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HW 100 Received Audio Distortion

Mar 12th 2017, 13:33

W3WCG

Joined: Apr 4th 1998, 00:00
Total Topics: 0
Total Posts: 0
After restoration, my hw 100 transmitter works perfectly with excellent audio reports verified by other hams capable of making accurate measurements; bandpass measured at 200 to 2800 hertz. The received audio sounds very raspy and takes very fine tuning to get a reasonably understanding of what is being said. The audio stage measured bandpass is down 40% at 400 hertz but increases rapidly and is fairly flat out to 3500 cps. The speaker has been replaced, circuit voltages are within specifications and the product detector has be substituted with a transistor design but the problem is still there. Being the SSB bandpass transformer (T 202) is used in both transmitt and receive mode it's reasonable to believe the problem is not there. Request thoughts from fellow hams.
Mar 13th 2017, 18:51

W1VT

Super Moderator

Joined: Apr 4th 1998, 00:00
Total Topics: 0
Total Posts: 0
You should keep in mind this is an economy rig in an era where audio standards weren't as high as they are now.

http://www.northland-drifters.net/HW101/HW101MOD.pdf
While this is for the revised HW101, I believe both rigs suffered from similar audio problems. There was inadequate BFO injection, which mean the IF signal was stronger than the BFO injection, resulting in raspy audio. In those days hams rode the RF gain, cutting back on the RF signal to keep the BFO signal from being overwhelmed in the product detector. The relatively wide audio bandwidth out to 3500 makes this sound worse. A cheap fix is to roll off the audio bandwidth.

Zack W1VT
ARRL Senior Lab Engineer

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