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K3 - AFSK anamoly? No replies, try again

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Mike Murray-4

K3 - AFSK anamoly? No replies, try again

I played a bit in the RTTY RU this weekend with my new-to-me K3 to learn the
operation and iron out any kinks in my setup. Everything worked well except
for a problem (?) on receive. I was able to easily tune in signals and
copy using MMTTY, but when I tuned to the other side of zero beat I could
easily hear the same signal. Obviously, it was inverted, but I was surprised
to even hear it at all. Is this normal or do I have something setup
incorrectly?

Mike - W0AG
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Joe Subich, W4TV-4

Re: K3 - AFSK anamoly? No replies, try again

It sounds to me as if you have selected an inappropriate roofing filter
or have improperly configured the filter offset.

What roofing filter are you using and what [DSP] bandwidth?

73,

... Joe, W4TV

On 1/6/2016 11:40 AM, Mike Murray wrote:

> I played a bit in the RTTY RU this weekend with my new-to-me K3 to learn the
> operation and iron out any kinks in my setup. Everything worked well except
> for a problem (?) on receive. I was able to easily tune in signals and
> copy using MMTTY, but when I tuned to the other side of zero beat I could
> easily hear the same signal. Obviously, it was inverted, but I was surprised
> to even hear it at all. Is this normal or do I have something setup
> incorrectly?
>
> Mike - W0AG
> ______________________________________________________________
> Elecraft mailing list
> Home: http://mailman.qth.net/mailman/listinfo/elecraft
> Help: http://mailman.qth.net/mmfaq.htm
> Post: mailto:[hidden email]
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> Message delivered to [hidden email]
>

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Nr4c

Re: K3 - AFSK anamoly? No replies, try again

In reply to this post by Mike Murray-4

I saw your original post. Im not sure I understand your question.
If you to the point where you are correctly lined up on both frequencies and getting good decode as " zero-beat", yes you can hear the tones and possibly even decide when listening to only one tone.

Sent from my iPhone
...nr4c. bill

> On Jan 6, 2016, at 11:40 AM, Mike Murray <[hidden email]> wrote:
>
> I played a bit in the RTTY RU this weekend with my new-to-me K3 to learn the
> operation and iron out any kinks in my setup. Everything worked well except
> for a problem (?) on receive. I was able to easily tune in signals and
> copy using MMTTY, but when I tuned to the other side of zero beat I could
> easily hear the same signal. Obviously, it was inverted, but I was surprised
> to even hear it at all. Is this normal or do I have something setup
> incorrectly?
>
> Mike - W0AG
> ______________________________________________________________
> Elecraft mailing list
> Home: http://mailman.qth.net/mailman/listinfo/elecraft
> Help: http://mailman.qth.net/mmfaq.htm
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Bob McGraw - K4TAX

Re: K3 - AFSK anamoly? No replies, try again

In reply to this post by Mike Murray-4

Seems strange to me. Don't or haven't noticed it with my K3S. I would
think they perform about the same in this regard.

73
Bob, K4TAX

On 1/6/2016 10:40 AM, Mike Murray wrote:

Eric Swartz - WA6HHQ

Re: K3 - AFSK anamoly? No replies, try again

Administrator

In reply to this post by Mike Murray-4

This sounds like a crystal filter offset setting is incorrect. (Also check to
make sure your IF shift setting on the front panel is not set to an extreme.)

Check the setup menu entry for each crystal filter and its offset setting. 8
pole filters should be set to a zero offset. 5 pole filters should be set equal
to the + or - number marked on the filter or the label stuck inside the radio
(typically on the top cover.)

Setup of the filters is described in the K3 manual. (I believe the assembly
manual, but it may be in the operating manual.)

73,

Eric
/elecraft.com/

On 1/6/2016 8:40 AM, Mike Murray wrote:

Mike Murray-4

Re: K3 - AFSK anamoly? No replies, try again

In reply to this post by Bob McGraw - K4TAX

Bob, Joe, Bill & Mike,

Since I'm new to RTTY, I probably didn't describe my question in correct
terminology - I mainly only operate CW. I'll try again....

