[AMRadio] AM Amps


Geoff w5omr at w5omr.shacknet.nu
Tue Jan 11 20:04:23 EST 2005


Geoff wrote:
> Gary Schafer wrote:
> 
>> By "legal power out of the 813's" I assume you mean 375 watts carrier?
> 
> 
> Why assume something that is false??
> 
> That statement is -designed- to put you on edge, Gary.  Perhaps it's 
> just my perception, but it simply appears as if you're not paying 
> attention.
> 
> NO WHERE does it say that 375w of carrier is the 'legal' limit.
> 
> The LEGAL limit is 1500w PEP output.  It's just a point of reference, 
> that if you modulate a 375w signal with a sine-wave to 100% audio, then 
> you will reach 1500w pep output.  The truth of the matter is, we don't 
> -speak- in sine-wave.  Our voices are rather asymetrical.  Some of us 
> have voices that are rather 'peaked'.  In order for the audio amplifying 
> equipment to properly modulate 375w of carrier, instead of needing to 
> only be 50% of the carrier, or 187.5w of needed audio, you -might- wind 
> up needing an audio system with the capability of producing upwards of 
> 600w of AUDIO.
> 
> (ref: http://w5omr.shacknet.nu/~wa5bxo/asyam/Amplitude%20Modulation.htm)
> 
> THIS IS NOT TO SAY that you'll be pushing your positive peaks that high, 
> but in order to keep your signal clean, and well within "good 
> engineering practice", you certainly don't want any flat-topping or 
> distortion.  Anything in the audio system that does -not- allow your 
> audio to be clean and free of distortion then, by definition, wouldn't 
> be operating within "good engineering practice".

While I'm at it, I'll say, again, that if I wasn't covered up 
with neighbors, I'd run my rig at around 500w DC Input (around 
1500v @ 350mA), make sure that the modulator was capable of 
cleanly modulating the signal, and let the positive peaks float 
up to wherever they like, -as long as- my negative peaks don't 
pinch/cut the carrier.  If it's 2500w PEP, then so be it.

(where'd I leave my black cowboy hat and six-shooter? ;-))

As it is, with neighbors on *ALL* sides of me, during the 
day-time, I limit the power output of the 250TH final to 100w 
OUTPUT (and probably reaching 500+wpep out) and between midnight 
and 6am, it's at 200w carrier (around 800wPEP out, w/o cutting 
the carrier off, with negative peaks)

73 = Best Regards,
-Geoff/W5OMR (aka: AM Outlaw)

(p.s.  Does anyone (other than K4KYV) remember the phrase:
"When AM Kilowatts are outlawed, then Outlaws will run AM 
Kilowatts!"?)




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