I am having a lot of trouble understanding the proper method to align
the crystal filter section (off the output of 3rd IF transformer)in an
SX-71. The manual suggests "rocking" the signal generator around the
IF frequency (455khz) while turning the IF transformer slug and
monitoring the output level to find a null between two peaks. You are
supposed to set the slug to the null. The output tone is to be created
using the BFO set for 1kz at the IF frequency. I don't understand what
is creating the peaks and null... the rocking of the generator or the
adjusting of the slug? There is a huge null created just by rocking
the generator as the beat frequency drops from 1khz to zero and then
ramps up again on the other side. I can't imagine this is the null,
but it overpowers anything else I am seeing. Then how do I set the
slug at the null point, when its impact is hardly discernible? I could
be out to lunch, but why not use a sweep generator and scope to
actually look at the wave shape being passed through that section of
the IF. Or, why not just adjust the slug to provide the highest peak
at the crystal frequency (which is actually 456.7khz) as is
recommended for the rest of the IF section?

BTW, this is my first communications receiver. Up to now I have been
restoring test equipment, broadcast radios, and a couple of TVs (all
tube gear). Any and all advice would be much appreciated. So far in my
aligning the SX-71, I seem to have increased the ringing caused when
the filter is used to the point it seems hardly useful. I don't know
if that was caused by misadjusting this particular slug, or because I
aligned the rest of the IF to exactly to the crystal instead of just
455khz, which is what they said to do. I have recapped the unit (just
the papers), replaced a few far out of range resistors and changed a
couple of weak tubes.

Dan

"geojunkie" wrote in message
om...
I am having a lot of trouble understanding the proper method to align
the crystal filter section (off the output of 3rd IF transformer)in an
SX-71. The manual suggests "rocking" the signal generator around the
IF frequency (455khz) while turning the IF transformer slug and
monitoring the output level to find a null between two peaks. You are
supposed to set the slug to the null. The output tone is to be created
using the BFO set for 1kz at the IF frequency. I don't understand what
is creating the peaks and null... the rocking of the generator or the
adjusting of the slug? There is a huge null created just by rocking
the generator as the beat frequency drops from 1khz to zero and then
ramps up again on the other side. I can't imagine this is the null,
but it overpowers anything else I am seeing. Then how do I set the
slug at the null point, when its impact is hardly discernible?

This is very difficult to do with a standard service type signal
generator. You need one that tunes very slowly around 455kc. The null
you are looking for is very sharp.

I did this a couple of years ago on my SX-62. I found the instructions
in the manual confusing, but basically you are looking for the deepest
difference between the bottom of the null and the top of the peak.
"Rocking" means tuning the signal generator up and down a few tens of
cycles or so to feel out the null and peak. The adjustments will change
the frequencies of the notch and peak slightly. So you are manually
sweeping back and forth, back and forth, and so on.

You don't really need the BFO, if you monitor the voltage of the AVC
line.


I could
be out to lunch, but why not use a sweep generator and scope to
actually look at the wave shape being passed through that section of
the IF.

That would work if you can sweep slow enough. The crystal rings too
much with a 60 cps sweep speed.


Or, why not just adjust the slug to provide the highest peak
at the crystal frequency (which is actually 456.7khz) as is
recommended for the rest of the IF section?

That's probably fine. Getting the crystal filter just right is more
important in the narrowest modes, like CW. It also helps with SSB, it's
not so important with AM. The null can be helpful with hets, but it
takes a bit of practice to use.

It's too bad the single crystal filter doesn't help much with adjecent
channel selectivity, which what is really needed for good AM DXing.

Also, the peak/null of the filter is so narrow that the normal receiver
drift has to be constantly compensated for.


BTW, this is my first communications receiver. Up to now I have been
restoring test equipment, broadcast radios, and a couple of TVs (all
tube gear). Any and all advice would be much appreciated. So far in my
aligning the SX-71, I seem to have increased the ringing caused when
the filter is used to the point it seems hardly useful.

Well, the ringing at least that tells you your crystal is still good.
Doesn't this crystal filter have a switch between sharp, narrow and
broad? The ringing should go down as the filter goes to it's broader
positions. I have a couple of single crystal filter radios. They will
both demodulate CW and SSB with the ringing crystal filter in the sharp
position. It's not a useful feature, at least for SSB. Tuning is
hypercritical, and normal drift will detune it within seconds.



I don't know
if that was caused by misadjusting this particular slug, or because I
aligned the rest of the IF to exactly to the crystal instead of just
455khz, which is what they said to do. I have recapped the unit (just
the papers), replaced a few far out of range resistors and changed a
couple of weak tubes.

