DT Value Question #Timesync


Charles Albert
 

Greetings, all...
 
There was a recent discussion about how important the time sync is and just when to decide not to mess with the clock and such, but there is one question I did not see addressed in that thread, though with the heavy clipping it's more than possible I may have missed it.
 
Isn't the DT value some sort of combination of your station's time and the receiving station's time?
 
I ask because there is one local station here that always reports my DT value as 0.1 no matter what. At first, when I saw this, I would check my system clock. It was typically within 2 ms of the various standards. No other stations were reporting an issue with my DT, and there seemed to be no problems decoding signals in either direction.
 
I came to the conclusion that it is at least as likely that the station reporting me with a DT of 0.1 is (very) slightly off time as it is that I am off sync.
 
Or am I missing something in this analysis?
 
Take Care & 73
de KC6UFM
Charles
 


 

Charles,

 

I wouldn’t say a DT of 0.1 is a problem. I see other stations within a range of about +/- 0.3 s. As long as the average DT you see is close to 0 you are OK. And yes you are correct DT is the difference between your timing and the other station’s timing.

 

73 Phil GM3ZZA

 

Sent from Mail for Windows 10

 

From: Charles Albert
Sent: 07 August 2021 07:29
To: wsjtx@groups.io
Subject: [WSJTX] DT Value Question #Timesync

 

Greetings, all...

 

There was a recent discussion about how important the time sync is and just when to decide not to mess with the clock and such, but there is one question I did not see addressed in that thread, though with the heavy clipping it's more than possible I may have missed it.

 

Isn't the DT value some sort of combination of your station's time and the receiving station's time?

 

I ask because there is one local station here that always reports my DT value as 0.1 no matter what. At first, when I saw this, I would check my system clock. It was typically within 2 ms of the various standards. No other stations were reporting an issue with my DT, and there seemed to be no problems decoding signals in either direction.

 

I came to the conclusion that it is at least as likely that the station reporting me with a DT of 0.1 is (very) slightly off time as it is that I am off sync.

 

Or am I missing something in this analysis?

 

Take Care & 73

de KC6UFM

Charles

 

 


--
73 Phil GM3ZZA


Reino Talarmo
 

Hi Charles,

The DT values is the time difference between transmitted station timing and your PC timing. As Phil said 0.1 s fine for FT8 and FT4. That time delay DT contains all signal processing delays both in the distant transmitter and your receiver. Delays in analog implementations such as in FT1000MP are small, but in digital signal processing that delay, especially at reception, could be hundreds of milliseconds. It cannot be compensated at the same time both in transmitter and receiver.
I don’t know exactly how PTT delay setting in wsjt-x is affecting to that value. Probably it just delays the timeslot, but it could as well just cut the beginning of the timeslot. I should test that, hi!

73, Reino OH3mA

 

From: main@WSJTX.groups.io [mailto:main@WSJTX.groups.io] On Behalf Of Philip Rose via groups.io
Sent: 7. elokuutata 2021 10:04
To: main@WSJTX.groups.io; wsjtx@groups.io
Subject: Re: [WSJTX] DT Value Question #Timesync

 

Charles,

 

I wouldn’t say a DT of 0.1 is a problem. I see other stations within a range of about +/- 0.3 s. As long as the average DT you see is close to 0 you are OK. And yes you are correct DT is the difference between your timing and the other station’s timing.

 

73 Phil GM3ZZA

 

Sent from Mail for Windows 10

 

From: Charles Albert
Sent: 07 August 2021 07:29
To: wsjtx@groups.io
Subject: [WSJTX] DT Value Question #Timesync

 

Greetings, all...

 

There was a recent discussion about how important the time sync is and just when to decide not to mess with the clock and such, but there is one question I did not see addressed in that thread, though with the heavy clipping it's more than possible I may have missed it.

 

Isn't the DT value some sort of combination of your station's time and the receiving station's time?

 

I ask because there is one local station here that always reports my DT value as 0.1 no matter what. At first, when I saw this, I would check my system clock. It was typically within 2 ms of the various standards. No other stations were reporting an issue with my DT, and there seemed to be no problems decoding signals in either direction.

 

I came to the conclusion that it is at least as likely that the station reporting me with a DT of 0.1 is (very) slightly off time as it is that I am off sync.

