AO-91: *No* uplink frequency changes needed for Doppler shift
I am puzzled why I am seeing announcements going out from apparently several sources indicating user UHF uplinks need to be changed to adjust for Doppler shift near to their own AOS and LOS. I'm seeing this posted from the AMSAT-UK website as well as other places.
The FOX1-B UHF receiver has automatic frequency control (AFC) that will slew the uplink users signal to the middle of the IF filter and the discriminator if s/he is anywhere within about +/- 10 kHz of the nominal uplink frequency. From what I remember, the worst case UHF Doppler shift was about +/- 8.5 kHz.
There should be *NO* need at all to 'predistort' the uplink transmission frequency to correct for uplink Doppler shift - that was the whole purpose of going through the complexity of adding AFC to the receiver I designed. The AFC was certainly working fine during testing. Just use the posted nominal uplink center frequency - that's all.
This, by the way, is true for 1-A as well. Only one of 1-Cliff or 1-D has the AFC knowingly disabled. I guess we will see how that 'experiment' works when they get out of the barn.
73
John... WB4LNM AMSAT FOX RF Design Team
Have you tried operating this way during a pass?
It doesn’t work on AO85 really. If you’re more than 5khz off on the uplink your audio tends to sound terrible (for example, using my IC-821H). AO-91 doesn’t seem to be any different in my initial tests over the past couple of nights. You don’t have to be exactly on frequency, especially if you are running power, but it is much easier to get in and your audio sounds much better if you do adjust reasonably close for doppler during the pass.
Maybe somebody else from engineering or ops can speak to this after the frequency sweeps they did over the last few days. Mine are just informal user tests based on my experiences making a few hundred QSOs on AO-85, and now about 20 on AO-91.
Congrats on the great receiver sensitivity by the way! The new bird is performing extremely well. I was able to get in AOS to LOS this evening, testing at 50mW with a handheld 7 element Arrow II and TH-D72 antenna.
73,
- Matthew NJ4Y
Sent from my iPhone
On Nov 23, 2017, at 20:56, John Klingelhoeffer via AMSAT-BB amsat-bb@amsat.org wrote:
I am puzzled why I am seeing announcements going out from apparently several sources indicating user UHF uplinks need to be changed to adjust for Doppler shift near to their own AOS and LOS. I'm seeing this posted from the AMSAT-UK website as well as other places.
The FOX1-B UHF receiver has automatic frequency control (AFC) that will slew the uplink users signal to the middle of the IF filter and the discriminator if s/he is anywhere within about +/- 10 kHz of the nominal uplink frequency. From what I remember, the worst case UHF Doppler shift was about +/- 8.5 kHz.
There should be *NO* need at all to 'predistort' the uplink transmission frequency to correct for uplink Doppler shift - that was the whole purpose of going through the complexity of adding AFC to the receiver I designed. The AFC was certainly working fine during testing. Just use the posted nominal uplink center frequency - that's all.
This, by the way, is true for 1-A as well. Only one of 1-Cliff or 1-D has the AFC knowingly disabled. I guess we will see how that 'experiment' works when they get out of the barn.
73
John... WB4LNM AMSAT FOX RF Design Team _______________________________________________ Sent via AMSAT-BB@amsat.org. AMSAT-NA makes this open forum available to all interested persons worldwide without requiring membership. Opinions expressed are solely those of the author, and do not reflect the official views of AMSAT-NA. Not an AMSAT-NA member? Join now to support the amateur satellite program! Subscription settings: http://www.amsat.org/mailman/listinfo/amsat-bb
I worked a station last night who didn’t check the frequencies before the pass. He was transmitting at 435.220 MHz when I worked him - 30 kHz low. He sounded terrible, but it worked.
I’m still not sure it’s a great idea to advise that stations stay at center frequency, I suppose time and experimentation will tell.
73,
Paul, N8HM
On Fri, Nov 24, 2017 at 03:04 Matthew Stevens matthew@mrstevens.net wrote:
Have you tried operating this way during a pass?
