[AMPS] IMD

[Steve Thompson]

-----Original Message-----
From: Peter Chadwick <Peter.Chadwick@zarlink.com>
To: @AMPS <amps@contesting.com>; 'John T. M. Lyles' <jtml@lanl.gov>; '2'
<2@vc.net>
Date: 18 September 2001 08:06
Subject: RE: [AMPS] IMD


>
>Rich said:
>
>>Few AB1-grid driven. or AB2-GG amplifiers have as much distortion as
>>modern transceivers.
>
>As evidenced by the published test figures on, for example,  the TS2000.
>Interesting, since modern MOSFET PA's are supposedly very linear.
The latest LDMOS does look quite good, but its mainly targeted at UHF and uW
comms systems. Whenever I test the regular DMOS used for most hf/vhf
applications it usually comes up with a banana shaped Po/Pi characteristic -
there isn't a substantial true linear portion. If you get the load line and
bias levels right, you can usually get mediochre 3rd order IMD, reasonable
5th and good beyond that, so the occupied spectrum can be better than an
equivalent bipolar.

I reckon the real problem with the TS2000 is just that the transmit chain is
run too hard in order to reach the magic 100W spec. The reviews suggest it
improves a lot for backing off the power, so there's probably more than one
stage compressing at the same time. Smacks of a mix of duff design, duff
engineering and penny pinching. No excuse for any of it.

Steve


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