Dan

There's good reasons the manufacturers gave up on the single crystal
filter decades ago. The ceramic and multipole crystal filter are easier
to use, and have much better adjacent channel selectivity. But they can
be fun to use, once you get the knack.

Frank Dresser

I think you just turned the light on for me. I have been sweeping
through a much broader range and this is what was causing the BFO to
swing through 0hz. I have an HP606a and am monitoring with a 5245L, so
I can move in small increments. I will watch much closer and try more
subtle movements. I also will give the AVC a try, as that would
eliminate any audio frequency related swing in output level from the
equation.

I did try a sweep last night and it worked very well on normal IF
setting... a beautiful textbook curve. With the crystal filter engaged
(it has two settings, broad and sharp) and the phasing set at zero it
just about wipes out the signal. You can get it back in by turning the
phasing, but then I got the oscillation type of ringing that you
mentioned would likely happen with a 60hz sweep. Thus, I could not get
a clean curve with the filter on using the sweep. I was going to
trying better connections tonight, but perhaps it is inherent in the
crystal.

There is conflicting information in my 3 sources (Sams, the manual,
and a tech bulletin on alignment) that I am still unclear about: The
tech bulletin mentions to set the phasing control to have the plates
1/2 meshed during this procedure and to reset the knob so that this
becomes zero. The other sources don't even mention where to set the
phasing at all... yet it has a big impact. So should the filter put
the null in the center of what the IF is passing or off to one side
(my gut says to one side, but I have no reference)? Where would "zero"
on the knob normally be in relation to all this?

Using this radio has been a lot of fun. I figured out how to use the
BFO to bring in SSB transmissions, and of course it is great for CW.
The phasing and BFO combined with some strange signals out there can
create some incredible 50s science fiction sound effects... I guess I
am easily entertained. After aligning the am is working the best I
have ever heard, and I am getting commercial broadcasts from literally
all over. I might be getting the HAM bug.

Dan

"geojunkie" wrote in message
om...
I think you just turned the light on for me. I have been sweeping
through a much broader range and this is what was causing the BFO to
swing through 0hz. I have an HP606a and am monitoring with a 5245L, so
I can move in small increments. I will watch much closer and try more
subtle movements. I also will give the AVC a try, as that would
eliminate any audio frequency related swing in output level from the
equation.

I did try a sweep last night and it worked very well on normal IF
setting... a beautiful textbook curve. With the crystal filter engaged
(it has two settings, broad and sharp) and the phasing set at zero it
just about wipes out the signal. You can get it back in by turning the
phasing, but then I got the oscillation type of ringing that you
mentioned would likely happen with a 60hz sweep. Thus, I could not get
a clean curve with the filter on using the sweep. I was going to
trying better connections tonight, but perhaps it is inherent in the
crystal.

I tried sweeping mine at 60Hz, and it was only semi-readable. I think
it would have worked better at maybe 10Hz.


There is conflicting information in my 3 sources (Sams, the manual,
and a tech bulletin on alignment) that I am still unclear about: The
tech bulletin mentions to set the phasing control to have the plates
1/2 meshed during this procedure and to reset the knob so that this
becomes zero. The other sources don't even mention where to set the
phasing at all... yet it has a big impact. So should the filter put
the null in the center of what the IF is passing or off to one side
(my gut says to one side, but I have no reference)? Where would "zero"
on the knob normally be in relation to all this?

Does the scale on the knob have the zero in the middle, something
like -5 0 +5? Try adjusting the filter for the largest signal
difference between the peak and the null. That should be your mid/zero
point.

I'll post a couple of pages from the 1955 ARRL handbook on the
alt.binaries.picture.radio group.



Using this radio has been a lot of fun. I figured out how to use the
BFO to bring in SSB transmissions, and of course it is great for CW.
The phasing and BFO combined with some strange signals out there can
create some incredible 50s science fiction sound effects... I guess I
am easily entertained. After aligning the am is working the best I
have ever heard, and I am getting commercial broadcasts from literally
all over. I might be getting the HAM bug.

Dan

Listen for the digital SW modes which sound a little like an old
propeller airplane. Play with the filter and BFO. Very amusing,
something to do when the 3 Stooges aren't on. Or when Joe Besser turns
up.

Frank Dresser

Out of curiosity, where are you guys reading the output of the IF? After
the detector or right at the transformer output?
Thanks

--
Brian Denley
http://home.comcast.net/~b.denley/index.html
"Frank Dresser" wrote in message
...

