[Elecraft] How to outfit a K3 for JT65HF or JT9

[Joe Subich, W4TV]

On 4/21/2014 8:51 PM, Sam Morgan wrote:
 > don't forget the K3's tunable Notch, I have found it works quite well
 > to attenuate those offending S9 +30 signals.

The Manual notch is outside the AGC loop - it can not protect the AGC
system from pumping and as such only serves to protect the sound card
from overload.  It does not prevent blocking of the AGC.

73,

    ... Joe, W4TV


On 4/21/2014 8:51 PM, Sam Morgan wrote:
> don't forget the K3's tunable Notch, I have found it works quite well to
> attenuate those offending S9 +30 signals. The width is just shy of a
> JT65 signal, but if you make sure to cover the low end it works. You can
> watch it working in the waterfall. I always run with the K3's AGC
> off...ymmv
> sm
>
> On 4/21/2014 7:39 PM, Don Wilhelm wrote:
>> The situation on HF is different.  If there is a station within the
>> passband at S-9+30, it is on the borderline for activating the Hardware
>> AGC.  That signal should be moved outside the roofing filter passband to
>> reduce its response in the K3 first IF (and DAC input).
>>
>> Signals with strength less that S-9+30 can be easily handled by the DSP
>> in the K3 and likely also by the K3 DSP of the JT65HF algorithms without
>> overload.
>>
>> The situation being addressed is the case where there is a strong
>> undesired signal that will activate the hardware AGC and cause 'pumping'
>> in the receiver response.  That is where the roofing filters come into
>> play (and consideration for their phase shift). The narrow filters will
>> have greater group delay and greater phase shift - that is just a 'fact
>> of life'.
>>
>> If there are no S-9+30 signals in the receiver passband, the combination
>> of the K3 DSP and application DSP can handle it quite nicely.
>>
>> In other words, for best JT65HF, keep your filters wide so the JT65
>> software can do its job.  If you find an extremely strong signal inside
>> the K3 IF passband, narrowing the filter width may help, it all depends
>> on the filters you have installed and the frequency difference between
>> the offending strong signal and your desired station.
>>
>> Bottom line - when operating JTx modes (or other digital modes) learn to
>> recognize those conditions where the K3 Hardware AGC is being
>> activated.  If Hardware AGC is not an issue, the DSP in either the K3 or
>> the JTx software/firmware should be able to handle it.
>