[Orion] Orion and Inrad 762

[Bill Tippett]

Do we have any idea how good the Inrad 762 might be at very close 
spacings?  Let's take another look at the Inrad plot below.  I've marked 
points below which show a total bandwidth of about 1300 Hz at -30 dB 
attenuation on the skirts.  Assuming the #762 is correctly centered, this 
means signals at a spacing of 650 Hz or more should be attenuated by at 
least 30 dB, which means that their IMD products will be attenuated by at 
least 90 dB.  If we further assume interference is coming primarily from 
one side, we can use PBT to shift 250 Hz which should effectively yield ~90 
dB IMD rejection at 400 Hz spacings on one side of the passband (of course 
the other side of the passband would also shift 250 Hz also reducing the 90 
dB IMD rejection to signals at 900 Hz spacings and above...still better 
than any other receiver I know of).  My estimates have not been verified by 
actual measurements yet but I am hoping Sherwood or someone will be able to 
confirm them in the near future and will post any results here.

http://users.vnet.net/btippett/inrad_.htm (see new plot at very bottom)

                                                 73,  Bill  W4ZV