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Poor Low audio frequency response on JT65 mode with my K3 ?

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Clifford Hynds

Poor Low audio frequency response on JT65 mode with my K3 ?

Hope someone has an answer,

I am a recent owner of the K3 having just bought a K3, P3 and KPA500
station from another ham.

Probably you would have to be a regular user of the JT65 mode to notice but
I seem to get little or no output when I am below about -500hz or so on the
waterfall on JT65HFand nothing really at -1000Hz, fine from there up.

Probably affect other data modes also ?

I am using line in/out on the K3 and DATA mode so no equalisation,

Had no problems with other rigs FT847,FT817 and TS950SDX had no problems
with the low end.

Could be as simple as increasing the input capacitor for the line audio or
as the audio is controlled by the DSP perhaps an upgraded DSP unit. The K3
is in the < 1000 Serial numbers 718 if i remember not in front of it at the
moment.

Hope someone has an answer,
thanks
Cliff VK2CCJ
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Lyle Johnson

Re: Poor Low audio frequency response on JT65 mode with my K3 ?

If you are referring to receiver bandwidth, then you can adjust the
SHIFT and WIDTH controls to adjust the audio passband response.

73,

Lyle KK7P

> I am a recent owner of the K3 having just bought a K3, P3 and KPA500
> station from another ham.
>
> Probably you would have to be a regular user of the JT65 mode to notice but
> I seem to get little or no output when I am below about -500hz or so on the
> waterfall on JT65HFand nothing really at -1000Hz, fine from there up...

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Jim Brown-10

Re: Poor Low audio frequency response on JT65 mode with my K3 ?

In reply to this post by Clifford Hynds

On 11/13/2012 4:04 PM, Clifford Hynds wrote:
> I am using line in/out on the K3 and DATA mode so no equalisation,

It isn't clear whether your problem is on TX or RX, so I'll respond to
both. For RX, check the bandwidth settings of your K3 (front panel, can
be used as width and shift or as high pass and low pass). That will
affect the RX bandwidth.

For TX, the K3 DSP is programmed so that there's a high pass filter at
about 200 Hz in all digital modes. This in firmware, and cannot be
changed.

Another possible cause if your problem is TX is that you might be
transmitting through a filter that's too narrow. You should be
transmitting through either the 2.7 kHz of 2.8 kHz roofing filter.

Yet another possible cause of a TX problem is a relatively small value
capacitor in series with the audio drive feeding the Line Input.
Elecraft misguidedly chose to make their input and output impedances 600
ohms, thinking that was the "pro" standard, which has not been true for
nearly 50 years. A small value cap in series would cause a low
frequency rolloff. Pro audio inputs are typically 5kOhms or so, and pro
outputs are typically about 100 ohms.

And yet another possible cause of low frequency rolloff is an open
shield connection on the audio cable. Note also that the K3 audio
inputs are unbalanced, even though they use transformers. So, for a
3-circuit TRS plug, the tip is hot, the ring is hot for the other
channel, and the sleeve is common. The line input has hot on tip, no
connection on the ring, and common (shield) on the sleeve.

Hope this helps,

73, Jim K9YC
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Don Wilhelm-4

Re: Poor Low audio frequency response on JT65 mode with my K3 ?

In reply to this post by Clifford Hynds

Cliff,

The K3 defaults to a 400 Hz bandwidth when selecting DATA A mode. unless
you have previously set some other width.

I am not sure about the negative bandwidth values you have indicated,
but I am going to assume that those are just "dashes" and not negative
signs.

I suggest you look at the width and shift (or HiCut and LoCut) to obtain
the filter bandwidth that you desire for digital modes.

When working with a waterfall display, you may want a wide bandwidth,
but if you are tuning for a single signal with the K3 VFO knob, you will
want a more narrow bandwidth.

73,
Don W3FPR

On 11/13/2012 7:04 PM, Clifford Hynds wrote:

> Hope someone has an answer,
>
> I am a recent owner of the K3 having just bought a K3, P3 and KPA500
> station from another ham.
>
> Probably you would have to be a regular user of the JT65 mode to notice but
> I seem to get little or no output when I am below about -500hz or so on the
> waterfall on JT65HFand nothing really at -1000Hz, fine from there up.
>
> Probably affect other data modes also ?
>
> I am using line in/out on the K3 and DATA mode so no equalisation,
>
> Had no problems with other rigs FT847,FT817 and TS950SDX had no problems
> with the low end.
>
> Could be as simple as increasing the input capacitor for the line audio or
> as the audio is controlled by the DSP perhaps an upgraded DSP unit. The K3
> is in the < 1000 Serial numbers 718 if i remember not in front of it at the
> moment.
>
> Hope someone has an answer,
> thanks
> Cliff VK2CCJ
> ______________________________________________________________
> 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
>

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Iain MacDonnell - N6ML-2

Re: Poor Low audio frequency response on JT65 mode with my K3 ?

