[TenTec] Inrad 762

[Bill Tippett <btippett@alum.mit.edu>]

Hi Toby,

W4CAK wrote:
>Has anyone tried putting the New Inrad #762 in the 500hz slot of the 
Orion.  Since the 1khz filter does an excellent job down  to 380 hz, would 
this not be a better use of the 762?

        That won't work very well for several reasons:

1.  The 500 slot always has the second amplifier engaged...thus it
should still be introducing IMD products.

2.  The 4-pole Inrad 762 has less insertion loss than standard 8-pole
500 Hz filters, aggravating the fact that the 500 position already has
too much gain, even for the standard 500 Hz filters.  TT used a
fixed 12 dB gain amplifier for both the 500/250 slots.  That is a
good match for the 250's high insertion loss but too much for a 500.

3.  The center frequency of the 762 is 9.001500 but Orion thinks
the 500 position has a 9.000750 Hz center frequency.  Thus the
filter will not be correctly centered, although you can partially
compensate for this by using both C.F. Adjust and PBT.  I think
it can be made to work for UCW but not LCW (could be the other way
around in the case you propose).  If you compensate using PBT,
signals will disappear any time you switch to a different roofing
filter.

        I went through the same thinking when first looking into this
filter issue, but I tried installing the 500 Hz filter into the
1000 Hz position.  That doesn't work well either for similar reasons.

        Just plug your 762 into the 1000 Hz slot and everything works fine.
If your 1800 slot is empty, put your 1000 there.  If you already have
an 1800, simply set your 1000 aside...you'll never miss it for reasons
I've explained many times (1800 & 1000 being equivalent IMD fighters
down to 2 kHz spacings where the 762 will take over and is far
superior to either).

                                                73,  Bill  W4ZV



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