[Elecraft] OT: Spectogram question

[Tim]

Hi foks -
I'm a bit confused.regarding Spectogram. I am just finishing up a DSWII-20
QRP transceiver and I want to use Spectogram to make sure the BFO frequency
tone is at 800 Hz.  This can be adjusted while monitoring with Spectogram.
The problem is that I do not really know how to set spectogram up to measure
this. When I use it for my K2 I follow Tom Hammond's notes by rote - but do
not really understand it very well.
  I set the upper freq range at 810 and the lower at 790. The rest is pretty
much the way Tom has it set for the K2. What I see is a square edged wave
that has several wide peaks. The highest peak is roughly between my
frequency markers. Periodically the wave disappears and after a bit shows up
again - something to do with sampling rate?
  When I listen to the tone on phones, the volume is quite a bit greater
than the side tone - so it is hard to match by ear. Hope this makes sense.
  In short can someone tell me how to set the parameters to accurately
adjust the tr BFO freq to 800? Thanks for any tips.
73/Tim NZ7C