[Elecraft] Spectrum not clean.

[Don Wilhelm]

Jesus,

While the spurious output from the K2 is specified at -40 dBc or better, and
all the spurs that you report meet that specification, I do admire your goal
to keep the spectrum as clean as possible.  The specs do state that -50 dBc
is typical.

A bit of calculation on the 15 meter spur indicates that the 3rd harmonic of
the BFO may be mixing with the VFO frequency.  I would be inclined to try a
low pass filter with a cutoff frequency near 8 MHz before the BFO input to
the transmit mixer.

Your spurs only occur on bands where the VFO is lower than the output
frequency, and on those bands, the bandpass filters are more critical to the
elimination of spurs.  You should check to be certain all the components in
the BPF are correct for those bands.

As for the low power on 12 and 10 meters, the first place to look is T2.  Be
certain the turns are spaced and positioned just like the diagram in the
manual and it should be mounted 2 to 3 mm above the board.  It will self
support on its leads.

73,
Don W3FPR

> -----Original Message-----
>
> My K2 is full operative since 10-febr, today I decide to see in the
> spectrum analizer how clean is the output and check the power output in
> a calibrated power meter.
> The K2 has the ATU inside, so aditional filter in in line with the output.
> Power is 13.2W from 3.5 to 18, down to 12W at 21Mhz, 6.5 at 24Mhz and 7
> at 28.
> The spectrum has 2 spurious signals at 21 Mhz, up and down the carrier
> there are 2 signals 45 db down and spacing 1.41Mhz from carrier.
> At 24 Mhz spurius are up and down too, -43 db from carrier an spaced 312
> Khz.
> At 28 Mhz sigs are -53 db down and spaced 484Mhz.
> Spectrum in the other bands down 21Mhz was very clear.
>
> Any idea about how to eliminate or reduce this spurious signals, and get
> some more power at 24 and 28Mhz ?
>
>
> Thanks. Jesús, EA1DAV.
>
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