Topband: Unofficial archive of the works from the early pioneers of Amateur Radio's digital communications era

Tue Dec 25 11:26:14 EST 2018

JC,

Thanks for this "very cool" info.
Actually, the technique has even older origins: it has been used in coherent 
radars as a jamming countermeasure since the 60-s.
Today, CCW could be implemented in an SDR transceiver in software. It would 
make CW work as good, or better, than FT8 on 160 m. CCW could be used by 
DXpeditions. It would improve QSO rates because it would be able to resolve 
the pile-up much better (in 10 Hz steps). It would also allow the smaller 
stations a better shot at the DX (just like FT8 does).
I guess CCW did not take off because it required new hardware. But today 
software could do all that.

73,
George
AA7JV/C6AGU

On Mon, 24 Dec 2018 19:35:03 -0500
  <n4is at n4is.com> wrote:
> What is CCW?
>
> Amateur Radio Coherent CW was invented by Ray Petit, W7GHM.  He is also the
> inventor of Clover now manufactured by HAL Communications.  The first
> amateur QSO was by Andy McCaskey, WA7ZVC using a Ten-Tec PM-1.  CCW was
> promoted by Chas. Woodson (Woody), W6NEY a professor at Stanford University.
> Woody published a newsletter in the early 1970's.  Ade Weiss, W0RSP wrote
> some articles in CQ and Woody, W6NEY publish a series of articles in QST in
> 1979 - 1981 period.  In February 1994 VE2IQ published his circuit for CCW
> using a PC and DSP techniques.  Peter Lamb, G3IRM wrote a newsletter on CCW
> techniques in the early 1990's. 
>
> CCW moved on to BPSK techniques and is presently being used on 80 meters.  A
> lot of this work, software, etc. is available on the web. The ARRL had
> information in the 1980's handbooks and still has some material in the
> current issues.
>
> Amateur CCW was developed before we had nice microprocessors, DSP and other
> current technology. It's been around for 25 years, is only as complex as an
> SSB transmitter, and certainly within the building ability of all most all
> amateurs.  One does not need power ... it is a QRPp mode. 
>
> CCW is slow ... 12 wpm CW.   You need a good freq standard, but today we can
> use GPS timing (see TAPR web site). It works in noise and under poor
> conditions and has been proven to work on the ham bands.
>
> See all that  here.
>
> https://midnightdesignsolutions.com/ccw/
>
> 73
> JC
> N4IS
>
>
> -----Original Message-----
>From: Topband <topband-bounces at contesting.com> On Behalf Of JC
> Sent: Monday, December 24, 2018 6:46 PM
> To: 'K4SAV' <RadioXX at charter.net>; topband at contesting.com
> Subject: Re: Topband: FT8 - How it really works
>
> Jerry
>
> The new mode FT8 is not all that new, actually, there are several aspects to
> consider, like detect  the signal,  decode the signal detected, make a
> decision to accept the decoded signal. The improvement on signal to noise
> ratio concept is very old, just the internet made  it possible with time
> synchronization. The decode uses new algorithms and some very intelligent
> way to guest the decoded signal.
>
> Check this out. 1975 Sept QST; Coherent cw test! 
> Experiments show 20 db
> Signal Boost over QRM,
>
>  http://www.arrl.org/files/file/Technology/tis/info/pdf/7509026.pdf
>
> The improvement on signal to noise ratio is just because a narrow bandwidth.
> The gates opens at the right millisecond window. On FSK the secret salvage
> is time synchronization.  You can record the audio and play it back, the
> decode will happen only if you synchronize the time of the recording with
> the time in ms of the PC clock.
>
> I did that, and it worked, I have a SDR QS1R and using HDSDR software to
> record the I/Q file, RF file. I used to record rare DX expedition signal and
> the bandwidth is 50 KHz, I can see the FT8 guys on 1840, My question was ,
> can I decode them from the digital file recorded several month ago?
>
> I started plaining the file at the top of the second count, and voalah!!!,
> The WSJT-X decoded several station, weak as -21 db. The weak signals are
> there, buried in the noise on my old digital recorded file.
>
> Then I decided to test my HWF, the practical result measuring cw signal is
> that the signal to noise increase around 20 db, 10 db due the directivity
> RDF 11.5 and another 10 db from the polarization filter. The Horizontal WF
> attenuation on vertical signals is over -90 db. The manmade noise vertical
> polarized is reduced below the MDS of the receiver and cannot be amplified
> by the receiver.
>
> The IC-7800 has two identical receivers. I connected my HWF on receiver MAIN
> and the TX antenna on the receiver SUB, I installed two instances of the
> WSJTX program, one for each receiver. After 15 minutes the number of decodes
> on the HWF was 20 or times more than the vertical full size vertical, my TX
> antenna 120 Ft high.
>
> Signals decoded around -21 db on the vertical was decoded on the HWF 0 to +1
> db. Signals  less the -5db decoded on the HWF was not decoded using the
> vertical, The HWF was decoding hundreds of signals that would be -40 db on
> the decode using the vertical.
>
