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The 20m version of the NC2030 mixes the 3 MHz PTO with the 11.059 MHz VXO output. 11.059 +
3.0 = 14.059 MHz. The VXO provides a small tuning range which is used to provide transmit-receive
offset. Half of an 8:1 analog multiplexer is used to select the offset voltage that gets routed to the VXO
varactor diodes, which are a pair of inexpensive 1N4007s diodes.
The analog multiplier, a 4051, selects between two different voltage sources, one an on board trimmer
pot that is used to set the 600 Hz transmit offset, and the other, a front panel pot, used to set the RIT
receive frequency. These two voltage sources are selected based upon the state of both the transmit state
(signal TX_D2+) and the spot switch.
The use of the spot switch sets the receiver to the transmit frequency, which is nominally 600 Hz lower
than the frequency the receiver uses. This allows the user to tune the transmitter to the exact same
frequency as another station simply by turning on the spot switch and tuning the other station to zero
beat. When the spot switch is turned off, the user will be right on the transmit frequency. At that point,
the RIT can be used to adjust the pitch of the received signal.
It should be noted that for the 30m version, a 13.0 MHz crystal is used, and the PTO is lowered to 2.9
MHz. 13.0 – 2.9 = 10.1 MHz.
Norcal NC2030 v5
12-18-05
Page 119 of 128
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