Hi George!
W5YR wrote:
Doubtlessly, the roofing filters improve the ORION performance - the coming
ARRL Labs tests will quantify this. But owners of the RX-340, Pegasus and
Jupiter and now the Argo, all with IF-DSP architecture and no narrow roofing
filters seem to do quite well in their applications. But, I gather that the
ORION is aimed at a much more difficult set of operating conditions and is
designed accordingly.
Your last sentence is key. In everyday use, most of us will never
notice the difference between Orion and anything else, unless we
happened to have a very close neighbor. The signal strengths Orion is
designed to handle are very strong indeed, the type you see when you are
parked close to W8JI or W3LPL on 160 meters...or RW2F or RU1A on 10
meters when it is wide open to Europe. It's not unusual for these
stations to be 40-50 dB over S9 at my location with my antennas.
An S9+40 dB signal is typically around -30 dBm. ARRL's IMDDR3
and IP3 tests are specified for interfering signals at -17 dBm, which
equates to S9+53 dB. Orion's IP3 measurements are specified for
interfering signals at 0 dBm or S9+70 dB!
Unless a person is using very high gain antennas (i.e. stacked
Yagis) or has a very close neighbor, or is operating in a multi-
transmitter environment, it is very unlikely that they would ever
encounter signal strengths at the levels that cause IMD problems.
My 10 meter stack has ~22 dBi of gain at the optimum takeoff
angle. The strongest stations I recall when 10 meters was wide open
were in the 45-50 dB over S9 range. On 160 meters, occasionally I
will see W8JI or W8LRL hit 50 dB over S9. Of course a local neighbor
only 2 miles away running 100 watts to an inverted-L on 160 will
totally peg my S-meter (FT-1000MP pegs at +60). I recall using
attenuation of ~12 dB to bring his signal back on scale, so that means
he is near the level Orion's IP3 is specified for (S9+70 dB or 0 dBm).
The average ham using a trap vertical or dipole antenna on the
HF bands (especially above 80 meters) will probably never see the
signal strength levels which cause IMD products. This is why most
of us are quite happy with whatever we are using today. Orion is
truly designed for corner cases which appeal mainly to contesters or
low-band (160/80) DXers where strong interfering signals are likely
to cause problems. I'll caution that the exception to this rule is
if you had a very close neighbor, or perhaps when you take your radio
out to Field Day and try to use it on CW when another station is on
SSB on the same band. Otherwise, if the maximum signals you see
are S9+20 to 30 dB, you are unlikely to have the type of IMD problems
Orion will solve.
73, Bill W4ZV
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