A Better Way To Tune Shortwave

The distortion caused by frequency selective fading can be noticeably reduced by making the receiver AGC much slower than it normally is.

The AGC's purpose is to
keep the audio level relatively constant with varying signal strength.

The problem is that it tries to do that by reacting to the carrier strength.

During a frequency selective
fade, when the carrier fades, the AGC, mistakenly thinks the audio level has decreased, and increases the gain.

This causes the distortion to sound much worse than it is. 

You can test this with your receiver if you have an RF gain control.

Find a station that is fading and distorted, then turn the AGC off and set the RF gain to the same loudness.

You will find that the distortion is much less annoying.

If possible it is a good idea to modify the receiver AGC to allow an additional much slower setting, or modify the existing slow setting. 

A 3 or 4 second recovery time seems to work well.

It is usually as simple as adding a capacitor to the AGC line.

I added a 2.2mf to my HQ-100.

If modifying the receiver is not practical, just switch the AGC off and use the manual RF gain control when experiencing distortion caused by fading.

Using this procedure with the SD-1 will improve reception even more.


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