Lost (but found?) Secret Sauce for AO-73

Shortly after AO-73 was launched, I had decent success working several stations, but only after adjusting my uplink frequency up about 8500 Hz from the published value.  Unfortunately, I never calibrated SatPC32 the correct way, so I was always entering that value as a XIT offset to my IC-9100.  Before this year’s field day, I figured I would correct the calibration, and had no issue doing this for both FO-29 and AO-7.  However I was no longer able to hear myself anywhere on the AO-73 downlink, despite adjusting my uplink by +/-12 KHz.

I had pretty much given up on the bird, when I worked Jeff, NX9B, on FO-29 during Field Day.  I emailed him, thanking him for the contact and mentioned my troubles.  He responded that he too had issues with the published uplink/downlink relationship, and supplied me with his SatPC32 DOPPLER.SQF entries for AO-73.

I tried his values, and adjusted my Sat32PC “Upl. Calibr. (Hz)” setting until I heard myself.  This took ANOTHER 5200 Hz at the start of the pass, shifting upward to 6200 Hz by mid-pass.

I was VERY surprised to find that from the satellite’s point of view (Doppler corrected to reflect the frequencies at the satellite), I was at 145.960 (the middle of the published satellite TX pass-band), and the satellite RX was 435.159.  That is 9 KHz outside of the published pass-band for the TX, and 19 KHz above the published relationship between RX and TX.  Again, these values are about 6 KHz higher than those used by Jeff.

Unfortunately my testing was limited as the bird went out of eclipse about mid-pass and the transponder was turned off.

I confirmed this again on the 2nd pass at approximately 03:08 UTC.  At a satellite TX of 145.960.384, the published satellite RX value would have been 435.139.616.  Instead I saw that the RX value was 435.159.616 — this was 20 KHz higher than the published value).

(I verified that the TLE that was being used by Sat32PC matched up with those published by Celestrak On July 27, 2015).  I also verified that the AO-73 entry in AmsatNames.txt was correct (39444 13066AE  AO-73) )

FUNCUBE-1 (AO-73)       
1 39444U 13066AE 15208.17816161 .00000549 00000-0 76602-4 0 9990
2 39444 97.7279 269.4651 0059736 6.9191 353.2833 14.80359877 89338
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6 Responses to Lost (but found?) Secret Sauce for AO-73

  1. brad says:

    so there sound be a update source for doplar.sqf , like more often ?

    • robert says:

      Hi Brad,

      Well I’m not aware of anyone who updates the DOPPLER.SQF files — seems to be a hodgepodge of individuals posting as birds are added. Part of the reason is that the frequencies entered depend on the gear the person is using. What is good for me and my rig might not be good for yours (different crystal inaccuracies, temperature dependencies, etc.). With regard to AO-73, that is a internal spacecraft issue and depends on internal temperatures — so it moves all over the place. No good way to predict that — you just have to find it every orbit. My issue with AO-73 is the swing is so large that some folks might not even try that far away.

      73, Bob, WB4SON

  2. brad says:

    i hear guys swing the transmitter frequency key down sweeping the band looking for the mix , i cant seem to work that out on my ts-2000x , the morse key wont o anything in ssb mode…

  3. brad says:

    maybe something like this the second line i added so i could use the code key to give me something to listen for , better then using the mic as less bandwidth used i guess ?

    do i have the doppler.sqf frequency relationship close now ?
    AO-73,145960,435159,USB,LSB,REV,0,0,Voice U/V

    if this isnt enough , could i list make 10 listings for ao-73 and ‘CAT’ menu my way
    down the list until one works ?
    ( need waterfall view )

    im thinking we could r e a l l y use some sort of chat room or data base to share this
    or a button you click like update keps….

    i would love to see a a video on how operators are doing all this now… not much on youtube for satpc32 , but i did learn a few tricks that way so far.
    73 brad ko6kL

    • robert says:

      Hey Brad,

      Setting up a CW mode like you did will certainly allow you to run CW, BUT that will have a separate frequency setting from the SSB version. You might be better off with just the SSB entry, then go ahead and click the C+ mode in SatPC32 which will put the rig into CW mode, but use the SSB offsets.

      From the AMSAT UK website “- 435.150 – 435.130 MHz Uplink LSB- 145.950 – 145.970 MHz Downlink USB. Passband may be up to 15 kHz higher depending on on-board temperatures”. In fact they suggest keeping your RX steady and adjusting TX to keep your signal in the passband.

      Don’t forget you have SatPC32 Uplink corrections you can dial in in whatever step size you want. I usually do that until I find my CW signal.

      Unfortunately there is no way to predict what the offset will be from pass to pass. Pretty soon you just get used to finding your own signal manually.

      73, Bob, WB4SON

  4. Brad says:

    it would really help to see someone do all this on a youtube video and watch the video a few times. i didnt know satpc32 had a cq button……
    and dont understand the ‘SAT’ menu yet except to use to to switch modes … U/V or V/u is it’s listed there….

    can you predict the input offset from the beacon frequency compared to listed frequency ?
    hope to lash up a 1.2ghz antenna this weekend and get on the FM sat mode sunday…

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