Receiver Alignment Section; Lo Filter Tune Up; Figure 121. With Pto Screw Fully Inserted, Adjust Tuning Knob To Have A Small Amount Of Front Panel; Figure 122. Location Of Lo Trim Caps C58, C60 And Tp3 In The Upper Left Corner Of The Board - NORCAL NC2030 Manual

Figure 121. With PTO screw fully inserted, adjust tuning knob to have a small amount of front panel clearance.

Receiver alignment section

LO Filter tune up

Figure 122. Location of LO trim caps C58, C60 and TP3 in the upper left corner of the board

This has already been done one using the soda straw version of the L13 PTO coil. We will repeat that
previous step now using the final PTO coil.
The goal is to get a voltage between 1 and 1.5v DC across the entire band at TP3 after we have the PTO
set to the final frequency. That has not been done yet, so the peaking being done here is simply to
provide a signal to the internal AFA frequency counter so that we can start moving the PTO to its final
frequency.
The LO filter section is composed of two tuned circuits, one tuned by C58 and the other tuned by C60.
The voltage is measured at TP3 using a normal voltmeter on a low voltage range such as a 2 or 3v scale.
Although variable capacitors C58 and C60 can be turned over a 360 degree range, the actual tuning
range is done over a 180 range. Turning these capacitors over a 360 degree range simply makes the
variable capacitors pass through their tuning range twice.
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What will be done here is to move C58 a fraction of a turn (roughly 1/10 ), then sweep C60 through its
tuning ranging looking for a peak, then go back to C58 and turn another fraction and try again. Once a
peak is found, adjust both C58 and C60 for the best peak. C60 is the more critical setting of the two
caps, so be sure to do tuning sweeps with C60 and incremental changes in C58.
Norcal NC2030 v5 12-18-05
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