[wsjt-devel] signal report RST

[Reino Talarmo]

Hi All,

There has been many situation, where FT8 signal quality is less than perfect 
due to hum, actually hum related harmonics. In one example hum related 
sidebands were down relative to the intended signal:

Delta frequency, signal strength

-600 = 10 x 60 Hz, -41 dB

-240 = 4 x 60 Hz,  -29 dB

-120 = 2 x 60 Hz,  -24 dB

 

In some contest we use RST reports assuming that readability is 5, which is 
valid as long as signal is decoded; operator could give a lower value based on 
waterfall, but that’s not reliable). Signal strength value is based on the S/N 
value, which is a good way to report signal strength instead of 599 as used in 
many CW contests. The signal tone is assumed always to be perfect and is 
reported as 9. The above shows how in real life situation unfortunately is not 
always so good. 

 

In the CW Tone quality values are defined a bit differently in various sources, 
but this list gives the idea:

T (cw only)

1 Sixty cycle a.c or less, very rough and broad

2 Very rough a.c., very harsh and broad

3 Rough a.c. tone, rectified but not filtered

4 Rough note, some trace of filtering

5 Filtered rectified a.c. but strongly ripple-modulated

6 Filtered tone, definite trace of ripple modulation

7 Near pure tone, trace of ripple modulation

8 Near perfect tone, slight trace of modulation

9 Perfect tone, no trace of ripple or modulation of any kind

 

The above example could fall in somewhere between 5 to 8, perhaps close to 6.

I know that that we can live without an actual Tone value reporting, but 
sometimes those hum related sidebands do prevent decoding of other signals and 
it would be nice to have a way to report it to the sender in contests. Perhaps 
Tone report selection in contest mode could be added into the list on least 
important nice features. 
(Of course somebody could send me a free text such as ‘OH3MA RST 597’ or ‘OH3MA 
TONE 7’ or ‘OH3MA T 7’)

 

73, Reino oh3ma 

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Re: [wsjt-devel] FT8 ghost signals

[David Tiller]

The ones at 710, 830, and 950 are exactly 120 Hz apart - 2x the US line 
frequency. The 350 and is 6x60 Hz away from 710 (and exact multiples of 120 Hz 
from all of the others as well).

You've got 950 Hz (the presumed fundamental), 950 - 120, 950 - 240, and 950 - 
600. Missing would be the subharmonics between 350 and 710 Hz (.

The second pair are almost 360 Hz apart. It sounds like there's some AC mixing 
going on.
--
David Tiller
Sr. Architect/Lead Consultant | CapTech
(804) 304-0638 | 
dtil...@captechconsulting.com



On Jul 13, 2019, at 2:29 PM, Bill Barrett 
mailto:w2pky...@gmail.com>> wrote:

Hello Reino-

190708_22401550.313 Rx FT8-24  0.3  350 WC4H W4I R-13
190708_22401550.313 Rx FT8-12  0.3  710 WC4H W4I R-13
190708_22401550.313 Rx FT8 -7  0.3  830 WC4H W4I R-13
190708_22401550.313 Rx FT8 17  0.3  950 WC4H W4I R-13

190708_22404550.313 Rx FT8-24  0.3  350 WC4H W4I 73
190708_22404550.313 Rx FT8-14  0.3  709 WC4H W4I 73

Thanks for the tip.
Here is the episode.

Bill W2PKY



On Sat, Jul 13, 2019 at 1:46 PM Reino Talarmo 
mailto:reino.tala...@kolumbus.fi>> wrote:
Bill,
Do you happen to have an ALL.TXT on that situation? If so what was the 
frequency difference between those sub-harmonics?
73, Reino oh3ma
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Re: [wsjt-devel] FT8 ghost signals

[Reino Talarmo]

Hi Roland,

Yes there are now and then 100 or -100 Hz differences and some with 50 or -50 
Hz. The latter is an indication that 50 Hz mains is overloading some section of 
audio path. It may also happen at the receiver side. I did not analyzed, if 
this is the case on those 50 Hz instances. But a lot of less than 100 Hz or 50 
Hz or some random value; most probably those are airplane reflections.

73, Reino oh3ma

 

From: roland.hartm...@web.de [mailto:roland.hartm...@web.de] 
Sent: 13. heinäkuuta 2019 22:42
To: 'WSJT software development' 
Subject: Re: [wsjt-devel] FT8 ghost signals

 

Hello Bill,

 

on wspr there is the same symptom. 

I have filtered the calls with my ID where such one came in last month.

Maybe more helpful – there is the exact frequency of such more entries.

You can find it as attachment.

 

73 – DK4RH Roland

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Re: [wsjt-devel] FT8 ghost signals

[Reino Talarmo]

Thanks Bill

I calculated frequency differences and my conclusion is that there is no 
ghosts, but only AM or/and FM modulation possibly in a power amplifier due to 
less than perfect power supply filtering and possible overdriving so that 
output power follows the supply voltage variations. This is a typical 
modulation result, when the modulating voltage waveform is triangle with  a 
sharp rise time. Not all modulation sidebands are strong enough to be decoded.

