[Amps] 3cx3000A7 driver

[Karl-Arne Markström]

Peter,

You are certainly right...

Making a medium to high power HF transmitter with "close-in" noise sidebands of 
-160 dBc/Hz would be a very difficult task indeed.

It is not only the spectral purity of all oscillators involved that count, but
also the aggregated noise properties of the amplifiers and level control loops.

Having been deeply involved with military "co-located" HF systems in the past,
I fully appreciate the efforts put into "high-end" HF hardware by their designers, 
i.a. the necessity of building the input end of an HF power amplifier in the 
same way as a receiver low-noise amplifier, not to degrade the overall SNR. 

Despite these efforts, it is still uncommon to find better noise floors than -150 dBc/Hz at 20 kHz spacing
for "production" HF equipment.

An account of the design philosophies required to approach these levels of performance can be found
in a paper "A New Generation of HF Power Amplifiers" by K G Nygren in the Proceedings of the Nordic HF Conference HF92, which goes into the design considerations for the ITT-Standard Radio SSA1020 1 kW MOSFET amplifier.

Having accomplished transmitter and receiver sideband noise floors of -160 dBc/Hz, at, say, 10 kHz spacing, the next major task would be finding a way of reducing the IM sidebands of  tunable SSB transmitters to corresponding levels....

73/

Karl-Arne
SM0AOM


----- Original Message ----- 
From: "Peter Chadwick" <g3rzp at g3rzp.wanadoo.co.uk>
To: "Harold Mandel" <ka1xo at juno.com>; <g3rzp at g3rzp.wanadoo.co.uk>; "'Frank Goenninger'" <frgo at mac.com>; <amps at contesting.com>
Sent: Sunday, July 23, 2006 9:14 AM
Subject: Re: [Amps] 3cx3000A7 driver


> Hal said:
> >This radio is built for the future.
> 
> In tomorrow's world -160dB(c) per cycle may actually be
> a force to contend with......<
> It may be, although I have severe doubts about the technology needed. This is because, in the final analysis, low phase noise requires high power. S/N becomes osc power over thermal plus implementation noise. Modern IC technologies are pushing to smaller geometries, which mean lower voltages and so SNRs are tending to drop. Implementing a DDS to go fast without needing a BIG heatsink (e.g. the old Plessey SP2001 500MHz ECL DDS) becomes a bit of a difficulty - you need to do it in CMOS. But reduced geometry CMOS has reduced SNR, because of the lower voltage swings. It also has leakage problems, which can also degrade SNR, as well as lead to higher current consumption - which is why in the company I work in, we're still pretty well confining ourselves at the moment to using 0.18 micron CMOS, especially as we need RF analogue characterisation.  In any case, until everyone else on the band has rigs of equal performance, there's not that much advantage, and as far as IMD goes, for
>   the majority of people, need. See my 2002 QEX article.
> 
> 73
> Peter G3RZP
> _______________________________________________
> Amps mailing list
> Amps at contesting.com
> http://lists.contesting.com/mailman/listinfo/amps
> 
> 
> -- 
> No virus found in this incoming message.
> Checked by AVG Free Edition.
> Version: 7.1.394 / Virus Database: 268.10.3/395 - Release Date: 2006-07-21
> 
> 


-- 
No virus found in this outgoing message.
Checked by AVG Free Edition.
Version: 7.1.394 / Virus Database: 268.10.3/395 - Release Date: 2006-07-21