Eric:
I have been using the Inrad 751 (250hz, 6.3Mhz IF), 752 (2.1khz, 9Mhz)
and 753 (400hz, 9Mhz IF) since purchasing the Omni 6+ new in October
'98. The 756 (2.4khz, 9Mhz, 10 pole filter) was installed in March.
The TT 285 (500hz) and 288 (1.8khz) are also in the 6.3Mhz PBT IF. I am
very pleased with this lineup, particularily on cw. I recently touched
up the alignment of the BFO on the rig and find that the filters are
very symmetrical and sharp. What can be heard on the 500hz filter is
eliminated when the 250hz filter is switched in. The filter loss also
seems to be less with the Inrad filters, possibly due to better
impedence matching in the filter circuit. It's more difficult to
characterize the change to the 756 filter as I do not have the
capability of making any measurements. I have received excellent cw and
audio reports since installing the filter and can only expect that the
symmetrical skirts, 2 additional poles with 10 poles total, and a shape
factor of 1.4 improves the performance of the radio. George at Inrad has
provided a chart with each filter showing a sweep of the particular
filter's characteristics. The filter's actual width at the -6db point
typically is wider than what the model number would suggest. For
example, the 751 filter is 350hz and the 756 is 2.488khz wide. Eric,
you asked for recommendations....so here it is. If you do not have any
optional SSB filters, get the TT 288. This filter is a very good, all
around SSB and cw filter. After that, a 756 would be a good option.
Inrad now also offers a 2.8khz first IF(primary filter) and PBT IF
filter which is a definite option. However, I personally think that
going to a wider filter than necessary on today's crowded bands is
counter-productive (my opinion only, no mail required!). The 2.8khz
first IF filter was originally proposed to eliminate a problem that some
rigs exhibited. This topic has been well documented on the reflector.
Good luck with your Omni 6+!
Greg, K7KJ
Portland, OR
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