[Amps] MLA-2500 question
Ian White, G3SEK
G3SEK at ifwtech.co.uk
Sat Dec 13 09:21:35 EST 2003
Roger Parsons wrote:
>Neither of my MLA2500s has a reflected power
>monitoring position - other versions may have. I think
>that the purpose of the trimmer is to try and make the
> flat across the frequency range.
As Steve said, it's intended to be a 'bridge balance' or directivity
adjustment, to make the forward power indications independent of load
mismatch.
All SWR meters and directional wattmeters have this pre-set adjustment,
in one form or another. Sometimes it's a variable capacitor or resistor,
but sometimes it's a built-in fixed value. In the Bird slugs it's a
bendable capacitive tab.
However, this directivity adjustment doesn't directly affect broadband
performance. That is rather a separate issue...
>It fails
>miserably....
Some SWR bridge designs are broadband, others not. Most HF directional
wattmeters use the Bruene bridge - the one where the line passes through
a toroid - because it is inherently broadband. Or should be, unless
there's a serious design error...
--
73 from Ian G3SEK 'In Practice' columnist for RadCom (RSGB)
Editor, 'The VHF/UHF DX Book'
http://www.ifwtech.co.uk/g3sek
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