[TenTec] #218 filter
Dr. Gerald N. Johnson
geraldj at storm.weather.net
Tue Oct 3 14:09:14 EDT 2006
On Tue, 2006-10-03 at 07:21 -1000, Ken Brown 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
Another technique that works is to use spectrum analyzer software on a
PC with sound card and let it display the noise spectrum of the received
audio with the noise of a dead band at the receiver antenna connector.
The longer the averaging, the smoother the response curve will be.
73, Jerry, K0CQ,
All content copyright Dr. Gerald N. Johnson, electrical engineer
More information about the TenTec