"Scott Dorsey" wrote in message
...
In article , Brian Hill
wrote:
"Randy or Sherry Guttery" wrote
in message

To align the IF correctly - one needs a sweep generator.
And yes - not
aligned correctly - they would imitate the nearest "barn
door" for
bandwidth.

Yes a sweep gen and oscilloscope are nice in this regard
but the job can be
done correctly using a accurate sig gen or at least close
enough for this
type of rig.

I believe that the IF on the AR-88 is peaked and not
staggered, which
means you can indeed get away with just a signal generator
and a scope.

Again, the IF on the AR-88 may be pretty tight for
something with only
LCR networks, but it's not anywhere near as tight as
crystal or mechanical
filters will allow. This is either a substantial
advantage or disadvantage
depending on your application.
--scott

--

I just rechecked the instruction book for the AR-88, the
IF is indeed peaked, not stagger tuned. What may confuse the
issue is that two of the transformers have variable coupling
and two also are double stages, that is, there are four
coils and what amounts to a filter in the transformer. The
stages should be peaked when at the minimum bandwidth
setting without the crystal filter. In that setting the
transformers are all slightly undercoupled so should have
single peaks. The complex transformers result in better
skirt selectivity than simple transformers would give with
the same number of IF stages. The selectivity will not be as
good as the 6 or pole mechanical or crystal lattice filters
found in many newer receivers but should still be very good
in comparison to most receivers. This IF is unique in having
both double IF transformers _and_ variable coupling. A
similar transformer, but without the variable bandwidth, is
found in the National HRO-60 (and I think also the HRO-50).
While "visual" tuning using a sweep oscillator and scope
will probably result in more accurate tuning, or at least
easier tuning, conventional methods should work fine with
some care. A similar condition is met in other receivers
with variable bandwidth IFs such as the Super Pro series,
the SP-600 and some others. The coupling method used by RCA
and Hammarlund results in a symmetrical pass band at all
settings, some others, notebly the system in the
Hallicrafters SX-28, do not.
Note that there is no external phasing control for the
crystal filter on the AR-88, it has an internal trimmer.
Some other versions of the receiver (like the CR-88) do have
an external phasing control with some re-arrangements of the
controls on the front panel.
RCA used hundreds of these receivers in triple diversity
combinations at RCA Communications facilities and singly at
Radiomarine shore stations. They are not a match for the
better, later designed, double or triple conversion
receivers such as the Collins 51J or R-390 series, for one
thing no single conversion receiver can match the very high
image rejection of the double conversion types at
frequencies above about 10mhz.
The 6SG7 tubes used in the AR-88 RF and IF stages are
about equivalent to the 6BA6 with somewhat higher
capacitance due to the octal base.
A great many of these receivers, particularly the ones
used in diversity set-ups were not equipped with signal
strength meters but they can be added (if you can find them)
to any of them.
There are operating and maintenance handbooks at several
sources on the web.


--
---
Richard Knoppow
Los Angeles, CA, USA