[TenTec] #218 filter

Ken Brown ken.d.brown at hawaiiantel.net
Tue Oct 3 13:21:42 EDT 2006

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.


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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