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Re: [Amps] 4CX10 000J

To: <amps@contesting.com>, "Mark Hill" <g4fph@mjha.co.uk>
Subject: Re: [Amps] 4CX10 000J
From: "Tom W8JI" <w8ji@w8ji.com>
Date: Mon, 3 Jul 2006 06:55:43 -0400
List-post: <mailto:amps@contesting.com>
> Surely, for purity and on SSB, a Yaesu FT-1000MP Mk-V with 
> th PA set
> to class 'A' would not insult too much?!  Is the Rockwell 
> even better?

Most amateur transceivers are in the -30dB PEP range for low 
odd-order IM products. Even without ALC operation they 
aren't very good. With ALC they can be worse, but the 
duration of ALC "spits" is very short and so I disagree that 
the ALC problems are as harmful overall as made out to be.

In order to cause bothersome QRM, the unwanted or spurious 
signal has to take out a portion of the desired signal in a 
combination of time and level and the time duration of an 
ALC spit is generally very short compared to the time of the 
desired info on voice. Unless it is very strong compared to 
the desired signal, it will have no ill effect when from a 
single source.

Most of the harmful stuff is the actual IM, so even if the 
1000MP MKV suffers from slow leading edge ALC response it 
would be a big improvement.

As for "phase noise" what someone else posted is true. The 
noise of low level stages has been worse in the transmitters 
I have measured than synthesizer noises, mostly shot noise 
or diffusion noise in low level transistor stages. Most of 
the broadband noise in my FT1000D comes from a single FET 
that is used to control ALC.  That FET is after the SSB 
filters, so the full bandwidth of that noise makes it to the 
antenna. The receiver is the same way, a single FET of the 
same type in the last IF just beyond the filters sets the 
receiver broadband noise floor.

I've looked into all of this carefully because I needed to 
be able to receive noise floor signals (and I have a very 
low background noise level here) while my transmitter is 
running at full power.

73 Tom 


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