the input rate of receiver

[highflyer]

Hi, I checked the max. input rate of different receivers. some of them can reach 80Mbit/s, some of them are only 15Mbit/s. is it important to have the receiver with high input bit? what 's the max input rate for TV normally? thanks.

[Channel Hopper]

Normally the 15Mbit/sec would be allocated to the minimum spec on a comercial receiver (or one used for older style reception on a dedicated transmission for subscriber card only)

For this type of hobby the best ones to go for are 1 - 35 (or even 45) Mbit/s
(though a while ago there were receivers in the Echostar and Manhattan brand name that claimed these figures, but could not reach 32Mbit/sec.

Are you sure you have got the right specification?

[highflyer]

thanks, at least it is declared in the spec of Maxplus 2100+ (made in S. Korea). there is anther parameter called demod. rate, which is 2~45Ms/s. what's the difference between these two parameters?

[spiney]

Bits/sec refers to i.f. passband of the receiver. Max bitrate is (approx) twice frequency passband. Too narrow passband filtering of the i.f. will distort the signal and increase demodulation error rate.

Symbol rate depends on modulation system used, which - at least currently - is QPSK for satellite (2 symbol bits per phaseshift).

[spiney]

Oops, hang on, I might have got that the wrong way round, it could be "user bits per phase symbol", rather than "bit symbols per phase shift".

Sorry, it depends how the terms are initially defined, offhand I can't remember without looking it up!

(added) having just looked, it seems I did get it right way round 1st time (phew!), ie it's defined as "bits per symbol"!