CW beacon in FSK?

  • I would like to ask AMSAT-DL to consider operating the CW beacon in FSK, i.e. with constant carrier.


    There are IARU-R1 recommendations concerning (terrestrial) uWave beacons using FSK, but that's an administrative issue.


    My main argument is that it's relatively difficult to precisely fine tune the RX feed with a pulsating signal. Also during the two (too short imho) carriers QSB is visible (depending on my local situation and the situation above Bochum (clouds etc), which can be around +/- 3 dB and then it's too short to align within the precision needed after averaging the SNR.


    I am doing measurements with several prototypes of dielectric lenses and have an accuracy of around 1 dB and experience slight differences in results when e.g. optimizing on the 11199.8 MHz beacon compared to the QO-100 10489.550 MHz beacon.


    Is AMSAT-DL willing to reflect on this?

  • FSK (F1A) is a normal narrow band mode and not referred to as 'FM' (e.g. F2A in this case). As long as the spectral impact is narrow enough, there is no problem.


    The upper beacon also fluctuates

  • Hi Remco,

    thanks for the proposal.

    I agree with your arguments. I observed the same, the CW keying makes it sometimes difficult to concentrate on the beacon level when optimizing things. Additional carrier times were added later to improve this, but F1A like on some terrestrial beacons sound OK to me too..

    I will discuss with our team and Mario DL5MLO who is the author of the LEILA software and beacon generation.

    73s Peter

    Peter Gülzow | DB2OS | AMSAT-DL member since 1983 | JO42VG

  • I agree,

    too short for measurements.

    What about an 1 min constant carrier on exactly 10489.55 MHz between the cycles?

    I receive the beacon on 10489.550,070 Hz and on 10489.550,120 Hz in the morning.

    (with GPSDO-RX)

    Can this be confirmed?

    73s Karsten

  • DB2OS : Thanks for your consideration.


    DL1QC : That is also a possibility, just like (uWave) beacons. A carrier for several minutes and then identification/message/whatever.


    Concerning frequency accuracy (which is not the main topic, but I can rename the thread so that it falls into ; -) : bear in mind that the satellite still has some Doppler in the order of a few 10 Hz due to the fact it's not totally rock stable in its 'geostationary cube'. Furthermore the beacon signals aren't generated in the satellite itself, so the reference needs to propagate an additional ~37000 km where perhaps other (propagation?) issues may arise.


    So from my perspective I can't confirm if your values are (absolute) right but I also noticed some 'offset' and changes in the offset, but I didn't test it in such a way to determine if there is a 'day' or 'night' offset.


    Perhaps you can measure the 11199.8 MHz (H) beacon from Es'hail-1 ? It's not exactly on 11199.800 MHz (but a few kHz off), to determine if you've the same offset pattern (day vs night).

  • I would vote for FSK as it allows me to measure it more accurately but to include a period of carrier, not too long, every so often. I have found the current CW beacon useless for measurements and use the FSK. If you had two beacons from the same GPS locked reference and top and bottom we could do some interesting ranging and geo-location experiments.


    Mike

  • I receive the beacon on 10489.550,070 Hz and on 10489.550,120 Hz in the morning.

    (with GPSDO-RX)

    Can this be confirmed?

    Kepler elements of QO-100 show +- 20 Hz worth of doppler on 10489.550 MHz. As the beacon is generated on the ground, you have to multiply by two, so +-40 Hz over a day. Totally expected.

  • Hello Achim,


    thanks for the explanation the shift.

    But may be I´m wrong with my measured 70 Hz up-shift?

    In other words: shifting down beacon frequency by 90 Hz should minimize the absolute error.

    Or my RX-chain (GPDSO-LNB + separate GPSDO- locked RX (2x) is wrong.

    An signal-injection (GPSDO) on 10.489.550 000 Hz gives in RX the exact 10489.550 000 Hz.

    Maybe the main error is between my ears.



    73s

    Karsten

  • Hi Karsten,

    you forgot one component in the whole signal chain of unknown frequency accuracy.. you know which one?

    :)

    Frankly, I am delighted that so many OMs can measure this level of accuracy. Hats off to you!

  • another hint: we can measure our uplink frequency and our downlink frequency to super high precision as we can lock it to GPS, cesium and god knows what.. but there is another variable on top of doppler..

  • The proven existence of gravity waves which have impact on the size of the universe, therefore the wavelength changes, therefor the frequency ; -)


    (no, just kidding)


    On board LO converter (in LNB) may wobble a bit? (according to Paul)

  • DB2OS Almost ... I will look up the IARU (R1) standard for you. Keep you posted.
    (I was VHF-manager of VERON Netherlands, so I have the Handbook somewhere)
    (albeit that it's on the net now .. it was a long time ago ... ; -)


    Edit: Found it. See excerpt picture below (from VHF-mgr handbook IARU R1)

    (assuming R1 is 'close enough for the footprint of Es'hail-2 / QO-100)


    The standard is ... the carrier is on the nominal frequency (10489.550000 MHz). If it transmits its message, first the carrier goes to 'space' (400 Hz lower, so 10489.549600 MHz), remains there for a while and then sends the 'mark' (read: information) at the nominal frequency (10489.550000 MHz), then a period of 'space' (10489.549600), and then the carrier back at 10489.550000 MHz.


    Having deployed a 50 MHz beacon for years (and being involved in the recommendation) the argument is that above 9 MHz USB is the amateur standard, so a listener (tuned zero beat in USB at the 'space') will/can/may hear the beacon as A1A (see text below).


    So, deltaF = 400 Hz (or 500 Hz)


    Hope this helps you.


    PS. If the freq boundary of .550000 is a hard limit, it can be reversed, so that in LSB the beacon can be received in 'A1A', but I think 400 Hz 'violence' is acceptable ; -)


  • With the CW first beacon after roughly on the satellite.Use broadband video beacon carefully adjust the Angle and the polarization and LNB.This is my way...So that we can achieve the best alignment effect