The rate of change of Doppler is a sinusoidal function, so... Think of a sine wave: the change in amplitude is highest close to the zero crossing and smallest around the plus and minus maximums.
73, Ed - KL7UW At 09:28 AM 1/8/2010, Mark L. Hammond wrote: >I think part of the subject that confuses most of us (me included!) is >that while at TCA the offset is 0, the RATE of change on either side >of TCA is higher than at AOS or LOS. So, the actual frequency >offset is BIGGEST at LOS and AOS, but the rate of change is slow (it >doesnt' change much). It's easier to tune. At TCA you should hear >the satellite at the "actual" frequency, but not for long because the >change in frequency is fastest right before and right after...you tune >like crazy to keep up. > >Maybe that will make sense to somebody...but I won't promise :) > >Also---don't forget---a 10kHz offset at 2M is 30kHz at 70cm (and one >is increasing in freq while the other is decreasing...) > >Use SatPC32 and you just about forget about having to do anything, and >watch it happen--good chance to see what is really going on. > > >73, > >Mark N8MH > >On Fri, Jan 8, 2010 at 1:11 PM, Pete Rowe <ptr...@yahoo.com> wrote: > > Hi Greg > > I'm confused. It seems to me that the place when Doppler is zero > is when the satellite is about half way through the pass. This is > when the Doppler goes from positive (coming at me) to negative > (going away from me). It seems like this place would be the time of > closest approach (TCA) and not way out on the horizon when I see > maximum Doppler. > > What am I missing? > > > > 73, > > Pete > > WA6WOA > > > > --- On Thu, 1/7/10, Greg D. <ko6th_g...@hotmail.com> wrote: > > > > From: Greg D. <ko6th_g...@hotmail.com> > > Subject: [amsat-bb] Re: probably simple > > To: glasbren...@mindspring.com > > Cc: amsat-bb@amsat.org > > Date: Thursday, January 7, 2010, 7:34 PM > > > > > > Hi Drew, > > > > SatPC32 is probably an excellent program (I'm on Linux here, so > can't use it), and if you've got the automation available, that's > certainly the best way to go. And, by definition, the lower the > elevation, the farther away the satellite is, so your DX contacts > are going to be at the edges of the pass. > > > > But any pass where you are really stretching the footprint is > going to be a low elevation pass. The more you stretch, the lower > the pass. In the limit, I think Bob's ultimate pass has a peak at > .001-degrees for both stations. If you're doing that, then you're > at TCA, and zero doppler. > > > > That's all I meant to convey, > > > > Greg KO6TH > > > > > >> Date: Thu, 7 Jan 2010 05:53:13 -0500 > >> From: glasbren...@mindspring.com > >> To: ko6th_g...@hotmail.com > >> CC: w7...@comcast.net; amsat-bb@amsat.org > >> Subject: Re: [amsat-bb] Re: probably simple > >> > >> Greg D. wrote: > >> > Hi Bob, > >> > > >> > Whatever the satellite, if you're trying to stretch the > footprint, your sked is always going to be at the peak of > elevation, for that fleeting moment when the satellite is a few > degrees above the horizon. That means that you're always going to > be at zero doppler shift, and the math will always be the > same. Find yourself once at TCA on any pass, and lock them > in. The numbers will be the same for your sked. > >> > > >> > Good luck, > >> > > >> > Greg KO6TH > >> > > >> > > >> I wouldn't agree with that statement at all. Most of my long haul > >> contacts on AO-7, FO-20 and 29, and now HO-68, are right after AOS or > >> just before LOS, certainly not at TCA. Use my recent QSOs on HO-68 with > >> Argentina as an example. Even when I work Europe on AO-7 it is at the > >> beginning or end of a pass...not the middle. > >> > >> Bob, SatPC32 will show you the frequency with Doppler shift, and the > >> Doppler shift. A little subtraction or addition and you have > what you want. > >> > >> 73, Drew KO4MA > > > >_______________________________________________ >Sent via amsat...@amsat.org. 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 73, Ed - KL7UW, WD2XSH/45 ====================================== BP40IQ 500 KHz - 10-GHz www.kl7uw.com 500-KHz/CW, 144-MHz EME, 1296-MHz EME DUBUS Magazine USA Rep dubus...@hotmail.com ====================================== _______________________________________________ Sent via amsat...@amsat.org. 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
