[TenTec] #218 filter

[Bob Cunnings]

Another way, if you have a PC with a soundcard, is to use a spectrum
analyzer program like Spectrogram  to characterize the filter using
band noise as input.

This is the technique used by K2 builders to set up the adjustable IF
filters. I used this approach to find the centering adjustment for the
218 and 217 filters in my Orion (I used a program called Spectrum Lab,
found at http://www.qsl.net/dl4yhf/ ).

Bob NW8L

On 10/3/06, Ken Brown <ken.d.brown at hawaiiantel.net> wrote:
> The easiest way to check a filter (if having the expensive lab equipment
> is easy) is to sweep it with a spectrum analyzer / tracking generator.
> If you don't have access to one of those ( not the kind of gear
> accountants typically can bring home from the office for a weekend )
> Then you can do the same thing manually by tuning across a CW carrier
> and logging the audio output level at perhaps 50 Hz intervals. The AGC
> needs to be turned off, and you do need an AC voltmeter or other
> instrument such as an oscilloscope to tell you the audio level. Plot the
> data on a cartesian plane. You need to make a audio output level versus
> frequency plot.  You also need to have the  BFO frequency far enough
> from the skirt of the filter so that the low end audio rolloff of the
> audio stages does not mess up you measurements at that end of the plot.
> You probably also want to do the same to another known good (not
> necessarily the same bandwidth) filter.
>
> I think you need a basic analog, or at least not too digital, radio to
> do this. The Orion will probably not be the radio to use for this
> measurement, unless you have control of the BFO frequency, and can
> really turn off all forms of automatic gain control.
>
> DE N6KB
>
> J.Reed wrote:
> > Good morning John, I'm a bit too dumb to answer the question but I also would
> > be 'interested' in knowing how to test it myself. I have the Orion-1 and maybe
> > could try it out doing the same test as you have described.  When you replaced
> > the Omni-D '218' with the new one, did you feel it made any difference?  That
> > would be important I assume...  Jim Reed, W3RYJ...
> >
> >
> >
> >   ----- Original Message -----
> >   From: John T. Fleming
> >   To: 'Discussion of Ten-Tec Equipment'
> >   Sent: Tuesday, October 03, 2006 10:08
> >   Subject: [TenTec] #218 filter
> >
> >
> >   I have a 218 filter that I took out of my Omni D years ago and replaced it
> >   with a new 218.  I don't remember if it is off frequency or what is the
> >   problem with it.  I found it in the junk drawer in the original box in
> >   moving to Florida.  Is there any easy way to check it out?  I was thinking
> >   of putting it in my Orion to see if it works.  But I don't think that will
> >   really give me a true answer.  I have all filters in the Orion already.
> >
> >   If I put it in the Orion and set the menu to select only the 1.8 filter and
> >   then tune in WWV and set the radio to upper or lower sideband and offset the
> >   frequency 1,500 hertz and watch the signal strength as I tune, will that
> >   tell me if the center of the frequency is correct?  My back ground is
> >   accounting and I need and accept all of the help I receive.  Thanks.
> >
> >   73
> >   John
> >              <\
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> >
> >
> >
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