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K3 RTTY spectrum

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Kjeld Holm

K3 RTTY spectrum

For the RTTY people,
You may all know already but I did not - therefore this info.
In ARRL National Contest Journal September/October 2013 issue on page 3 to 7
the article RTTY Spectrum Measurement is discussing bandwidth issues and
other issues regarding transmission of RTTY. For the ones of you who have
access to this publication: Read it. For others the conclusion is as I read
it: Switch on the AFSK TX filter in the Config menu (page 53 in the K3
manual).
Vy 73 de OZ1CCM Kel
Kjeld Holm

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Ken Chandler

Re: K3 RTTY spectrum

Kjeld et al
I think I'm right in saying, you cannot use this filter if your running AFSK and 2tone !!

Ken.. G0ORH

Sent from my iPad

> On 9 Jun 2014, at 11:01, "Kjeld Holm" <[hidden email]> wrote:
>
> For the RTTY people,
> You may all know already but I did not - therefore this info.
> In ARRL National Contest Journal September/October 2013 issue on page 3 to 7
> the article RTTY Spectrum Measurement is discussing bandwidth issues and
> other issues regarding transmission of RTTY. For the ones of you who have
> access to this publication: Read it. For others the conclusion is as I read
> it: Switch on the AFSK TX filter in the Config menu (page 53 in the K3
> manual).
> Vy 73 de OZ1CCM Kel
> Kjeld Holm
>
>
>
> ______________________________________________________________
> Elecraft mailing list
> Home: http://mailman.qth.net/mailman/listinfo/elecraft
> Help: http://mailman.qth.net/mmfaq.htm
> 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]

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Joe Subich, W4TV-4

Re: K3 RTTY spectrum

On 2014-06-09 6:40 AM, Ken Chandler wrote:
>
> I think I'm right in saying, you cannot use this filter if your
> running AFSK and 2tone !!

Not true! If one is running AFSK *always use AFSK A* and set
CONFIG:AFSK TX = FIL On.

The AFSK TX Filter cleans up any hum on your sound card from bad
connections, grounding issues, or distortion from over drive. However,
with the K3 one can get the same narrow transmit spectrum by using FSK
without the issues of AFSK.

73,

... Joe, W4TV

On 2014-06-09 6:40 AM, Ken Chandler wrote:

> Kjeld et al
> I think I'm right in saying, you cannot use this filter if your running AFSK and 2tone !!
>
> Ken.. G0ORH
>
> Sent from my iPad
>
>
>> On 9 Jun 2014, at 11:01, "Kjeld Holm" <[hidden email]> wrote:
>>
>> For the RTTY people,
>> You may all know already but I did not - therefore this info.
>> In ARRL National Contest Journal September/October 2013 issue on page 3 to 7
>> the article RTTY Spectrum Measurement is discussing bandwidth issues and
>> other issues regarding transmission of RTTY. For the ones of you who have
>> access to this publication: Read it. For others the conclusion is as I read
>> it: Switch on the AFSK TX filter in the Config menu (page 53 in the K3
>> manual).
>> Vy 73 de OZ1CCM Kel
>> Kjeld Holm
>>
>>
>>
>> ______________________________________________________________
>> Elecraft mailing list
>> Home: http://mailman.qth.net/mailman/listinfo/elecraft
>> Help: http://mailman.qth.net/mmfaq.htm
>> 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]
> ______________________________________________________________
> Elecraft mailing list
> Home: http://mailman.qth.net/mailman/listinfo/elecraft
> Help: http://mailman.qth.net/mmfaq.htm
> 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]
>

Joe Subich, W4TV-4

Re: K3 RTTY spectrum

> Essentially AFSK will need to be used the same as FSK, tuning not
> mousing.

As it should be ...

> With AFSK TX = FIL OFF you can wander around the waterfall if you
> wish. Not necessarily the best idea for the reasons given by Joe.