 

Or am I missing something in this analysis?

 

Take Care & 73

de KC6UFM

Charles

 

 


--
73 Phil GM3ZZA


Bill Somerville
 

Hi Reino,

PTT timing does not affect the time synchronization of the message symbols. This should not be a surprise since late started transmissions are often decoded.

73
Bill
G4WJS.

On 07/08/2021 09:10, Reino Talarmo wrote:

Hi Charles,

The DT values is the time difference between transmitted station timing and your PC timing. As Phil said 0.1 s fine for FT8 and FT4. That time delay DT contains all signal processing delays both in the distant transmitter and your receiver. Delays in analog implementations such as in FT1000MP are small, but in digital signal processing that delay, especially at reception, could be hundreds of milliseconds. It cannot be compensated at the same time both in transmitter and receiver.
I don’t know exactly how PTT delay setting in wsjt-x is affecting to that value. Probably it just delays the timeslot, but it could as well just cut the beginning of the timeslot. I should test that, hi!

73, Reino OH3mA

 

From: main@WSJTX.groups.io [mailto:main@WSJTX.groups.io] On Behalf Of Philip Rose via groups.io
Sent: 7. elokuutata 2021 10:04
To: main@WSJTX.groups.io; wsjtx@groups.io
Subject: Re: [WSJTX] DT Value Question #Timesync

 

Charles,

 

I wouldn’t say a DT of 0.1 is a problem. I see other stations within a range of about +/- 0.3 s. As long as the average DT you see is close to 0 you are OK. And yes you are correct DT is the difference between your timing and the other station’s timing.

 

73 Phil GM3ZZA

 

Sent from Mail for Windows 10

 

From: Charles Albert
Sent: 07 August 2021 07:29
To: wsjtx@groups.io
Subject: [WSJTX] DT Value Question #Timesync

 

Greetings, all...

 

There was a recent discussion about how important the time sync is and just when to decide not to mess with the clock and such, but there is one question I did not see addressed in that thread, though with the heavy clipping it's more than possible I may have missed it.

 

Isn't the DT value some sort of combination of your station's time and the receiving station's time?

 

I ask because there is one local station here that always reports my DT value as 0.1 no matter what. At first, when I saw this, I would check my system clock. It was typically within 2 ms of the various standards. No other stations were reporting an issue with my DT, and there seemed to be no problems decoding signals in either direction.

 

I came to the conclusion that it is at least as likely that the station reporting me with a DT of 0.1 is (very) slightly off time as it is that I am off sync.

 

Or am I missing something in this analysis?

 

Take Care & 73

de KC6UFM

Charles

 

 


--
73 Phil GM3ZZA



William Smith
 

Whenever I run my histogram program I find the peak at 0.1s, but I figure it’s just one of those things. 🤷‍♂️

73, Willie N1JBJ


On Aug 7, 2021, at 6:18 AM, Bill Somerville <g4wjs@...> wrote:


Hi Reino,

PTT timing does not affect the time synchronization of the message symbols. This should not be a surprise since late started transmissions are often decoded.

73
Bill
G4WJS.

On 07/08/2021 09:10, Reino Talarmo wrote:

Hi Charles,

The DT values is the time difference between transmitted station timing and your PC timing. As Phil said 0.1 s fine for FT8 and FT4. That time delay DT contains all signal processing delays both in the distant transmitter and your receiver. Delays in analog implementations such as in FT1000MP are small, but in digital signal processing that delay, especially at reception, could be hundreds of milliseconds. It cannot be compensated at the same time both in transmitter and receiver.
I don’t know exactly how PTT delay setting in wsjt-x is affecting to that value. Probably it just delays the timeslot, but it could as well just cut the beginning of the timeslot. I should test that, hi!

73, Reino OH3mA

 

From: main@WSJTX.groups.io [mailto:main@WSJTX.groups.io] On Behalf Of Philip Rose via groups.io
Sent: 7. elokuutata 2021 10:04
To: main@WSJTX.groups.io; wsjtx@groups.io
Subject: Re: [WSJTX] DT Value Question #Timesync

 

Charles,

 

I wouldn’t say a DT of 0.1 is a problem. I see other stations within a range of about +/- 0.3 s. As long as the average DT you see is close to 0 you are OK. And yes you are correct DT is the difference between your timing and the other station’s timing.

