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Re: [Amps] Expert 2K / lack of specs /

To: Jim Thomson <jim.thom@telus.net>
Subject: Re: [Amps] Expert 2K / lack of specs /
From: "Joe Giacobello, K2XX" <k2xx@swva.net>
Reply-to: k2xx@swva.net
Date: Sun, 10 Mar 2013 12:36:39 -0400
List-post: <amps@contesting.com">mailto:amps@contesting.com>
I believe that some on this forum were interested in the IMD specs for the 2K. The data that were generated for FCC approval can be found here: http://g4ujs.shacknet.nu/spe_2k-fa.pdf

They seem pretty good. The thing that bothers me is that the drive they used to obtain 1,500W out was about twice what I require. Makes me wonder if the unit that was used to generate the data was different from those currently on the market.

73, Joe
K2XX

On 3/10/2013 9:19 AM, Jim Thomson wrote:
Date: Wed, 6 Mar 2013 11:18:18 +1030
From: "Leigh Turner"<invertech@frontierisp.net.au>
To:<amps@contesting.com>
Subject: Re: [Amps] Expert 2K / lack of specs / pragmatism prevails


When homebrewing big SS amps I've found designing 'em big and de-rating them
a couple of dB below sat Po yields plenty adequate IMD performance for clean
ham band SSB use. Certainly commensurate with the IMD of modern transceiver
PA stages and their associated ALC Tx power control loops.

Inefficiency is the inevitable trade-off one makes when wanting to run the
SS amp clean.

Leigh
VK5KLT

##  leigh, there would be no loss in eff, IF you used bigger devices, or more 
of them.
The inefficiency starts up when you design a 1 kw amp,,and then operate it at 
500w.
Its cleaner at 500w, but its inefficient.  Reduce the voltage a bit, like 41%, 
and eff
is back on track, but imd suffers due to lower voltage used.

## Instead, used devices rated for 2 kw output, design the amp for 1 kw output,
run the highest voltage possible and eff will be  as high as it gets.   IMD 
will be a lot lower,
and devices will run cooler.   Trade off is you require more devices or bigger 
ones.  heck,
the cooling can be based on 1 kw output, and also the pwr supply.

##  enough of these freescale devices may be the ticket. loads of power
AND low imd for a change.   Just cuz you don’t hear imd when listening to
an S-9 signal on a noisy band doesn’t mean there is no imd.  listen to the
same station, but at 40 over S-9, on a quiet band, and presto, imd is easy to
spot.   If IMD is only 30 db below pep ( arrl method), IMD  will be 10 db
over S-9.   IMD really needs to be down  60 db below pep, when listening
off freq.

##  Its’ the IMD 7-9-11-13-15th that causes all the problems.  Class A  and 
some type
of sliding bias scheme would work  or the eq of EBS.   Or just operate the 
devices at
well below their max ratings, like 1/3 their rating.

##  You don’t see this lousy imd in the commercial /marine/aviation world.

Jim  VE7RF


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