I'm using DATA A/AFSK A, setup for low tones (915/170) and the RTTY dual-PB
filter. To illustrate what I'm hearing/seeing, imagine tuning down from
14.090 until you hear and can decode an RTTY signal. Then continue tuning
down 915 Hz (to what I probably erroneously referred to as zero beat) and
then down another 915 Hz, I can now hear the same signal but inverted
(slightly weaker, but definitely there). It is not decodeable, but it is
definitely there. I assumed (yeah, I know) that the opposite sideband
should be suppresed, but I think that's what I'm hearing. Any advice will
be appreciated.

Mike - W0AG

On Wed, Jan 6, 2016 at 12:28 PM, Bob McGraw K4TAX <[hidden email]>
wrote:

> Seems strange to me. Don't or haven't noticed it with my K3S. I would
> think they perform about the same in this regard.
>
> 73
> Bob, K4TAX
>
>
> On 1/6/2016 10:40 AM, Mike Murray wrote:
>
>> I played a bit in the RTTY RU this weekend with my new-to-me K3 to learn
>> the
>> operation and iron out any kinks in my setup. Everything worked well
>> except
>> for a problem (?) on receive. I was able to easily tune in signals and
>> copy using MMTTY, but when I tuned to the other side of zero beat I could
>> easily hear the same signal. Obviously, it was inverted, but I was
>> surprised
>> to even hear it at all. Is this normal or do I have something setup
>> incorrectly?
>>
>> Mike - W0AG
>> ______________________________________________________________
>> 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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Don Wilhelm-4

Re: K3 - AFSK anamoly? No replies, try again

Mike,

Is the mark tone in MMTTY set to the same frequency as you have set in
the K3?
IIRC, the default mark tone in MMTTY is 2175.

73,
Don W3FPR

On 1/6/2016 6:47 PM, Mike Murray wrote:

Lyle Johnson

Re: K3 - AFSK anamoly? No replies, try again

In reply to this post by Mike Murray-4

Mike,

It could be that the band is quiet, this is a strong signal (S7 or more)
and as you tune through to the opposite sideband the AGC is kicking up
the gain so you hear the signal down some 70 dB or so, but if it is a
strong signal on an otherwise fairly quiet band, you may hear it.

73,

Lyle KK7P

On 1/6/16 4:47 PM, Mike Murray wrote:

> Bob, Joe, Bill & Mike,
>
> Since I'm new to RTTY, I probably didn't describe my question in correct
> terminology - I mainly only operate CW. I'll try again....
>
> I'm using DATA A/AFSK A, setup for low tones (915/170) and the RTTY dual-PB
> filter. To illustrate what I'm hearing/seeing, imagine tuning down from
> 14.090 until you hear and can decode an RTTY signal. Then continue tuning
> down 915 Hz (to what I probably erroneously referred to as zero beat) and
> then down another 915 Hz, I can now hear the same signal but inverted
> (slightly weaker, but definitely there). It is not decodeable, but it is
> definitely there. I assumed (yeah, I know) that the opposite sideband
> should be suppresed, but I think that's what I'm hearing. Any advice will
> be appreciated.
>
> Mike - W0AG
>
> On Wed, Jan 6, 2016 at 12:28 PM, Bob McGraw K4TAX <[hidden email]>
> wrote:
>
>> Seems strange to me. Don't or haven't noticed it with my K3S. I would
>> think they perform about the same in this regard.
>>
>> 73
>> Bob, K4TAX
>>
>>
>> On 1/6/2016 10:40 AM, Mike Murray wrote:
>>
>>> I played a bit in the RTTY RU this weekend with my new-to-me K3 to learn
>>> the
>>> operation and iron out any kinks in my setup. Everything worked well
>>> except
>>> for a problem (?) on receive. I was able to easily tune in signals and
>>> copy using MMTTY, but when I tuned to the other side of zero beat I could
>>> easily hear the same signal. Obviously, it was inverted, but I was
>>> surprised
>>> to even hear it at all. Is this normal or do I have something setup
>>> incorrectly?
>>>
>>> Mike - W0AG
>>> ______________________________________________________________
>>> 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]
>>
> ______________________________________________________________
> Elecraft mailing list
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> Post: mailto:[hidden email]
>
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> Please help support this email list: http://www.qsl.net/donate.html
> Message delivered to [hidden email]

Don Wilhelm-4

Re: K3 - AFSK anamoly? No replies, try again

Mike,

If you do find it is AGC that is producing that 'unwanted sideband'
response, you may want to investigate your AGC slope and threshold settings.
To give you some guidance, look at my webpage www.w3fpr.com article on
"Noisy K3". I would suggest that you set those AGC parameters in CW or
SSB mode to suit your preferences.