Don,

JT65 spots include an offset from the center of the (2kHz) audio
passband, which is nominally centered at 1270.46Hz, so a "DF" of -500
would be at audio frequency ~770Hz, and DF-1000 would be ~270Hz.

I have a software macro for setting up for JT65, which includes
"MD6;DT0;BW0200;IS 1270;"

To give genuine JT65 signal reports, you want the full 2kHz of audio,
as the signal report is dB value relative to the "noise figure" across
that 2kHz.

73,

~iain / N6ML

On Tue, Nov 13, 2012 at 9:47 PM, Don Wilhelm <[hidden email]> wrote:

> Cliff,
>
> The K3 defaults to a 400 Hz bandwidth when selecting DATA A mode. unless
> you have previously set some other width.
>
> I am not sure about the negative bandwidth values you have indicated,
> but I am going to assume that those are just "dashes" and not negative
> signs.
>
> I suggest you look at the width and shift (or HiCut and LoCut) to obtain
> the filter bandwidth that you desire for digital modes.
>
> When working with a waterfall display, you may want a wide bandwidth,
> but if you are tuning for a single signal with the K3 VFO knob, you will
> want a more narrow bandwidth.
>
> 73,
> Don W3FPR
>
> On 11/13/2012 7:04 PM, Clifford Hynds wrote:
>> Hope someone has an answer,
>>
>> I am a recent owner of the K3 having just bought a K3, P3 and KPA500
>> station from another ham.
>>
>> Probably you would have to be a regular user of the JT65 mode to notice but
>> I seem to get little or no output when I am below about -500hz or so on the
>> waterfall on JT65HFand nothing really at -1000Hz, fine from there up.
>>
>> Probably affect other data modes also ?
>>
>> I am using line in/out on the K3 and DATA mode so no equalisation,
>>
>> Had no problems with other rigs FT847,FT817 and TS950SDX had no problems
>> with the low end.
>>
>> Could be as simple as increasing the input capacitor for the line audio or
>> as the audio is controlled by the DSP perhaps an upgraded DSP unit. The K3
>> is in the < 1000 Serial numbers 718 if i remember not in front of it at the
>> moment.
>>
>> Hope someone has an answer,
>> thanks
>> Cliff VK2CCJ
>> ______________________________________________________________
>> 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
>>
>
> ______________________________________________________________
> Elecraft mailing list
> Home: http://mailman.qth.net/mailman/listinfo/elecraft
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> Post: mailto:[hidden email]
>
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Joe Subich, W4TV-4

Re: Poor Low audio frequency response on JT65 mode with my K3 ?

Iain,

> To give genuine JT65 signal reports, you want the full 2kHz of audio,
> as the signal report is dB value relative to the "noise figure" across
> that 2kHz.

JT65 "signal reports" are dB relative to the total noise in a 2.5 KHz
bandwidth (see Joe Taylor's web site).

> I have a software macro for setting up for JT65, which includes
> "MD6;DT0;BW0200;IS 1270;"

That's a bit narrow ... the DF is relative to 1270 and represents the
sync bit (the lowest tone) and the JT65A signal is just under 200 Hz
wide. You really need BW0240; to pass the highest possible signal
(DF=1000) with JT65-HF by W6CQZ and WSJT9 by Joe Taylor decodes a full
3 KHz (-1200 to +2800 Hz) which means "IS 01500;BW0300;" is not
unreasonable.

Still, the original report has some validity ... if I transmit with
DF, <-800 it takes more audio drive (increase line in or sound card
TX level) to maintain proper ALC level. It's not a lot ... from Line
In = 10 at DF=0 to Line In = 20 at DF= -1000. The bigger problem is
that the gain is very sloped across the 200 Hz when operating at
DF below -850 and the power output will vary almost 3 dB between the
lowest and highest tone in the JT65 constellation. For that reason
I do not like to use a DF less than 800 (lowest tone about 470 Hz).

