K3 - RTTY FSK mode bandwidth


Ronald PA3EWP
 

Hello,

 

Yesterday I was configuring a K3 for a friend.

I noticed some strange effect that I have never seen and I can’t find a solution for it.
Maybe it is simple, I don’t know.

 

I can receive RTTY signals when the bandwidth is 2 kHz, if I reduce the bandwidth the to 500 Hz or lower, the signals are gone.

The shift is default in the center, I have to turn the Shift, to hear the signals again, then I can decode it perfectly.

With the RTTY Dual BPF filter it did not decode at all.

 

With my own K3’s I have no problems at all.

I hope someone has a solution for it.

 

73

Ronald, PA3EWP


Ken K6MR
 

You probably have the Mark tone set to a different value than your decode software.  Hold <Pitch> and set the Mark tone to match.  Or change your software to match.  They have to be the same value.

Ken K6MR 


From: Elecraft-K3@groups.io <Elecraft-K3@groups.io> on behalf of Ronald PA3EWP via groups.io <r.stuy1@...>
Sent: Sunday, October 2, 2022 2:35 AM
To: Elecraft-K3@groups.io <Elecraft-K3@groups.io>
Subject: [Elecraft-K3] K3 - RTTY FSK mode bandwidth
 

Hello,

 

Yesterday I was configuring a K3 for a friend.

I noticed some strange effect that I have never seen and I can’t find a solution for it.
Maybe it is simple, I don’t know.

 

I can receive RTTY signals when the bandwidth is 2 kHz, if I reduce the bandwidth the to 500 Hz or lower, the signals are gone.

The shift is default in the center, I have to turn the Shift, to hear the signals again, then I can decode it perfectly.

With the RTTY Dual BPF filter it did not decode at all.

 

With my own K3’s I have no problems at all.

I hope someone has a solution for it.

 

73

Ronald, PA3EWP


Jim Brown
 

On 10/2/2022 2:35 AM, Ronald PA3EWP via groups.io wrote:
I can receive RTTY signals when the bandwidth is 2 kHz, if I reduce the bandwidth the to 500 Hz or lower, the signals are gone.
Study the WSJT-X User Guide, on their website. It clearly states that the receiver should be set to the full SSB bandwidth of 2.7-2.8 kHz. I've run my K3 that way with all WSJT modes, including a very early third party JT65 multi-decoder, JT-HF by W6CQZ, for more than ten years.

The phase shift produced by narrow filters degrades decoding.

73, Jim K9YC


Jim Brown
 

Sorry, I mis-read this question. K6MR has the right response.

73, Jim K9YC

On 10/2/2022 10:14 AM, Jim Brown wrote:
On 10/2/2022 2:35 AM, Ronald PA3EWP via groups.io wrote:
I can receive RTTY signals when the bandwidth is 2 kHz, if I reduce the bandwidth the to 500 Hz or lower, the signals are gone.
Study the WSJT-X User Guide, on their website. It clearly states that the receiver should be set to the full SSB bandwidth of 2.7-2.8 kHz. I've run my K3 that way with all WSJT modes, including a very early third party JT65 multi-decoder, JT-HF by W6CQZ, for more than ten years.
The phase shift produced by narrow filters degrades decoding.
73, Jim K9YC


Milt
 

Ronald (and others),


With amateur radio RTTY, the mark tones are typical at 2125 Hz and the space is at 2295 Hz in the pass
band when the mode is set to SSB.  For this reason, when the BW is at 2 kHz the tones are detectable
because they are some what within the 2 kHz pass band. The RTTY signal is lost when the filter bandwidth
is reduced in the SSB mode because the RTTY tones are no longer within the pass band of the filter setting.
(Same principle applies if low tones are being used).

RTTY can be received with the mode set to LSB/USB,  Data A, AFSK or FSK on the K3(s).

BUT... even though LSB/USB and  Data A can  be used for RTTY, these modes should be avoided and AFSK
or FSK (depending on the transmitter modulation type) instead.