73,
Don W3FPR

On 1/6/2016 7:43 PM, Lyle Johnson wrote:

> Mike,
>
> It could be that the band is quiet, this is a strong signal (S7 or
> more) and as you tune through to the opposite sideband the AGC is
> kicking up the gain so you hear the signal down some 70 dB or so, but
> if it is a strong signal on an otherwise fairly quiet band, you may
> hear it.
>
> 73,
>
> Lyle KK7P
>
> On 1/6/16 4:47 PM, Mike Murray wrote:
>> Bob, Joe, Bill & Mike,
>>
>> Since I'm new to RTTY, I probably didn't describe my question in correct
>> terminology - I mainly only operate CW. I'll try again....
>>

Joe Subich, W4TV-4

Re: K3 - AFSK anamoly? No replies, try again

In reply to this post by Mike Murray-4

> Since I'm new to RTTY, I probably didn't describe my question in
> correct terminology - I mainly only operate CW. I'll try again....

And I'll ask my questions again ... what *ROOFING FILTER* and what DSP
bandwidth are you using?

As Eric said in reply to your posting, this sounds like the offset is
incorrect on the roofing filter and allowing you to tune "past" zero
beat. This is particularly true if you are using the SSB filter and
a wide DSP setting instead of the more typical CW filter (500 Hz)
centered on the mark/space tones (915/1085 Hz in your case).

Note: RTTY is typically lower sideband with MARK being the lower audio
tone and space being the higher audio tone because of the "reversal"
that occurs in the audio to RF translation. In the K3 AFSK A is LSB
but DATA A is USB ... if you are using them interchangeably that may
also be causing you some confusion.

73,

... Joe, W4TV

On 1/6/2016 6:47 PM, Mike Murray wrote:

Mike Murray-4

Re: K3 - AFSK anamoly? No replies, try again

Joe, et.al.,

I finally got back to the shack to check the setup. It looks like I was
actually using a 1.8 kHz SSB roofing filter in conjunction with the 500 Hz
dual PB DSP filter. I also checked the filter offsets which were all at
0.0 (all 8 pole) and I was using AFSK A mode. Is the effect I'm seeing due
to use of the 1.8 filter or do I have more research to do?

Thanks for everyone's input and patience - seems like the learning curve is
getting worse with age.

Mike - W0AG

On Wed, Jan 6, 2016 at 6:14 PM, Joe Subich, W4TV <[hidden email]> wrote:

>
> Since I'm new to RTTY, I probably didn't describe my question in
>> correct terminology - I mainly only operate CW. I'll try again....
>>
>
> And I'll ask my questions again ... what *ROOFING FILTER* and what DSP
> bandwidth are you using?
>
> As Eric said in reply to your posting, this sounds like the offset is
> incorrect on the roofing filter and allowing you to tune "past" zero
> beat. This is particularly true if you are using the SSB filter and
> a wide DSP setting instead of the more typical CW filter (500 Hz)
> centered on the mark/space tones (915/1085 Hz in your case).
>
> Note: RTTY is typically lower sideband with MARK being the lower audio
> tone and space being the higher audio tone because of the "reversal"
> that occurs in the audio to RF translation. In the K3 AFSK A is LSB
> but DATA A is USB ... if you are using them interchangeably that may
> also be causing you some confusion.
>
> 73,
>
> ... Joe, W4TV
>
>
> On 1/6/2016 6:47 PM, Mike Murray wrote:
>
>> Bob, Joe, Bill & Mike,
>>
>> Since I'm new to RTTY, I probably didn't describe my question in correct
>> terminology - I mainly only operate CW. I'll try again....
>>
>> I'm using DATA A/AFSK A, setup for low tones (915/170) and the RTTY
>> dual-PB
>> filter. To illustrate what I'm hearing/seeing, imagine tuning down from
>> 14.090 until you hear and can decode an RTTY signal. Then continue tuning
>> down 915 Hz (to what I probably erroneously referred to as zero beat) and
>> then down another 915 Hz, I can now hear the same signal but inverted
>> (slightly weaker, but definitely there). It is not decodeable, but it is
>> definitely there. I assumed (yeah, I know) that the opposite sideband
>> should be suppresed, but I think that's what I'm hearing. Any advice will
>> be appreciated.
>>
>> Mike - W0AG
>>
>> ______________________________________________________________
> 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]
>

Don Wilhelm-4

Re: K3 - AFSK anamoly? No replies, try again

Mike,

That effect should have nothing to do with the 1.8kHz filter.

