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[Amps] HV MOSFETs for RF

To: <amps@contesting.com>
Subject: [Amps] HV MOSFETs for RF
From: "Jim Thomson" <jim.thom@telus.net>
Date: Thu, 11 May 2017 10:28:36 -0700
List-post: <amps@contesting.com">mailto:amps@contesting.com>
Date: Wed, 10 May 2017 19:01:40 -0500
From: "Kevin Stover, AC0H" <kstover@ac0h.net>
To: amps@contesting.com
Subject: Re: [Amps] HV MOSFETs for RF

<All,

<IMHO the problem with today's 100W radios is that they are designed for 
<12V finals. Comparing a "modern" solid state radio designed to run on 
<12V finals to a Collins 32S-3 is borderline ridiculous. There is a price 
<to be paid for "no tune" and using 12V finals makes it worse.

<If I was designing a final section for one of these rigs it would be a 
<pair of 50V MRF-150's derated to 150W max out. They're plentyful, 
<comparatively cheap, probably close to a matched pair of 6146B/W's for 
<TS-520.
<Of course there are going to be people who are unhappy not being able to 
<run the rig "all knobs to the right", to the max of a pair of 
<MRF-150's...300W, but too bad. Buy someone else's rig.

<I'd bet a final section built and run like that would hit -40 IMD 
<running full tilt boogey. Add a little pre-distortion and we'd hit -50dB.

<The days of the 12V SSPA in rigs are numbered, or should be.

<So... that leaves me with a rig that will do -45 to -50 IMD and an amp 
<(AL-1500, Ameritron's number) that'll do -38. Hmmmm.

<Let the anecdotes fly.



###  marine SSB gear runs just fine on 11-12 vdc..and meets ITU IMD specs,
go figure.   Before that, marine ssb gear would meet the even more stringent 
FCC specs. 

##  A  DC to DC converter would perhaps solve a loot of issues, and still
allow for 12 vdc operation.   The car audio folks have already figured that one 
out.

##  The  2 x VRF-151  SS amp in the arrl hand book has good imd, when  run
at 200-250 w out..and superb at 100-150w.   A local buddy built it. 

##  300W with 2 x MRF-150s is pushing your luck.   If you wanted
300w out, use 4  x MRF-150s. 

##  use the pre-distortion, and take the sample from the output of your 
AL-1500, and its   -38  will improve to –48 to –52...problem solved. 

Jim  VE7RF




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