With AFSK/FSK the filter pass band center frequency is automatically adjusted to compensate to the CF of
the mark/space tones thus allowing for the pass band to be narrowed to the bandwidth.

When operating one of the WSJT-X  modes, the DATA A is the mode of choice as this disables audio
compression and equalization. Both of which will have an undesired consequences TX & Rcv 

br

Milt
AD5XD

On 2022-10-02 4:35 AM, Ronald PA3EWP via groups.io wrote:

Hello,

 

Yesterday I was configuring a K3 for a friend.

I noticed some strange effect that I have never seen and I can’t find a solution for it.
Maybe it is simple, I don’t know.

 

I can receive RTTY signals when the bandwidth is 2 kHz, if I reduce the bandwidth the to 500 Hz or lower, the signals are gone.

The shift is default in the center, I have to turn the Shift, to hear the signals again, then I can decode it perfectly.

With the RTTY Dual BPF filter it did not decode at all.

 

With my own K3’s I have no problems at all.

I hope someone has a solution for it.

 

73

Ronald, PA3EWP



Rick NK7I
 

++ Response woven with.

On 10/2/2022 12:52 PM, Milt wrote:
With amateur radio RTTY, the mark tones are typical at 2125 Hz and the space is at 2295 Hz in the pass
band when the mode is set to SSB.  For this reason, when the BW is at 2 kHz the tones are detectable
because they are some what within the 2 kHz pass band. The RTTY signal is lost when the filter bandwidth
is reduced in the SSB mode because the RTTY tones are no longer within the pass band of the filter setting.
(Same principle applies if low tones are being used).

++ IF the center of the filter is not moved to the intended tones, which should be the first decision when decoding RTTY tones.  This is the most likely situation for the friend's K3, recenter the filter to match the tones.


RTTY can be received with the mode set to LSB/USB,  Data A, AFSK or FSK on the K3(s).

BUT... even though LSB/USB and  Data A can  be used for RTTY, these modes should be avoided and AFSK
or FSK (depending on the transmitter modulation type) instead.

++ VERY misleading, approaching wrong information. 

Data A is near perfect for computer generated RTTY tones, the user selects the tones desired, centers the filter (and bandwidth) on those tones for optimal receive.  Some of this depends on the software chosen (HRD, MMTTY others) but it's quick and simple; Data A is fine but doesn't allow Dual Peak filtering.

For K3 (K4) created signals (FSK) using the FSK mode selects the tones, dual peak filtering if desired and presets the filter center.  The dual peak filters are available for AFSK if one needs finer RX control than Data A.

There is more than one way to produce RTTY with Elecraft (and most other radios).  It's left to the user to find the best method for that station from the variety of options.


With AFSK/FSK the filter pass band center frequency is automatically adjusted to compensate to the CF of
the mark/space tones thus allowing for the pass band to be narrowed to the bandwidth.

++ True


When operating one of the WSJT-X  modes, the DATA A is the mode of choice as this disables audio
compression and equalization. Both of which will have an undesired consequences TX & Rcv 

++ ALL of the data modes (not U/LSB) disable audio processing (and NR) producing better results.

73,
Rick nk7i


Milt
AD5XD

On 2022-10-02 4:35 AM, Ronald PA3EWP via groups.io wrote:

Hello,

 

Yesterday I was configuring a K3 for a friend.

I noticed some strange effect that I have never seen and I can’t find a solution for it.
Maybe it is simple, I don’t know.

 

I can receive RTTY signals when the bandwidth is 2 kHz, if I reduce the bandwidth the to 500 Hz or lower, the signals are gone.

The shift is default in the center, I have to turn the Shift, to hear the signals again, then I can decode it perfectly.

With the RTTY Dual BPF filter it did not decode at all.

 

With my own K3’s I have no problems at all.

I hope someone has a solution for it.

