Elecraft P3 High-Performance Panadapter Manual - Manual (Page 21)

21
Spurious signals generated in the transceiver are
sometimes visible as well. As you tune the
transceiver you may see carriers that scroll across
the screen much faster than other signals,
sometimes tuning in the opposite direction. These
are created by high-order harmonics of the VFO,
BFO and other signal sources in the transceiver.
Normally you won't hear them in the receiver
unless one falls within the I.F. passband, but they
are easy to see on the panadapter display because of
its much wider bandwidth.
This is a shot of a local AM broadcast station,
illustrating the use of peak hold to show the shape
of the modulation spectrum, which extends to plus
and minus 10 kHz from the carrier and then drops
off abruptly to meet FCC regulations.
Normally the P3 display is frozen while the K3 is
transmitting. However if you temporarily
disconnect the RS232 cable between the P3 and K3,
that function is disabled and it is possible to view
your own transmissions for test purposes. The
signal level is rather weak as it depends on random
leakage in the K3's I.F. chain, so you may need to
experiment with
R E F L V L
on the P3 and the power
level and frequency band on the K3 to get an
adequate signal. Also, the frequency may not be
exactly centered on the display due to the effect of
crystal filter offsets in the K3.
The following image shows a typical LSB spectrum
obtained in this way. Peak hold is enabled in order
to get a better view of the spectrum shape. Notice
that the low audio frequencies (on the right) are
much stronger than the high audio frequencies. A
flatter spectrum is considered desirable to improve
the signal's "punch" in the presence of noise and
interference, especially when speech compression is
used. The P3 is a handy tool for adjusting the
transmit equalizer in the K3.
The previous image also illustrates an important
point when using markers. On SSB, the frequency
that is shown on the display of the K3 transceiver is
the suppressed carrier frequency. When you QSY
the transceiver using MKR A or MKR B on the P3,
that is the frequency the K3 will go to. So on bands
where LSB is used, you should place the marker
just above the spectrum of the SSB signal you are
trying to net (approximately in the center of the
above display) and for USB, place the marker just
below the spectrum.