wrote in message
...
On Feb 18, 10:16 pm, Bill M wrote:
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.
I had this exact problem with the Hallicrafters 5R10A.

With my signal generator set to 30 MHz, the image at 30.91
MHz was
maybe 1 dB lower. However, when I set my generator to 15
MHz (the low
end of Band 4), the image at 15.91 MHz was much less
noticeable. So,
the set is a reasonably good performer so long as you avoid
using the
high end of Band 4.

-Dave Drumheller, K3WQ

I had this same problem tuning up a Hallicrafters
S-20R, this RX goes to 44 mhz with only one RF stage so the
image rejection at the top frequency is almost nil.
Hallicrafter's did use an LO at lower than signal frequency
in some cases, for instance the S-36, a receiver that goes
up to about 143 mhz has the LO lower than signal frequency
on the top band only. The IF is about 5 mhz so the 10 mhz
difference probably made it easier to get sufficient LO
output. The S-20R appears to have the LO at higher than
signal frequency on all bands. The performance and
calibration are slightly, but noticably, better with the LO
on the correct side. Hallicrafters made some receivers with
no RF stage but tuning to the 40 mhz range, they probably
have no detectable difference in response between desired
and image signals. There should be a slight difference in
the dial calibration but it may be masked by drift in the
oscillator coil.
BTW, while many of these receivers had no adjustment
for the low end of the oscillator or RF stages its usually
possible to tune them by adjusting the coils. For instance,
on the S-20R the turns are held in place by wax so its
possible to move them around a bit and fasten them back down
again by either re-heating the existing wax (with the tip of
a soldering iron or a concentrated heat gun) or by melting a
bit of new bee's wax (can be had from art supply stores)
onto the coil. Some RX may be found to have an adjustment
section on the coil or sometimes an isolated shorted turn
that can be moved around to adjust the inductance.

--

--
Richard Knoppow
Los Angeles
WB6KBL