Hi Greg, Drew, etc
This conversation is starting to make my head hurt! My example is to connect with some of our European friends. Some of them I share maybe a 60 second window, with PA1TNO it is less than 30 seconds. I have had several false starts in that I heard Paul 2E1EUB, by the time I located my downlink on his, he was gone. I want to predetermine where to set my uplink for a given downlink. There just is no the time be looking around. Like I said this is probably simple I'm just have trouble getting my thinking around the concept. Also if say I am planning on a downlink of 145.950 will Paul be looking at the same frequency? In the past these concepts never concerned me as there was always plenty of time to yak it up with the locals on AO-7.
73 Bob W7LRD
CN87 Seattle, Wa.
----- Original Message ----- From: "Andrew Glasbrenner" glasbrenner@mindspring.com To: "Greg D." ko6th_greg@hotmail.com Cc: w7lrd@comcast.net, amsat-bb@amsat.org Sent: Thursday, January 7, 2010 9:30:44 PM GMT -08:00 US/Canada Pacific Subject: Re: [amsat-bb] Re: probably simple
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 all,
Here's my (updated!) answer:
I think you're going to need to depend on a computer prediction program. I use Predict on Linux, but there is also a PC version. Predict, at least, can tell you what the doppler-adjusted up and downlink would be for a specific satellite-perceived frequency pair. I have mine set up for mid-bandpass up and down on the linear birds, i.e. what the zero doppler values are for the satellite itself. The program then tells me what I should tune the radios to, so that the satellite hears my signal at mid-bandpass, and I hear the return at the correct pitch. Then, if your sked is at some other frequency you'll need to add or subtract to compensate. For example, if the sked is set up for 10 khz above mid-passband, I think you can just add 10 khz from your computer-predicted uplink, and subtract 10 khz from the predicted downlink (for an inverting passband), and be really close. If the sked is 10 khz below mid-band, subtract 10 from the up, and add 10 to the down. Both you and the other station will need to do the same thing, both focusing on the satellite's perception of your signals. Your individual numbers could be very different.
I hope I've got it right this time,
Greg KO6TH
Date: Fri, 8 Jan 2010 05:58:39 +0000 From: w7lrd@comcast.net To: glasbrenner@mindspring.com CC: amsat-bb@amsat.org; ko6th_greg@hotmail.com Subject: Re: [amsat-bb] Re: probably simple
Hi Greg, Drew, etc
This conversation is starting to make my head hurt! My example is to connect with some of our European friends. Some of them I share maybe a 60 second window, with PA1TNO it is less than 30 seconds. I have had several false starts in that I heard Paul 2E1EUB, by the time I located my downlink on his, he was gone. I want to predetermine where to set my uplink for a given downlink. There just is no the time be looking around. Like I said this is probably simple I'm just have trouble getting my thinking around the concept. Also if say I am planning on a downlink of 145.950 will Paul be looking at the same frequency? In the past these concepts never concerned me as there was always plenty of time to yak it up with the locals on AO-7.
73 Bob W7LRD
CN87 Seattle, Wa.
----- Original Message ----- From: "Andrew Glasbrenner" glasbrenner@mindspring.com To: "Greg D." ko6th_greg@hotmail.com Cc: w7lrd@comcast.net, amsat-bb@amsat.org Sent: Thursday, January 7, 2010 9:30:44 PM GMT -08:00 US/Canada Pacific Subject: Re: [amsat-bb] Re: probably simple
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
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Bob W7LRD,
I disagree that Doppler shift will be zero when your window to work northern EU is optimum.
In SatPC32, I just did a Tracking->Preview and determined that when the AO-07 footprint includes both the northwest USA and northern Europe, the down link Doppler is +2.8 and up link Doppler is -8.3.
Note, the numbers +2.8 and -8.3 were for orbit #60844. I also determined that if a different orbit, then you get different Doppler shifts. Determine the pass that you wish to attempt a contact and use the Doppler numbers you get from Tracking->Preview for that pass.
Next pick a frequency using VFO mode in SatPC32 and do some experimenting. You may need to waste a window of opportunity, but using a ratio of -8.3/2.8 uplink to downlink Doppler, you should be able to do a respectable calculation.
Another problem: The Doppler for the station in northern-EU will likely be different than yours. This means you might wish to coordinate with the station over there as you attempt contact. When I tried to enter grid JPnn into SatPC32, it would not accept it. It calculated NAN (not a number) for latitude. Don't know what that's about.
