[TenTec] NB verses NR

Rick - DJ0IP / NJ0IP Rick at DJ0IP.de
Mon Dec 15 13:53:16 EST 2014


It is as Carl said, if you have a narrow filter before the NB tap, it simply
won't work.
In the country, you probably won't need it anyway unless you have an
electric fence nearby.

I can't recall the filter plan on the original OM6.
If you series two filters on separate IF frequencies, you get at least 10dB
more ultimate attenuation than if you series them on the same IF frequency.
Don't ask me why, I've long sense forgotten.  This was explained by DL1BU in
about 1979 in a CQDL test of the old Icom 730.  I "think" I still have that
article saved somewhere.  Not sure if I could find it again.

The problem with placing two filters directly in series is, you will drop
about 6dB of gain, assuming they are narrow filters.  This needs to be
compensated for with a low gain, low distortion amp.  I also used two 9 MHz
filters in series with my old Argonaut 509; I replaced the original 4-pole
xtal filter with an 8-pole KVG XF-9B, then placed a 6-pole 500 Hz Yaesu
filter behind it. The signals I could no longer hear due to the additional
insertion loss were too weak to work anyway with only 5w.

Ten-Tec was already managing stage-gain better than the JA OEMs when they
developed the OM5.
In fact it goes back all the way to the original Omni where they had
different gain depending on the band.
However they improved it even more when developing the OM7.

At the end of the day, if it is working for you and you are happy with it,
then it was a good move.
That's how I judged my dual-filter in the Argonaut, even though I knew it
was technically no exactly kosher to do it that way.

73 - Rick, DJ0IP
(Nr. Frankfurt am Main)

-----Original Message-----
From: TenTec [mailto:tentec-bounces at contesting.com] On Behalf Of Peter
Sent: Monday, December 15, 2014 6:13 PM
To: tentec at contesting.com
Subject: Re: [TenTec] NB verses NR


I have two of the roofing filters kits from Inrad; they are connected in
series... since I have the basic Omni VI, I only have one NARROW filter
selection on the front panel... so I have one of the roofing filters always
in line. Narrow drops the SSB roofing filter, and selects the board with the
CW filter. It is in series with the input to the monolithic roofing filter
on the 9 MHz IF board.  My understanding is that the NB sampling is after
this filter, but I could be mistaken.

Fortunately, being in a rural area I don't have much need for noise
blankers.  I've often wondered if just buying better quality IF filters from
Inrad would reduce the need to cascade additional filters at 9 MHz to
improve the skirt selectivity.

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