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Message-ID: <E649192C49894E7A947DF3111F30B689@JimPC>
From: "James Moritz" <james.moritz@btopenworld.com>
To: <rsgb_lf_group@blacksheep.org>
References: <002801cc7e08$6e9ec9c0$0401a8c0@xphd97xgq27nyf> <4E839D14.5080105@telus.net> <002f01cc7e84$49295490$0401a8c0@xphd97xgq27nyf> <004901cc7ebd$3d0db910$0401a8c0@xphd97xgq27nyf> <4E849D17.3030607@telus.net>
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Date: Thu, 29 Sep 2011 19:06:48 +0100
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Subject: Re: LF: Wilkinson combiner
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Dear Mal, Scott, LF Group,

The Decca design does not only use a combining transformer (effectively 
connecting the 3 PA module outputs in parallel). Each PA module has a "guard 
circuit" RF current limiter that protects the individual PA in the event of 
a low-impedance antenna fault, or a fault in one of the other PAs. The Decca 
design concept provides a measure of redundancy - if one PA fails, a new 
module can be "hot swapped" while the other two continue to produce some 
output. This isn't really needed for an amateur radio TX - with the bigger 
SMPS MOSFETs available today, it is easier and cheaper to design and build a 
single large PA.

But with a large antenna as you often describe, a high power PA really 
shouldn't be necessary - 100 - 200W should be plenty to reach 1W ERP. If it 
really takes so much power, perhaps you really need to investigate why your 
antenna efficiency is so dismal before running up your electricity bill!

Cheers, Jim Moritz
73 de M0BMU