Tom continues to exhibit the symptoms of his recent overdose on "nice"
pills, to the benefit of everybody:
>You'd better consider phase and gain errors in the amplifiers,
>especially if the amplifiers have filters in each PA and you
>combining after the amplifiers (or driving separate antennas).
>
>You also have to consider SWR induced phase errors on transmission
>lines that are not exact multiples of 1/4 wl.
>
>As a general rule, it isn't a good idea to combine amplifiers if they
>each have low-pass filters or worse yet tunable networks, unless you
>have a way of measuring and adjusting phase and level.
Exactly.
The Motorola design notes don't explicitly state those issues, but they are
precisely documented. Input and output combining is shown AT the
amplifiers. For HF, 1/4 WL will never be seen in a box-o-amps. At VHF or
UHF, 1/4 WL can be seen and MUST be considered. At UHF, 1/4 WL
splitters/combiners are easily realized in stripline on a PCB.
In properly designed splitter/combiner-connected amps, phase and gain error
tend to cancel rather than to add at HF. As frequency rises, your mileage
variance increases too.
Filters are most economically applied before the input splitter and after
the output combiner.
Got new products for Dayton, Tom? Doesn't matter. I speak for most of the
list users when I offer my heartfelt "Thank you" for your sharing real and
accurate information. Please keep it coming.
Yeah, I'll still give you an occasional poke from my iridium-plated
rettysnitch when you say something silly, but other than that -- the more
hard and accurate info you share about what you sell, the more furiously
that information will drive new equipment sales AND dramatically reduce
your tech support calls.
In the "information wants to be free" mind-set of the internet, the more
information you give away, the more people will spend money on your
non-informational, for-profit products.
Why? Simply because they have the information they need to use your
product for their desired needs.
Duh.
Jim N6OTQ
=========================
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