Bob,

I concur with Alan regarding SatPC32.

I used AO-7 the other evening for the first time in a couple of months and my up and down links were spot on first time!

David KG4ZLB

Alan P. Biddle wrote:

Bob,

SATPC32?

As long as the spacecraft systems are good, and AO-7 will wander a bit, I can always find myself. A quick tweak requiring a few seconds, and I am in business.

Alan WA4SCA

-----Original Message----- From: [email protected] [mailto:[email protected]] On Behalf Of Bob- W7LRD Sent: 06 January, 2010 14:44 To: [email protected] Subject: [amsat-bb] probably simple

Happy New Year all

This is probably simple, however, I need a quick and simple way of determining my uplink frequency given a specific downlink frequency. Usually I will just send a few dits to find myself. When trying to work a sked footprint edge to edge I need to be at the right frequency at the right time, without hunting around for myself. I am refering to AO-7

73 Bob W7LRD

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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

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

I understand, but with all due respect your assumption is incorrect that long distance QSOs are always at TCA and zero Doppler, even theoretically . This is only the case when the two stations are at near right angles to the track of the satellite.

Use the following example. If I want to work LU5BOJ/O in FG75 from EL88 on HO-68, my only windows are at either LOS or AOS, depending on whether it is an ascending or descending pass. Neither pass will be a low pass for either station, and neither QSO will occur at TCA or zero Doppler.

In Bob's case, let's look at his next possible window with Paul, 2E1EUB in IO92. Bob is in CN76. At the beginning of the 1 minute window tomorrow at 1251Z, Bob's Doppler shift on 432 is -3.68 khz.

On the next mutual window at 1452Z, the beginning Doppler is -7.93 khz. On the next, at 2020Z, it's -8.3 khz. None of these windows are over 2 degrees elevation, and none are at TCA for either station.

When you have 60s to make the QSO, being right dead on frequency is essential.

Respectfully, Drew KO4MA

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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Hi Mark, Pete, all,

So, please forget my suggestion about TCA as being an easy way to predict where one should set their dial when setting up for a footprint-stretching sked. That only works if the satellite is passing directly between the two stations, at 90-degrees to a line that runs between them. Being on the West Coast, most DX for me is to the East, and since most of our satellites are in polar orbits, the model kind of fits. But it's a special case for most everyone else.

You are absolutely right that the rate of change in Doppler shift is greatest at TCA, and is proportional to the frequency. When manually tuning the 2.4 ghz downlink on an overhead AO-51 pass, one needs to continually spin the dial. It's a physics demonstration at its finest.

Greg KO6TH

Date: Fri, 8 Jan 2010 13:28:10 -0500 Subject: Re: [amsat-bb] Re: probably simple From: [email protected] To: [email protected] CC: [email protected]; [email protected]

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

_________________________________________________________________ Hotmail: Trusted email with powerful SPAM protection. http://clk.atdmt.com/GBL/go/196390707/direct/01/

Correct

On 08-Jan-10 18:11, Pete Rowe 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?