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

[Sam Morgan]

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.

-- 
GB & 73
K5OAI
Sam Morgan