565 manual
September 2003
Part #74279
Printed in USA
6
included only because AM and FM operation
would require them, and because some
operators with an interest in “hi-fidelity” SSB
audio will require receiver bandwidths higher
than the typical 2.4 kHz communications
grade roofing bandwidth would allow.
Certainly the use of either a 20 kHz or 6 kHz
wide roofing filter has the potential to allow
overall receiver performance (dynamic
range and third-order intercept point) to be
seriously compromised by loud closeby
signals. For serious receiver use, like weak
signal DXing and contesting, a much smaller
roofing bandwidth than 20 or 6 kHz is
necessary. In ORION for SSB use, it can be
as little as 1.8 kHz for roofing. For CW, it
can be as little as 250 Hz, depending on the
installation of optional filters.
For some recommended real-world
examples of how roofing filters affect overall
receiver performance, please look at recent
ARRL Product Reviews from QST magazine
where dynamic range and third-order
intercept are measured at 20 kHz and 5 kHz
signal spacings. For our competitors’
transceivers, the 5 kHz spacing numbers are
always significantly worse than the 20 kHz
spacing numbers – this is because of the
presence of test signals under a 15 to 20
kHz wide roofing filter vs. outside the filter.
