[Elecraft] TX/RX Discrepancy

Wed Jan 22 11:08:00 2003

Hi

I went out to the lab and tried it on my K2. The reference control voltage
and the VFO control voltage do not change from receive to transmit on USB or
LSB when keying the transmitter. You will see a shift in CW mode because the
side tone is added in on receive. If the control voltages are changing on
your K2 then you need to track down why. The +8 volt supply is regulated on
the control board so a control board swap may help isolate a problem on the
supplies if that is what is causing the frequency shift. Note you must key
the transmitter, not use tune for this to work. Pressing tune in USB or LSB
is the same as CW and you will get a shift in voltage.

Hope some of this helps you locate your problem

Don Brown
KD5NDB

----- Original Message -----
From: "Don Brown" <[email protected]>
To: <[email protected]>; <[email protected]>
Sent: Wednesday, January 22, 2003 9:02 AM
Subject: Re: [Elecraft] TX/RX Discrepancy

> 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,