[Elecraft] TX/RX Discrepancy

Wed Jan 22 10:06:00 2003

Hi

When set to usb or lsb the transmit and receive frequency should be the same
so if you measure the reference oscillator control voltage at pin 1 of U6A
it should be the same for transmit or receive as well as the VFO control
voltage at pin 7 of U6B should not change from transmit to receive. If these
voltages are changing check the +8 volt supply (8B) and the 5 volt supply
(5B) if these voltages are stable then the problem is most likely firmware
related or a bad DAC or synthesizer chip (not likely). I would swap out the
firmware from the other radio first (just swap the control boards). I have
not actually tried the above tests on my K2 so I am not sure of the method
but I will go out and do it and let you know what I get. If the transmit and
receive frequencies are different something must be telling the VFO to
change or a power supply is changing somewhere That should be reflected in
the VFO control voltages.

Don Brown
KD5NDB

----- Original Message -----
From: "Trevor Day" <[email protected]>
To: <[email protected]>
Sent: Wednesday, January 22, 2003 7:34 AM
Subject: Re: [Elecraft] TX/RX Discrepancy

> Hi All,
> Continuing from yesterday, I have carried out Cal PLL on all bands.
> When carrying out the Rx Mode SSB Filter test from p15/16 of the KSB2
> manual, to get the LSB BFO freq of 4913.5, the BFO parameter is 160 ie.
> BF1t160L (This seems too high?)  When I try to set the USB frequency of
> 4916.30, I can only reach 4916.24 equating to a BFO parameter of 255
> (the upper limit).
>
> Looking at spectrogram, when I have Cal Fil enabled, the passband of the
> filter is centred around 800 Hz, tailing off at around 300 with a
> gradual drop off on the high side to 2500 Hz.  When I disable Cal Fil
> (revert to freq display) the passband shifts left and changes shape
> becoming almost a CW response centred on 500Hz, dropping low to 0Hz and
> high to 1kHz.  I have checked that this is the same filter (Op1)
> selected in both cases.
>
> Just to remove one variable, I have exchanged the KSB2 with my own after
> doing the checks below, but before doing the checks above, and found no
> difference. In other words, I still saw a frequency discrepancy between
> tx and rx. The KSB2s are now back with their respective units.
>
> I remain somewhat puzzled.....help!
>
> Thanks,