Re: [TenTec] INRAD Orion roofing filters?

[Bill Tippett <btippett@alum.mit.edu>]

KE5C wrote:
has anyone stuck a 2100 Hz and a 400 Hz
INRAD in an Orion instead of the TT's?

        I'm using the Inrad 400 Hz.  I chose it because it has a slightly
narrower bandwidth (455 Hz vs 500+ Hz) and was on sale at the time.
It works fine but is specified for slightly more insertion loss than
the TenTec 217 (9 dB vs. 7.5 dB).

        The main thing to remember with all roofing filters is that in the
Automatic mode, they will not be switched in until about 75% of the
nominal Ten-Tec filter bandwidth.  This means they will switch in at the
following points, independent of the actual filter bandwidth:

Filter position Switchpoint
"1800"          1400-1410
"500"           370-380
"250"           190-200

There is slight hysteresis in the switch points, so the roofing filter
is switched from 2400 to 1800 as you narrow the DSP setting to 1400 Hz
from higher values, and it switches to 2400 when you widen the DSP to 1410 
Hz from lower values.

        Regarding the 2100 Hz Inrad, it is actually 2200 Hz, so I doubt you
would notice much difference with the standard 2400 Hz filter.  If you
do put it into the "1800" position, just remember it will not switch in
"Auto" mode until ~1400 Hz as noted above.  When I used my TT218 (which
is actually 1900+ Hz) in the CQWW SSB, I simply locked the filter in
the "1800" position for the contest.  By adjusting PBT to +150 and RX
EQ to -10, I could copy quite well with DSP BW set anywhere from 2000
to 1600 Hz.  I normally left DSP at 2000 and adjusted it down only if 
necessary.

        As I mentioned before, I was amazed how easy it was to copy weak
signals with Orion in the CQWW , which I attribute to both excellent
IMD performance (reduces passband noise due to distortion products) and
the Digital AGC (which helps with signal QSB at the noise floor).

                                                73,  Bill  W4ZV 

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