Parameter Reading Reliability

[Derrick]

I've noticed that the modulation parameters shown by CrazyScan can be different for repeated tests. Here are 2 readings of 37,5W, 12509H.

..apparently the bit rate is calculated with the shown parameters and does not necessarily represents the actual rate.

[sotos65]

That's normal, on acm/vcm modulation transmission parameters change all the time. You may be interested in this (by CrazyCat)

http://rickcaylor.websitetoolbox.com/post?id=5427372

[Derrick]

..then please explain why on 37W, 12514V the output mux is constant (tsreader) but according to the modulation parameters it's not though it says single input.

[crazycat]

@Derrick

ACM/VCM transponders can contain BBFrames with different modcode (often in different multistream substreams).

Read about advanced satellite networking solutions on NewTec site - http://www.newtec.eu/applications/backb ... ng/flexacm

And also possible combine QPSK modulation with 8PSK, 16/32APSK. Used as backup carrier for clients with very bad weather.

[sotos65]

..then please explain why on 37W, 12514V the output mux is constant (tsreader) but according to the modulation parameters it's not though it says single input.

I can't tell what's exactly happening on this given transmission. What's for sure is that acm/vcm modulation does exactly that, dynamically changes the parameters of a DVB-S2 transmission to compensate weather and/or bandwidth demands.

[Derrick]

..well, imho in most cases it's not ACM because it simply doesn't make sense. It's mainly used for vsat but for sure not for feeding a terrestrial DVB-T network.
The coding mode doesn't read ACM but ACM/VCM

[crazycat]

on receiver side ACM and VCM is same. Stream can contain BBFrames with diffrent modcode or dummy frames for filling free bandwidth.

Standard broadcast version of STV090xBA demod can only receive DVB-S2 with constant modcode BB Frames, and can't process dummy frames. In 6925 used advanced version STV0900AA demod, which can receive this 'advanced' DVB-S2 streams.

[sotos65]

..well, imho in most cases it's not ACM because it simply doesn't make sense. It's mainly used for vsat but for sure not for feeding a terrestrial DVB-T network.
The coding mode doesn't read ACM but ACM/VCM

Sorry, don't understand. If they are not ACM/VCM (this is the way this modulation almost always appear) then what are they if the are decoded without a problem with a card that supports ACM/VCM modulation (as TBS 6925 does), but not with other (standard DVB-S2 CCM modulation) cards or standalone decoders? There are already some known cases of transmissions of tv channels with ACM/VCM modulation that are not receivable with standard receivers or cards. 12718,H,36512 in Atlantic Bird 1 is one of them (Multiple Input Stream transmission, with four transport streams), a second one is 11914,H,27500 on Astra 1G with some italian sport channels. In any case most of ACM/VCM transmissions are indeed data....

[Derrick]

btw. there seems to an error in crazyscan's reading of "spectral inversion" (swapped IQ). It has to be the other way round. Transponders that are shown as "normal" are inverted and vice versa

[crazycat]

There are already some known cases of transmissions of tv channels with ACM/VCM modulation that are not receivable with standard receivers or cards. 12718,H,36512 in Atlantic Bird 1 is one of them (Multiple Input Stream transmission, with four transport streams), a second one is 11914,H,27500 on Astra 1G with some italian sport channels. In any case most of ACM/VCM transmissions are indeed data....

BlindScan read coding type flag from MATYPE header info of BBFrames ( CCM or VCM/ACM). Multistreams with DVB-T muxes really use constant coding (often 8PSK, 5/6), but contain dummy frames for filling unused transponder bandwidth. So can't be received with STV090xBA.