Norcal VFO

[K9ACT]

I built a NorCal VFO and it works fine but I need some help using it.

There does not seem to be any on line help so I am hoping someone here has one.

At power up, it runs and I can't seem to find out how to stop it, i.e., key it.  Perhaps there is a Start button somewhere to stop it but I can't find it.

I have been over the keying info in the manual a hundred times and it makes so sense and does not seem to apply to simply keying it with a PTT switch in spite of that term appearing in the instructions.

Any one have any experience with this thing?

js

[W1EUJ]

If the VFO was intended for the NorCal series of transceievers, I do know that keying in the  Norcal 40a is done by cutting power to the transmit mixer; the VFO runs as long as the transciever is switched on.

[Rob K2CU]

If you are talking about the FCC-1/2 combo, then I can suggest the following. The Key in signal to the FCC-1 board seems to be for telling the counter about IF shift so that it will display the correct frequency when used in a transceiver scenario. When the two boards are combined, the same signal tells the FCC-2 DDS function what frequency to output for either receive or xmit.

The VFO is does not have an on/off feature AFAK. The key out on the FCC-2 board is a pass through/driver to take an RS232 control line for external control of the transceiver that the unit is to be used with.  More a PTT function. The manual mentions tying the key in on board 1 to the key out of board 2 to let the PC interface control the operation between receive frequency generation vs xmit freqency.

However, looking at the specs on the AD9834, it might be possible to work with the FS (full scale) adjustment. According to the datasheet. the output current from the DAC is:

IOUT FULL SCALE = 18 × VREFOUT/RSET
VREFOUT = 1.20 V nominal, RSET = 6.8 kΩ typical.

That resistor is R3 and goes to ground. I have no idea if the part would tolerate this pin being open circuited or not, but perhaps it could be used by putting a key in series with it to ground. Open circuit should result in minimal output, perhaps zero. Let us know if you try messing with it and how it works.
You may want to read over the part's datasheet to see if anything is mentioned about it.  Or, send Norcal an email on the question. In either, I would isolate the resistor/AD9834 input from the outside world, ie a key jack, to keep possiblity of ESD away from the part. perhaps a transistor and fet combination with the transistor seeing the key and providing an "On" bias to the gate of the FET which grounds the resistor. Again, beware of what may happen to the part. They are a bear to install, unless you have the tools.

[Rob K2CU]

Just for information, I applied some 1 KHz audio through a .01 uF cap to the top of R3. with about 1V PP applied I got about 50% AM modulation out of the FCC2. I imagine that if the value of R3 were increased to reduce the CW amplitude, then 100% modulation would be possible. One limit is the output driver stage. The gain will have to be set so that you get full Peak to Peak output swing without clipping. BTW, the 50% 1KHz modulation was real clean.

[KF1Z]

I don't think there is an actual "off"

But, you can use the IF shift function on either TX or RX....
You can set that pretty low... maybe to zero...

Or, try to key a resistor into the output level adjustment pot on the fcc-2  ?