JTDX timing

Sergey KN7K

Sorry it if a little bit off topic.

Why do i see a large Lag Time while my Dimension4 show small correction?

Is there anything can be done to minimize it? Or is it normal?

Thanks,

Sergey, KN7K

My radio synchronized by external GPSDO

K1UO Larry

The LAG is associated with the processing power (PC threads and RAM capability) of your PC and the amount of signals it is trying to decode/process each JTDX cycle. Your time is fine and actually looks normal for typical PC performances. Hover your mouse over the circled LAG area you show marked and you should get a popup explaining what it is.

Martin AA6E

I agree that the apparent offset is probably due to signal processing delay on receive. There would probably be a different, smaller delay between your local computer clock and the RF on transmit. As long as these delays are under a second or so there's nothing to worry about.

Al K0VM

FT8 is very tolerant of timing error of less than +-2 seconds. If the time difference between you and the station you're trying to receive is less than 2 seconds there should be no effect in your ability to decode him. As you go above 2 seconds, the decodes stop abruptly.

Typical delay in a Flex receiver due to DSP + DAX is 300 milliseconds. Sharper DSP filter have more delay.

AL, K0VM

Sergey KN7K

Ok, Thanks everyone!

I was thinking my Dimension4 is not in sync with PC.

Sergey, KN7K

Erik Carling EI4KF

+1.35 could cost you some decodes, especially if JTDX would have otherwise pulled put station(s) on a 2nd or 3rd decoding pass under a strong station already decoded if given a chance. This lag (timing) in JTDX has nothing to do with DT - you can see that your average DT is 0.24 seconds which is nearly perfect. The start of your transmissions will still be timely but you are losing 1.35 seconds of the 2.36 seconds given to the decoding window. Therefore lag is obviously important but not critically so, it depends on your usage. If you don't care too much, don't worry about it.

If DXing is important then it might be good to know that processing power is relevant but so are the decoding settings you have defined in JTDX.

Ensure: decoding Threads is set to one less than available in your computer. Example: 8 cores, 16 threads so set it at 15.

Adjust number of decoding cycles down one (3 to 2 or 2 to 1) and check the affect on lag and number of stations decoded.

Experiment with decoder sensitivity. Using subpass is great for powerful computers but does cause lag in slower machines.

Do not use SWL mode.

When a reasonably fast computer is used, JTDX can be "maxed out" and lag is still negative:

For slower machines aim for +0.50 seconds by adjusting the decoding levels.

Sergey KN7K

Thank you Eric, yes it seems like lag <0.5 when I change number of cycles from 2 to 1.

Probably my i7 is not very powerful.

Sergey