73, Reino

 

From: Bill Barrett [mailto:w2pky...@gmail.com] 
Sent: 13. heinäkuuta 2019 21:29
To: WSJT software development 
Subject: Re: [wsjt-devel] FT8 ghost signals

 

Hello Reino-

 

190708_22401550.313 Rx FT8-24  0.3  350 WC4H W4I R-13
190708_22401550.313 Rx FT8-12  0.3  710 WC4H W4I R-13 360 = 3 x 120
190708_22401550.313 Rx FT8 -7  0.3  830 WC4H W4I R-13 120
190708_22401550.313 Rx FT8 17  0.3  950 WC4H W4I R-13 120

 

190708_22404550.313 Rx FT8-24  0.3  350 WC4H W4I 73
190708_22404550.313 Rx FT8-14  0.3  709 WC4H W4I 73

 

Thanks for the tip.

Here is the episode.

 

Bill W2PKY

 

 

 

On Sat, Jul 13, 2019 at 1:46 PM Reino Talarmo mailto:reino.tala...@kolumbus.fi> > wrote:

Bill,

Do you happen to have an ALL.TXT on that situation? If so what was the 
frequency difference between those sub-harmonics?

73, Reino oh3ma

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Re: [wsjt-devel] FT8 ghost signals

[Bill Barrett]

Hello Reino-

190708_22401550.313 Rx FT8-24  0.3  350 WC4H W4I R-13
190708_22401550.313 Rx FT8-12  0.3  710 WC4H W4I R-13
190708_22401550.313 Rx FT8 -7  0.3  830 WC4H W4I R-13
190708_22401550.313 Rx FT8 17  0.3  950 WC4H W4I R-13

190708_22404550.313 Rx FT8-24  0.3  350 WC4H W4I 73
190708_22404550.313 Rx FT8-14  0.3  709 WC4H W4I 73

Thanks for the tip.
Here is the episode.

Bill W2PKY



On Sat, Jul 13, 2019 at 1:46 PM Reino Talarmo 
wrote:

> Bill,
>
> Do you happen to have an ALL.TXT on that situation? If so what was the
> frequency difference between those sub-harmonics?
>
> 73, Reino oh3ma
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Re: [wsjt-devel] FT8 ghost signals

[Reino Talarmo]

Bill,

Do you happen to have an ALL.TXT on that situation? If so what was the 
frequency difference between those sub-harmonics?

73, Reino oh3ma

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Re: [wsjt-devel] FT8 ghost signals

[Rich Zwirko - K1HTV]

From: Joe Taylor 
Sent: 10 July 2019 01:41
To: WSJT software development 
Subject: Re: [wsjt-devel] FT8 ghost signals

Hi Conrad,

On 7/8/2019 18:29, Conrad PA5Y wrote:
> In fact Martin, sometimes they clearly AP reflections are but often they
are not. They have no discernible doppler slant at all and appear to be a
fixed offset and have me completely puzzled. I regularly see 2 or 3 'ghost'
signals between 6 and 20dB lower in amplitude than the main signal on 2m
from stations with 100W to a 9ele or more. Stations can be several hundred
km away from me. The offsets vary between 70-150 Hz and can be positive or
negative.  In order to have a doppler shift something must be moving and
with an offset of 100Hz or more quite quickly. You would think therefore
that the frequency offset would change and it often does not but remains
static for several periods and then just disappears. How on earth can this
happen? I have no reasonable explanation for it but I assure you it is real.
>
> Aircraft scatter on 6m occurs of course but not so often, however during
intense Es events sure enough I also see these ghosts on 6m and again no
shift. It really is very puzzling indeed.

Evidently what's puzzling you is Doppler shifts that remain nearly constant
for a minute or so.  Aircraft at 10,000 meters can be line-of-sight visible
at distances up to several hundred km.  With typical aircraft speeds, in
such cases the geometry for bi-static reflections will not change much over
a minute.  So the Doppler shift can remain nearly constant.  Does this not
make sense?

-- Joe, K1JT

= = =
Joe, I understand why we can see and decode one Doppler shifted signal, but
how do you explain 2 or 3 extra Doppler reflections from the same station?

BTW, congrats on working 5T5PA on 50.323 F/H. Johannes peaked at +11 at
16:36Z when I worked him and more than an hour later he is still at a
steady +4 to +6 dB here in VA. I chatted w/him using JTAlert and he said he
is having lots of fun working so much 6M DX in the F/H mode.

73,
Rich - K1HTV
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Re: [wsjt-devel] FT8 ghost signals

[Bill Barrett]

I am right on the glide path for south bound aircraft to Tampa Intl A.P.
about 50 miles north.
Don't know if that has anything to do with the following observation.
My radio is the Flex 6700 so have a panoramic view of the FT8 segment.
Earlier last week during a strong Eskip session saw a station from Ga, 406
miles NNE,  produce 4 sub-harmonic decodes
Happened to be listening to the audio at the time and it sounded unusually
musical.
Looked over at the Pan and saw what appeared to be a station with unlimited
sub-harmonics extending even below .313
The unusual amount of ghost signals only lasted on transmission.
Sorry I don't have a screen shot or saved .wav file.

