AO-7 Mode A Reception

Discussion in 'Satellite and Space Communications' started by KS1G, Sep 18, 2021.

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  1. KS1G

    KS1G Ham Member QRZ Page

    AO-7 is in continuous sunlight, so will be alternating between Mode B (U/V) and Mode A (V/10M) operation.
    1. For the folks successfully receiving the Mode A downlink, what are you using for an antenna? My HF inverted-V doesn't seem to be sufficient so far, have not heard a thing. If you own a preamp, is it helping at all?

    2. How far off does the 10M downlink seem to be from "spec"? (E.g. SatPC32 corrections for uplink/downlink in Doppler.SQF).

    Thanks! 73 Steve KS1G
     
  2. K7WDO

    K7WDO Ham Member QRZ Page

    Mode A was a tricky one when I tried it last time it was on. My receive setup was an OCF 40m dipole, 10m preamp, and FT-857 on receive. It took a few passes, but I started to find certain sweet spots where I could hear AO-7 better than others. So the pattern of your HF antenna will have a big impact on how you hear it. I know one operator who had a 10m dipole and an 80m dipole, and oddly enough, the 80m did better on Mode A.

    There isn't a lot of activity on Mode A so without the beacon, it's hard to tell if you're just not hearing it or nobody's on. The best you can do is transmit through the whole pass to see if you hit the right lobe on your HF antenna and start to hear your signal. Mode A does seem to take more uplink power than Mode B, but even running higher power, it doesn't seem to be triggering any FM warble that you get on Mode B when you're running too much power and need to back off.

    So the best I can say it just keep experimenting with it until you get a feel for what direction you can hear Mode A from and build from there. As for the accuracy of the Doppler.SQF file, I don't use SatPC32 so I can't comment on that one. Doppler shift was pretty low from what I remember.
     
  3. K3RLD

    K3RLD Ham Member QRZ Page

    Steve, believe it or not, I've got a horizontal-ish G5RV-Jr strung in my trees about 30 feet up that actually works for Mode A. I've tried it a few times and heard myself on the downlink, but of course there is rarely anybody else on, so never made a contact.

    I can't remember what the offset is from published, but I do recall it being "close enough" for a GQRX user to shift over. Not sure if it was within a 3kHz filter, though.
     
    WE4B likes this.
  4. N4UFO

    N4UFO Ham Member QRZ Page

    Did not need a preamp to work Mode A from NC using a small beam. (I might have heard it on my 160m top loaded vertical as well.) BUT when I used to work RS-12/13 back in the day, had a mirage preamp in the shack and that definitely helped. Never used software, but when manually tuning, transmitting exactly mid band, downlink was within a few khz +/- doppler as expected. It was quite weak and you really have to listen for the downlink, for sure.

    Checking my log, I have made about 18 contacts contacts on Mode A over a 5 year period... (split about evenly between SSB & CW) It might take a bit to find somebody, as said, rarely anybody on. I talked to myself on quite a few passes! o_O;):D

    GL & 73!
     
    K0UO likes this.
  5. KS1G

    KS1G Ham Member QRZ Page

    I was able to **barely** hear myself a few times on the 9/19 1920z pass a few minutes ago. I think AO-109 might be louder(!). 42 deg max pass to my east & NE, best reception seemed to be after TCA. Which could be just the antenna pattern. I had to run 10-20W uplink; much less than 10 and I faded away. Nice steady signal, however, zero FMing vs. the Mode B transponder. Heard one other station when I tuned around, but could not get the call. I needed to add about 700kHz of "correction" to Doppler.sqf, which is not bad at all.

    Time to find the 10M preamp and dig out the Buddipole.
     
  6. N4UFO

    N4UFO Ham Member QRZ Page

    Right On! I love it when persistence results in success! :D
     
    KS1G likes this.
  7. KS1G

    KS1G Ham Member QRZ Page

    Thanks! Found the Buddipole (hope the coax is still good) & preamp (don't know if it works yet). Maybe I'll have it all together for the next Mode A day. In the meanwhile, I again could barely hear myself on the last pass and heard but could not pull out the calls on a SSB QSO. Step by step.... My last experience with Mode A was the RS-10/etc. birds; slightly stronger downlink from those!
     
  8. N4UFO

    N4UFO Ham Member QRZ Page

    I never worked RS-10 but was really active on RS-12/13, but mostly Mode K. I bought a 2m SSB rig and when in KA Mode, I found Mode K MUCH easier to work it with. Sold the 2m rig. ;) I even worked in Europe on Mode K when HF bands were open. (footprint over US) I heard we are supposed to be getting another Mode K bird... With sunspots coming up, THAT might be a way to get DXCC on satellites. There was a station near Charlotte that got DXCC just on that bird! (N4ZC, now SK)
     
  9. K7WDO

    K7WDO Ham Member QRZ Page

    Took three tries here, but finally managed to get a signal through on Mode A this afternoon. First half of the pass wasn't too great, but the latter half wasn't doing too bad. Not sure if it was my antenna or AO-7's orientation, but if you're having trouble early on, try again later in the pass. Like KS1G, I was running 10-20W on the uplink so it takes some power to get in.

    Also, it looks like the mode change is around 0:00z. The Mode A pass I caught was at 23:00z but on the follow up pass at 01:00z, it was back on Mode B.
     
  10. KS1G

    KS1G Ham Member QRZ Page

    Progress report on the 2021-09-23 2056 UTC pass, alternating between the 80-10M inverted-V (oriented WNW-SSE with bend at center) and a Buddipole at 12 ft oriented broadside to the satellite path. So the pass was roughly aligned with the inverted-V's northern leg. The 25'-ish RG58 buddipole cable (they don't sell that any longer), an ARR 10M preamp, and ~50 ft of RG58 I have run to the outside as to connect to whatever becomes a backup or 2nd antenna. S3-S4 noise on the Buddipole (neighbors' electronic toys mostly) w/o preamp. About S2 noise on the inverted V. So not a quiet location. Was able to hear myself approaching TCA and for a few minutes after TCA on the Buddipole with the preamp on. Seemed a bit stronger than what I remembered from the last time. ~20w on the uplink.

    What's exciting is I got an email after the pass from KE9AJ, he copied me at S3-4 using a hustler vertical at ground level! (must be in a really quiet location). He didn't have his Arrow or 10M Moxon set up, or we might have had a QSO (especially if I heard him better than I heard myself).

    Next steps: I have a replacement Buddipole balun on order, will let me replace their stock RG58 with much lower loss coax and place the preamp at the antenna. Then play with height, lower might be better for satellites. Since KE9AJ was getting me on a vertical, I could set up as a "buddistick" and see how it goes. I might ask another ham in the area with a excellent HF setup and a quiet location if he can listen for me (or relocate there for an AO-7 pass?).
     
    K4BAD likes this.

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