[TenTec] 221 CW filter insertion loss

Thu Feb 10 19:12:57 EST 2005

I have come to the conclusion that there are wide variations in filter 
attenuation for the same model filter. It should be easy to measure with a 
signal generator and scope however the I/O impedance might be a factor that 
could skew the readings.

Steve Ellington
N4LQ at iglou.com
----- Original Message ----- 
From: "Roger Borowski" <K9RB at bellsouth.net>
To: <tentec at contesting.com>
Cc: <ni0c at earthlink.net>
Sent: Thursday, February 10, 2005 6:52 PM
Subject: Re: [TenTec] 221 CW filter insertion loss

> 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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