[amsat-bb] LongJiang and Doppler correction

Tue May 29 16:37:57 UTC 2018

Dear All,

May be a stupid question for the experts, but genuine from me.

Has anyone received any FT4G beacon signal from the Longiang Sats so far?

I have being trying to do so for the past week without success.

73

Jean Marc (3B8DU)

> On May 26, 2018, at 8:54 PM, Nico Janssen <hamsat at xs4all.nl> wrote:
> 
> 
> In the coming days the doppler shift on the 70 cm downlink of
> LongJiang 2 will vary between +2000 and -2200 Hz (for my QTH).
> This can easily be calculated with GMAT using the script I published
> a couple of hours ago (see my earlier post).
> 
> 73,
> Nico PA0DLO
> 
> On 26-05-18 17:44, charlie at sucklingfamily.free-online.co.uk wrote:
>> Michael
>> 
>> I think that there are three main components to the Doppler shift for a
>> satellite orbiting the moon.
>> 
>> 1.  Earth rotation moving the observer toward the moon at moonrise (+ve
>> Doppler) and moonset (-ve).
>> 
>> 2.  Earth-moon distance variation (smaller than 1, and very slowly
>> changing in comparison).
>> 
>> 3.  Orbital velocity of the satellite itself.
>> 
>> 1 and 2 are easy to work out using EME software, eg WSJT-X or Moonsked.  I
>> can't help with 3.
>> 
>> Taking today as an example, total of 1 and 2 for the moon vary from ~ +3
>> to -4.5kHz at S-Band.
>> 
>> With DSN satellites many of us use(d) JPL Horizons to calculate Doppler
>> shift for Deep Space missions.  Observing the Doppler shift change when
>> probes were captured by the target planet was quite interesting (a slowly
>> changing shift to a cyclic one).
>> 
>> 73
>> 
>> Charlie G3WDG
>> 
>>  > I find that an interesting question. One would think that since the moon
>>> orbits the earth at a much much slower rate than a satellite that there
>>> would be almost no Doppler correction required. If you compensate for the
>>> speed of the orbit around the moon that is also at a much lower speed than
>>> a Earth satellite would be traveling at. Earth satellites are in the
>>> 17,000 mph range and moon satellites are in the 2000 mile an hour range
>>> orbiting speed. Also the chance that the satellite orbiting the moon could
>>> be at such an axis where it is in full visibility the earth the whole
>>> time, at that point there would not be a Doppler correction based upon
>>> satellite velocity only the moon's velocity. Will be interesting to hear
>>> the experts chime in on this.
>>> 
>>> Michael Vivona
>>> Sent from my iPad
>>> 
>>> On May 25, 2018, at 5:49 PM, Stefan Wagener <wageners at gmail.com> wrote:
>>> 
>>> The problem will not be the pointing (you could just point to the moon :-)
>>> Pending distance, speed and orbit around the moon and position to earth,
>>> you might have a difficult time adjusting for doppler. I let more
>>> knowledgable folks chip in on this one.
>>> 
>>> Stefan, VE4NSA
>>> 
>>>> On Fri, May 25, 2018 at 2:40 PM Jordan Trewitt <jmtrewitt at gmail.com>
>>>> wrote:
>>>> 
>>>> If it was the 70 cm downlink, you might be able to schedule something
>>>> with
>>>> someone else's SATNOGS station (idk how that'd work with getting a
>>>> rotator
>>>> to work though), if they have a large enough yagi that is.
>>>> -Jordan
>>>> KF5COQ
>>>> 
>>>>> On Fri, May 25, 2018, 12:46 PM Zach Metzinger <zmetzing at pobox.com>
>>>>> wrote:
>>>>> 
>>>>>> On 05/25/18 11:25, Nico Janssen wrote:
>>>>>> 
>>>>>> It is confirmed from China that LongJiang 2 has performed a
>>>>>> successful braking maneuver, so that it is now in lunar orbit.
>>>>>> No further details yet.
>>>>> Nico,
>>>>> 
>>>>> Do you know of any WebSDRs which are pointed and tuned to the downlink
>>>>> signals?
>>>>> 
>>>>> 73,
>>>>> 
>>>>> --- Zach
>>>>> N0ZGO
>>>>> 
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>> 
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