Wavecom W61PC V7.5.0 - Manual (Page 70)

60  First start WAVECOM Decoder W61PC/LAN Manual V7.5
Average Factor
After choosing an Average Factor from the context menu, the average of up to 64 measurements may
be displayed at each step. A value of "1" turns averaging off. The averaged display of several measure-
ments is very helpful when monitoring MFSK and FDM transmissions or during heavy fading. The averag-
ing function may also be selected by double-clicking the Avg: field in the upper status bar.
Window Type…
Four window functions Rectangle, Hamming, Hanning and Blackman may be selected. The selection of
a window type influences the accuracy of the signal spectrum measurement. Good frequency resolution is
obtained using the rectangular window, however the rectangular window also causes heavy distortion due
to its poor side-lobe suppression characteristics. A window should be chosen according to the user’s re-
quirements; each window type has its own characteristics as listed below.
The user should be aware that changes in the received signal can cause the display of spurious spectral
lines or aliasing ("false" frequency display) in FFT measurements. Depending on the keying frequency and
the magnitude of the frequency shift, the aliased frequencies may even be stronger than the desired sig-
nal.
Window Type Signal Type Frequency Resolution Spectral Leakage Amplitude Accuracy
Blackman Random Poor Best Poor
Hamming Random Good Fair Fair
Hanning Random Good Good Fair
Rectangular Transient Best Poor Poor
Period...
From the Period menu the time unit per measurement may be selected. The lowest value is 50 ms corre-
sponding to 20 FFT’s/s. For the highest value of 10,000 ms a measurement is done once every 10 sec-
onds.
Peak Hold…
For easy tuning, switch on Peak Hold in the Options menu on. The tone spectrum appears in the FFT
window after a short delay and the frequency range can be changed as required using the cursors as
shown below.
If you select max Decay, then a decay value can be set. This allows to use the peak hold functions during
thunderstorms or if tuning the receiver.