[TenTec] Re: NAR filter is OMNI-6

[Ken Brown]

Roy Koeppe wrote:

>About,
>
>"I have an Omni VI with 2.4K, 1.8K, 500 and 250hz filters but the NAR
>slot
>is empty.  Can someone tell me what I would add to the NAR filter for CW
>operation and why would I want to do this when the filters that are
>already there seem to work real nice..."
>  
>
If "the filters that are already there seem to work real nice" then 
perhaps you would not want to bother with the added expense for no 
improvement. When would there be an improvement? If you have a strong 
signal inside the bandpass of the stock 2.4 kHz bandwidth 9 MHz IF 
filter (but not in the narrower 6.3 MHz IF filter), that causes 
degradation of readability of a weaker signal inside your narrower 6.3 
MHz IF filter, then a narrower (narrower than 2.4 kHz, not necessarily 
narrower than the filter in the 6.3 MHz IF) filter in the 9 MHz IF could 
make an improvement. This typically happens in contests or DX pileups.

The choice of which filter to use as your optional narrow 9 MHz IF 
filter is not quite as simple as just using the narrowest one you can 
get. Yes the narrowest one you can get will give you the best 
performance as far as picking out a weak signal next to a strong one, 
however you loose some flexibility that way. With a wider filter in the 
9 MHz IF you can use to PBT to move the 6.3 MHz filter bandpass around 
within the 9 MHz filter bandpass. This allows you to select a signal 
without changing the pitch as would happen using the RIT or VFO. If the 
9 MHz IF is  really narrow, then the PBT has to be left in the position 
where both the 9 MHz and 6.3 MHz filter bandpasses coincide, or you get 
no signal through at all.

This is why it is nice to have more than one 9 MHz narrow option filter, 
and why I sorta wish I had an Omni VI + instead of a plain Omni VI. For 
tuning around the 2.4 kHz standard 9 MHz filter is a bit too wide, and 
the 500 Hz 9 MHz filter in my Omni VI is a bit too narrow. For digging a 
weak one out from between strong signals the 500 Hz narrow option 9 MHz 
IF filter is real good. I wish I had an inbetween option. No space for 
one in my radio. Having space for only one, I think the 500 Hz one is a 
good choice.

DE N6KB