It does seem that the K3's low frequency roll off is a bit severe in
DATA A. It may be roofing filter related. Although I'm using a 2.8,
if the center is at 1500 Hz the -6dB shoulder would be around 100 Hz
which would explain the 3 dB slope below 400 Hz +/-. The roll off
might be even more pronounced with the 2700 Hz (5 pole) filters
since they are less flat than the 2800 (8 pole) filters).

It might be nice if there were an option to move the roofing filter
center to 1300 Hz for transmit in DATA A.

73,

... Joe, W4TV

On 11/14/2012 1:49 AM, iain macdonnell - N6ML wrote:

> Don,
>
> JT65 spots include an offset from the center of the (2kHz) audio
> passband, which is nominally centered at 1270.46Hz, so a "DF" of -500
> would be at audio frequency ~770Hz, and DF-1000 would be ~270Hz.
>
> I have a software macro for setting up for JT65, which includes
> "MD6;DT0;BW0200;IS 1270;"
>
> To give genuine JT65 signal reports, you want the full 2kHz of audio,
> as the signal report is dB value relative to the "noise figure" across
> that 2kHz.
>
> 73,
>
> ~iain / N6ML
>
>
>
> On Tue, Nov 13, 2012 at 9:47 PM, Don Wilhelm <[hidden email]> wrote:
>> Cliff,
>>
>> The K3 defaults to a 400 Hz bandwidth when selecting DATA A mode. unless
>> you have previously set some other width.
>>
>> I am not sure about the negative bandwidth values you have indicated,
>> but I am going to assume that those are just "dashes" and not negative
>> signs.
>>
>> I suggest you look at the width and shift (or HiCut and LoCut) to obtain
>> the filter bandwidth that you desire for digital modes.
>>
>> When working with a waterfall display, you may want a wide bandwidth,
>> but if you are tuning for a single signal with the K3 VFO knob, you will
>> want a more narrow bandwidth.
>>
>> 73,
>> Don W3FPR
>>
>> On 11/13/2012 7:04 PM, Clifford Hynds wrote:
>>> Hope someone has an answer,
>>>
>>> I am a recent owner of the K3 having just bought a K3, P3 and KPA500
>>> station from another ham.
>>>
>>> Probably you would have to be a regular user of the JT65 mode to notice but
>>> I seem to get little or no output when I am below about -500hz or so on the
>>> waterfall on JT65HFand nothing really at -1000Hz, fine from there up.
>>>
>>> Probably affect other data modes also ?
>>>
>>> I am using line in/out on the K3 and DATA mode so no equalisation,
>>>
>>> Had no problems with other rigs FT847,FT817 and TS950SDX had no problems
>>> with the low end.
>>>
>>> Could be as simple as increasing the input capacitor for the line audio or
>>> as the audio is controlled by the DSP perhaps an upgraded DSP unit. The K3
>>> is in the < 1000 Serial numbers 718 if i remember not in front of it at the
>>> moment.
>>>
>>> Hope someone has an answer,
>>> thanks
>>> Cliff VK2CCJ
>>> ______________________________________________________________
>>> 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
>>>
>>
>> ______________________________________________________________
>> 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
> ______________________________________________________________
> 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
>

W7GJ, Lance

Re: Poor Low audio frequency response on JT65 mode with my K3 ?

In reply to this post by Clifford Hynds

Hi Cliff,

I assume you have been using the DATA mode, which has less receive bandwidth for some
reason (I think it is because of the Firmware). That is why I still always use the
USB position for JT65. With USB it is possible to have a much broader receive
bandwidth.

I also lways use compression to make sure that all the tones of different frequency
provide the same output. The only downside to using USB position for JT65 is that
you can't use anything other than a flat audio transmit spectrum, so I have made no
custom TX adjustments for my microphone.

I understand that not all digital modes operate the same way, so the above settings
might not provide the best performance for modes like PSK31. But since JT65 can be
operated in class C, it is pretty forgiving. GL and VY 73, Lance

On 11/14/2012 12:04 AM, Clifford Hynds wrote:

--
Lance Collister, W7GJ
(ex WA3GPL, WA1JXN, WA1JXN/C6A, ZF2OC/ZF8, E51SIX, 3D2LR, 5W0GJ, E6M)
P.O. Box 73
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