[TenTec] 221 CW filter insertion loss

[Roger Borowski]

Chuck, I've presently got the #219 filter in N-1 ands the #221 in N-2
positions along with the #'s 282/285/288 filter choices in the 6.3MHz. IF
string. I find myself not using the 285 ever. The 282 along with either the
219 or the 221 have identical signal strength readings but the copyability
of weak signals for me is far better with the #221 lower pitch filter.
Before I got the #221, I had a #217 and found that I never used it and opted
to try the #221 in its place as both the 250Hz. bandwidth filters seemed to
me to have better performance from a standpoint of loss as well as adjacent
frequency rejection, when cascaded with either of the 500 Hz. filters or the
pair of cascaded 500 Hz. filters (285/217). I will sometime soon, most
likely when I receive the INRAD special order roofing filter kit made to 500
Hz. center frequency audio tone offset, remove the 219 and replace it with
the 216 I recently obtained to allow for more optimal use with the digital
modes in conjunction with the 285 filter or maybe even the 282. I'll also
surely find a way to activate the new roofing filter only when N-2 (#211
filter) is in use for CW mode only as N-1 will be used only for digital
modes with a far different offset than the 500Hz offset roofing filter will
be optimized. I might guess that your #221 filter may have excessive loss as
although the spec's indicate additional loss over that of the #217 filter,
as similar to the #219, I have seen just the opposite effect here. I can't
say anything about comparisons to any INRAD filters, as I've never had any
for the Omni VI Plus. It also is a possibility that my #217 had excessive
losses to explain what I had experienced, but I can say I was somewhat
disappointed in it, by comparison to the 219 and certainly the 221.
The 221 TenTec filter finally added the degree of excellence over all the
other transceivers I've used for weak signal reception in my 44 years of 160
Meter DX'ing. It now equals the receiving abilities of my TS-950SDX and
hopefully will exceed that of the TS-950SDX with the addition of the new
roofing filter centered at 500Hz. I'm also very much looking forward to
adding the INRAD roofing filter kit to my TS-950SDX when it becomes
available. FWIW, the TS-950SDX has the factory 270/250Hz. filters for CW,
which, in my experiences, is a cut above both it's predecessors, the TS-830S
and TS-930S (with the same filter bandwidth combinations). All rigs were
originally purchased new by me, so I have lots of time listening to these
various rigs. The newest of the Kenwood collection being the TS-950SDX
purchased over 12 years ago now.
I just wanted to state that I'm in awe over your disappointment of the #221
TenTec filter performance in your Omni VI Plus and feel that there must be
something wrong especially since sensitivity in my model 564 is quite ample
with the cascaded 282/221 or 282/219 and never have required me to use the
AF gain beyond 75%, even with the 20dB. Attenuator ON and the RF Gain also
backed down a bit. I'll certainly be interested in what you find when you
reinstall the #221 filter and if you have a #219 for comparison, the gain
(or loss) should be similar with either of the 250Hz. filters, with just the
pitch frequency being the difference. That's what I see here, Chuck. Please
keep me in the loop on this as well as if you hear anything from George at
INRAD as to when he has enough commitments to start the manufacturing of the
special order roofing filters to match the 221 offset frequency. I'm still
hoping that the March time frame is on target.
vy 73, -=Rog-K9RB=-

----- Original Message ----- 
From: "Chuck Guenther" <ni0c at earthlink.net>
To: <tentec at contesting.com>
Sent: Thursday, February 10, 2005 11:30 AM
Subject: [TenTec] 221 CW filter insertion loss


I recently acquired the coveted 221 filter from a nice ham who had one
unused still in the box from Ten Tec.  I installed it in my Omni VI, Opt. 1
with CW roofing filter mod from INRAD.

It was a big disappointment.  The insertion loss made it unusable on most
bands.  I promptly reinstalled my INRAD 753 in the 9 MHz position.
According to the specs, the difference should not have been as great as I
observed.  The INRAD 753 has a nominal insertion loss of about 9 dB, while
the 221 is specified at 14.0 dB.  I estimated a theoretical loss of an
additional 2-3 dB due to the mismatch in center frequencies of the 221 and
the roofing filter.  So, there's a difference of 7-8 dB.  Yet, the 221 was
unusable on 160m, 30m and 40m-- signals were down at least 3 s-units. The
receiver seemed starved for gain.  Only on 80m was it useable.
In fact, the difference was so great that I went outside and worked on my
antenna for several hours before concluding it was my filter.

I suppose this particular unit has excessive loss.  I'm planning to try it
out again when I receive the new roofing filter from INRAD (the special
order one with 500 Hz offset to match the 221).  I expect, though, that the
INRAD 753 (400 Hz BW CW filter with 600 Hz offset) will prevail.

This is the second 250 Hz filter I've tried in the 9 MHz position.  I should
have listened to Stan at Ten Tec Sales, who (at the time I ordered the Omni
VI) told me I wouldn't like a 250 Hz filter up front.

73 de Chuck  NI0C
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