I would go with Lyle's suggestion that it is the AGC that is allowing
you to hear the opposite sideband of strong signals.

To give that suspicion a quick check, turn off the preamp and add
attenuation, then reduce the RF Gain as necessary to protect your ears.
Then turn off the AGC. Tune to a moderately strong signal such that you
can decode it well.
Now tune to the opposite sideband. Do you hear a significant drop in
the opposite sideband? If so, your AGC settings may need some work.
If not, there is a problem with the opposite sideband response in your
K3 - reload the DSP firmware, and if no help there, contact K3support.

One other thought - did you experience this with only one RTTY station?
If so, that one station may be operating with a Double Sideband signal,
and what you are hearing is the same as what would be heard by any other
station listening to that signal.

73,
Don W3FPR

On 1/7/2016 5:24 PM, Mike Murray wrote:
> Joe, et.al.,
>
> I finally got back to the shack to check the setup. It looks like I was
> actually using a 1.8 kHz SSB roofing filter in conjunction with the 500 Hz
> dual PB DSP filter. I also checked the filter offsets which were all at
> 0.0 (all 8 pole) and I was using AFSK A mode. Is the effect I'm seeing due
> to use of the 1.8 filter or do I have more research to do?
>
>

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k6dgw

Re: K3 - AFSK anamoly? No replies, try again

In reply to this post by Mike Murray-4

Maybe. The K3 offers so many ways to configure things, not all
combinations are guaranteed to be optimal. You might also try not using
the dual PB DSP, my experience has been that MMTTY and 2TONE decode a
bit better without it. I have the "stock" 2.7 KHz filter, and a 5-pole
500 Hz. I normally run RTTY contests with 300 Hz DSP, and 915 Hz MARK
AFSK-A. I find that decode accuracy starts to degrade below 300 Hz DSP BW.

73,

Fred K6DGW
- Northern California Contest Club
- CU in the Cal QSO Party 1-2 Oct 2016
- www.cqp.org

On 1/7/2016 2:24 PM, Mike Murray wrote:

> I finally got back to the shack to check the setup. It looks like I was
> actually using a 1.8 kHz SSB roofing filter in conjunction with the 500 Hz
> dual PB DSP filter. I also checked the filter offsets which were all at
> 0.0 (all 8 pole) and I was using AFSK A mode. Is the effect I'm seeing due
> to use of the 1.8 filter or do I have more research to do?

> Mike - W0AG

______________________________________________________________
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Wes (N7WS)

Re: K3 - AFSK anamoly? No replies, try again

In reply to this post by Mike Murray-4

Assuming that when the OP says "tuning" he is turning the VFO knob, then here's
my take. All of the worry about roofing filters (gad how I hate that term) is
for nothing. The crystal filters in conjunction with so-called hardware AGC are
there to protect the delicate 2nd mixer from overload in the presence of strong
signals. (Conventional wisdom says "protect the DSP" but the mixer is way weaker
than the DSP. )

Absent that condition, the demodulation BW is set in DSP and non-hardware AGC is
developed in that same bandwidth. Depending upon the strength of the desired
signal and AGC threshold and slope, some amount of AGC will be developed when
the desired signal is within the DSP BW. Hence there is some amount of gain
reduction in play. When you tune to the opposite sideband, that AGC gain
reduction goes away, raising the amplitude of the unwanted sideband with respect
to the desired signal. In other words, you cannot measure opposite sideband
rejection unless 1) the gain remains constant or 2) some amount of known
attenuation is included and accounted for in the calculation. This is pretty
much what Lyle was talking about earlier.

One more thing. If we understand that a superhetrodyne receiver is nothing more
than a narrow BPF that can be tuned over the spectrum then that "roofing filter"
that overlays the DSP filter tunes right along with it. The belief that
somehow when you tune "below zero beat" the crystal filter stays put while the
DSP passband moves is silly.

