Vectronics VEC-1402DK - Manual (Page 16)

VEC-1402DK Instruction Manual High Performance 2 Meter Pre-Amp Kit
14
! 2. Using a hex alignment tool, adjust the coil slugs until they are even with
the top of the coil form.
! 3. While observing the signal strength indicator, slowly turn the coil slugs
into the coil until the signal becomes strongest. You may need to lower
the signal generator output accordingly to prevent signal-meter saturation
as alignment progresses.
! 4. Coil pairs L1, L2 and L3, L4 interact with each other (as L1 is adjusted,
the tuning of L2 may be affected slightly, etc.). To achieve best
sensitivity and optimum out-of-band rejection, alternately peak each pair
of coils until no further improvement is noticed.
Important note: If you have access to a Sinadder TM , or SINAD type signal-to-
noise meter, you may use it to find the optimal alignment point. Lacking a
signal-strength meter, view the receiver's audio output signal on an oscilloscope
and adjust the preamp for minimum noise-ripple on the 1-kHz sine wave. Do so
by connecting the ‘scope to the radio's speaker terminals, or to a plug installed in
the radio's phone jack.
Off-air Method:
Set up your preamp and receiver, as described above, using an antenna in place
of the signal generator.
! 1. Tune in a weak steady signal. A distant repeater signal is best--it will
transmit from a fixed location and remains "keyed up" during both sides
of the transmission. In the absence of an S-meter, the signal must have
audible background hiss in order for you to determine whether the signal
is getting stronger or weaker as you align the preamp. As a signal gets
stronger, the background noise, or “hiss,” will diminish . Take note of
signal variations caused by atmospheric conditions or passing aircraft
when attempting an alignment using off-air signals.
! 2. Carefully adjust each coil so it peaks for maximum signal strength
(highest signal-strength reading, or best quieting). Repeak each pair of
coils (pair L1, L2 and pair L3, L4) until no further improvement is
noticed. Again, a weak signal may become overly strong as the preamp
stages are brought into resonance. Find a weaker signal and continue with
the alignment.
This completes the preamp alignment.
OPERATION INSTRUCTIONS