Among other reasons for *not* using wideband transmit and mousing
around the waterfall, take a listen to some of the signals on JT65
or JT9 ... many of them have high levels of broadband noise from
their sound cards that may be only 15 or 20 dB below the tone.
That noise is also attenuated significantly by the AFSK TX filter
resulting is a much cleaner signal (and significantly less QRM).

73,

... Joe, W4TV

On 2014-06-09 10:52 AM, Mike Harris wrote:

> Not a universal truth.
>
> The AFSK TX filter is centred around your selected tone (pitch)
> frequency pair. You will have to tune each RTTY signal you wish to call
> with the VFO. Meaning you cannot leave to K3 tuned to one frequency and
> wander around the waterfall picking off stations by using for example
> the MMTTY NET function. It only takes around +/- 300Hz offset from the
> normal tone pair and your TX output has gone, evidenced by loss of RF
> output and a vanished ALC reading. The K3 knows nothing about the
> actual tone pair being passed to it other than what we tell it.
>
> Essentially AFSK will need to be used the same as FSK, tuning not mousing.
>
> With AFSK TX = FIL OFF you can wander around the waterfall if you wish.
> Not necessarily the best idea for the reasons given by Joe.
>
> If I remember correctly the NCJ article showed that at the the time of
> writing the K3 AFSK TX spectrum was cleaner than that of FSK. I believe
> it also mentioned that Elecraft was tweaking the waveform to improve the
> FSK spectrum. I no longer have the article so cannot confirm this and
> apologise if this statement is incorrect.
>
> Regards,
>
> Mike VP8NO
>
>
>
> On 09/06/2014 10:01, Joe Subich, W4TV wrote:
>>
>> On 2014-06-09 6:40 AM, Ken Chandler wrote:
>> >
>>> I think I'm right in saying, you cannot use this filter if your
>>> running AFSK and 2tone !!
>>
>> Not true! If one is running AFSK *always use AFSK A* and set
>> CONFIG:AFSK TX = FIL On.
>>
>> The AFSK TX Filter cleans up any hum on your sound card from bad
>> connections, grounding issues, or distortion from over drive. However,
>> with the K3 one can get the same narrow transmit spectrum by using FSK
>> without the issues of AFSK.
>>
>> 73,
>>
>> ... Joe, W4TV
>>
>>
>> On 2014-06-09 6:40 AM, Ken Chandler wrote:
>>> Kjeld et al
>>> I think I'm right in saying, you cannot use this filter if your
>>> running AFSK and 2tone !!
>>>
>>> Ken.. G0ORH
>>>
>>> Sent from my iPad
>>>
>>>
>>>> On 9 Jun 2014, at 11:01, "Kjeld Holm" <[hidden email]> wrote:
>>>>
>>>> For the RTTY people,
>>>> You may all know already but I did not - therefore this info.
>>>> In ARRL National Contest Journal September/October 2013 issue on page
>>>> 3 to 7
>>>> the article RTTY Spectrum Measurement is discussing bandwidth issues
>>>> and
>>>> other issues regarding transmission of RTTY. For the ones of you who
>>>> have
>>>> access to this publication: Read it. For others the conclusion is as
>>>> I read
>>>> it: Switch on the AFSK TX filter in the Config menu (page 53 in the K3
>>>> manual).
>>>> Vy 73 de OZ1CCM Kel
>>>> Kjeld Holm
>

Kjeld Holm

Re: K3 RTTY spectrum

In reply to this post by Joe Subich, W4TV-4

"The AFSK TX Filter cleans up any hum on your sound card from bad
connections, grounding issues, or distortion from over drive. However, with
the K3 one can get the same narrow transmit spectrum by using FSK without
the issues of AFSK." Written by Joe Subich, W4TV

