"- - 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.
---
.................................................. ..........
Regards from Reg, G4FGQ
For Free Radio Design Software go to
http://www.btinternet.com/~g4fgq.regp
.................................................. ..........

Receiver local oscillator tracking.

After calculating L and C component values, program OSCTRACK allows the main
2(or 3)-gang tuning capacitor to be varied over its full range, sweeping
frequency between the band edges, simultaneously displaying the tracking
error in kilohertz or as a fraction of the received tuning frequency.


The multi-gang circuitry and calculations were devised in the 1920's with
the advent of the Superheterodyne Receiver and the 1930's multi-grid
frequency-changer tubes. All had to be extremely tediously worked out with
slide-rules or log tables. Just think what the old boys could have
accomplished had this program then been available.
----
.................................................. ..........
Regards from Reg, G4FGQ
For Free Radio Design Software go to
http://www.btinternet.com/~g4fgq.regp
.................................................. ..........

"Reg Edwards" wrote -

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.
---
.................................................. .........
Regards from Reg, G4FGQ
For Free Radio Design Software go to
http://www.btinternet.com/~g4fgq.regp
.................................................. .........

Reg Edwards wrote:

Receiver local oscillator tracking.

The multi-gang circuitry and calculations were devised in the 1920's with
the advent of the Superheterodyne Receiver and the 1930's multi-grid
frequency-changer tubes. All had to be extremely tediously worked out with
slide-rules or log tables. Just think what the old boys could have
accomplished had this program then been available.

I wouldn't be surprised if Edwin Armstrong could do it in his head.


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Receiver local oscillator tracking.

The multi-gang circuitry and calculations were devised in the 1920's
with
the advent of the Superheterodyne Receiver and the 1930's multi-grid
frequency-changer tubes. All had to be extremely tediously worked out
with
slide-rules or log tables. Just think what the old boys could have
accomplished had this program then been available.

======================================

I wouldn't be surprised if Edwin Armstrong could do it in his head.

======================================

To solve the problem of calculating the four values of the trimming and
padding capacitors, two coil inductances, for given capacitance of the main
two-gang tuning capacitor, and for given edges of the frequency band,
involves the solution of four simultaneous quadratic eequations.

Edwin would have needed the assistance of at least a pencil and an empty
cigarette pack.