Wes N7WS

On 1/7/2016 3:24 PM, Mike Murray wrote:

> Joe, et.al.,
>
> I finally got back to the shack to check the setup. It looks like I was
> actually using a 1.8 kHz SSB roofing filter in conjunction with the 500 Hz
> dual PB DSP filter. I also checked the filter offsets which were all at
> 0.0 (all 8 pole) and I was using AFSK A mode. Is the effect I'm seeing due
> to use of the 1.8 filter or do I have more research to do?
>
> Thanks for everyone's input and patience - seems like the learning curve is
> getting worse with age.
>
> Mike - W0AG
>
> On Wed, Jan 6, 2016 at 6:14 PM, Joe Subich, W4TV<[hidden email]> wrote:
>
>> Since I'm new to RTTY, I probably didn't describe my question in
>>> correct terminology - I mainly only operate CW. I'll try again....
>>>
>> And I'll ask my questions again ... what *ROOFING FILTER* and what DSP
>> bandwidth are you using?
>>
>> As Eric said in reply to your posting, this sounds like the offset is
>> incorrect on the roofing filter and allowing you to tune "past" zero
>> beat. This is particularly true if you are using the SSB filter and
>> a wide DSP setting instead of the more typical CW filter (500 Hz)
>> centered on the mark/space tones (915/1085 Hz in your case).
>>
>> Note: RTTY is typically lower sideband with MARK being the lower audio
>> tone and space being the higher audio tone because of the "reversal"
>> that occurs in the audio to RF translation. In the K3 AFSK A is LSB
>> but DATA A is USB ... if you are using them interchangeably that may
>> also be causing you some confusion.
>>
>> 73,
>>
>> ... Joe, W4TV
>>
>>
>> On 1/6/2016 6:47 PM, Mike Murray wrote:
>>
>>> Bob, Joe, Bill & Mike,
>>>
>>> Since I'm new to RTTY, I probably didn't describe my question in correct
>>> terminology - I mainly only operate CW. I'll try again....
>>>
>>> I'm using DATA A/AFSK A, setup for low tones (915/170) and the RTTY
>>> dual-PB
>>> filter. To illustrate what I'm hearing/seeing, imagine tuning down from
>>> 14.090 until you hear and can decode an RTTY signal. Then continue tuning
>>> down 915 Hz (to what I probably erroneously referred to as zero beat) and
>>> then down another 915 Hz, I can now hear the same signal but inverted
>>> (slightly weaker, but definitely there). It is not decodeable, but it is
>>> definitely there. I assumed (yeah, I know) that the opposite sideband
>>> should be suppresed, but I think that's what I'm hearing. Any advice will
>>> be appreciated.
>>>
>>> Mike - W0AG
>>>
>>> ______________________________________________________________
>>

Mike Murray-4

Re: K3 - AFSK anamoly? No replies, try again

After doing some more testing in last weekends RTTY contest, it appears
that I made an erroneous statement as to what I was hearing and where.
What I found is that as I tune down in frequency and find a signal that
will decode, if I then tune down another 170 Hz I'll hear the inverted
signal. Still using dual passband DSP filter at 400 Hz and 400 Hz, 8 pole
roofing filter as before. I have a brief video on uTube showing the effect
at:

*http://tinyurl.com/hxykq9c <http://tinyurl.com/hxykq9c>*

Anyone have additional thoughts as to what's causing this or where I should
look next?

Mike - W0AG

On Thu, Jan 7, 2016 at 9:41 PM, Wes (N7WS) <[hidden email]> wrote:

