Latency 1.4.....Improvement?

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I just had a conversation with a "contesting" friend who said he avoids the Flex due to slow "turn-around" time particularly in SSB mode. It causes him to be one syllable behind the other radios in a contest thus loosing points. According to the QST review, the turnaround time is 138 ms for the 6300 and an even slower 140 ms for the 6700. Looking through reviews of other radios I see number like 38 etc. So I was wondering if ver 1.4 made any improvements in that area which we could pass along to others? I'm not a contester so I'm happy but apparently it is at least a perceived problem among contesters. 73  
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Steve N4LQ

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Posted 4 years ago

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Steve - N5AC, VP Engineering / CTO

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Relays have nothing to do with these measurements.  The measurements are a result of signals passing through the signal chain in the receiver and the transmitter.  As one of my radio mentors was fond of saying "all the delay comes from the quality of the final filter."  This is a hard concept to wrap your head around if you are not familiar with it, but the net-net is that the better filter you provide at the final sampling rate, the more latency is introduced.  The FLEX-6000 is the first radio I am aware of to provide variable-depth filters.  We can significantly reduce the delay by reducing the filtering and we can do this dynamically.  Even the FLEX-5000 with PowerSDR did not have this capability.

Our read when we designed the signal chain for sideband was that a little latency was less important than good filtering.  So we "maxed out" the filtering capabilities for sideband.  The filter dynamically changes width in DIGx modes and in CW.  If you would like to try out a shorter latency with reduced filtering capabilities, try running in DIGU instead of USB and set your filter width to greater than 2kHz.  The latency will go down to what we consider to be a very minimal level.  

The ARRL and others are not used to measuring radios that have complete flexibility in how things like this are controlled and so they put the radio in a given position and took a measurement.  The measurement is accurate for that one setting, but is not a complete picture of what the radio can do (and in this case doesn't explain the tradeoff that we made).  I'm sure I would have done just what they did.  As you guys probably know by now, if you provide a compelling case for making a change in the radio there are very few things we cannot change.  You can try using DIGU and let us know if you prefer it like this.  There is actually a table in the owners manual with this information along with a description of how it works (see 29.6.4 on page 140).  
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George Molnar, KF2T, Elmer

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Thanks for the info - learned something new today!
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KY6LA - Howard, Elmer

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That explains why I found the latency so low when running DIGU and DAX Audio when remoting...
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k0eoo

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Thanks Steve, FRS made the right choice.  Better filters serve us ALL, every day and every contact....
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KY6LA - Howard, Elmer

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You actually do not need to do that much to achieve a "Contest" Mode with the lowest latency in the market...

All you need to do is to route your TX and RX audio via a DAX Channel.. and then have your device (speaker and mike) listen to those channels..

I could provide your friend with screen shots as to how to do it as that is how I do it with iPad Remoting via DAX..before Remote was available in 1.4

BTW,,, at times I get hit with the contesting bug and I can be a serious contestor... I have won my ARRL section using SDR's and have placed 2nd in World and #1 NA in a JIDX SSB Contest... so I can speak with some authority about contesting..... 

It always helps to have a contesting station.. I have a 6700. SPE 2K-FA and a SteppIR MonstIR @85' located 600'ASL 1KM from the Pacific Ocean.. so by definition I will always do well in an Asia Pacific Contest without trying too hard.

So what is the difference between #2 in the world and #10 in the world when I was not trying too hard......

Basically its the operator's skill...

that 100ms latency is a mental factor.. if no one had pointed it out there is absolutely not doubt that  it would not be an issue..as a great operator can win with even a lowly ICOM IC-756 Pro3...
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Stu Phillips - K6TU, Elmer

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Turn around time is an issue - perhaps less so in phone than in CW or RTTY but there is an issue.

The ARRL review of the K3 says its turn around time is measured as 25 mS.  The same figure for the 6700 is 184 mS.  In both cases this is transmit to receive turnaround.  Some other numbers from ARRL review...  FTDX5000 - 66 mS, TS-590 - 30 mS, IC7800 - 15 mS...

Flex 5000 - 29 mS - and this has brick wall filters too...

Like Chris N6WM, I am a serious contester and I have a reasonably competitive mid-sized station. Whenever possible in all modes, I run a frequency - I call CQ and try to maximize my rate.

The issue with turn around time in both CW and RTTY is that I miss part of the call that is sent back to my CQ.  In RTTY, its common that someone sends their callsign twice - if both print ok, I don't have to ask for a repeat to verify that I have the call correctly.  Yes, there are other opportunities to verify the call but that's not the point.

Its not the additional 149 mS that is the sole issue - its whether I have to get a fill or miss copy the call as the result of the delay.  If I have to do this frequently enough, its an issue.  Why?  Because in a contest where I will make > 1500 QSO's, even a couple of seconds per Q translates into meaningful operating time in the course of a 48 hour contest when your rate is 60-100 Q's per hour...

