[Elecraft] Calibration of BFO

[Tom Hammond NØSS]

Rich:

>I am having trouble setting up the center frequency of the narrow bandpass
>filters (FL3 and FL4). I have gone through the "Calibration Functions"
>section of the manual and each of the various and many guides on how to use
>"Spectrogram," however, it seems like one correction offsets the other. I am
>fairly sure how to adjust the bandpass width, but get confused on adjusting
>the position of the bandpass and the BFO.  The band pass is at the desired
>width but when I try to get it at the desired center frequency, the received
>frequency is shifted.  For example, when I try to setup a 1.00 kHz bandwith
>centered at 1.00 kHz for FL4 on USB (20 Meters) for PSK, the received signal
>shifts by more than 50 Hz. If left this way, a QSO ends up "walking" up the
>band with each exchange.

A shift in the received frequency, generally indicates that the BFO for the 
selectesd filter has been set to the opposite side of the filter center 
frequency.

To determine filter center, select a moderate-to-narrow filter bandwidth, 
then crank the BFO from one end of its tuning range to the other (0 thru 
254, or the reverse). At some point you will find that the tone of the 
background noise is at it's lowest point. THIS indicates the center of the 
filter passband. WRITE this frequency down.

Now, knowing the center of your filter passband, ensure that all of your 
LSB and CWn BFO settings are LOWER than filter center, and that all of your 
USB and CW Rev BFO settings are ABOVE filter center.

>I am trying to get the minimal change of the received frequency with the
>desired bandpass centered on the desired frequency. Could you please explain
>how to adjust: 1. The center frequency, 2. The BFO, 3. The Band-width, and
>4. Which order to adjust these.  Is there any interaction with these? Should
>I run CALL PLL between any of these adjustments?  Should the CW, USB or LSB
>be set first?

There is NO(!) significant interaction, if any at all.

Filter center should determined first. So you'll know which side of the 
filter the BFO should be placed for the selected mode.

Generally, you'll select the filter number, then the bandwidth, and then 
position the BFO to center the signal on top of the sidetone marker, or 
BETWEEN the passband markers if using SSB.

There is NO required 'order' for setting CWn CW Rev, LSB, USB... they're 
all independent of each other and do NOT interact with each other.

In general, you should not see a frequency of more than 20 Hz between 
modes, if everything is properly adjusted.

Hope this helps,

Tom Hammond   N0SS