> Assuming that when the OP says "tuning" he is turning the VFO knob, then
> here's my take. All of the worry about roofing filters (gad how I hate
> that term) is for nothing. The crystal filters in conjunction with
> so-called hardware AGC are there to protect the delicate 2nd mixer from
> overload in the presence of strong signals. (Conventional wisdom says
> "protect the DSP" but the mixer is way weaker than the DSP. )
>
> Absent that condition, the demodulation BW is set in DSP and non-hardware
> AGC is developed in that same bandwidth. Depending upon the strength of
> the desired signal and AGC threshold and slope, some amount of AGC will be
> developed when the desired signal is within the DSP BW. Hence there is
> some amount of gain reduction in play. When you tune to the opposite
> sideband, that AGC gain reduction goes away, raising the amplitude of the
> unwanted sideband with respect to the desired signal. In other words, you
> cannot measure opposite sideband rejection unless 1) the gain remains
> constant or 2) some amount of known attenuation is included and accounted
> for in the calculation. This is pretty much what Lyle was talking about
> earlier.
>
> One more thing. If we understand that a superhetrodyne receiver is
> nothing more than a narrow BPF that can be tuned over the spectrum then
> that "roofing filter" that overlays the DSP filter tunes right along with
> it. The belief that somehow when you tune "below zero beat" the crystal
> filter stays put while the DSP passband moves is silly.
>
> Wes N7WS
>
>
>
>
> On 1/7/2016 3:24 PM, Mike Murray wrote:
>
>> Joe, et.al.,
>>
>> I finally got back to the shack to check the setup. It looks like I was
>> actually using a 1.8 kHz SSB roofing filter in conjunction with the 500 Hz
>> dual PB DSP filter. I also checked the filter offsets which were all at
>> 0.0 (all 8 pole) and I was using AFSK A mode. Is the effect I'm seeing
>> due
>> to use of the 1.8 filter or do I have more research to do?
>>
>> Thanks for everyone's input and patience - seems like the learning curve
>> is
>> getting worse with age.
>>
>> Mike - W0AG
>>
>> On Wed, Jan 6, 2016 at 6:14 PM, Joe Subich, W4TV<[hidden email]>
>> wrote:
>>
>> Since I'm new to RTTY, I probably didn't describe my question in
>>>
>>>> correct terminology - I mainly only operate CW. I'll try again....
>>>>
>>>> And I'll ask my questions again ... what *ROOFING FILTER* and what DSP
>>> bandwidth are you using?
>>>
>>> As Eric said in reply to your posting, this sounds like the offset is
>>> incorrect on the roofing filter and allowing you to tune "past" zero
>>> beat. This is particularly true if you are using the SSB filter and
>>> a wide DSP setting instead of the more typical CW filter (500 Hz)
>>> centered on the mark/space tones (915/1085 Hz in your case).
>>>
>>> Note: RTTY is typically lower sideband with MARK being the lower audio
>>> tone and space being the higher audio tone because of the "reversal"
>>> that occurs in the audio to RF translation. In the K3 AFSK A is LSB
>>> but DATA A is USB ... if you are using them interchangeably that may
>>> also be causing you some confusion.
>>>
>>> 73,
>>>
>>> ... Joe, W4TV
>>>
>>>
>>> On 1/6/2016 6:47 PM, Mike Murray wrote:
>>>
>>> Bob, Joe, Bill & Mike,
>>>>
>>>> Since I'm new to RTTY, I probably didn't describe my question in correct
>>>> terminology - I mainly only operate CW. I'll try again....
>>>>
>>>> I'm using DATA A/AFSK A, setup for low tones (915/170) and the RTTY
>>>> dual-PB
>>>> filter. To illustrate what I'm hearing/seeing, imagine tuning down from
>>>> 14.090 until you hear and can decode an RTTY signal. Then continue
>>>> tuning
>>>> down 915 Hz (to what I probably erroneously referred to as zero beat)
>>>> and
>>>> then down another 915 Hz, I can now hear the same signal but inverted
>>>> (slightly weaker, but definitely there). It is not decodeable, but it
>>>> is
>>>> definitely there. I assumed (yeah, I know) that the opposite sideband
>>>> should be suppresed, but I think that's what I'm hearing. Any advice
>>>> will
>>>> be appreciated.
>>>>
>>>> Mike - W0AG
>>>>
>>>> ______________________________________________________________
>>>>
>>>
>>>
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Joe Subich, W4TV-4

Re: K3 - AFSK anamoly? No replies, try again

Are you *absolutely sure* you are using the 400 Hz IF filter? By ear,
it sounds as if you have a wider IF filter that is centered on the
carrier and allowing the image to reach the DSP.

Since your display shows FL4, is it possible that you have all your
filters reversed?

73,

... Joe, W4TV

On 2/18/2016 11:56 AM, Mike Murray wrote:

