Maintenance on the NB Transponder!

Quote from DB2OS

Hi Ed PY2RN ,

the earth covered by QO100 is now in shadow, i.e. less thermal noise? Could that be a reason? I noticed the same.. In addition, every 5-9 seconds I'm seeing a burst over the passband (only)... maybe radar? The horizontal small bands.. I changed some settings in the lower part.. an the tombstone same level as 2 days ago..

Anyone having similar observations?

73s Peter

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Hi Peter, same behavior during the day here. I have not noticed these bursts in my RX here, may be some heavy clouds at your location?

73 Ed.

Hi Peter,
same observations here. I also can see a general degradation of the signals, except C/N.

But, as we had massive storms over here (peak 122 km/h), I can't be sure, that my dishes are still aligned properly.

The "sweeps" look to me, as somebody is trying to optimize a feed with higher power.

Keep in mind, I was able to make a SSB-QSO with a 75cm dish @ 40mW. So this might be anything.

Best,
Wilm

PS.: Measured with a "raped" CMU-200

In my opinion : Perfect. Noise floor at 6 S/N now an beacon peaking s 9 :

Very good now ! No more noise around the beacons. Congratulations ! 73s de Roland PY4ZBZ

Very good Job !

I tried to have the same conditions and to compare the transponder before and after the new settings.

I'm not sure if these are the real differences.

The first image is 20-02-2019, the second is today 23.03.2019

Hi Peter,

between the two images there is a month of difference.

During this month I had a strong wind that moved my dish but I think I aligned it as before.

At this point I have doubts.

In essence, what changes have been made to the transponder?

73, Lucio

I made the comparison also on the WB transponder and the accounts are back. My dish was realigned like a month ago. Slightly better.

So the differences on the NB transponder seem real to me.

Images are, the first of 17-01-2019 and the second of today 24-03-2019.

@DH2VA

Achim, sorry. We wrote at the same time.

Thanks for the reply.

Quote from DH2VA

I8LYL former I0LYL we had the NB transponder adjusted twice in this period to optimize the dynamic range (and not waste satellite power into noise). The transponder gain was decreased by 4 dB on Feb 28th and another 6dB on March 13th. So in total this should amount for 10dB less transponder noise, which is close to what you see.

But as you still see the transponder noise, your system is still fine. Note that the beacon levels have been increased as well.

How does this adjustment would affect stations with small receiving antennas and small TX power? I am thinking about portable stations, for example horn for RX and helix for TX. I know initial specification for ground station that rely on dish antennas, but we had numerous successful tests with not so directional antennas and less gain.

YU7RSX There is an ITU-document about Es'hail-2 where ground station parameters are presented (as 'benchmark'). The challenge now is to tweak the parameters such that the (NB) transponder is 'on par' with these parameters (user requirements) and C/N. This means that (regrettably?) ground stations with too small RX down- or TX-uplink capabilities have a 'challenge' and have to adapt their settings to be 'on par' per user requirements. So stations with too much link budget have to back off, and stations with too low link budget have to 'back up'.

If I understand right, some QRP stations that could work via TP before gain reduction are not able to work any more?

YU7RSX depends that your reference level is ... Key is 'what is the reference?' and (how I see it) that has to be determined (in due time).

There are several 'knobs' to tune ... the challenge is to dial them towards the most 'optimal' position. And from what I experienced from AMSAT-DL is that they are trying to do exactly this.

Congrats to AMSAT team no more skirts surrounding the beacons!
And these few last days at this time (around 00:30UTC) I can see these noise wide bursts showing in the WF.

73 Ed PY2RN in GG66LW with 1.2M offset dish / standard pll lnb, SDRPlay RSP2 + SDR Console V306

Quote from YU7RSX

If I understand right, some QRP stations that could work via TP before gain reduction are not able to work any more?

No, it does not affect "QRP stations". It does affect stations with small receive equipment only.

I can still make the same S/N ratio with my QRP station. However, before this change people reported receiving with only a bare LNB (no dish) and/or with very small dishes, and that will no longer be possible.