6500 Delay in FT8

Patrick

The latest versions of wsjt-x will high light (add background highlight) to the DT measurement if it is out of spec. That is the point where it may have difficulty decoding the incoming signals. I think it triggers at about 1.75 to 2.0 seconds. 0 to .6 is nominal. You will sometimes see -.1 to -.2 occasionally.

BL7IB

It is reasonable to assume, when we transmit using FlexRadio, there is also small delay in comparson with analog rig?

If this is true, is there any setting in either Flexradio or WSJT to offset it?

(not splitting hairs but increase chance of packet being decoded)

Tim - W4TME

@BL7IB There is not an offset value in WSJT-X to compensate for inherent signal propagation delays in the radio. With the FLEX-6000, this is a few hundred milliseconds, well within spec.

Patrick

I think there are three types of timing differentials. First is processing, time needed to do the A TO D function including demodulation to audio level, which I have to say is probably less then 1 ms on average in the radio. Next is processing of the Audio by wsjt-x and again less then 1 ms in the computer, but also has sample reception time which is set to a set time in both FT8/4. The last time is the measurement in the DT, which times the time difference between the two communicating stations. Which is shown for all decoded signals. That time seems to average about .2 to .6 seconds for most stations. So the first two are pretty much set by the processing power of the computing devices being used. The last I think should able to be set, but requires the ability to set an offset into the clock timing that controls the T/R function of the radio/application timing. The transmit and PTT delays set in ms increments has minimal effect and only in a negative direction. That is why there would be need for a station clock offset in the tenths of a second to be able to bring DT to closer to 0 DT. Any way, this thesis is my understanding. If I am wrong, I hope that someone will comment with accurate explanation. Thanks!

Tim - W4TME

From a pragmatic standpoint, I have over 10,000 FTx QSOs in the log and never missed a one with a +0.3 DT.

If that level of accuracy was needed, no one would be making QSOs.

Patrick

Yes, for sure... actually I have worked a few stations at 2 seconds and was able to decode. The wsjt-x have very robust decoding.

Tim - W4TME

@Patrick Indeed it does. 😃

Bill W2PKY

FT8 protocol sends the calls twice so if the received signals are strong and in the clear chances are that a transmission can be decoded with very significant delay.

David Decoons, wo2x

FT8 2.2.2 has three decode cycles now and FT4 has two. That was one of the new features of version 2.2.

@BL7IB I have been working China in the morning from the east coast of U.S. and timing on decodes has been 0.3 to 0.4 range when both stations are using software to sync timing to a known good source. Even analog radios have delays which are part of the analog to digital external interface used such as a SignalLink USB or similar.

The timing for T/R turnaround in Flex radios is minimal compared to propagation delays and is well within the decode limits of WSJT-X.

Dave wo2x