http://www.geocities.com/va3ttn/UsingOrionRX.pdf
Excellent work Sinisa! I only wish I had this 6 months
ago when I first received my Orion...I've come to similar
conclusions but this would have greatly increased my learning
curve. I hope Ten-Tec will consider adding this to Orion's
documentation, but highly recommend everyone print a copy
for their use until the manual is revised.
A few questions and observations (referenced sections):
1. Sensitivity > Adjustment. After setting Threshold slightly
above the noise level, I often find that the S/N of very weak
signals right at the noise floor can be improved by reducing
RF Gain. Is this equivalent to "fine tuning" between Threshold
steps? It seems to work that way for me. This is also a much
more intuitive way to tune for really weak signals in a contest,
assuming you have Threshold set properly for 99% of the
signals that are not near the noise floor.
2. AGC Threshold. Your comments on the ergonomics are
correct, and there may be an opportunity for Ten-Tec to improve
this in a future firmware update. I've learned to use it the way
it is, but many may not be willing to invest the effort to do this.
3. Roofing filters. I agree with your comments on the IM
degradation of the 500/250 positions. ARRL first noted this
in their Expanded Test Report which caused me to investigate
substituting an Inrad 600 Hz kit to replace the standard 1000 Hz
roofing filter.
http://dayton.akorn.net/pipermail/tentec/2004-January/041729.html
4. Roofing filters > IM Performance. I am pleasantly surprised
by the IM performance of the 250 Hz filter. Apparently this is a
combination of two factors:
a. The ~10 dB insertion loss is more closely matched by the
12 dB additional gain stage for the 500/250 positions. This is
not true for the 500 Hz filter since its ~6 dB insertion loss is being
overcompensated by ~6 dB with the 12 dB additional gain.
b. The 250 Hz bandwidth does not allow degradation at 700 Hz
spacings which we see in your 500 Hz filter IM measurements.
Do you have any thoughts or comments? I expect the 600 Hz
replacement for the 1000 Hz filter will show similar IM performance
at 700 Hz spacings to what the standard 1000 Hz now shows at
2.0 kHz spacings.
5. Roofing filters > Notes. Did you actually measure IM performance
with PREAMP ON or are you simply basing your comments on theory?
ARRL's measurements indicate IMD performance at 1 kHz spacings
of 91 dB with PREAMP ON versus 84 dB with PREAMP OFF. I have
had some private discussions with W2VJN at Inrad, and he indicates
this is not unusual for IM spacings outside the roofing filter BW.
6. DSP filters. I agree with your comments on centering DSP filters
for very weak signals using very narrow bandwidths. I sometimes use
the waterfall display in K6STI's DSP Blaster to do this, especially when
using the Coherent CW BPF in his software, which requires phase
lock tuning.
Thanks again for your excellent work and summary. This is
without a doubt one of the most useful documents any Orion user will
find anywhere!
73, Bill W4ZV
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