[Elecraft] K3 and QSK

Thu Dec 4 14:02:04 EST 2014

One of the pieces of advice for operating the K3, is to use the minimum
amount of gain in the RF/IF string. This is done by setting ATT/PRE/RF gain
so that there is only a moderate amount of band noise with no signal, then
setting audio for a comfortable level on signals with AGC engagement. This
keeps from having the radio "roar" in your ears all the time, particularly
with fast AGC.

If ATT/PRE/RF gain are always running wide open, the QSK noise is
predominately from starting RX state with this unnecessary gain level. For
example listening on my 160 transmit antenna I always run with ATT in line,
and RF gain backed off just a little.

Also, with the deliberate short transition times for CW QRQ, one must
understand that one is modulating the "channel" content with a square wave.
>From the physics, some degree of click MUST be generated if the "channel"
has loud content because the RF/IF string is operating wide open with
signal content and modulated with a on-off transition deliberately set by
the operator.

If a delay is introduced to whack off the click, you have just defeated the
desired extremely short transition of CW QRQ.

Which one do you want, modulation of channel content with extremely short
transition which allows you to hear anything between fast bauds, or a
"rounded off" transition that doesn't hear stuff at the transition edge,
but doesn't have any "sharp" sounds.

Me, I do NOT want the "rounded off" transitions, because I want to hear as
much as possible in the interbaud time, and don't care if it makes the
stuff sound "harsh". I find the harshness greatly minimized by not running
ATT/PRE/RF gain wide open all the time, and using fast AGC with CONFIG: AGC
- F  = 200.

One firmware thing that could help to some degree (if it isn't already done
this way) is to start the AGC in the new interbaud space with a value held
over from the prior interbaud space.

I definitely don't have the CW QRQ problems that others seem to be
describing.

73, Guy.

On Thu, Dec 4, 2014 at 10:00 AM, Joe Subich, W4TV <lists at subich.com> wrote:

>
>  The amplitude of this click depends on the amount of noise or signals
>> in the 'channel'. When listening to rx noise with no antenna, there's
>> no click. The worst case is a big pileup.
>>
>
> It would appear that the K3 is momentarily running at full gain when
> returning from transmit, the "click" being full gain until the AGC can
> react to signal levels 'in the channel'.   That supposition can only be
> confirmed by Lyle or Wayne but you might be able to moderate the click
> by turning off AGC and riding the RF gain.
>
> 73,
>
>    ... Joe, W4TV
>
>
>
> On 2014-12-04 9:05 AM, Vic Rosenthal wrote:
>
>> Tommy,
>>
>> I have 8 pole filters for 400, 1000 and 2800 Hz. I am almost always using
>> the 400 on CW. I use QRQ mode whenever possible. I found various sources of
>> clicks including bias switching in my amplifier, and a switched power
>> source for my Pixel Loop. I removed everything to isolate the problem. All
>> tests were done in TX TEST mode, no RF generated.
>>
>> The most bothersome K3 generated noise is a click when returning to
>> receive state. You hear it in full or semi- QSK mode when returning to
>> receive. The amplitude of this click depends on the amount of noise or
>> signals in the 'channel'. When listening to rx noise with no antenna,
>> there's no click. The worst case is a big pileup. There is also a noise
>> that is hard to describe, sort of a fuzziness around the sidetone. That
>> also depends on the amount of signal and noise in the background.
>>
>> Turning down either the audio or RF gain helps with both artifacts, but
>> makes the output lower than desirable.
>>
>> I talked to Wayne and Lyle a long time ago about possible ways to
>> ameliorate these noises and they had some ideas, but I haven't heard
>> anything recently.
>>
>> Vic 4X6GP/K2VCO
>>
>>  On Dec 4, 2014, at 3:22 PM, Chester Alderman <aldermant at windstream.net>
>>> wrote:
>>>
>>> Hi Vic,
>>>
>>> With interest, I read your emails about the K3 QSK and the noise it
>>> produced and I have a question for you. I’ve had my K3 for about three
>>> years and I purchased it with a full complement of CW filters for both
>>> receivers, including the 8-pole 250 hz filter. I normally run my radios in
>>> full QSK, but of course, depending on sending speed, running the K3 in full
>>> QSK means you lose too many other good features.
>>>
>>>
>>> I never really noticed the noise generated while in full QSK until
>>> recently, and it is quite bad! About a year ago I changed my 8-pole 250 hz
>>> filter to the 5 pole 250 hz filter and actually I think that is when I
>>> started noticing how bad the pumping and generated noise from my K3
>>> sounded. Of course I run AGC-Fast, with no preamp (unless on 10m and then
>>> only seldom have the preamp turned on).
>>>
>>>
>>> My question to you is do you have the 250 hz filter installed in the
>>> main Rx and if so, is it the 8-pole or the 5-pole? I think right after
>>> Christmas I am going to re-install my 8-pole filter just to see if that has
>>> any bearing on the awful QSK noise.
>>>
>>> Also, have you had any response from Elecraft on this issue?
>>>
>>>
>>> Thanks for any comment Vic and 73,
>>>
>>> Tom – W4BQF
>>>
>>>  ______________________________________________________________
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