Anyone have a handle on UL/DL Relationship

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Anyone have a handle on UL/DL Relationship

Postby WB4SON » Mon Nov 25, 2013 3:10 am

Spent a pass trying to hear my signal. Fairly decent signals from others in the Passband so I was hearing OK

Has anyone figured out the relationship between UL and DL yet so I can get things dialed in a bit closer?

73, Bob, WB4SON
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Re: Anyone have a handle on UL/DL Relationship

Postby M0SAT » Mon Nov 25, 2013 8:12 pm

Hello Bob

What software are you using. I am using SatPC32 and can't find my uplink after 3 days!

Very depressing, it's never taken me this long to find my own signal but as there is heavy usage here in Europe and I don't just want to "clatter about" in the uplink it's taken a lot longer than hoped.

I was going to start a thread asking for someone to send me their doppler files, but as you have started this I thought I would show empathy to you and hope someone might help us both!

Good luck getting on.

73 de Dave M0SAT (IO91TP)
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Re: Anyone have a handle on UL/DL Relationship

Postby WB4SON » Mon Nov 25, 2013 8:52 pm

Hey Dave,

I am using SatPC32. I can hear the DL just fine but no luck at all on hearing myself. I confirmed I was OK running FO29 and VO52 so things seem Ok so I suspect operator error on my part, although the Passband seems to be set correctly. I have tried CW on two good passes and have zero luck despite trying up to 100 watts out on 435. A monitor receiver is picking my Xmit up just fine. I tried UL offsets up to +/- 20 KHZ with no success either.

So I'm stumped but will try again tonight. That's why I was asking if folks had an idea of what the UL to DL relationship was in reality.

73, Bob, WB4SON
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Re: Anyone have a handle on UL/DL Relationship

Postby WB4SON » Tue Nov 26, 2013 12:48 am

During a very shallow pass tonight (max 4 deg), I "might" have heard my downlink, but if so it required a 11KHz offset on top of Doppler. I find it hard to believe the UL and DL are that far apart, so this is probably still operator error on this end, but I sure would love to hear from others to see if their UL is appearing on their DL without significant adjustment.

73, Bob, WB4SON
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Re: Anyone have a handle on UL/DL Relationship

Postby VK2FBRB » Tue Nov 26, 2013 1:57 am

G'day Bob,

Do you mean you were hearing yourself 11 kHz away from the expected downlink frequency?

Ie, given the expected frequencies:

TX: 435.130 LSB = RX: 145.970 USB
TX: 435.135 LSB = RX: 145.965 USB
TX: 435.140 LSB = RX: 145.960 USB
TX: 435.145 LSB = RX: 145.955 USB
TX: 435.150 LSB = RX: 145.950 USB

Were you transmitting on something like 435.140, but heard yourself on 11 kHz above or below 145.960?

Cheers,
Ben VK2FBRB
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Re: Anyone have a handle on UL/DL Relationship

Postby WB4SON » Tue Nov 26, 2013 2:43 am

Just completed first CW QSO with NM3B, Wayne, in PA (I'm in RI). Prior failures were due to failing to apply a large enough UL correction factor to get my signal to appear in the downlink.

I'm using SatPC32, which adjusts for both UL and DL Doppler. I can set it to show me what frequencies are heard by the satellite or by my rig. The published DL/UL of 145.960/435.140 is from the satellite perspective, of course. Both of those signals are subject to Doppler, which makes them different at the ground -- but that correction is taken care of by SatPC32, as long as the PC time and the TLE is accurate.

So in my case, my DL was close to 145.955 (at the satellite, not at my rig). I would have expected my UL to be 435.145 (at the satellite, not at my rig). Instead my UL had to be adjusted to be 435.155 (at the satellite) -- I had to shift my UL up by 10KHz in order to be heard on the DL.

That +10KHz adjustment varied over the course of the pass from about 8.5KHz to 10.5KHz -- so it is an indication that the Doppler correction is a tad bit off. Usually there is some sort of correction that must be applied to the published relationship (like 145.960/435.140) and the one you need to use when the bird is in space. I'm used to seeing values like +/-250Hz to +/-2500Hz (like on VO52/AO7/FO29). So this one just caught me by surprise since it was more like 10000 Hz -- so large that I never even looked that far away prior to this last pass.

