50w. But for polar orbiting Leos this is not good.
73, Ed - KL7UW At 10:20 AM 5/30/2009, Bob Bruninga wrote: > > It also has a null on an overhead pass. > >But that is quite insignificant. Looking at the gain plot of a 3/4 >wave vertical (the 19.5" whip on 70cm) it is only down say 6 to 10 >dB above 85 degrees. BUT the satellie is 10 dB or more closer when >it is above 50 degrees which more than makes up for any loss of gain >straight up. see plots on >www.aprs.org/rotator1.html > >But yes, there can be a complete fade when it is perfectly directly >overhead (extremely rare). But since the satellite is only above 50 >degrees only 5% of the time, it is only above 85 degrees only 1/8th >of that 5%, or much less than 1% of all access times. Again, losing >less than 1% of access time due to a possible less than 1% chance of >a fade is nothing to be concerned about. Just 2 cents worth... > Bob, Wb4APR > > >> For mobile work on AO27, SO50, AO51 > >> a 2 meter quarter wave whip is all > >> you need... > > > >Absolutely, For a 19.5" whip in center of roof: > > > >1) Has 5 dBi gain above 20 deg on 2m > >2) Has 7+ dBi gain above 30 deg on 70cm > >3) Is an omni > >4) does not sacrifice 3 dB for circular > >5) Above 25 deg, satellite is 6 to 10 dB closer! > >6) works the birds solid for the center of high passes > >7) Simplicity at its best! > > > >Read about it: www.aprs.org/rotator1.html > > > > Disadvantage: The only disadvantage is TIME. > > On the above web page you can also see that > > satellites spend 70% of their daily pass > > times below 25 degrees. BUT! For those best > > passes in the morning and the evening (or > > whenever) you can make solid contacts while > > mobile for about 5 minutes. > > > > Also note, that you do NOT need any tracking > > program to predict passes. AO51 schdule > > repeats evry 5 days for example. Just write > > down the CENTER pass of the morning and > > evening for each day for 5 days. Update > > those 10 times on a small 3/5" card on the > > dash about once a month or so will predict > > all passes whenever you are mobile. There > > will be a pass 100 minutes earlier and 100 > > minutes later each day too. So you can > > predict all 6 passes a day from those same > > 10 times. > > > > See how: www.aprs.org/MobileLEOtracking.html > > > > Bob, WB4APR > >_______________________________________________ >Sent via [email protected]. Opinions expressed are those of the author. >Not an AMSAT-NA member? Join now to support the amateur satellite program! >Subscription settings: http://amsat.org/mailman/listinfo/amsat-bb _______________________________________________ Sent via [email protected]. Opinions expressed are those of the author. Not an AMSAT-NA member? Join now to support the amateur satellite program! Subscription settings: http://amsat.org/mailman/listinfo/amsat-bb
