"Bill M" wrote in message
...
Tio Pedro wrote:
wrote in message
...
I recently refurbished a Hallicrafters 5R105 and, while performing a
re-alignment, discovered that on the Band 4 (14 to 31 MHz) the local
oscillator (LO) is below the station frequency, whereas on the three
lower bands, the LO is above.

So my question is this: Why engineer a tuning system for the high end
of the shortwave spectrum to place the LO below the station
frequency?

-Dave Drumheller, K3WQ

It would be unusual. A quick check is to see if the LO is above
or below the signal at the LOW end of the tuning range. I've
quite a few shortwave sets that were properly aligned for
high side injection at the low end, and improperly set for
low side injection at the upper end of the band.
Needless to say the midrange sensitivity was practically nil.

It's pretty easy to set the
high end of dial for the wrong side LO injection because
of the wide authority range of the LO trimmer.

I can't think of any advantage--usually high side inj.
is beneficial on the lower ranges to keep LO harmonics
from falling the tuning range or the RX.

Pete


Its a real gripe of mine! The image rejection is so poor on the top band
of many consumer grade radios that its really a moot point and the only
way to guess which side the injection goes is by evaluating which side
suffers the worse dial tracking...and often thats so close a call its
difficult to say which was intended.

-Bill

It is not a moot point... Usually the bottom tracking is fixed on
the higher bands (no padder or slug for the LO coil). If the LO on
the high end of the dial is set to the wrong side,
the mid band sensitivity will
be Zilch. Usually checking LO frequency on the lowest end
of the dial will show if it is supposed to be hi or lo side injection.