[K3] Filters for mixed JT65 and JT9 HF

[Frank Precissi]

On Tue, Oct 8, 2013 at 9:35 AM, Bob <[hidden email]> wrote:

>  But it isn't magic, just applied mathematics.


To most of us, that is considered magic!

Frank
KG6EYC

--
CW: NAQCC #6554 | SKCC #10435 | FISTS #16155 | SOC #1038 | FPQRP #3186
Digital: FHC #4224 | 30MDG #6370 | DMC #5698
Gear: K3 #7164 | KX3 #1787
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[Joe Subich, W4TV-4]

 > It seems to me on HF one is simply inviting in more signals which can
 > potentially de-sense the RX.  That wipes out the benefit of the weak
 > signal mode.  I really doubt these band segment is devoid of users of
 > different high power modes.

Yes and no ... there are occasional issues with a high power (or local
medium power) user.  However, when the K3 is run with AGC off there is
typically 70 to 80 dB of dynamic range between the "no signal" band
noise floor and an S9+20 dB signal.  As long as the sound card does not
clip on the loudest signal - or the loudest signal does not drive the
K3 into the hardware AGC range - there will not be a problem.

If there is a signal that drives the K3 into hardware AGC or is loud
enough to cause the sound card to clip, one can always "dial in" a
narrow IF filter unless the interfering signal is "on top of" the
desired signal.  In that regard JT65/JT9 are no different than CW or
RTTY ... use the tools your transceiver gives you.

73,

    ... Joe, W4TV


On 10/8/2013 11:54 AM, Brian Alsop wrote:

> I wonder if someone who has significant WSJT-X experience would like to
> pontificate of the real benefit of squeezing out another KHz of
> bandwidth out?
>
> It seems to me on HF one is simply inviting in more signals which can
> potentially de-sense the RX.  That wipes out the benefit of the weak
> signal mode.  I really doubt these band segment is devoid of users of
> different high power modes.
>
> Maybe WSJT-X is magic....
>
>
> 73 de Brian/K3KO
>
> On 10/8/2013 15:34, Joe Subich, W4TV wrote:
>>
>> Bob,
>>
>> On 10/8/2013 10:28 AM, Bob wrote:
>>  > Hi Joe,
>>  >
>>> I disagree with your adamant public statement as the -10 dB points
>>> even with the filter center shifted up to 2000 Hz are at 300 Hz and
>>> 3800 Hz -- That's 3500 Hz edge to edge, not 4000.
>>
>> I believe your measurements are incorrect.  Using an XG3 at -73 dBm
>> for a signal source and an audio spectrum analyzer connected to the
>> Line Out of K3 S/N 622 with an *unmodified* DPS board and original
>> transformers on the KIO3, the audio is -4 dB at 300 Hz/-15 dB at 200
>> Hz and -5dB at 4000 Hz/-14 dB a 4200 Hz.
>>
>> Put another way, the measured -6dB points are 263 - 4016 Hz (BW[6 dB]
>> = 3753 Hz) and measured -10dB points are 222 - 4142 Hz (BW [10dB] =
>> 3920 Hz).  Those numbers are close enough to 4 KHz for me to be adamant
>> that the K3 works very well in "broadband mode" with either the FM or
>> AM filters in WSJT-X.
>>
>> Moving the LF limit down to 50 Hz as in the case of SSB isn't going to
>> make a significant difference because the transformers have a good deal
>> of effect there.  Duplicating the LF measurement in SSB with LO=0.00
>> moves the -10dB point down by only 50 Hz (170 Hz).
>>
>> That the K3 is down less than 6dB at 4KHz is the key - could it be a
>> bit better, yes but at what cost?  Audio frequencies below 300 Hz have
>> little value for WSJT-X receive (they're more than -1KHz from the old
>> 1270 Hz "0 dF") and even with the roll off WSJT-X performs very well
>> at -200 Hz.  Split handles any transmit bandwidth issues in any case.
>>
>> 73,
>>
>>     ... Joe, W4TV
>>
>>
>> On 10/8/2013 10:28 AM, Bob wrote:
>>> Hi Joe,
>>>
>>> I disagree with your adamant public statement as the -10 dB points even
>>> with the filter center shifted up to 2000 Hz are at 300 Hz and 3800
>>> Hz --
>>> That's 3500 Hz edge to edge, not 4000.  This has also been confirmed by
>>> Lyle himself, who agrees that widening the bandwidth 400-600 HZ would
>>> be a
>>> good thing to do.
>>>
>>> I've also confirmed this with two other K3 owners.  If your DSP
>>> response is
>>> wider then consider yourself lucky because others don't experience the
>>> same
>>> thing.
>>>
>>> 73, Bob, WB4SON
>>>
>>>
>>> On Mon, Oct 7, 2013 at 4:51 PM, Joe Subich, W4TV <[hidden email]>
>>> wrote:
>>>
>>>>
>>>> On 10/7/2013 4:39 PM, Bob wrote:
>>>>
>>>>> Just be aware that current DSP firmware in the K3 limits the receive
>>>>> bandwidth to something around 3400 Hz. So even if you have a wider
>>>>> filter, like the 6 KHz AM filter, you will not be able to utilize the
>>>>> full 4 KHz bandwidth of WSJT-X for JT65/MT9 modes.
>>>>>
>>>>
>>>> Absolutely *not* true ... I regularly receive 200 to 2400 Hz in DATA A
>>>> with the FM (or AM) filter.  It is simply a matter of adjusting the
>>>> High and Low cut frequencies to 200/4200 or shift/Width to 2200/4000.
>>>>
>>>> I have been doing that ever since K1JT offered me a pre-release look
>>>> at the "wideband" decoding support in WSJT-X with no issues other than
>>>> some CAT problems with the interface to CI-V Commander from DXLab
>>>> Suite which K1JT and AA6YQ resolved quite quickly.
>>>>
>>>> 73,
>>>>
>>>>     ... Joe, W4TV
>>>>
>>>>
>>>>
>>>> On 10/7/2013 4:39 PM, Bob wrote:
>>>>
>>>>> Just be aware that current DSP firmware in the K3 limits the receive
>>>>> bandwidth to something around 3400 Hz.  So even if you have a wider
>>>>> filter,
>>>>> like the 6 KHz AM filter, you will not be able to utilize the full 4
>>>>> KHz
>>>>> bandwidth of WSJT-X for JT65/MT9 modes.
>>>>>
>>>>> Lyle is aware of this issue and it is on his list to work on in the
>>>>> future.
>>>>>
>>>>> And even if you are in Split mode, rest assured that you know exactly
>>>>> where
>>>>> you are transmitting -- on the exact audio offset indicated on the
>>>>> display.
>>>>>    Operating Split is the way to go.  The only drawback I've seen is
>>>>> that
>>>>> WSJT-X does nothing to make sure the K3 is in the Split mode, it just
>>>>> assumes it is.
>>>>>
>>>>> 73, Bob, WB4SON
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>>>
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