Hi gang,
I'm aligning an S-38E. I have the manual from Bama which is very
helpful, but there is no mention of whether the LO is high side or low
side injection. The oscillator (and RF for that matter) coils have no
slugs, there is only a trimmer cap to set at the high end of each band.
Since the oscillator trimmer will reach either high or low side, I
wonder which one is correct. Perhaps with no way to set the inductance
at the low end, it really doesn't make much difference?

Seems like this is not too bad a little rx considering it is
essentially an All American Five with a bandswitch.

Thanks
Bob WB0POQ

"Bob Liesenfeld" wrote in message
...
Hi gang,
I'm aligning an S-38E. I have the manual from Bama which is very
helpful, but there is no mention of whether the LO is high side or low
side injection. The oscillator (and RF for that matter) coils have no
slugs, there is only a trimmer cap to set at the high end of each
band.
Since the oscillator trimmer will reach either high or low side, I
wonder which one is correct. Perhaps with no way to set the
inductance
at the low end, it really doesn't make much difference?

Seems like this is not too bad a little rx considering it is
essentially an All American Five with a bandswitch.

Thanks
Bob WB0POQ


Try high side on the first 3 bands, low side on band 4. That should get
the oscillator traking reasonably closely with the dial. If not, switch
band 4 from low side to high side.

Frank Dresser

"Bob Liesenfeld" wrote in message
...
Hi gang,
I'm aligning an S-38E. I have the manual from Bama which is very
helpful, but there is no mention of whether the LO is high side or low
side injection. The oscillator (and RF for that matter) coils have no
slugs, there is only a trimmer cap to set at the high end of each band.
Since the oscillator trimmer will reach either high or low side, I
wonder which one is correct. Perhaps with no way to set the inductance
at the low end, it really doesn't make much difference?

Seems like this is not too bad a little rx considering it is
essentially an All American Five with a bandswitch.

Thanks
Bob WB0POQ

Just a few general notes if no answers forth coming:

1: Measure the LO with a counter at the low end (if there is no
adjustment for setting the low end of the tuning);
that will tell you if that band uses hi or lo side injection.
It makes a big difference if set wrong!!!

2: If the osc. section of the tuning cap uses smaller sized plates, the
radio is probably hi side injection.

Peter

Uncle Peter wrote:


Just a few general notes if no answers forth coming:

1: Measure the LO with a counter at the low end (if there is no
adjustment for setting the low end of the tuning);
that will tell you if that band uses hi or lo side injection.
It makes a big difference if set wrong!!!

Not on an S-38! It probably won't track well enough to determine for sure.


2: If the osc. section of the tuning cap uses smaller sized plates, the
radio is probably hi side injection.

Ya might want to rethink that suggestion Pete. Any set with AM band on
it will have smaller osc plates.

I was recently struggling with a cheapo little SW radio and it
tracks/tunes/rejects images about the same (which means not very good)
no matter which way ya go on the upper band. Low side may have had an
edge in this particular case but it would take a jury of sharp-eared
engineers to decide.

-Bill M

"Bob Liesenfeld" wrote in message
...
Hi gang,
I'm aligning an S-38E. I have the manual from Bama which is very
helpful, but there is no mention of whether the LO is high side or low
side injection. The oscillator (and RF for that matter) coils have no
slugs, there is only a trimmer cap to set at the high end of each
band.
Since the oscillator trimmer will reach either high or low side, I
wonder which one is correct. Perhaps with no way to set the
inductance
at the low end, it really doesn't make much difference?

Seems like this is not too bad a little rx considering it is
essentially an All American Five with a bandswitch.

Thanks
Bob WB0POQ


Be sure the bandspread capacitor is fully open during alignment.

Frank Dresser

"- - Bill - -" exray@coquidotnet wrote in message
...
Uncle Peter wrote:


Just a few general notes if no answers forth coming:

1: Measure the LO with a counter at the low end (if there is no
adjustment for setting the low end of the tuning);
that will tell you if that band uses hi or lo side injection.
It makes a big difference if set wrong!!!

Not on an S-38! It probably won't track well enough to determine for
sure.


My S-38s track pretty well. The maximum error is about the width of the
dial pointer. That's on a S-38(No suffix), 5R10A and a S-38D. Band 4
is most sensitive to lead dress, and fussing around with it helped.

In each case, high side injection gave a much greater error.



2: If the osc. section of the tuning cap uses smaller sized plates,
the
radio is probably hi side injection.

Ya might want to rethink that suggestion Pete. Any set with AM band
on
it will have smaller osc plates.