I am competitive with my 6700 - in fact, I continue to exceed my previous personal bests in each contest where I make a concerted effort.  Some of this is modest skill improvement (I keep thinking after each contest how to do better in the next one) but I credit the radio for its reception capabilities as well as the much lower fatigue level that results from it's operation.

How much of an issue does the additional turn around time represent?  Hard to quantify but in RTTY I can SEE the issue - it audible in CW and Phone.

Chris rightly points out that contesters are heavily spec driven - it sure would be nice to see the turn around time addressed if for nothing other than the comfort level for the serious contester.  Even that said, I believe that getting into the 50mS range would significantly reduce the possibility of having to ask for a fill or repeat.

Stu K6TU
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George - AB4FH

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Ditto. Respectfully, George
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Barry N1EU

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Ditto, my experience says otherwise.

Barry N1EU
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Chris Tate - N6WM, Elmer

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Stu I agree 100%.  This is an issue that is going on my list as a problem requiring Optimization to reach the top bar.  Our racecars(signature rigs) need to be tuned for maximum performance. Think of the boost in QSO count Howard and Ken would get with the turnaround latency resolved! 5,10, 50?  This could be a winning difference. I want my flex to be my primary contest rig.  We have to have that level of optimization for mass adoption of the platform by the contest community.  They are a fickle group that obsess over numbers like cw rise times, easily selected optimized filters and, yes turn around times.

  My suggestion for Flex Radio would be to take some of the weaknesses being brought out by the testing lab and get them turned around Quickly.  The vendor of the current #1 preferred contest platform does this quite effectively.

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Ken - NM9P, Elmer

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Bill, Stu and others...
While I am flattered to be mentioned in the same sentence with contesting greats like Howard and Stu, I am not in the same league.  (Though, thanks to the 6500 I am getting better!)

However...here are some expanded thoughts after additional thought and feedback from others...

As a Phone & CW S&P-er..., the slightly higher latency hasn't hampered my rate nearly as much as the improved TX quality and superior RX sensitivity, selectivity, RX IMD/Blocking figures, reduced operator fatigue, and other improvements have added to my contesting experience.

Adjusting my timing and operating habits has eliminated any defect upon the beginning of my transmission.

I have had to make adjustments, however upon the end of my transmissions.  
In the beginning, I found that I was getting off the footswitch just a hair too early and cutting off the last half of the last letter in my call...."November Mike Nine Pa...."  instead of "papa."  This caused me to miss a few stations or required repeats until I learned to be a little faster on the press of the footswitch and a little slower on the release.  VOX operations wouldn't matter once you got the delay set correctly.

However... As Stu has mentioned, I can see how a longer latency-induced turnaround time could be a hindrance when running a frequency on RTTY or other Digital modes...perhaps even CW, though my CQ skills fer running a frequency rather than S&P would be the severe limiting factor at my station!

Long ago, when AMTOR was gaining popularity, they were trying to shave turn around times down to <25 ms, if I remember correctly.  Some were even trying for <15 ms?

I am a big fan of the brickwall filters...I almost always use 50 Hz when DXing or Contest S&P to give me the best chance of hearing a station.  When running split, I run the "much wider" 250 Hz filter on the "mob" frequency so I can get a better picture of what is around the station being worked and give me a better chance of finding a hole or hearing the next station up or down.   (I can't believe I am calling 250 Hz a "wider" filter!  It used to be the standard for "narrow.")

However, I can see that there might be some occasions where I might be willing to sacrifice a little bit of sharpness in order to gain some improvement in turn-around.  That might mean running 50 Hz reduced slope instead of 100 Hz, which would still be great compared to most other rigs.  IF... and it is a big IF... This could be selected and turned off at will.
I would not be willing to sacrifice my ultimate filter performance on CW & SSB permanently. 

Perhaps it could be implemented in DIGI only?  Or defined per-mode at the user's discretion?

This would be an interesting for the FRS staff to have as they work on V.1.5...
I don't know how much time could be shaved off of other procedures and timing loops, but it seems reasonable that while fine-tuning all the other functions they might do a complete sweep (again) of the timing elements and other things that contribute to latency and turn-around time.  (I am sure that they have swept this many times in the past already.)


Anyway... my $.02

Ken - NM9P
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Chris Tate - N6WM, Elmer

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"This would be an interesting for the FRS staff to have as they work on V.1.5...
I don't know how much time could be shaved off of other procedures and timing loops, but it seems reasonable that while fine-tuning all the other functions they might do a complete sweep (again) of the timing elements and other things that contribute to latency and turn-around time.  (I am sure that they have swept this many times in the past already.)"

Spot on.   I dont agree that some trade off is the best approach.   I would also add some specific ease of use filters, for example  a RTTY specific filter that would not require the invocation of the XIT/RIT, to be on qrg etc.  Click and run.  no time to mess or worry with stuff when logging at 300 qph.

~C./N6WM

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