It doesn’t work on AO85 really. If you’re more than 5khz off on the uplink your audio tends to sound terrible (for example, using my IC-821H). AO-91 doesn’t seem to be any different in my initial tests over the past couple of nights. You don’t have to be exactly on frequency, especially if you are running power, but it is much easier to get in and your audio sounds much better if you do adjust reasonably close for doppler during the pass.
Maybe somebody else from engineering or ops can speak to this after the frequency sweeps they did over the last few days. Mine are just informal user tests based on my experiences making a few hundred QSOs on AO-85, and now about 20 on AO-91.
Congrats on the great receiver sensitivity by the way! The new bird is performing extremely well. I was able to get in AOS to LOS this evening, testing at 50mW with a handheld 7 element Arrow II and TH-D72 antenna.
73,
- Matthew NJ4Y
Sent from my iPhone
On Nov 23, 2017, at 20:56, John Klingelhoeffer via AMSAT-BB <
amsat-bb@amsat.org> wrote:
I am puzzled why I am seeing announcements going out from apparently
several sources indicating user UHF uplinks need to be changed to adjust for Doppler shift near to their own AOS and LOS. I'm seeing this posted from the AMSAT-UK website as well as other places.
The FOX1-B UHF receiver has automatic frequency control (AFC) that will
slew the uplink users signal to the middle of the IF filter and the discriminator if s/he is anywhere within about +/- 10 kHz of the nominal uplink frequency. From what I remember, the worst case UHF Doppler shift was about +/- 8.5 kHz.
There should be *NO* need at all to 'predistort' the uplink transmission
frequency to correct for uplink Doppler shift - that was the whole purpose of going through the complexity of adding AFC to the receiver I designed. The AFC was certainly working fine during testing. Just use the posted nominal uplink center frequency - that's all.
This, by the way, is true for 1-A as well. Only one of 1-Cliff or 1-D
has the AFC knowingly disabled. I guess we will see how that 'experiment' works when they get out of the barn.
73
John... WB4LNM AMSAT FOX RF Design Team _______________________________________________ Sent via AMSAT-BB@amsat.org. AMSAT-NA makes this open forum available to all interested persons worldwide without requiring membership.
Opinions expressed
are solely those of the author, and do not reflect the official views of
AMSAT-NA.
Not an AMSAT-NA member? Join now to support the amateur satellite
program!
Subscription settings: http://www.amsat.org/mailman/listinfo/amsat-bb
Sent via AMSAT-BB@amsat.org. AMSAT-NA makes this open forum available to all interested persons worldwide without requiring membership. Opinions expressed are solely those of the author, and do not reflect the official views of AMSAT-NA. Not an AMSAT-NA member? Join now to support the amateur satellite program! Subscription settings: http://www.amsat.org/mailman/listinfo/amsat-bb
Hi All, HRD (Ham Radio Deluxe) has just sent me an email wanting me to buy the latest license for ver-6. I replied to them that I would love to if they have fixed the know long standing issue with Doppler control of inverting satellites. I received a prompt reply with the typical "never heard if this" attitude without actually saying it. He wants to know what my station setup is. Radio, Windows version, connection, etc. I wonder if one of you fine gentlemen can give a knowledgeable description of the exact circumstance and issues.It has been several years since I tried and failed with HRD and I don't actually remember the particular circumstances, and, so I don't have to go all through loading everything back on my computer and working through all the scenarios to find the problem. thanks in advance. Michael VivonaKC4ZVA EL98
What if we consider it from a different perspective... Say two signals of approximately identical strength are transmitting to AO-91. One has adjusted for Doppler so the signal is showing up at the center of the bird passband all during the pass. The other has not, as is about 8 KHz on the high side when the bird is approaching.
Wouldn't the signal closer to the center of the RX passband be the one more likely captured?
Therefore wouldn't there be an advantage to adjusting for Doppler?
73, Bob, WB4SON
participants (5)
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Bob -
John Klingelhoeffer -
Matthew Stevens -
mvivona＠yahoo.com -
Paul Stoetzer