[AMRadio] Re: Gates BC250L efficiency


Larry Taft ltaft at charter.net
Wed Sep 29 22:48:01 EDT 2004


The measurements were done several years ago with an old HP 851/8551 
analyzer and I didn't write down the data. I'll do the tests again with my 
Tek 2712 and plot the results. The only question is "When?"

What I see in my rounds of making the NRSC spectrum plots on AM broadcast 
stations is an occasional increase in harmonics over the previous 
year.  Many times the engineer will say that they had a recent nearby 
lightning strike.  Checking the harmonic trap series cap usually finds the 
problem as that gets blown by the lightning surge.  The increased harmonics 
don't show on the station metering as the only RF meter is current in the 
feedline to the antenna.  The change in power is minuscule and not noticed 
on the meters.  But the station is out of spec for harmonics.

Larry  K2LT
T and T Measurements
800-687-9161

At 06:30 PM 9/29/2004 -0400, you wrote:

>Well, if not going into a dummy load, the swr would go up.
>Just because you run an antenna tuner does not mean
>the amp is running clean and not wasting power in harmonics.
>
>Measure the TR-7 by itself and its likely clean, and overdriving the amp
>is likely the problem.
>
>Modern solid state rigs likely wont allow much harmonics out unless
>you tweak things inside for more power out than they are supposed to run.
>Most will put out quite a  bit of extra power if you tweak the alc circuit,
>but it wont be clean.
>
>Brett
>N2DTS
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