Hi Gary a quick look at the circuit in the Handbook shows that the "Ext VFO"
input goes straight to the input of a cmos divider running from 12v Vdd so
you will need a signal in excess of about 9v p-p to drive it. Cmos
transitions are around the vdd/2 point, so you might try putting a pair of
highish value resistors (say 47k) to form a potential divider biassing the
divider and then apply the DDS through a cap. Dont leave it like this for
service as the divider stage will "oscillate" as it will have no noise
immumity. You really need an extra driver stage on your DDS to make it swing
+/- 12v.
Cheers de Alan G3NYK
[email protected]
----- Original Message -----
From: "G4WGT - Gary" <[email protected]>
To: "Rsgb_Lf_Group" <[email protected]>
Sent: 31 January 2004 13:46
Subject: LF: G0MRF 300 w Tx
Hi all at LF,
Can anyone advise me regarding using an external vfo on the 300 w
transmitter external vfo option. Has anyone used this feature? Connecting
to
the external vfo input pin produces no output. I have just built the
KG6CYN
DDS VFO offered by the G-QRP CLUB.
Output: Buffered 1 Vpp into 50 Ohms for 50KHz to 40 MHz - Non Buffered
Output also provided.
The original can be found at http://www.qsl.net/kg6cyn/DDS_Project.htm
Similar e-mail to David direct.
Thanks & 73
Gary - G4WGT
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