PX3 for locating ft8 interference?

[Tox]

I've been using a kx3 to play with ft8. Finding intermittent severe
QRM is rendering it deaf to due desense. (Signals that are coming in
at -5 disappear from the waterfall when the source fires.)

The waterfall in WSJT-X is only really useful for a few kHz of view,
and I suspect that if the interference is notchable, it is outside
that passband.

Would the PX3 still give a full 200kHz of view to help with (maybe)
adding a notch useful for being able to then hear ft8?

I do have RTL-SDR, and Kerberos SDR, but haven't set them up for fear
of blowing out the front end when transmitting, haven't found an
equivalent to the MFJ autosensing TR switch that is solid state and
can withstand 100w of transmit.

Thanks in advance,
Scott
AD6YT

--
Scott Small
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[Jim Brown-10]

On 1/13/2020 7:10 AM, Tox wrote:
> I've been using a kx3 to play with ft8. Finding intermittent severe
> QRM is rendering it deaf to due desense. (Signals that are coming in
> at -5 disappear from the waterfall when the source fires.)

There is some bad advice in the setup instructions for WSJT-X to set the
RX audio drive to the computer at 30 dB indicated on the green level bar
at the bottom right of the display. This WILL cause weak signals to be
lost to the decoder in the presence of a very strong one. I've learned
to set that audio drive level so that, with RX signals present, that
green bar is around 70 dB but never turns red (a bit over 80 dB).

For those reading the mail -- the logic is simple. The A/D converter has
a dynamic range of about 90 dB. The green bar shows where the top of
that 90 dB is set. Let's say a very strong signal, 50 dB over S9, takes
over the AGC and hits the computer at 40 dB. Another signal in the
waterfall would have to be S9 +10 dB to be decoded -- any weaker signal
falls below the range of the A/D! But if I set the green bar to 75 dB,
an S9 signal would be 25 dB above the bottom of the decoder. Each S-unit
is 5 or 6 dB (depending on each mfr's definition of an S-unit); if 5 dB,
S8 would be 20 dB above the bottom, S7 15 dB, S6 10 dB, S5 5 dB. Now, a
signal between S4 and S5 can be decoded.

Another point. The appearance of the spectrum display can be deceiving,
making signals appear wider than they are. WSJT-X can decode signals
that appear to be covered by strong adjacent signals. The apparent
covering is an artifact of how the waterfall is able to display
amplitude of the received signal. The decoder sees "beneath" what the
display shows.

73, Jim K9YC
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[Tox]

Thanks - I actually do already adjust AF to about 65dB.

Scott
AD6YT

On Mon, Jan 13, 2020 at 10:20 AM Jim Brown <[hidden email]> wrote:

>
> On 1/13/2020 7:10 AM, Tox wrote:
> > I've been using a kx3 to play with ft8. Finding intermittent severe
> > QRM is rendering it deaf to due desense. (Signals that are coming in
> > at -5 disappear from the waterfall when the source fires.)
>
> There is some bad advice in the setup instructions for WSJT-X to set the
> RX audio drive to the computer at 30 dB indicated on the green level bar
> at the bottom right of the display. This WILL cause weak signals to be
> lost to the decoder in the presence of a very strong one. I've learned
> to set that audio drive level so that, with RX signals present, that
> green bar is around 70 dB but never turns red (a bit over 80 dB).
>
> For those reading the mail -- the logic is simple. The A/D converter has
> a dynamic range of about 90 dB. The green bar shows where the top of
> that 90 dB is set. Let's say a very strong signal, 50 dB over S9, takes
> over the AGC and hits the computer at 40 dB. Another signal in the
> waterfall would have to be S9 +10 dB to be decoded -- any weaker signal
> falls below the range of the A/D! But if I set the green bar to 75 dB,
> an S9 signal would be 25 dB above the bottom of the decoder. Each S-unit
> is 5 or 6 dB (depending on each mfr's definition of an S-unit); if 5 dB,
> S8 would be 20 dB above the bottom, S7 15 dB, S6 10 dB, S5 5 dB. Now, a
> signal between S4 and S5 can be decoded.
>
> Another point. The appearance of the spectrum display can be deceiving,
> making signals appear wider than they are. WSJT-X can decode signals
> that appear to be covered by strong adjacent signals. The apparent
> covering is an artifact of how the waterfall is able to display
> amplitude of the received signal. The decoder sees "beneath" what the
> display shows.
>
> 73, Jim K9YC
> ______________________________________________________________
> Elecraft mailing list
> Home: http://mailman.qth.net/mailman/listinfo/elecraft
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> Post: mailto:[hidden email]
>
> This list hosted by: http://www.qsl.net
> Please help support this email list: http://www.qsl.net/donate.html
> Message delivered to [hidden email]

--
Scott Small
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[Conrad PA5Y]

That makes perfect sense to me Jim, however I have my AGC threshold set quite high to stop contest mush. I will let you know how I go on during this summer's 6m Es season which is a particularly harsh test in this neck of the woods. I may have to adjust the AGC for 50.313 which is the new 'centre of activity'

73

Conrad PA5Y

-----Original Message-----
From: [hidden email] <[hidden email]> On Behalf Of Jim Brown
Sent: 13 January 2020 19:20
To: [hidden email]
Subject: [Elecraft] Setting Up For WSJT-X Receive Levels

On 1/13/2020 7:10 AM, Tox wrote:
> I've been using a kx3 to play with ft8. Finding intermittent severe
> QRM is rendering it deaf to due desense. (Signals that are coming in
> at -5 disappear from the waterfall when the source fires.)

There is some bad advice in the setup instructions for WSJT-X to set the RX audio drive to the computer at 30 dB indicated on the green level bar at the bottom right of the display. This WILL cause weak signals to be lost to the decoder in the presence of a very strong one. I've learned to set that audio drive level so that, with RX signals present, that green bar is around 70 dB but never turns red (a bit over 80 dB).

For those reading the mail -- the logic is simple. The A/D converter has a dynamic range of about 90 dB. The green bar shows where the top of that 90 dB is set. Let's say a very strong signal, 50 dB over S9, takes over the AGC and hits the computer at 40 dB. Another signal in the waterfall would have to be S9 +10 dB to be decoded -- any weaker signal falls below the range of the A/D! But if I set the green bar to 75 dB, an S9 signal would be 25 dB above the bottom of the decoder. Each S-unit is 5 or 6 dB (depending on each mfr's definition of an S-unit); if 5 dB,
S8 would be 20 dB above the bottom, S7 15 dB, S6 10 dB, S5 5 dB. Now, a signal between S4 and S5 can be decoded.

Another point. The appearance of the spectrum display can be deceiving, making signals appear wider than they are. WSJT-X can decode signals that appear to be covered by strong adjacent signals. The apparent covering is an artifact of how the waterfall is able to display amplitude of the received signal. The decoder sees "beneath" what the display shows.

73, Jim K9YC
______________________________________________________________
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Please help support this email list: http://www.qsl.net/donate.html Message delivered to [hidden email]
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