> I think the s/n reported by the program as ball part is actually very good
> and close to the real s/n improvement of 2 Hz BW, depending on the mode.
>
> The only real way to increase signal to noise ratio is increasing the
> directivity of the RX antenna, more real RDF means real signal to noise
> ratio improvement. I used real because it is very easy to destroy the
> directivity with integration, leaking, intermodulation, low noise figure
> etc.
>
> One bad concept, bidirectional unterminated beverage with two lobes one in
> the back and one front, it just does not work because the RDF is 6 db down a
> terminated beverage. Same for BOG's the RDF is bad, a K9AY works better
> because has more RDF. A simple Flag can deliver 9 db RDF is tis easy to hide
> too. Two Flags in phase 11.5 db and four Flags 14 db RDF, and a very clean
> pattern besides real broadband from 1 MHz to 10 MHz
>
> As you can see on the ARRL 1975 article, there is nothing new about
> improvement of signal to noise ratio reducing the bandwidth. On the article,
> the test was CW at 12 wpm and 9 Hz filter BW , no ring using WWV as time
> source for the synchronization. 
>
> That was state of the art back in the early 70's, almost 50 years ago.
>
> 73's
> JC
> N4IS
>
>
> -----Original Message-----
>From: Topband [mailto:topband-bounces at contesting.com] On Behalf Of K4SAV
> Sent: Monday, December 24, 2018 3:10 PM
> To: topband at contesting.com
> Subject: Re: Topband: FT8 - How it really works
>
> Although I have finished my FT8 testing, there is one final thought I would
> like to leave with you, and also to correct one statement I made earlier.
> Someone thought FT8 measured the noise in the interval when the FT8 signals
> were off, and I replied that would result in a real S/N number.  That is not
> true as you will see in the info below.  You would get a real S/N number if
> the RF was sampled, but not if the audio is sampled.
>
> I spent many years designing electronic circuits professionally, so I still
> think that way.  So for a few minutes lets think about a circuit that can
> decode something below the noise floor .If you think about FT8 or anything
> similar, from a designers point of view, you suddenly realize that making a
> statement of "the circuit can decode down to X dBs below the noise floor" is
> almost an impossible task, that is, if you are talking RF noise floor as
> most people will be assuming.
>
> Since you will be dealing with audio, not RF, the receiver will convert the
> RF into audio and compress it into something that has a lot less dynamic
> range.  How much less? Say the volume is set to a level such that the
> strongest signals do not clip, then how far down is the noise? 
> You can expect that to vary on each band too.
>
> Now comes a real complication.  If you were taking samples in the RF world,
> you could see the noise level on your S meter and estimate it relative to
> the strongest signals.  However your circuit will be dealing with audio.
> Surprisingly, when the signals disappear, the receiver AGC voltage drops and
> the receiver gain increases.  That produces a lot more audio signal.  The
> audio noise in the case of no signals becomes higher than the audio level
> for strong signals if you are using USB bandwidth and receiving something
> similar to FT8. That condition is not nearly as pronounced when using a
> narrow CW bandwidth.  Even if you put the receiver into AGC slow mode it
> won't hold for the 3 seconds when FT8 is off, so you still get the increased
> audio in the off period.  Then there will be a sudden increase in audio when
> the first signal reappears, until the ACG kicks in and lowers it.  This
> happens even with fast AGC selected. It's fast enough that you don't notice
> it when listening, but if you put a scope on it you can see it.  Yeah, all
> that surprised me too when first thinking about it. 
> Take a close listen and
> see if you agree. If you can't hear it, put it on a scope or anything that
> displays an audio waveform and it will become very obvious.
>
> If you made a statement that this circuit can decode X dBs below the noise
> floor, most people will be thinking RF noise floor.  So what is it in the
> audio world that represents the noise floor in the RF world, and what would
> your statement mean?
>
> Of course you could turn off the AGC and decrease the receiver RF gain and
> that would make the audio very low when the signals disappear.  That would
> also severely limit the dynamic range for your circuit since you would no
> longer have the compression supplied by the receiver.. Your circuit would
> have to cover a much wider dynamic range, similar to what a receiver does.
> So your circuit would need what? maybe 100 dB dynamic range to cover the
> strongest signals to the weakest noise floor, forgetting about decoding
> below the noise floor.  Actually that wouldn't really happen because
> receivers can't produce a dynamic range of 100 dB in the audio. They may do
> it in the RF world, but not in audio.  
> Receivers have no need to do that.
>
> Jerry
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