Re: [Amps] MLA-2500 question

["Ian White, G3SEK" <G3SEK@ifwtech.co.uk>]

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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