[Amps] SPE 2K RTTY Duty Cycle / spectral cleanliness

[amsctalx at comcast.net]

Spectral purity is even more important in amateur radio, as individual stations do not have fixed frequency assignments ('channels') and no analysis of the consequences of interference occurs prior to transmission. The practical outcome of this is that some stations, especially those using a '12V DC' transceiver set to full output power and then amplified, produce -60dBm sidebands at my QTH. 

Some of you may be content transmitting several watts of interference, but many of us aren't and take whatever reasonable steps we can to prevent it. 

73, 

Mike - N8MSA 

----- Original Message -----

From: "Leigh Turner" <invertech at frontierisp.net.au> 
To: amps at contesting.com 
Sent: Friday, May 22, 2015 9:10:53 AM 
Subject: Re: [Amps] SPE 2K RTTY Duty Cycle / spectral cleanliness 


All good valid points that you make here Kevin. 

There is also an equal fascination / obsession in some ham radio quarters 
with IM3 and levels! We are talking here of HF amateur / ham band 
transmitters NOT professional transmitters where spectral cleanliness is 
more important. 

It's the higher order IM stuff / crud that has to be curtailed... 

The modern trend towards Adaptive pre-distortion techniques works well to 
clean up mediocre PA transistors and sort of turn a sow's ear into a silk 
purse. 

Leigh 
VK5KLT 

-----Original Message----- 
From: Amps [mailto:amps-bounces at contesting.com] On Behalf Of Kevin Stover 
Sent: Friday, 22 May 2015 10:28 PM 
To: amps at contesting.com 
Subject: Re: [Amps] SPE 2K RTTY Duty Cycle 

There are NO 12V final amateur transceivers that make -40dB IM3, none. Never 
have been, never will be. The best are at -33 to -35. 

Those transceivers capable of 200 Watts are all usinng 28 or 50V finals and 
can reach -40 depending on the low pass filter used behind the PA.It's time 
for the manu's to get rid of this fascination with running everything off a 
battery. 

The most expensive part of any SS amp is NOT the finals themselves it's the 
LPF that will take 1500 watts and keep harmonics legal (-43db HF, -60dB 6m). 
That's not IM3. Name the amp that hits an IM3 of -40. The 8877 will come 
close, the Russian triodes won't, none of the tetrodes will do it. 


-- 
R. Kevin Stover 
AC0H 
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