[Orion] Orion subreceiver

[Bill Tippett]

N7US wrote
 >I understand that the Orion's subreceiver is general coverage and is not
nearly the receiver that the main receiver is for the ham bands.  What's the
practical significance of the poorer subreceiver?

         It has significantly worse IMD and BDR performance
than the Main RX, but it depends how you use it whether
that is important or not.  I normally use the Sub RX only
in split operation to listen on my TX frequency (for example
to find the stations DX is working in a pileup).  These
signals are normally strong enough that IMD is not a big issue.

 >Now for the more technical question from an accountant:   Comparing an Orion
with its +24 dBm (at 5 kHz) 3OIMD with a radio with +40 dBm 3OIMD but only a
6 kHz roofing filter, say an IC-7800, or maybe one that also has a 3 kHz
roofing filter, say a new FTDX9000, would the Orion's narrower roofing
filters more than offset the poorer 3OIMD?

         Don't be misled by the high 3rd order intercept (NOT 3rd
order IMD) numbers...they are typically at 100 kHz interfering
signal spacings.  Both the FT9000 and IC-7800 have significantly
worse IMD performance at close spacings (1-2 kHz).  This has been
documented by at least 4 independent parties for the IC-7800
(ARRL, RSGB, Sherwood Engineering and W8JI) and it will likely
be the same for the FT9000 once it is tested).

         Here are some sites to study:

http://www.w8ji.com/receivers.htm (overview)
http://www.w8ji.com/receiver_tests.htm (understanding MDS, BDR and IMD)
http://www.w8ji.com/receiver%20IM3%20sorted.htm (comparisons
ranked in order of best IMD at 2 kHz spacing)
http://www.sherweng.com/presentation.html (Sherwood Dayton Paper)
http://www.sherweng.com/table.html (Sherwood 2 kHz IMD measurements)
http://www.elecraft.com/K2_perf.htm#5%20kHz%20numbers (ARRL summary)
(RadCom tests not available except to RSGB members but you can
probably find comparative data searching "Orion 7800 RadCom"

One caution on the ARRL summary.  The published results are shown
for 5 kHz only, and the IC-7800 (and K2) doesn't look too bad there.
However both degrade significantly at 2 kHz and in fact are phase
noise limited at 2 kHz (ARRL, RSGB and Sherwood reports all show
this for the 7800).  How many contests/pileups have you heard
recently with 5 kHz spacing between signals?  :-)

 >Being an accountant, I can appreciate the cost difference of the Orion
versus the other two.  (What's the Icom jacket worth?)

         I'm not an accountant but I would guess over $7000.  :-)

                                                         73,  Bill  W4ZV