> After doing some more testing in last weekends RTTY contest, it appears
> that I made an erroneous statement as to what I was hearing and where.
> What I found is that as I tune down in frequency and find a signal that
> will decode, if I then tune down another 170 Hz I'll hear the inverted
> signal. Still using dual passband DSP filter at 400 Hz and 400 Hz, 8 pole
> roofing filter as before. I have a brief video on uTube showing the effect
> at:
>
> *http://tinyurl.com/hxykq9c <http://tinyurl.com/hxykq9c>*
>
> Anyone have additional thoughts as to what's causing this or where I should
> look next?
>
> Mike - W0AG
>
> On Thu, Jan 7, 2016 at 9:41 PM, Wes (N7WS) <[hidden email]> wrote:
>
>> Assuming that when the OP says "tuning" he is turning the VFO knob, then
>> here's my take. All of the worry about roofing filters (gad how I hate
>> that term) is for nothing. The crystal filters in conjunction with
>> so-called hardware AGC are there to protect the delicate 2nd mixer from
>> overload in the presence of strong signals. (Conventional wisdom says
>> "protect the DSP" but the mixer is way weaker than the DSP. )
>>
>> Absent that condition, the demodulation BW is set in DSP and non-hardware
>> AGC is developed in that same bandwidth. Depending upon the strength of
>> the desired signal and AGC threshold and slope, some amount of AGC will be
>> developed when the desired signal is within the DSP BW. Hence there is
>> some amount of gain reduction in play. When you tune to the opposite
>> sideband, that AGC gain reduction goes away, raising the amplitude of the
>> unwanted sideband with respect to the desired signal. In other words, you
>> cannot measure opposite sideband rejection unless 1) the gain remains
>> constant or 2) some amount of known attenuation is included and accounted
>> for in the calculation. This is pretty much what Lyle was talking about
>> earlier.
>>
>> One more thing. If we understand that a superhetrodyne receiver is
>> nothing more than a narrow BPF that can be tuned over the spectrum then
>> that "roofing filter" that overlays the DSP filter tunes right along with
>> it. The belief that somehow when you tune "below zero beat" the crystal
>> filter stays put while the DSP passband moves is silly.
>>
>> Wes N7WS
>>
>>
>>
>>
>> On 1/7/2016 3:24 PM, Mike Murray wrote:
>>
>>> Joe, et.al.,
>>>
>>> I finally got back to the shack to check the setup. It looks like I was
>>> actually using a 1.8 kHz SSB roofing filter in conjunction with the 500 Hz
>>> dual PB DSP filter. I also checked the filter offsets which were all at
>>> 0.0 (all 8 pole) and I was using AFSK A mode. Is the effect I'm seeing
>>> due
>>> to use of the 1.8 filter or do I have more research to do?
>>>
>>> Thanks for everyone's input and patience - seems like the learning curve
>>> is
>>> getting worse with age.
>>>
>>> Mike - W0AG
>>>
>>> On Wed, Jan 6, 2016 at 6:14 PM, Joe Subich, W4TV<[hidden email]>
>>> wrote:
>>>
>>> Since I'm new to RTTY, I probably didn't describe my question in
>>>>
>>>>> correct terminology - I mainly only operate CW. I'll try again....
>>>>>
>>>>> And I'll ask my questions again ... what *ROOFING FILTER* and what DSP
>>>> bandwidth are you using?
>>>>
>>>> As Eric said in reply to your posting, this sounds like the offset is
>>>> incorrect on the roofing filter and allowing you to tune "past" zero
>>>> beat. This is particularly true if you are using the SSB filter and
>>>> a wide DSP setting instead of the more typical CW filter (500 Hz)
>>>> centered on the mark/space tones (915/1085 Hz in your case).
>>>>
>>>> Note: RTTY is typically lower sideband with MARK being the lower audio
>>>> tone and space being the higher audio tone because of the "reversal"
>>>> that occurs in the audio to RF translation. In the K3 AFSK A is LSB
>>>> but DATA A is USB ... if you are using them interchangeably that may
>>>> also be causing you some confusion.
>>>>
>>>> 73,
>>>>
>>>> ... Joe, W4TV
>>>>
>>>>
>>>> On 1/6/2016 6:47 PM, Mike Murray wrote:
>>>>
>>>> Bob, Joe, Bill & Mike,
>>>>>
>>>>> Since I'm new to RTTY, I probably didn't describe my question in correct
>>>>> terminology - I mainly only operate CW. I'll try again....
>>>>>
>>>>> I'm using DATA A/AFSK A, setup for low tones (915/170) and the RTTY
>>>>> dual-PB
>>>>> filter. To illustrate what I'm hearing/seeing, imagine tuning down from
>>>>> 14.090 until you hear and can decode an RTTY signal. Then continue
>>>>> tuning
>>>>> down 915 Hz (to what I probably erroneously referred to as zero beat)
>>>>> and
>>>>> then down another 915 Hz, I can now hear the same signal but inverted
>>>>> (slightly weaker, but definitely there). It is not decodeable, but it
>>>>> is
>>>>> definitely there. I assumed (yeah, I know) that the opposite sideband
>>>>> should be suppresed, but I think that's what I'm hearing. Any advice
>>>>> will
>>>>> be appreciated.
>>>>>
>>>>> Mike - W0AG
>>>>>
>>>>> ______________________________________________________________
>>>>>
>>>>
>>>>
>> ______________________________________________________________
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> ______________________________________________________________
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Don Wilhelm-4

Re: K3 - AFSK anamoly? No replies, try again

In reply to this post by Mike Murray-4

Mike,

For strong signals the filtering may let some of the opposite sideband
get through the filters.
What is the relative S-meter reading for the true sideband and the
opposite sideband?

