[RFI] Audio Amplifiers RFI

[HP]

In a VHF contest -on 6 meters - I was getting bursts of wide trashy noise - pulsing like a drum beat . 
Seemed to be peaking north of me . So I went out with my ICOM R10 hand held rx and just the rubber duck ant -- 
As soon as I got to alley I could hear bass notes pulsing at same rate as the RF noise . The neighbors outside 
audio system was oscillating on 6 meters (and who knows where else) in sync with the bass notes !!!! 

On 15 meters - It was even worse even some of the trash during the melody phrases. 
Fortunately I think it must have destroyed itself - 

So you probably need to add what happens when the amp starts to clip as well as various non resistive loads 
to decide if the amp is "stable" 

I spent over 35 years doing solid state RF PAs - 90 percent of the work was making them stable under 
every conceivable condition. Now "audio" devices have higher Ft than a lot of the "RF" devices I had 
when I retired in1998. 

Hank K7HP 






Date: Mon, 5 Oct 2020 14:07:53 +0000 
From: "Cianciolo, Paul, W1VLF" <pcianciolo at arrl.org> 
To: Bert <balmemo at sympatico.ca>, "rfi at contesting.com" 
<rfi at contesting.com> 
Subject: Re: [RFI] Speaking of audio amplifiers... an interesting case 
Message-ID: 
<BL0PR16MB252928E4DACE6B061C56A9F9B00C0 at BL0PR16MB2529.namprd16.prod.outlook.com> 

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Bert, 

Not really even 3 feet of wire failed muster. 
With a resistor as a load it did fine. 
Which was how I originally tested it. 

Another interesting fact was you could "tune" where you wanted the harmonics to be the strongest by varying the length of the speaker/power supply leads. 


73, 

Paul Cianciolo, W1VLF 
ARRL EMC?Engineer 

ARRL - The national association for Amateur Radio? 
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