Vectronics VEC-1402K - Manual (Page 14)

VEC-1402K Instruction Manual 2 Meter Pre-Amp Kit
12
Now that your inspection is completed, you're ready to begin the testing and
alignment phase of construction.
TESTING AND ALIGNMENT
The best way to align a preamp is with a calibrated signal
generator. However, it is also possible to align the VEC-1402K using off-air
signals. Alignment is easiest using a receiver that features a built-in signal-
strength meter (an analog meter is generally better than a digital one for
observing small changes in signal strength). If your receiver has no meter, you
may still conduct the test by listening to signals in the speaker—or by viewing
the audio waveform using an oscilloscope. The preamp must be powered from a
9-15 volt DC source during alignment.
Generator Method:
Begin by connecting the output side of your preamp to a FM receiver equipped
with a bar-graph or analog type S-meter. Connect the input side to your signal
generator's output jack. Adjust the generator as follows:
•
Frequency..........................146 MHz (mid-band)
•
Output Level .....................Start at -90 to -100 dBm (weak signal)
•
Modulation........................FM, 1 KHz tone at 3-5 KHz deviation
Power up the preamp, and adjust as follows:
! 1. Tune in the generator signal and adjust the generator output level for a ½
scale reading on the receiver S-meter. Do not exceed -20 dBm or overload
will result.
! 2. Using a hex alignment tool, adjust the slug in coil L1 until it is even with
the top of the coil form.
! 3. While observing the signal strength indicator, slowly turn the slug into the
coil until the point where the signal becomes strongest. This is typically 5
to 6 turns clockwise for 146 MHz.
Important Note: If you have access to a Sinadder TM , or SINAD type signal-to-
noise meter, you may use this in place of the receiver's S-meter to find the
optimal alignment point. Alternatively, if your receiver has no S-meter, you may
view the receiver's audio output signal on an oscilloscope and adjust the preamp
for minimum noise-ripple on the 1-khz sine wave.