73,
Don W3FPR

On 2/18/2016 11:56 AM, Mike Murray wrote:
> After doing some more testing in last weekends RTTY contest, it appears
> that I made an erroneous statement as to what I was hearing and where.
> What I found is that as I tune down in frequency and find a signal that
> will decode, if I then tune down another 170 Hz I'll hear the inverted
> signal. Still using dual passband DSP filter at 400 Hz and 400 Hz, 8 pole
> roofing filter as before. I have a brief video on uTube showing the effect
> at:
>
>

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Mike Murray-4

Re: K3 - AFSK anamoly? No replies, try again

Don,

If I recall correctly, the main signal was around S9 and the image at S7 or
so.

Mike

On Thu, Feb 18, 2016 at 5:30 PM, Don Wilhelm <[hidden email]> wrote:

> Mike,
>
> For strong signals the filtering may let some of the opposite sideband get
> through the filters.
> What is the relative S-meter reading for the true sideband and the
> opposite sideband?
>
> 73,
> Don W3FPR
>
> On 2/18/2016 11:56 AM, Mike Murray wrote:
>
>> After doing some more testing in last weekends RTTY contest, it appears
>> that I made an erroneous statement as to what I was hearing and where.
>> What I found is that as I tune down in frequency and find a signal that
>> will decode, if I then tune down another 170 Hz I'll hear the inverted
>> signal. Still using dual passband DSP filter at 400 Hz and 400 Hz, 8 pole
>> roofing filter as before. I have a brief video on uTube showing the
>> effect
>> at:
>>
>>
>>
>

Richard Ferch

Re: K3 - AFSK anamoly? No replies, try again

In reply to this post by Mike Murray-4

Don, as described that was NOT the opposite sideband. On the video the
stronger signal was at 14091.883 kHz on the dial. That is the frequency
of the mark tone; the space tone would have been at 14091.713 kHz. The
pitch in use was 915 Hz mark, so the suppressed carrier frequency would
be 14092.798 kHz and the center of the filter bandpass (the notch in the
dual passband filter pattern) would be at 14091.798 kHz (1000 Hz below
the suppressed carrier).

The second slightly weaker signal in the video was at 14091.720 kHz,
i.e. the higher of its two tones was virtually coincident with the lower
of the two tones from the first signal, and the second tone would be 170
Hz lower, at 14091.650 kHz.

A true opposite sideband signal response would have been at
14093.713/14093.883 kHz, nowhere near what was observed.

This resembles audio IMD more than an opposite sideband response. For
example, a heavily overdriven audio signal with two overlapping
simultaneous tones at 915 Hz and 1085 Hz might develop spurs at 745 Hz
and/or 1255 Hz, and one of those spurs combined with one of the intended
tones in the first signal would look a lot like the second signal in the
video.

My next question would be, do you see something similar if the dual
passband filter option is turned off, or only when it is turned on? I am
wondering whether some kind of aliasing phenomenon could exist in the
dual passband filter that might account for this.

73,
Rich VE3KI

W3FPR wrote:

> For strong signals the filtering may let some of the opposite sideband
> get through the filters.
> What is the relative S-meter reading for the true sideband and the
> opposite sideband?

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Jim Brown-10

Re: K3 - AFSK anamoly? No replies, try again

In reply to this post by Mike Murray-4

On Thu,2/18/2016 6:30 PM, Mike Murray wrote:
> If I recall correctly, the main signal was around S9 and the image at S7 or so.

I agree with W4TV that there is some sort of a setup problem. Things to
check: the assignment of the roofing filters, the settings for the
roofing filters, the position of the DSP IF (Shift/Width, Lo/Hi). If you
don't figure it out, call Elecraft Support. They'll help you work
through it.

73, Jim K9YC
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