Now that the ghost signals have been identified and reported seems they are
quite frequent.
Has anyone else noticed such a strong flurry of ghost signals?

Bill W2PKY


On Sat, Jul 13, 2019 at 9:29 AM Conrad PA5Y  wrote:

> It does, Joe.
>
> Thanks for the first convincing explanation that I have seen.
>
> Regards
>
> Conrad PA5Y
>
> -Original Message-
> From: Joe Taylor 
> Sent: 10 July 2019 01:41
> To: WSJT software development 
> Subject: Re: [wsjt-devel] FT8 ghost signals
>
> Hi Conrad,
>
> On 7/8/2019 18:29, Conrad PA5Y wrote:
> > In fact Martin, sometimes they clearly AP reflections are but often they
> are not. They have no discernible doppler slant at all and appear to be a
> fixed offset and have me completely puzzled. I regularly see 2 or 3 'ghost'
> signals between 6 and 20dB lower in amplitude than the main signal on 2m
> from stations with 100W to a 9ele or more. Stations can be several hundred
> km away from me. The offsets vary between 70-150 Hz and can be positive or
> negative.  In order to have a doppler shift something must be moving and
> with an offset of 100Hz or more quite quickly. You would think therefore
> that the frequency offset would change and it often does not but remains
> static for several periods and then just disappears. How on earth can this
> happen? I have no reasonable explanation for it but I assure you it is real.
> >
> > Aircraft scatter on 6m occurs of course but not so often, however during
> intense Es events sure enough I also see these ghosts on 6m and again no
> shift. It really is very puzzling indeed.
>
> Evidently what's puzzling you is Doppler shifts that remain nearly
> constant for a minute or so.  Aircraft at 10,000 meters can be
> line-of-sight visible at distances up to several hundred km.  With typical
> aircraft speeds, in such cases the geometry for bi-static reflections will
> not change much over a minute.  So the Doppler shift can remain nearly
> constant.  Does this not make sense?
>
> -- Joe, K1JT
>
>
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Re: [wsjt-devel] FT8 ghost signals

[Conrad PA5Y]

It does, Joe.

Thanks for the first convincing explanation that I have seen.

Regards

Conrad PA5Y

-Original Message-
From: Joe Taylor  
Sent: 10 July 2019 01:41
To: WSJT software development 
Subject: Re: [wsjt-devel] FT8 ghost signals

Hi Conrad,

On 7/8/2019 18:29, Conrad PA5Y wrote:
> In fact Martin, sometimes they clearly AP reflections are but often they are 
> not. They have no discernible doppler slant at all and appear to be a fixed 
> offset and have me completely puzzled. I regularly see 2 or 3 'ghost' signals 
> between 6 and 20dB lower in amplitude than the main signal on 2m from 
> stations with 100W to a 9ele or more. Stations can be several hundred km away 
> from me. The offsets vary between 70-150 Hz and can be positive or negative.  
> In order to have a doppler shift something must be moving and with an offset 
> of 100Hz or more quite quickly. You would think therefore that the frequency 
> offset would change and it often does not but remains static for several 
> periods and then just disappears. How on earth can this happen? I have no 
> reasonable explanation for it but I assure you it is real.
> 
> Aircraft scatter on 6m occurs of course but not so often, however during 
> intense Es events sure enough I also see these ghosts on 6m and again no 
> shift. It really is very puzzling indeed.

Evidently what's puzzling you is Doppler shifts that remain nearly constant for 
a minute or so.  Aircraft at 10,000 meters can be line-of-sight visible at 
distances up to several hundred km.  With typical aircraft speeds, in such 
cases the geometry for bi-static reflections will not change much over a 
minute.  So the Doppler shift can remain nearly constant.  Does this not make 
sense?

-- Joe, K1JT


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Re: [wsjt-devel] FT8 ghost signals

[Conrad PA5Y]

Not true Jim. Schipol is close enough for me to see the difference between AP 
scattered signals and these other 'ghost' signals. Take a look at where I am in 
JO21VO, start up airscout and look at the HUGE number of aircraft that are 
within easy reach of my location. I heavily rely on AP scatter in contests on 
432 and 1296. I admit that I am puzzled by this and have no other plausible 
explanation.

73

Conrad PA5Y

-Original Message-
From: Jim Brown  
Sent: 09 July 2019 11:46
To: wsjt-devel@lists.sourceforge.net
Subject: Re: [wsjt-devel] FT8 ghost signals

On 7/8/2019 3:29 PM, Conrad PA5Y wrote:
> Aircraft scatter on 6m occurs of course but not so often, however during 
> intense Es events sure enough I also see these ghosts on 6m and again no 
> shift.

Conrad, your observations are limited, I suspect, because you may not live near 
major airports. It is VERY common where I live now, with both myself and 
neighbor hams in the flight paths of two major airports (San Francisco and San 
Jose), as well as Oakland, Sacramento, and Monterey. 
When I lived in Chicago (before 2006), I was under the flight paths of O'Hare 
and Midway airports.

73, Jim K9YC


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