"geojunkie" wrote in message
om...
I think you just turned the light on for me. I have been sweeping
through a much broader range and this is what was causing the BFO to
swing through 0hz.

In article ,
"Frank Dresser" writes:

That would work if you can sweep slow enough. The crystal rings too
much with a 60 cps sweep speed.

The typical 60 Hz sweep rate is way too much even for the non-crystal narrow
selectivities of the HQ-180. I had to use an old and battered Wavetek with a
slow sweep (just a few Hz) at the 60 KC IF freq, to align a reasonable
compromise between the CW narrow peak and a decent symmetrical AM bandpass.

The problem was not ringing, just failure to respond at all in the short time
of a 60 Hz sweep. 73, Mike K.

Oscar loves trash, but hates Spam! Delete him to reply to me.

"Brian Denley" wrote in message
news:f_Szb.306235$ao4.1051208@attbi_s51...
Out of curiosity, where are you guys reading the output of the IF?
After
the detector or right at the transformer output?
Thanks

--
Brian Denley
http://home.comcast.net/~b.denley/index.html

If I remember the Hallicrafters instructions correctly, it's the AF
voltage at the speaker terminals with the BFO on.

I'd rather watch the DC voltage at the detector/AVC line.

But it's been a while.

Frank Dresser

Using sweep with the crystal at 60hz is not going to work. Too bad,
because it would be nice to see the pass band shape... I'll have to
check to see if my old sweep generator will take an external input
down at 10hz or lower, but then I don't know how I would sync to my
scope sweep.

The phasing control does have -5 to +5 and there are no stops. 2
sources don't mention where to set it during this alignment and the
third says half meshed and to set the knob to make that zero. It says
to leave it there for the rest of the alignment steps, which includes
peaking the whole IF section to match the crystal, which to me means
1/2 meshed should be on the peak and the null should be off to one
side (either frequency or phase control setting-wise).

I didn't have much luck with AGC voltage, perhaps I was latching on at
the wrong place. I tried the plate of the AGC rectifier and also
downstream of a resistor off the cathode. Didn't see any real swing
with generator frequency anywhere. Perhaps my inexperience really
shows here.

So, resorting back to speaker output voltage, I decided to try using
AM from the signal generator with the BFO off. Low and behold, I now
clearly hear and see (on the meter) the twins peaks and intervening
null. I just can't seem to discern them using the BFO as recommended
in all the tech sources. Wonder what I am doing wrong, or why AM
wouldn't be a good way to do this anyway? One thing is that I am
injecting post 2nd converter instead of at the tuning stator. Maybe
the BFO would work better as per instructions if I injected at the
stator as per instructions. I noticed that when injecting at the RF
point, slight movements of the tuning knobs changed the peaking
frequency, so I just thought why not inject straight into the IF
section. Am I missing some kind of additional alignment by so doing?

Anyway, using AM generator injection into the IF section I now can
tune to the null and hold it pretty steady. I noticed slight tapping
on the crystal bounced the null around, so I opened it up and wiped it
off and retorqued it. Didn't seem to change anything, so mechanical
feedback must be inherent in these beasts. Back to that slug on the IF
secondary feeding the crystal filter... the swing between peaks and
null is so vast that on the HP400 I am using they are several scale
settings apart. Makes it hard to tune for maximum swing between
rocking the generator, switching scales, and turning the slug. Is that
for sure what the slug does (maximize the db drop from peak to null)?
Or is it to tune the IF around some certain position of the phasing
control? I was noticing when switching the filter in and out that I
can tune the slug to where the peak without filter is the null when
the filter is switched in (with phasing 1/2 meshed and set to zero)...
is this possibly what I am trying to accomplish or is this just
coincidience?

Sorry to be such a nuisance, but I have searched all over the web and
this topic has not been clearly covered anywhere I could find. It
seems worthwhile to reach some kind of understanding as to just how to
align these crystal IF filters. All your feedback so far is really
helping, but I am someone that really wants to understand what the
heck I am doing, and I am not quite there yet. Perhaps this is a great
understatement.

Dan

geojunkie wrote:

Using sweep with the crystal at 60hz is not going to work. Too bad,
because it would be nice to see the pass band shape... I'll have to
check to see if my old sweep generator will take an external input
down at 10hz or lower, but then I don't know how I would sync to my
scope sweep.

