DTX1 Mux overflow question

[G4WIM]

Hi

I'm running a DTX-1 at 4000ksps and FEC 3/4 but when I select FEC 1/2 I get a MUX overflow message and the signal becomes corrupted.

Any ideas as to what is going on ?

73 Tim

[G4WIM]

ok - so it always helps to read the DTX1 manual, specifically page 17 where there's a formula for working out the relations ship between symbol rate and data rate....

However changing to a symbol rate of 4340ksps and FEC of 1/2 still causes the mux overflow message.

Any suggestions on how to run at FEC 1/2 without incurring the mux oveflow error ?

Back to reading the manual .......

aha - this post looks promising....

http://www.batc.org.uk/forum/viewtopic.php?t=3733

[g8vpg]

Tim,
I had the same problem two years ago when I first got my DTX1. You need to reduce the System/video bitrate - menu/encoder/AV input 1/video bitrate. I found a value of around 3600 worked well with FEC1/2 and 4ms/s. If you go to menu/status/program stream, you need to keep the total in the high 90%'s without going over 100%, when you get the MUX overflow. As you increase FEC, more data is used for error correction and less is available for video. Therefore, picture quality is slightly less at FEC1/2, but the signal is more resilient and will hold up better in marginal propagation conditions. We use a DTX1 in GB3ZZ and found that when we reduced FEC from 1/2 to 3/4, marginal stations lost the signal.
73 Shaun.

[G4WIM]

Hi Shaun,

yes, that was the answer - all good now and another lesson learned !

73 Tim