[RTTY] Measuring filter bandwidth

[Jerry Flanders <jeflanders@comcast.net>]

In the thread: Re: [WriteLog] AFSK on RTTY not LSB on 1000mp field,
At 08:09 2/23/04, Jim Smith wrote:

> .
> <snip>
> Have you actually checked the bandwidth of the filter(s) selected by your 
> Nar1 when in RTTY mode?  If you do get 500 or thereabouts for Nar1 and 250 
> or so for your Nar2, the next thing is to figure out how you're doing it. 
> <SNIP>
>
> 73 de Jim Smith   VE7FO



It is easy to check your passband performance (BW, slope, etc) if you have 
a sound card connected to the radio's output, as most of us do.

Analyzer2000 demo version is a free download on the web. It will run for 30 
minutes, and can then be restarted as many times as needed for 30 more. It 
will show the exact audio passband and let you quantify it. Takes a few 
minutes to learn it, but you don't need to learn all to check your bandwidth.

Tune to a quiet spot. With your live "white noise" audio showing in the 
Analyzer2000 screen, press "peak hold" button, wait 10 seconds, then press 
"freeze" button. Press the red vert ruler button, place it at the start 
point on the passband, press the blue vert ruler button, place it at end 
point. Read bandwidth from the ruler display panel.

You can use the horizontal rulers also, to evaluate the shape factor. They 
work similarly to let you find a point a specific nr of dB down the side 
before moving the vertical rulers to that point to check the bandwidth there.

GL

Jerry W4UK



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