 

73

Ronald, PA3EWP



Jim Brown
 

On 10/2/2022 12:52 PM, Milt wrote:
With amateur radio RTTY, the mark tones are typical at 2125 Hz and the space is at 2295 Hz in the pass
band when the mode is set to SSB.
These are the "default" tones by most RTTY software, but many serious RTTY contesters use lower tones (also standards) because they are easier to tune by ear. I use 915-1085 Hz for that reason.

For this reason, when the BW is at 2 kHz the tones are detectable
because they are some what within the 2 kHz pass band. The RTTY signal is lost when the filter bandwidth
is reduced in the SSB mode because the RTTY tones are no longer within the pass band of the filter setting.
(Same principle applies if low tones are being used).
Serious RTTY ops (contesters) have learned what I learned 30 years ago working in pro audio -- that the phase shift associated with filter skirts degrades decoding, and that 400-500 Hz is the best compromise for RTTY. Reduced bandwidth should be used only for very severe, close-in QRM, and restored to the wider bandwidth once that condition has cleared. I've run 48 hour RTTY contests at 400-500 Hz bandwidth, making well over 1,000 QSOs, and the top guys beat me by 10X!

73, Jim K9YC


Ronald PA3EWP
 

Hello,

 

Thanks for all the answers.

 

I have checked the pitch in (FSK D - 45BPS mode) in the K3 radio and that is configured for 2125 (like the other k3’s).

The problem still exists, if we reduce the bandwidth the center frequency is not automatically adjusted.

We have to use the shift to make the correction to put the signal in the center again.

And the Dual PB filter is not decoding at all the signal is out of the filters (shift is fixed in Dual PB).

 

I doubt it is the software because it is working with the other K3’s for many years.

All firmware of the radio has the latest version.

 

Any more suggestions?

(I hope it’s would be solved, next week we will be on 5R8), it would be fine to use the Dual PB filter.

 

73 Ronald

PA3EWP

 

 

Van: Elecraft-K3@groups.io <Elecraft-K3@groups.io> Namens Milt
Verzonden: zondag 2 oktober 2022 21:52
Aan: Elecraft-K3@groups.io
Onderwerp: Re: [Elecraft-K3] K3 - RTTY FSK mode bandwidth

 

Ronald (and others),


With amateur radio RTTY, the mark tones are typical at 2125 Hz and the space is at 2295 Hz in the pass
band when the mode is set to SSB.  For this reason, when the BW is at 2 kHz the tones are detectable
because they are some what within the 2 kHz pass band. The RTTY signal is lost when the filter bandwidth
is reduced in the SSB mode because the RTTY tones are no longer within the pass band of the filter setting.
(Same principle applies if low tones are being used).

RTTY can be received with the mode set to LSB/USB,  Data A, AFSK or FSK on the K3(s).

BUT... even though LSB/USB and  Data A can  be used for RTTY, these modes should be avoided and AFSK
or FSK (depending on the transmitter modulation type) instead.

With AFSK/FSK the filter pass band center frequency is automatically adjusted to compensate to the CF of
the mark/space tones thus allowing for the pass band to be narrowed to the bandwidth.

When operating one of the WSJT-X  modes, the DATA A is the mode of choice as this disables audio
compression and equalization. Both of which will have an undesired consequences TX & Rcv 

br

Milt
AD5XD

On 2022-10-02 4:35 AM, Ronald PA3EWP via groups.io wrote:

Hello,

 

Yesterday I was configuring a K3 for a friend.

I noticed some strange effect that I have never seen and I can’t find a solution for it.
Maybe it is simple, I don’t know.

 

I can receive RTTY signals when the bandwidth is 2 kHz, if I reduce the bandwidth the to 500 Hz or lower, the signals are gone.

The shift is default in the center, I have to turn the Shift, to hear the signals again, then I can decode it perfectly.

With the RTTY Dual BPF filter it did not decode at all.

 

With my own K3’s I have no problems at all.

I hope someone has a solution for it.

 

73

Ronald, PA3EWP