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 [email protected] 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. [email protected] wrote:

From: Greg D. [email protected] Subject: [amsat-bb] Re: probably simple To: [email protected] Cc: [email protected] 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: [email protected] To: [email protected] CC: [email protected]; [email protected] 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

---

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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 [email protected] ======================================