However if you're using CW & not SSB, this may make little difference. As long as you're getting a CW signal in the band pass of your RX, you should be able to copy.
And remember, the squeaky wheel gets the oil. Keep making noise about this on this BB until something works.
I know you wanted a simpler answer. Hope this does not seem too complicated. The Trig/Math to work this out is possible, but tricky.
Good luck.
73, Larry W7IN (home=DN27 Plains, Montana)
On 08-Jan-10 05:58, Bob- W7LRD wrote: I want to predetermine where to set my uplink for a given downlink.
If approximate frequency is sufficient (no consideration of doppler) then a sheet of graph paper with three frequency scaled drawn on it worked for me in the pre computer days.
Also if say I am planning on a downlink of 145.950 will Paul be looking at the same frequency?
No. You will both have different doppler shifts so, for a common uplink frequency, your downlink frequencies will differ.
Bob,
Years ago, Paul Williamson wrote a brief note on the tuning issue. It was prescient in the days of primitive computers, few rigs with easy remote frequency control, and very limited choices of tracking software. Take a look at KB5MU's One True Rule paper:
http://www.amsat.org/amsat/features/one_true_rule.html
If both operators are following it, and SATPC32 (and MacDoppler) does so perfectly, to a large extent it effectively sweeps the Doppler issue "under the rug." You can tune around, and always hear yourself when you key the rig and say "aaaaah." More importantly, if the other station, say 5Y4GB is using the similar technique, when you tune him in, he will hear you on frequency. If WA4SCA then joins the QSO, both of you will hear me on frequency, and I will hear both of you the same. Even more importantly, everybody will remain in sync over the pass. It happens all the time on AO-7, HO-68 in linear mode, etc.
As to your question about 145.950 MHz. If he tunes his RIG to that frequency, and you tune your RIG, you will NOT be on the same frequency initially. However, you will be close. +/- Doppler. This is equivalent to an HF station saying he will be tuning 14.210 MHz +/- 5 KHz. It requires a bit of initial tuning, but it is quick, and completely removes the worry about tuning the uplink radio. The software automagically does it for you. Once you tune him in, just talk. It is well worth the effort to absorb the technique, and as more stations use it, the easier it will be to talk without slowly drifting on top of others. Once you get above the V and U modes, the Doppler shift is so large, and changes so rapidly, that it is truly almost necesary.
With a slight modification to the exiting software, and a paradigm shift in how we think about what frequency we are on, it is possible to specify the "contact frequency" for everybody to use which will eliminate the initial hunting. But that is for another rant. ;)
Alan WA4SCA
-----Original Message----- From: amsat-bb-bounces@amsat.org [mailto:amsat-bb-bounces@amsat.org] On Behalf Of Bob- W7LRD Sent: 07 January, 2010 23:59 To: Andrew Glasbrenner Cc: amsat-bb@amsat.org Subject: [amsat-bb] Re: probably simple
Hi Greg, Drew, etc
This conversation is starting to make my head hurt! My example is to connect with some of our European friends. Some of them I share maybe a 60 second window, with PA1TNO it is less than 30 seconds. I have had several false starts in that I heard Paul 2E1EUB, by the time I located my downlink on his, he was gone. I want to predetermine where to set my uplink for a given downlink. There just is no the time be looking around. Like I said this is probably simple I'm just have trouble getting my thinking around the concept. Also if say I am planning on a downlink of 145.950 will Paul be looking at the same frequency? In the past these concepts never concerned me as there was always plenty of time to yak it up with the locals on AO-7.
73 Bob W7LRD
CN87 Seattle, Wa.
----- Original Message ----- From: "Andrew Glasbrenner" glasbrenner@mindspring.com To: "Greg D." ko6th_greg@hotmail.com Cc: w7lrd@comcast.net, amsat-bb@amsat.org Sent: Thursday, January 7, 2010 9:30:44 PM GMT -08:00 US/Canada Pacific Subject: Re: [amsat-bb] Re: probably simple
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 _______________________________________________ Sent via AMSAT-BB@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
participants (5)
-
Alan P. Biddle -
Bob- W7LRD -
Greg D. -
Larry Gerhardstein -
Nigel Gunn G8IFF/W8IFF