[RTTY] Yaesu RTTY power

[Anthony J. Cioffi]

I always was under the impression(from when Peter released the original PSK31) that low power was the order. Generally 10 watts max. Here I see stations indicating they run 30, 40 and even higher power for PSK. Does this not cause more harmonics, which are visible on the waterfall?

Sent From Blackberry

Anthony J. Cioffi
www.n2ki.com

-----Original Message-----
From: Kok Chen <chen at mac.com>
Sender: rtty-bounces at contesting.com
Date: Sun, 16 Jan 2011 10:39:24 
To: RTTY Reflector<rtty at contesting.com>
Subject: Re: [RTTY] Yaesu RTTY power


On Jan 16, 2011, at 10:21 AM, Ktfrog007 at aol.com wrote:

> For rag chewing, which is mostly  on PSK, I run 30-40W.  


Remember that PSK31 works under a different "rule."

PSK31 is, through the genius of Peter G3PLX, not simply PSK modulation but also is amplitude waveshaped.  If not for the amplitude waveshaping, PSK will have the same wide keying sidebands that you see on FSK signals.  

Instead, when you look at an idle PSK signal, all you see are just two carriers, 31.25 Hz from one another (unless the transmitter has poor IMD, when you will see more keying components).

However, this waveshaping also creates a crest factor of 3 dB.  If your transmitter clips at 100 watts, you should not set the average RF power, under the idle PSK31 modulation, to any greater than 50 watts.

This peak power to average power ratio is not such a big deal to hams.  But to professionals, crest factor matter since peak transmit power is sometimes a constraint in the design.  Because of that, PSK31 is probably not as useful to them, but the waveshaping of PSK31 a going to be a godsend when the sunspots come back again to face many more digital mode stations.

73
Chen, W7AY

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