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Old 18th Mar 2018, 11:26 pm   #7
Radio Wrangler
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Join Date: Mar 2012
Location: Fife, Scotland, UK.
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Default Re: Armstrong 625 receiver

In a regular long/medium wave broadcast set the incoming signal frequency of whatever station it is tuned to, is converted to a fixed intermediate frequency (IF) of about 465kHz.

This is a handy frequency at which to provide most of the set's gain and the selectivity which separates the wanted channel from its neighbours.

455Khz is higher than the top end of long wave, and lower then the bottom frequency of the medium wave band. There's a convenient gap there with no broadcasters, just a few navigation beacons for aircraft.

The Armstrong 600 is odd in that its IF is placed above the top of medium wave, so that it converts all RF that is covers upwards to this higher IF, hence it's an 'upconverter'

So long wave and medium wave are covered in just one long, wide bnd with no need for a gap in the middle. The lack of a gap is only useful if you have an aeroplane to steer and you have a direction-finding loop antenna on top of the plane.

An unusual quirk.

David
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