FW: [AMRadio] Ranger... good news, bad news


Gary Schafer garyschafer at comcast.net
Tue Nov 7 20:20:46 EST 2006



-----Original Message-----
From: amradio-bounces at mailman.qth.net
[mailto:amradio-bounces at mailman.qth.net] On Behalf Of Jack Schmidling
Sent: Thursday, December 07, 2006 5:49 PM
To: Discussion of AM Radio in the Amateur Service
Subject: Re: [AMRadio] Ranger... good news, bad news

Gary Schafer wrote:

>If you want to run 125 watts carrier out of the
> SB200 on AM that means you need to tune the amplifier up for 500 watts or
a
> little more output with the load and plate tune controls on the amp peaked
> for maximum output with a given amount of drive.

Not sure I understand the why of this.  I did all as you suggested but 
found when I was done that the plate tuning of the amp was exactly the 
same as if I tuned it originally with the 100w carrier.  The dip was 
exactly in the same place and the loading optimum is so broad that no 
change could be noted.


> Watching the scope on the output of the amplifier should show the
modulation
> peak voltage double what the carrier voltage is on the scope. If it
doesn't
> you haven't tuned up properly.

Interestingly, the only way I get the peak voltage to double is with the 
ricebox.  I can never seem to get more than about 50% increase with 
modulation.

js

The peak envelope power of an AM signal increases by 4 times over the
carrier power with 100% modulation.
The linear amplifier must be tuned at the peak envelope power level or the
peaks will never reach full power, the amplifier will flat top and splatter
and you will not sound good.

How much drive power did you have when tuning up the amp?
Were you using a rice box to tune the amp or the ranger?

If you don't see the scope voltage double with modulation you haven't tuned
up right. If you adjust the scope to say 2 centimeters with carrier then the
modulation peaks should hit 4 centimeters.

73
Gary  K4FMX






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