Not as I read the article - but I may be wrong.
" Effect of the K3 AFSK Transmit Filter
Rather than hacking the K3 to transmit
through a narrow roofing filter, an equal or
better result can be had by simply enabling
the AFSK transmit filter in the configuration
menu. This places a 400 Hz filter before
transmit audio arrives at the RF modulator
(this only applies to AFSK-A mode,
not DATA-A mode). This filter is centered
around the tones configured under the
radio's PITCH menu. The effect is similar
to what MMTTY and other programs do in
their software, but this is done in the radio's
DSP firmware.
The radio's manual says this filter can
serve to filter any noise that might be on
the audio input, and it certainly will do that,
but it has the additional benefit of filtering
keying sideband energy. Figure 9 shows
the result of MMTTY's unfiltered phasecontinuous
AFSK audio into the K3 with
the K3's AFSK filter enabled. Comparing
Figure 9 with Figure 3 demonstrates the
effect of the K3's AFSK filter, as both have
exactly the same audio input to the K3.
Attempts to overdrive the radio resulted
in no significant change in signal bandwidth.
Even when transmitting wideband
noise into the K3, the AFSK filter limits the
bandwidth. While it is possible to transmit
trash that is difficult or impossible to copy,
the K3's AFSK filter makes it unlikely that
it would generate much interference on
adjacent channels."

"An important point: Even given the K3's
transmit IMD, the occupied spectrum using
shaped FSK is much narrower than
that when using the internally generated
FSK synthesizer. FSK keying sidebands
are not unique to the K3; every radio that
uses phase-coherent for its internal FSK
generator will generate a wider spectrum
at essentially any power level. The only
differences will be in cases where the IF
filter cuts off the sidebands.
As an experiment, I decided to see
just how wide I could make my signal by
overdriving the K3's line input. I cranked
the PC's headphone output to 100 percent
and drove the ALC as hard as I could by
setting the line input gain to maximum (see
Figure 7). Some strange spurs show up in
the spectrum, but even those are below the
keying sidebands of the FSK transmitter
(see Figure 2). Even trying to transmit absolute
trash I wasn't able to make the AFSK
Figure 4 - AFSK with MMTTY using a 512 tap TX BPF with a
passband of from 2000 to 2400 Hz, 0 dBm
Figure 5 - AFSK with MMTTY with 512 tap TX BPF, 100 W
signal as wide as that of the internal FSK
generator. The rise in the noise floor over
the 2.8 kHz bandwidth occurs, because the
K3 amplifies noise from somewhere; at this
gain setting it is present whether or not anything
is plugged into the K3's line in jack.
This behavior is almost certainly specific
to the K3, because the K3 scales audio in
DSP before it ever enters the RF stages.
Other radios are not going to protect you
from yourself nearly as well, so you might
expect harmonic distortion and other bad
things with no limiting prior to the point of
RF modulation."
Oz1ccm Kel

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Joe Subich, W4TV-4

Re: K3 RTTY spectrum

> Not as I read the article -

The article was written before the latest update to the K3 FSK
generating DSP code in MCU 4.66 released 2013-03-22. The article
is simply out of date.

The release notes for 4.66 say:
> FSK-D KEYING BANDWIDTH GREATLY REDUCED: This change reduces the
> amplitude of the FSK-D keying sidebands by 25-30 dB at 500 Hz
> offset, giving teh K3 one of the cleanest FSK signals available.

The author of the NCJ article reviewed the K3 firmware while it
was still in beta here: http://www.frontiernet.net/~aflowers/k3beta/
The author's own web page contains the information in the NCJ
article here: http://www.frontiernet.net/~aflowers/k3rtty/k3rtty.html
By comparing the before and after spectrogram in the K3beta article
with the "before", 2-Tone, and filtered MMTTY spectrograms on the
"AFSK Bandwidth with waveshaping" page in the original article, you
will see that the new K3 FSK code is every bit as clean as the wave-
shaped AFSK *without* the problems associated with AFSK.

Note that the author's article on the web page shows the benefits of
the K3 AFSK TX filter in terms of being able to clean up all manner
of *intentional* abuse to the AFSK audio - abuse that would render
the AFSK signals from other transceivers an absolute festival of QRM.