 

73 Phil GM3ZZA

 

Sent from Mail for Windows 10

 

From: Charles Albert
Sent: 07 August 2021 07:29
To: wsjtx@groups.io
Subject: [WSJTX] DT Value Question #Timesync

 

Greetings, all...

 

There was a recent discussion about how important the time sync is and just when to decide not to mess with the clock and such, but there is one question I did not see addressed in that thread, though with the heavy clipping it's more than possible I may have missed it.

 

Isn't the DT value some sort of combination of your station's time and the receiving station's time?

 

I ask because there is one local station here that always reports my DT value as 0.1 no matter what. At first, when I saw this, I would check my system clock. It was typically within 2 ms of the various standards. No other stations were reporting an issue with my DT, and there seemed to be no problems decoding signals in either direction.

 

I came to the conclusion that it is at least as likely that the station reporting me with a DT of 0.1 is (very) slightly off time as it is that I am off sync.

 

Or am I missing something in this analysis?

 

Take Care & 73

de KC6UFM

Charles

 

 


--
73 Phil GM3ZZA






Bill Somerville
 

Hi Willie,

for a transmitting and receiving pair, both with accurate clocks and analog transceivers, around 100 mS DT values are normal. The delay is a combination of audio buffer latencies at each end plus DSP processing time at the Rx end, and a small contribution from propagation delay. Using SDRs will increase the delay, although the current crop of direct sampling SDR transceivers usually have quite low latencies.

73
Bill
G4WJS.

On 07/08/2021 11:21, William Smith wrote:
Whenever I run my histogram program I find the peak at 0.1s, but I figure it’s just one of those things. 🤷‍♂️

73, Willie N1JBJ


On Aug 7, 2021, at 6:18 AM, Bill Somerville <g4wjs@...> wrote:


Hi Reino,

PTT timing does not affect the time synchronization of the message symbols. This should not be a surprise since late started transmissions are often decoded.

73
Bill
G4WJS.

On 07/08/2021 09:10, Reino Talarmo wrote:

Hi Charles,

The DT values is the time difference between transmitted station timing and your PC timing. As Phil said 0.1 s fine for FT8 and FT4. That time delay DT contains all signal processing delays both in the distant transmitter and your receiver. Delays in analog implementations such as in FT1000MP are small, but in digital signal processing that delay, especially at reception, could be hundreds of milliseconds. It cannot be compensated at the same time both in transmitter and receiver.
I don’t know exactly how PTT delay setting in wsjt-x is affecting to that value. Probably it just delays the timeslot, but it could as well just cut the beginning of the timeslot. I should test that, hi!

73, Reino OH3mA

 

From: main@WSJTX.groups.io [mailto:main@WSJTX.groups.io] On Behalf Of Philip Rose via groups.io
Sent: 7. elokuutata 2021 10:04
To: main@WSJTX.groups.io; wsjtx@groups.io
Subject: Re: [WSJTX] DT Value Question #Timesync

 

Charles,

 

I wouldn’t say a DT of 0.1 is a problem. I see other stations within a range of about +/- 0.3 s. As long as the average DT you see is close to 0 you are OK. And yes you are correct DT is the difference between your timing and the other station’s timing.

 

73 Phil GM3ZZA

 

Sent from Mail for Windows 10

 

From: Charles Albert
Sent: 07 August 2021 07:29
To: wsjtx@groups.io
Subject: [WSJTX] DT Value Question #Timesync

 

Greetings, all...

 

There was a recent discussion about how important the time sync is and just when to decide not to mess with the clock and such, but there is one question I did not see addressed in that thread, though with the heavy clipping it's more than possible I may have missed it.

 

Isn't the DT value some sort of combination of your station's time and the receiving station's time?

 

I ask because there is one local station here that always reports my DT value as 0.1 no matter what. At first, when I saw this, I would check my system clock. It was typically within 2 ms of the various standards. No other stations were reporting an issue with my DT, and there seemed to be no problems decoding signals in either direction.

 

I came to the conclusion that it is at least as likely that the station reporting me with a DT of 0.1 is (very) slightly off time as it is that I am off sync.

 

Or am I missing something in this analysis?

 

Take Care & 73

de KC6UFM

Charles

 

 


--
73 Phil GM3ZZA