And I was talking about a CW contact, which means I had the UL shifted by about 700 Hz in order to produce my desired tone. So the UL correction factor for SSB would be about 700 Hz lower.

Anyway, mystery solved, but, as I said, it was enough of a shift from what I used to seeing that it was keeping me from making a contact until now.

73, Bob, WB4SON
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Re: Anyone have a handle on UL/DL Relationship

Postby wd9ewk » Tue Nov 26, 2013 3:34 pm

WB4SON wrote:So in my case, my DL was close to 145.955 (at the satellite, not at my rig). I would have expected my UL to be 435.145 (at the satellite, not at my rig). Instead my UL had to be adjusted to be 435.155 (at the satellite) -- I had to shift my UL up by 10KHz in order to be heard on the DL.


When I worked a pass last night around 0523 UTC, I found the same thing - move my uplink frequency up 10 kHz above what was originally published (+/- for Doppler through the pass). I had no problems hearing my CW through the transponder as I lined my radios up, and then proceeded to work two stations and even do some testing at different transmit power levels. This is a fun little satellite, and I will probably give it another try tonight from the back yard.

I didn't have time to prepare a video using the satellite audio and photos of my station, but will do so in the next couple of days. At the late hour I worked the satellite (approaching 10.30pm local time, or 12.30am Eastern time), there weren't as many stations on. I worked two others in SSB, and heard at least one or two CW signals sweeping through the transponder. Thankfully, there weren't any strong signals through the transponder that made it hard to hear myself.

My station - two FT-817NDs, transmitting normally at 5W, into an Elk handheld 2m/70cm log periodic. I'm not using preamps, and have a 10-foot/3m length of coax from antenna to diplexer, followed by 3-foot/1m lengths of coax from each band port on the diplexer to the radios. I plan on occasionally substituting my TH-F6A HT (with its all-mode receiver) in place of my receive 817 at some point, since I think the downlink should be strong enough to work with this HT.

73!
Patrick WD9EWK/VA7EWK
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Re: Anyone have a handle on UL/DL Relationship

Postby wd9ewk » Wed Nov 27, 2013 5:07 am

Hi!

I just worked a pass around 0412 UTC, and will be out in my yard for the western pass around 0545 UTC. I just uploaded a short video (satellite audio with slideshow) from the first FUNcube-1/AO-73 pass I worked last night. It can be viewed at:

http://www.youtube.com/watch?v=HQConRaseLQ

73!
Patrick WD9EWK/VA7EWK
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Re: Anyone have a handle on UL/DL Relationship

Postby wd9ewk » Thu Nov 28, 2013 3:30 am

Hi!

Here's another video (satellite audio with slideshow) from a pass late Tuesday evening here in North America. Mostly stations near the west coast of the USA and Canada, with one operator (AC0RA) in the central USA who stayed up until almost midnight to work the pass.

http://www.youtube.com/watch?v=PkDZxLYMSKY

73!
Patrick WD9EWK/VA7EWK
http://www.wd9ewk.net/ - Twitter: @WD9EWK
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Re: Anyone have a handle on UL/DL Relationship

Postby g0mjw » Thu Nov 28, 2013 12:31 pm

I managed much better last night on the frequency offset - I still have a +-2kHz error due to the Keps.

The uplink appears about +10kHz vs nominal and the downlink is about as expected. Deliberately tuning my uplink to make the downlink above 145.970 caused a fairly rapid loss so it is pretty tight. It is also very sensitive - my TS2000 minimum power setting is 5W which is about 2.5W at the antenna after the cable loss and it is still rather strong when the satellite is well oriented. There are quite large fades - presumably caused by spin and the antenna patterns as I am using circular polarisation. This makes matching the beacon level a challenge.

I have noticed some stations able to stay on frequency and others drifting with the Doppler. Quite a few are rock solid and I would like to know how they manage it as I can't.
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