[Elecraft] K1 birdies

Morrow, Michael A. [email protected]
Sat Jan 4 18:59:02 2003


Tony wrote:

> There seem to be birdies just below the band edge on all
> bands and at around 075-076 on the dial (eg 7.076). I can't
> work out that match that explains why they are there - can
> anyone give me a simple example of how they get there using
> say 7 MHz as an example?

The K1 receiver frequency is set by

f-rcv =3D X-fb - X-bfo - f-vfo

where:

Freq. of Zero-beat Received Signal =3D f-rcv
Freq. of Filter Board Crystal for Band in Use =3D X-fb
Freq. of Product Detector (BFO) Crystal (X6) =3D X-bfo
Freq. of VFO =3D f-vfo

I don't know where the weak signal about 1 kHz below the band edges at =
7, 10, 14, and 21 MHz is being generated in the K1 circuit.  I assume it =
ultimately derives from the oscillator for the front panel MPU, which =
oscillates at 3999.5 kHz on my K1.  But...it's completely normal, and it =
is so weak that any other strong signal masks it, and it is OUTSIDE the =
band.

On the other hand, there is a significant and unavoidable birdie around =
21072 kHz that is the seventh harmonic of the VFO.  You can always tell =
a VFO harmonic, for it will tune away very quickly since the receiver =
frequency and the VFO harmonic frequency are each changing in opposite =
directions as you tune across the birdie.  No other harmonics of the VFO =
(which runs from 2920 to 3090 kHz on my K1), nor of the BFO (4913.1 kHz =
on my K1), nor of the sum of the VFO and BFO, nor of the difference =
between the VFO and BFO, fall in the ham bands.

I also have a spurious signal somewhere around 14095 kHz, of uncertain =
origin, but apparently not from the VFO.

I have NO other in-band birdies, such as the one you mention on 7076 =
kHz.

> Question - a - should they be there and b- can I use them
> for anything - like alignment??

It has been suggested on this list a couple of years ago that the band =
edge signal could be used as an approximate CAL signal for VFO alignment =
in the absence of anything better.  Of course, that wouldn't work for =
the 17m band (K1 coverage starts at 18050 kHz), nor for the 30m band (K1 =
coverage starts at 10100 kHz) if you chose the 80 kHz VFO span option.

The only birdie I'd really like to reduce is the one at 21072 kHz.

73,
Mike / KK5F