[Elecraft] A question about low sensitivity

[VR2BrettGraham]

W3FPR suggested:

>Since you suspect that the receiver is being de-sensed by the AGC, try
>turning the AGC off and controlling the level with the RF Gain.  If things
>seem more 'normal' that way, I suggest you try adding a filter to the AGC
>IF - see LA3ZA's mod page for 2 examples of how to do that.

As I mentioned below, both BPFs have been tightened up (DL7ARJ?)
& selectivity in AGC chain (LA3ZA) have been implemented.

Where the AGC does not seem to be choking my K2, all I need is
switch to another rig in order to copy the desired signal.  When the
AGC dominates, obviously things get better on another rig.

Disabling the AGC on the K2 - where I know the AGC is not
responding to an image - results in only the slightest change,
so presumably it's close to where it needs to be.

On the bench, MDS is somewhere below lowest output level of
my sig gen (Marconi 2017... -131 dBm) & although it's just an
indication, once set there's quite a variation in what it takes to
achieve the same S-meter reading on different bands.

Nothing untoward seen when sweeping/peaking the BPFs, yet
the rig seems somewhat deaf without the AGC image response
rearing its ugly head & that deafness varies between bands -
almost like there's some sort of suck-out downstream of the
BPFs or other difference in response that is not necessarily
proportional to frequency.

Not sure what's wrong with my K2 - perhaps this is actually
normal behavior & my expectations of its performance are
unrealistic - but one thing I can say is that I wish I had peaked
the BPFs with spec-an/tracking-gen earlier as doing so has
made a big difference over what can be achieved otherwise &
this may also be something others may want to keep in mind
(most bands picked up about a dB & more importantly, response
across some bands flattened by 3-5 dB).

But my K2 still is inferior to a TS-950S with its horrific audio
IMD & spurs across the output that is as good as torture to
listen to - those really weak long path signals at bottom of
cycle simply are below what this K2 can hear.

73 & HNY/HLNY, VR2BrettGraham

> > -----Original Message-----
> > From: elecraft-bounces at mailman.qth.net
> > [mailto:elecraft-bounces at mailman.qth.net]On Behalf Of VR2BrettGraham
> > Sent: Thursday, December 29, 2005 7:39 AM
> > To: elecraft at mailman.qth.net
> > Subject: Re: [Elecraft] A question about low sensitivity
> >
> >
> > Compared against other rigs here, my K2 (24xx) seems deaf & more
> > so on some bands.
> >
> > Much less so now after aligning the BPFs with spec-an & tracking
> > gen - but still noticeable.
> >
> > This was before narrowing BPFs so as to avoid AGC responding to
> > out-of-band energy & may still be due in part to AGC even after
> > trying LA3ZA mod (a noticeable improvement, but seems to need
> > _much_ more help than that, at least in this part of R3 with decent
> > antennas).
> >
> > It became very obvious tuning across the band after adding LA3ZA
> > mod that sensitivity varies depending on energy level at the AGC
> > image frequency.
> >
> > But this apparently is not an issue in either R1 or R2.
> >
> > 73 & HNY/HLNY, VR2BrettGraham