[AMRadio] Monitoring Modulation Accurately

Bry Carling bcarling at cfl.rr.com
Fri Nov 15 13:34:55 EST 2013

I presume I can run my DX60 with a pair of GG 3-500z finals and have something like 125watts carrier out and some nice voice peaks...

Bry Carling

> On Nov 15, 2013, at 12:25 PM, "K5MYJ" <macklinbob at gmail.com> wrote:
> When using Controlled Carrier modulation PEAK POWER is important.
> As an example a DX-60 has an idling carrier power of about 12.5W. But voice peaks can reach as high as near 60W. Controlled Carrier can not go to ZERO!
> Bob Macklin
> Seattle, Wa.
> "Real Radios Glow In The Dark"
> ----- Original Message ----- From: "Rob Atkinson" <ranchorobbo at gmail.com>
> To: "W2XJ" <w2xj at w2xj.net>
> Cc: <amradio at mailman.qth.net>
> Sent: Friday, November 15, 2013 9:13 AM
> Subject: Re: [AMRadio] Monitoring Modulation Accurately
>> I agree with some of this but not all of it.  Peak power may be
>> everything if you are a slopbucketeer, but in ham AM, it's a bogus
>> power indicator--it's difficult to measure accurately, and gives a
>> false idea of your transmitting effectiveness because AM has a complex
>> waveform over time and frequency spectrum.   For AM I measure dead
>> carrier into a 50 ohm pure resistance with a Bird 43 and thermocouple
>> RF amp meter (you can also use a VTVM with a HP RF probe tapped off
>> the dummy load) and then under modulation let the chips fall where
>> they may, only making sure the negatives don't clip the carrier.
>> Others may obsess about peak power or PEP but I think it's a waste of
>> time.
>> Other reasons why obsessing over high positive peaks and peak power
>> are inadvisable:  If you go wildly asymmetric on the positives, you
>> may be technically clean if you limit negative to 95%, but you'll
>> still distort in a lot of receivers not equipped with sophisticated
>> detectors.   Extremely asymmetric AM has been shown to suffer more
>> from selective fading.   And, it doesn't really do anything for
>> getting through on the other end.  Instead, what really matters and
>> should be pursued as a goal, (if the operator cares about any of this)
>> is _high average_ audio power.  This is achieved with a combination of
>> compression and peak limiting.

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