[CQ-Contest] FT discussions

Fri Jun 7 11:45:53 EDT 2019

Ed,

Good points, as I said in our offline discussion. I hope you don’t mind me summarizing it here briefly. 

It isn’t exactly apples to oranges as you can definitely hear the 6Hz bandwidth signal when it is out-of-sync on time, for example. Where the software makes the difference is in differentiation between wall-to-wall 6Hz signals across the 2500 Hz (or wider) bandwidth. That’s why I would propose that any FT/JT entrant should have to enter a contest as “assisted.”  Of course, any RTTY contester also is technically “assisted” (software or hardware) in decoding, but let’s don’t go there. I propose the “assisted” category solution as a something that is workable to take into account some of the advantages that the FT/JT modes can, but not automatically do, offer. As you said, there are downsides to the FT/JT modes, and the jury is still out on whether they’ll ever replace the more traditional modes. 

As I said to you, in any contest situation it will ultimately come down to skill as the deciding factor. We may get score inflation in some contests due to the use of JT/FT modes making QSOs easier, but that rising tide will lift all boats and the best will still be the best. 

Thanks again, for the fair and polite conversation: something that’s often hard to find with the JT/FT mode discussion!

73
——
Dave Wright
K3DCW
FM18qt, Maryland, USA

“Real radio bounces off the sky"

On 7 June 2019 at 10:54:52, Edward Sawyer (edwards at sbelectronics.com) wrote:

Dave, A well constructed statement although since the human ear cannot be constrained to 6hz bandwidth, to my knowledge, the fact that a system can detect it in such conditions, doesn't make it "audible". Any more than we can hear a 20khz dog whistle - also inaudible.  

So, like it or not, the system is "detecting" inaudible signals.  

Time will tell whether the contesting community tolerates the downside of FT (x) vs the advantages of such low level signal detection.  

The FT4 attempt is already pulling 10db off of that advantage to attempt a functional system for contesting and it still didn't get rave reviews from the little I saw.  

FT8 has seriously sent a ripple through the DXing pond as people take the easy route to get on bands and honestly I think give some people a way to play that apparently didn't really enjoy playing.  

I think FT4 is going to suck the air out of the room (already seems to have) in the VHF contesting game and will do so in the digital contesting game if its allowed to. Not because its so much better for contesting but because a hoard of people have decided to do it at the expense of other modes.  

73  

Ed N1UR  

-----Original Message-----  
From: CQ-Contest [mailto:cq-contest-bounces at contesting.com] On Behalf Of Dave Wright  
Sent: Friday, June 7, 2019 8:28 AM  
To: cq-contest at contesting.com  
Subject: Re: [CQ-Contest] FT discussions  

QSO credit for logging inaudible signals.  
I’ve been trying to stay out of this argument, but this statement right here is representative of the kind of rhetoric that leads to the anti-JT/FT-mode hysteria, and shows the misinformation about the way the FT/JT modes handle and report SNR. It isn’t Jim’s (K1TN) fault, but is likely simply due to a misunderstanding of the WSJT-X signal reporting system.   

The FT/JT modes are NOT black magic. They ARE modes that have an excellent design and implementation. We commonly hear that these modes can work well below the noise floor, or are “inaudible" in Jim’s words. Part of that reason for the misinformation is the negative SNR numbers presented in the software. Well, to borrow some info from the WSJT-X manual, and a great explanation by Kok S Chen (W7AY), here’s what is actually happening and what that SNR figure actually means.   

“Unless you change the WSJT-X settings, the SNR is reported in an equivalent 2500 Hz noise bandwidth. The 8FSK detector in FT8 basically works with a 6.25 Hz bandwidth (unwindowed FFT), so there is a factor of 400, or 26 dB with respect to noise in the detector's bandwidth. When you decode a "-20 dB SNR" signal in FT8, it really has +6 dB SNR in the detector's noise floor. There is no miracle here -- FT8 simply uses very narrow bandwidth and slow baud rate.  The FEC helps too, especially when there is QSB.”  

Considering that FT4 is only good down to about -15dB (if I remember correctly), that means that it must be around 10 or 11dB above the noise floor for the detector to properly decode. Again, no magic involved here. The same effect can be had with CW and/or RTTY through the use of narrow filters and the like, albeit without the FEC coding of the FT/JT modes and the extremely narrow bandwidths.  I personally have never made a JT/FT mode contact where I couldn’t hear the other station. It may have been very weak, but it was audible.   

Again, I’m not trying to attack Jim (K1TN) here: I’m just sharing some info that was shared with me a while back when I asked similar questions.   

73  

——  
Dave Wright  
K3DCW  
FM18qt, Maryland, USA  

“Real radio bounces off the sky"  

On 7 June 2019 at 08:04:38, James Cain (jamesdavidcain at gmail.com) wrote:  

Re the comments by others, below, I disagree. Discussions about the FT modes absolutely belong on this reflector, because the FT modes are an existential threat to shortwave amateur radio that some of us have known for more than half a century.  

If this reflector can "discuss" cut numbers and the morality of using Super Check Partial, then it sure as hell can discuss QSO credit for logging inaudible signals.  

Jim Cain, K1TN  

-----  

"I suggest that discussions like this be moved over to the rttydigital reflector https://groups.io/g/rttydigital  

In November of 2018, folks on the rtty Reflector got tired of seeing postings about FT8 and FT4. The rttydigital Reflector was formed at that time for discussions of ALL digital modes. There are a lot of contesters on that reflector.  

Dave Hachadorian, K6LL Yuma, AZ"  
" … in my 24 or so years on CQ-Contest (and on Towertalk, before CQ-Contest was born), I've seen these things come and go many times.  
I would encourage the moderators to exercise their influence to deflect the group back to more mainstream concerns. This too shall pass.  

73, Pete N4ZR"  
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