[amsat-bb] Re: Re eggbeater performance - mobile
kl7uw at acsalaska.net
Sat May 30 12:14:38 PDT 2009
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
>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
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