[Elecraft] KX1 oustanding issues

[Ron D'Eau Claire]

Hi Sander:

>Audio still seems low, even with hi-fi quality earphones. =20
>I don't get any audio output till about the last 20 degrees=20
>of AF Gain rotation. For now I just keep the audio at max=20
>and even so it sounds quite soft.

The audio gain control does not "act" quite like most audio controls. =
You
might have a problem that is causing your maximum output to be low, but =
the
odd behavior of the gain control is normal. That is, the greatest change =
in
audio output comes over the last 1/4 revolution. This the opposite of =
most
audio gain controls. In this case, it is because the audio amplifier =
serves
two purposes: audio AGC amplifier and audio output amplifier. The audio =
IC
is running "wide open" at all times to drive the AGC rectifier D4. The =
audio
gain control is across the audio output to the headphones. This works =
FB,
but does not provide the nice logarithmic response we are used to in =
most
audio controls in which most of the gain change occurs at the low end of =
the
pot.=20

That said, the "soft" audio even at full gain might be connected to your =
RF
output problem.=20

Are you hearing a definite "peak" in the signal (or background noise =
level)
when you adjust the trimmer caps? If not, then something is wrong in the
input filter. (Relay K1, inductors L6, L7 and associated components). =
Double
check all solder connections. If you have a definite peak when you =
adjust
the filter it is probably FB.=20

How does the AGC act? Does it act "normal" like the text says? If so, =
then
your receiver and audio are probably normal and you have an issue with
low-sensitivity phones or earbuds.=20


>Without the ATU, I get=20

>7.100 MHz	0.3W
>10.100 MHz	4W=09
>14.100MHz	4W

>This is measured on an external power meter. =20
>Obviously there is something drastic wrong with 40m. =20
>I don't see any section in the troubleshooting about=20
>low transmit power on one band only, but I might=20
>have missed it.  Does anyone have any ideas about=20
>which parts to check for the 40m transmit path?

Low transmit power on one band only must be something happening in the
bandpass filter or relay switching. Do your external meter and the KX1 =
RF
indication agree (within a couple of tenths of a watt anyway) with the =
ATU
installed? The KX1 has a simple wattmeter, but it's a good one provided =
you
have a good dummy load attached. If they don't agree at least generally,
then something is wrong with the wattmeter!

If they do agree, then something is wrong in the low-pass filter (this =
will
produce low receive gain too - which might lead back to that "soft =
audio"
problem.=20

Is relay K2 switching? Wayne didn't include that detail in the Circuit
Description, so I don't know for certain, but the values suggest that K2
should be adding C46 and C49 to the filter on 40 (grounding the lower =
ends
of the caps) and opening them on 20. Is that happening? You could have a =
bad
relay, but first check the solder connections carefully. The most common
problem is a solder bridge or bad solder joint.=20


>Then also on the ATU, it tunes r9.9 into a dummy load. =20
>This also seems rather catastrophic, not just a toroid=20
>with windings slightly closer or wider than required.=20
>Are there any obvious things to check for?  Tuning into=20
>a long wire, it comes up with r1.0 and r1.1, but as Ron=20
>pointed out, this is just because it thinks it found a=20
>match and so may not mean much.

This issue may go away when you fix the RF output from the KX1, assuming =
the
output filter on the KX1 has a problem.=20

Ron AC7AC

Thanks all,
73's ZR6SW
Sander
KX1 #251


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