Satellite Communications/Video frozen


Good afternoon,

I had a problema in one satellite transmission yesterday

When I started to transmit in Ku band I check the RF level with

the satellite operatos and he said that the level it was ok

but something my transmission the video sometimes it frozens

I check the video source but it was ok

I also check the encoder output that is in ASI and it was ok

I had 2 modulators I changed to the other modulators and I get

better for a while but also started the video to frozen

what could be the problema?

the modulator?

the encoder?

what could be the device to make the video frozenj22 sometimes in the transmission?

my parameters to transmit were:

Fup = 14206.75H
Symbol rate = 3600
fec = 5/6
roll off = 0.25
BW = 4.5 MHz

Im looking forward to your answer
have a nice day


I assume that the input video stream is high quality and that it does not show freezing.

It appears that you are losing frame synchronization, which could be due to clockiing problems (bit slip) and/or marginal signal to noise ratio.

Bit Slip:

The following link has a presentation on clocking ( provides an overview of clocking.

It notes:

Slide 3 on page 2 of PDF: “The most important aspect in digital networking is clocking. The clock that quantifies the analog signal must be the same clock that reconstructs the signal at the other end. The only way to assure that the clock is accurate within the entire digital network is to have only one clock.”

Slide 10 on page 5 of PDF: “If you have two clocks in the same network, the difference between them will eventually result in a bit slip. A bit-slip results from one clock source being faster or slower than the other. How often a bit-slip occurs depends on the timing difference. Digitized voice circuits go unscathed from even very high rates of bit-slips.”

Signal to Noise Ratio:

If the SNR at the demodulator / bit synchronizer (D/BS) in your monitor circuit is too low, the D/BS may miss the frame synch word, resulting in a freeze that persists until the D/BS reacquires a frame synch word. I believe that this is less likely than a timing issue.

•   Download the PDF
•   Evaluate your timing chain

I hope that this helps. If so, I would appreciate it if you would complete the survey. If not, please advise.

Thomas E. Burke Ph.D., PMP

Satellite Communications

All Answers

Answers by Expert:

Ask Experts


Thomas E. Burke


No restrictions on questions.


Forty years of experience with satellite communications. Have held roles as system engineer on JPL Mariner 9 program and a program manager for a number of classified communication satellite programs. Served as head of TRW / Defense Communications Division / Engineering Development Operation, a 1,400-person organization responsible for all aspects of classified communication satellite design and development.

Ph.D. Chemistry, California Institute of Technology (1969) B.A. magna cum laude Chemistry, University of Minnesota (1962)

©2017 All rights reserved.