Here is what the author wrote of the new FSK code:

> Notice that the unshaped [original - W4TV] keying has clicks that
> will result in an S7 noise floor at 500 Hz spacing that very
> gradually flattens out to an S4 noise floor 1 KHz each side of
> transmitter, which is eventually limited (we hope!) by the IF filter
> in the transmitter. This makes it easy to see how loud signals
> placed every few kilohertz raises the noise floor of the entire band
> for everyone. The BW-reduced [new code - W4TV] signal is under S2 at
> 500Hz and drops off very rapidly into the noise as one tunes away. It
> is below the S1 noise floor of the receiver when tuned more than 700
> Hz away.

73,

... Joe, W4TV

On 2014-06-09 2:07 PM, Kjeld Holm wrote:

> "The AFSK TX Filter cleans up any hum on your sound card from bad
> connections, grounding issues, or distortion from over drive. However, with
> the K3 one can get the same narrow transmit spectrum by using FSK without
> the issues of AFSK." Written by Joe Subich, W4TV
>
> Not as I read the article - but I may be wrong.
> " Effect of the K3 AFSK Transmit Filter
> Rather than hacking the K3 to transmit
> through a narrow roofing filter, an equal or
> better result can be had by simply enabling
> the AFSK transmit filter in the configuration
> menu. This places a 400 Hz filter before
> transmit audio arrives at the RF modulator
> (this only applies to AFSK-A mode,
> not DATA-A mode). This filter is centered
> around the tones configured under the
> radio's PITCH menu. The effect is similar
> to what MMTTY and other programs do in
> their software, but this is done in the radio's
> DSP firmware.
> The radio's manual says this filter can
> serve to filter any noise that might be on
> the audio input, and it certainly will do that,
> but it has the additional benefit of filtering
> keying sideband energy. Figure 9 shows
> the result of MMTTY's unfiltered phasecontinuous
> AFSK audio into the K3 with
> the K3's AFSK filter enabled. Comparing
> Figure 9 with Figure 3 demonstrates the
> effect of the K3's AFSK filter, as both have
> exactly the same audio input to the K3.
> Attempts to overdrive the radio resulted
> in no significant change in signal bandwidth.
> Even when transmitting wideband
> noise into the K3, the AFSK filter limits the
> bandwidth. While it is possible to transmit
> trash that is difficult or impossible to copy,
> the K3's AFSK filter makes it unlikely that
> it would generate much interference on
> adjacent channels."
>
> "An important point: Even given the K3's
> transmit IMD, the occupied spectrum using
> shaped FSK is much narrower than
> that when using the internally generated
> FSK synthesizer. FSK keying sidebands
> are not unique to the K3; every radio that
> uses phase-coherent for its internal FSK
> generator will generate a wider spectrum
> at essentially any power level. The only
> differences will be in cases where the IF
> filter cuts off the sidebands.
> As an experiment, I decided to see
> just how wide I could make my signal by
> overdriving the K3's line input. I cranked
> the PC's headphone output to 100 percent
> and drove the ALC as hard as I could by
> setting the line input gain to maximum (see
> Figure 7). Some strange spurs show up in
> the spectrum, but even those are below the
> keying sidebands of the FSK transmitter
> (see Figure 2). Even trying to transmit absolute
> trash I wasn't able to make the AFSK
> Figure 4 - AFSK with MMTTY using a 512 tap TX BPF with a
> passband of from 2000 to 2400 Hz, 0 dBm
> Figure 5 - AFSK with MMTTY with 512 tap TX BPF, 100 W
> signal as wide as that of the internal FSK
> generator. The rise in the noise floor over
> the 2.8 kHz bandwidth occurs, because the
> K3 amplifies noise from somewhere; at this
> gain setting it is present whether or not anything
> is plugged into the K3's line in jack.
> This behavior is almost certainly specific
> to the K3, because the K3 scales audio in
> DSP before it ever enters the RF stages.
> Other radios are not going to protect you
> from yourself nearly as well, so you might
> expect harmonic distortion and other bad
> things with no limiting prior to the point of
> RF modulation."
> Oz1ccm Kel
>
>
>