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Re: LF: PA problem

To: [email protected]
Subject: Re: LF: PA problem
From: N1BUG <[email protected]>
Date: Fri, 10 Nov 2017 16:58:07 -0500
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Hello Rik,

Thanks for the good suggestion. I tried it on a battery removed from my lawn mower. I won't be needing the lawn mower for some months!
Running it from the battery does not significantly reduce the RF I
see on the amplifier +DC input lead. I can clean it up (mostly) by
putting a 100 uF bypass capacitor at that point.
73,
Paul N1BUG


On 11/10/2017 03:30 PM, Rik Strobbe wrote:
Hello Paul,

I just had a look at the circuit 
(http://qrp-labs.com/ultimate3/u3mods/lfamp.html).
One end of the output transformer connected is to the +13.8V should be "cold" 
(no RF).
As already mentioned regulated power supplies often behave strange to reverse 
(RF) currents.
To rule out any hickups of the power supply I would suggest to run the PA on a 
large (car) battery or an unregulated power supply (just transformer + 
rectifier + large C of at least 10000uF). Now the voltage at one end of the 
output transformer should be (almost) pure DC.
If the PA run fine (expected output power and efficiency) now you should focus 
on AC decoupling the power supply (proper shoke with serveral uF of good caps 
at both ends).

73, Rik  ON7YD - OR7T




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