Vectronics VEC-1292K - Manual (Page 14)

VEC-1292K Owner’s Manual Stereo Transmitter Kit
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sophisticated audio limiters to boost their average modulation level. Your
transmitter doesn't have this feature, so it's best to set the gain trimpots for
modulation that's slightly below commercial broadcast levels to prevent over-
modulation. Once a modulation level is set, adjust for channel balance. You
may find it helpful to wear stereo headphones for this particular adjustment:
#$ Listen to the signal on your FM receiver. Is the signal undistorted and clear?
#$ Look at your FM-receiver's stereo pilot--is it "locked up" to a stereo signal?
#$ Switch between mono and stereo--is there audible channel separation?
#$ Set the FM receiver's balance control to its center position.
#$ Adjust the transmitter's balance (R1) for equal volume from both channels.
If you don't have a good FM stereo monitor receiver or a well-balanced audio
source available, you may simply set the transmitter balance trimpot to its mid-
point. In most cases, this will yield satisfactory results.
If you have a specific transmitter operating frequency in mind, a FM receiver
with digital frequency readout will help you set the transmitter's oscillator
accurately (simply tune to that channel). If you merely wish to find a clear
channel, tune around for a good one that falls within the tuning range of the
transmitter's oscillator. Note that the FCC assigns FM channels for 200 kHz
spacing, starting 100 kHz above the band edge. Channel numbers progress from
88.1, 88.3, etc up to 107.9 MHz. You may find it beneficial to comply with this
standard, since some low-cost synthesized FM receivers tune in 200 kHz steps.
Begin the frequency-setting procedure by tuning your FM receiver to the desired
channel.
#$ Using an insulated tuning tool, adjust L3 until your transmitter is on
frequency.
If you have a discriminator indicator (or tuning meter) on your stereo receiver,
use this when fine-tuning L3. If this feature isn't available, set L3 for least-
distorted audio--making sure the receiver's stereo pilot illuminates. This
indicates the FM receiver is locked onto the transmitter's stereo sub-carrier.
Note that some frequency drift is normal for simple L/C tuned oscillator circuits,
so you should expect some variation in transmit frequency over time.
To adjust the transmitter's output peaking control, use your FM receiver's signal-
strength meter. If the meter deflects full scale during this operation, remove the
receiver's antenna to reduce sensitivity.
#$ Using an insulated tuning tool, set C12 for maximum meter deflection.