Re: [TenTec] NAR filter in Omni VI

[Jason Buchanan <jsb@digistar.com>]

Jim Brown wrote:

> That's a really good question, Jason. I've made very careful (and fairly precise) 
> spectrum measurements of my Omni V (just back from factory alignment) with 
> exactly that set of TenTec filters , plus a 500 Hz Ten Tec filter in the NAR 
> position. The addition of the 500 Hz NAR filter to the 250 Hz filter makes a 
> difference so slight (on the order of 3 dB in the skirts) that you wonder why you 
> bothered. A 250 Hz filter in the NAR position (which I have not measured) would 
> likely make enough difference to matter, but that's REAL narrow. If you're a 
> serious contester or DXer, that might be worth doing.   I would expect the 
> results in your Omni VI to be the same as in my Omni V. 
>
>  

Aha - I think I begin to understand now - in the Omni VI Opt.1 radio the 
default 2.4K filter "feeds" into the 1.8, 500 and 250hz filters, but 
when the NAR button is pressed to enable this filter, the 2.4K filter is 
switched out of the pipeline and the NAR filter is used instead - is 
this correct?  I can see how this would have a noticeable impact for 
interference rejection.

Speaking of factory alignment, one thing I have noticed is the 500Hz 
filter is about 2 or 3 S-units stronger than the 250Hz filter - I 
carefully adjusted the PBT to zero-beating against the 700Hz sidetone 
and another rig on my desk transmitting into a dummy load.  I can be 
dead-on centered for maximum signal strength with the 250Hz filter and 
then select the 500Hz filter and the 500Hz filter produces considerably 
louder audio from the speaker and about 3 S-Units stronger on the S 
meter.  Is this typical or do I need to consider filter replacement or 
alignment?

> I have not compared the InRad filters to the Ten Tec filters, but I just put InRad 
> filters in the 746 that I use on 6m, and I am quite pleased. They are a significant 
> improvement over the Icom filters, and sell for about the same price.  Maybe 
> someone can comment on InRad filters in your Omni VI. 
>  

I've thought about purchasing some INRAD filters but I am confused as to 
which ones to buy because I do not know how the 9MHz center frequency of 
the filter corresponds to the CW 700hz center frequency - for example, 
INRAD's website lists two 400Hz 9MHz filters, #753, 9000.6 KHz and #759, 
9000.7 KHz.  Does this mean the 9000.6 KHz filter is designed to center 
around a 600Hz sidetone and the 9000.7 is for 700Hz (keeping the PBT 
knob at 12:00 o'clock)?


I have been considering picking up #754 2.8K 9MHz filter depending on 
any reports I get about the CW click that some Omnis have - given that 
i've made only a half dozen contacts since I got the radio I am a bit 
premature to go off spending money on things I don't need - hi - but i'm 
an avid CW op and anything I can do within reason to improve picking out 
the QRP rigs in VK land is ok by me - hi



Thanks everyone for your replies!

Jason N1SU
"New Old" Omni VI owner    (from the New Old Lompoc House)

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