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@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
> > <\
> > ----- \ 0 _
> > ----------- _\\/\-%
> > ______(_)===(_)____
> >
> >
> >
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