The phasing control does have -5 to +5 and there are no stops. 2
sources don't mention where to set it during this alignment and the
third says half meshed and to set the knob to make that zero. It says
to leave it there for the rest of the alignment steps, which includes
peaking the whole IF section to match the crystal, which to me means
1/2 meshed should be on the peak and the null should be off to one
side (either frequency or phase control setting-wise).

I didn't have much luck with AGC voltage, perhaps I was latching on at
the wrong place. I tried the plate of the AGC rectifier and also
downstream of a resistor off the cathode. Didn't see any real swing
with generator frequency anywhere. Perhaps my inexperience really
shows here.

So, resorting back to speaker output voltage, I decided to try using
AM from the signal generator with the BFO off. Low and behold, I now
clearly hear and see (on the meter) the twins peaks and intervening
null. I just can't seem to discern them using the BFO as recommended
in all the tech sources. Wonder what I am doing wrong, or why AM
wouldn't be a good way to do this anyway? One thing is that I am
injecting post 2nd converter instead of at the tuning stator. Maybe
the BFO would work better as per instructions if I injected at the
stator as per instructions. I noticed that when injecting at the RF
point, slight movements of the tuning knobs changed the peaking
frequency, so I just thought why not inject straight into the IF
section. Am I missing some kind of additional alignment by so doing?

Anyway, using AM generator injection into the IF section I now can
tune to the null and hold it pretty steady. I noticed slight tapping
on the crystal bounced the null around, so I opened it up and wiped it
off and retorqued it. Didn't seem to change anything, so mechanical
feedback must be inherent in these beasts. Back to that slug on the IF
secondary feeding the crystal filter... the swing between peaks and
null is so vast that on the HP400 I am using they are several scale
settings apart. Makes it hard to tune for maximum swing between
rocking the generator, switching scales, and turning the slug. Is that
for sure what the slug does (maximize the db drop from peak to null)?
Or is it to tune the IF around some certain position of the phasing
control? I was noticing when switching the filter in and out that I
can tune the slug to where the peak without filter is the null when
the filter is switched in (with phasing 1/2 meshed and set to zero)...
is this possibly what I am trying to accomplish or is this just
coincidience?

Sorry to be such a nuisance, but I have searched all over the web and
this topic has not been clearly covered anywhere I could find. It
seems worthwhile to reach some kind of understanding as to just how to
align these crystal IF filters. All your feedback so far is really
helping, but I am someone that really wants to understand what the
heck I am doing, and I am not quite there yet. Perhaps this is a great
understatement.

Dan

Its simple to sync the scope to the generator. You can use a 555
timer chip and feed the ramp to the sweep input, and to the external
horizontal sweep input on the scope. There should be enough drive for
both, without adding an external buffer amp. Page 7, figure 4 of the
datasheet shows "ASTABLE OPERATION", or a "Multivibrator" configuration.
Use pin 6 to drive the generator and scope. Select the resistors and
capacitor in the timing circuit, and you can vary the sweep anywhere you
want. Sometimes a 1/10 Hz sweep is nice, because it is slow enough to
see everything.

As far as ringing in crystal filters, yes, its common.


http://www.national.com/ds.cgi/LM/LM555.pdf
http://www.national.com/an/AB/AB-7.pdf

--
20 days!


Michael A. Terrell
Central Florida

I aligned an HRO-50, starting with the phasing capacitor half-meshed.
(don't trust the knob at "half", look to see
if the phasing capacitor is half-meshed, and adjust the phasing
knob to read "5" at half meshed).

You shouldn't have the BFO on, it will cause confusion.
Capcitively couple the signal generator at the grid
of the preceeding stage, and connect an oscilloscope
via a divide-by-ten probe at the plate
of the following stage.
(this avoids disturbing the crystal filter stage
with stray capacitance from either the signal generator or the 'scope).

Slowly rock the signal generator output, and look for the null
on the 'scope (AGC off, a.m. mode), with phasing capacitor at "5",
half meshed.

With my receiver, the null was at 457.0 KHz.

Then all the IF transformers were aligned, using a 457.0 KHz
signal from the signal generator. The BFO "0" (BFO cap half meshed)
was set at 457.0 KHz.

geojunkie wrote:

I am having a lot of trouble understanding the proper method to align
the crystal filter section (off the output of 3rd IF transformer)in an
SX-71. The manual suggests "rocking" the signal generator around the
IF frequency (455khz) while turning the IF transformer slug and
monitoring the output level to find a null between two peaks. You are
supposed to set the slug to the null. The output tone is to be created
using the BFO set for 1kz at the IF frequency. snip