All the Hallicrafters SW radios I seen use the same size oscillator and
RF tuning capacitor sections. They use both a padder and trimmer for
the AM broadcast band. The S-38s use only trimmers for the higher
frequency bands. I certainly haven't seen them all, and that includes
the S-38E.



I was recently struggling with a cheapo little SW radio and it
tracks/tunes/rejects images about the same (which means not very good)
no matter which way ya go on the upper band. Low side may have had an
edge in this particular case but it would take a jury of sharp-eared
engineers to decide.

-Bill M


In my expirence with similar radios, the tracking should be good, the
peaking should be reasonably close but broad on the top 2 bands, and the
image rejection gets pretty poor above 10 Mc or so.

Frank Dresser

"- - Bill - -" exray@coquidotnet wrote in message
...
Uncle Peter wrote:


Just a few general notes if no answers forth coming:

1: Measure the LO with a counter at the low end (if there is no
adjustment for setting the low end of the tuning);
that will tell you if that band uses hi or lo side injection.
It makes a big difference if set wrong!!!

Not on an S-38! It probably won't track well enough to determine for
sure.


2: If the osc. section of the tuning cap uses smaller sized plates,
the
radio is probably hi side injection.

Ya might want to rethink that suggestion Pete. Any set with AM band on
it will have smaller osc plates.

I was recently struggling with a cheapo little SW radio and it
tracks/tunes/rejects images about the same (which means not very good)
no matter which way ya go on the upper band. Low side may have had an
edge in this particular case but it would take a jury of sharp-eared
engineers to decide.

-Bill M


1: It doesn't matter providing the set has fixed inductors;
the small-value trimmer used for setting the high end will not have enough
authority to permit setting injection improperly on the low end of the
tuning.
A frequency counter will usually determine the correct LO side for injection
if you check the LO at the low end of the tuning range.
You can set it wrong on the high end of the tuning range, but the radio
will
work like crap midband where it still has some front end selectivity.
You may think it is working, but unless you check
it across the full tuning range you might be surprised

2: The majority of sets I collect seem to have equal sized plates in the
osc. and mixer/rf sections? I don't think the offset oscillator section
came
into vogue until the late 30s or early 40s??

Pete

" Uncle Peter" wrote in message
news:4WqHb.13081$WQ3.12463@lakeread05...

"- - Bill - -" exray@coquidotnet wrote in message
...
Uncle Peter wrote:


:
1: work like crap midband where it still has some front end
selectivity.
You may think it is working, but unless you check
it across the full tuning range you might be surprised


I meant to say if the radio LO injection is set for the wrong end on an
upper HF band the LO will cross the signal frequency at some point
mid range for that band.

Pete

Uncle Peter wrote:

The majority of sets I collect seem to have equal sized plates in the
osc. and mixer/rf sections? I don't think the offset oscillator section
came
into vogue until the late 30s or early 40s??
===============================
All multi-band radios use equal sized tuning capacitor sections in the
local oscillator (LO) and Mixer/RF stages. Padder caps are used to
adjust the oscillator section to provide proper tracking.

Single-band sets often use a so-called "cut plate" tuning cap with a
smaller oscillator section. This eliminates the need for a padder
capacitor. But, the size of the oscillator section depends on the
relationship between the IF frequency and the tuning range.
Multi-band sets would need a different sized oscillator section for
each band. That is why the equal sized section tuning capacitor is
used in multiband sets and padder capacitors are used to reduce the
oscillator section capacity to the proper amount for each individual
band.

The top band on many low-cost, single-conversion sets (like the S-38
series) don't use a padder capacitor since the IF frequency is such a
small percentage of the signal frequency. These are the sets that
often have the LO on the low side of the signal frequency. If a
padder capacitor is used in the oscillator section, then the LO is on
the high side of the signal frequency for sure. If no padder is used,
then the LO may be on the high or low side. Unfortunately, the
alignment instructions seldom state the LO location. On the
Hallicrafters S-40, the LO is below the signal frequency on Band 4. I
determined this by experiment.

All this stuff is discussed in detail in the Radiotron Engineers
Handbook, 4th Edition, beginning on page 1002.

Best Regards,

Ed
Canyon Lake, TX

Superhet receivers.

For design of RF and local oscillator tuned circuits, L and C values for
correct tracking, download program OSCTRACK from website below in a few
seconds and run immediately.
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.................................................. ..........
Regards from Reg, G4FGQ
For Free Radio Design Software go to
http://www.btinternet.com/~g4fgq.regp
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