Max Frequency of SM 118A counter?

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  Anyone know the maximum frequency of a Heathkit SM-118A?
  I have been all over Google with little luck.
One guy said it would go to 1 GHz maybe 2 GHz, I don't think so.
                                     Mikek

Re: Max Frequency of SM 118A counter?

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As I vaguely recall, none of the early Heath LED counters went much
above about 500 MHz.

I couldn't find a free schematic or manual.  Open it up, look at the
prescaler chip, grab the Heath part number, and find the real chip
number from a parts cross reference.
<http://www.pestingers.net/heathkit_interface/Heathkit1/results_page.asp
Then, lookup the specs on the chip, which sets the upper frequency
limit.  For example, if the counter section works to 50MHz, and the
prescaler is a divide by 10 type, then your upper limit is 500MHz.

Totally useless YouTube video of the SM-118A in action:
<
http://www.youtube.com/watch?v=fDInbm0rFW0




--  
Jeff Liebermann     snipped-for-privacy@cruzio.com
150 Felker St #D    http://www.LearnByDestroying.com
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Re: Max Frequency of SM 118A counter?
On Sat, 25 Jan 2014, amdx wrote:

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Do you have a general idea on vintage?

Their first frequency counter, out in 1971, went to 15MHz, 20 if you were  
lucky.  But external prescalers soon followed, but they were generally  
divide by ten, so the upper limit was determined by how fast the prescaler  
could count, but also the upper limit of the counter itself.  Actually,  
in time Heathkit sold a matching prescaler, a box the same size as the  
counter.

Likely the second generation of Heathkit counter had a prescaler, I can't  
remember.  But timing is everything, if it came out shortly after the  
first one, it probably had limited range, not even 1GHz.  COming out  
later, you could put a 74S196 counter as your first counter and get up to  
50MHz, which then meant a divide by ten prescaler would give coverage to  
about 500MHz.  It took some time before the cheap frequency counters got  
up to where they read fairly high without a prescaler, and by then the  
prescalers had better high frequency ability.

I reemmber the model number, but I'm blank about the period or specs.

   Michael


Re: Max Frequency of SM 118A counter?

"Michael Black"

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** The Fairchild " 95H90"  was one of the early ones, dividing by 10 or 11.

Came out in the mid 1970s.

Upper limit was about 250MHz.

Ones that went to over 1GHz were much later and used the "Josephson Ring"  
idea  -  so they divided by numbers like 64 or 128.


...   Phil





Re: Max Frequency of SM 118A counter?
On Sat, 25 Jan 2014 21:48:38 -0500, Phil Hobbs

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The 11C90 was one of the first dual modulus prescalers.  I used it in
a VHF and an HF marine radio synthesizer.  It worked great.  I can't
say the same for the 11C44 phase/freq detector which provided a
challenge minimizing the dead band and reducing jitter.  The problems
would have been tolerable had the chips from the various Fairchild
factories performed identically.  Unfortunately, they did not.  We
resorted to tweaks specific to the 11C44 country of origin.  That
kludge held things together long enough for us to switch to the
Motorola MC12013 (10/11) prescaler, MC12014 control chip.  There was
also an MC10138 (2/5/10) doing something useful in the synthesizer.
The change would have happened sooner but the company was a spinoff
from Fairchild and such loyalties tend to die slowly.

--  
Jeff Liebermann     snipped-for-privacy@cruzio.com
150 Felker St #D    http://www.LearnByDestroying.com
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Re: Max Frequency of SM 118A counter?
wrote:

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Ooops, memory fault.  I just excavated the schematic of the Intech
M3600 HF SSB radio.  The synthesizer has the aforementioned Motorola
ECL prescalers, but the synthesizer phase detectors are still the
Fairchild 11C44.  I could swear that I killed that monster, but I
guess not.

You can see the problem in Fig 1 on Pg 229:
<http://books.google.com/books?id=nyxGjjF-cHIC&pg=PA229&lpg=PA229#v=onepage&q&f=false
The middle of the non-linear region is essentially flat.  That means
there's no change in phase detector output voltage for changes in
input phase.  The result is that the oscillator frequency just bangs
around between the phase detector dead zone limits producing rumbling
noises in the tx and rx audio.  There were several tricks for reducing
the problem, but all had undesirable side effects.


--  
Jeff Liebermann     snipped-for-privacy@cruzio.com
150 Felker St #D    http://www.LearnByDestroying.com
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Re: Max Frequency of SM 118A counter?
On 1/25/2014 11:45 PM, Jeff Liebermann wrote:
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Yeah, 4046es still have that problem.  Usually a 1 M resistor from PD2  
output to ground fixes it, because all you have to do is pull the  
quiescent point a few nanoseconds from the null.

Cheers

Phil Hobbs

--  
Dr Philip C D Hobbs
Principal Consultant
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Re: Max Frequency of SM 118A counter?
On Sun, 26 Jan 2014 14:26:34 -0500, Phil Hobbs

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To the best of my limited knowledge, it's a problem with all digital
phase detectors.  Anything that goes tri-state (i.e. open circuit
output) when locked is going to have a dead band.  I found that out
the hard way when I tried to replace the 11C44 with a D flip-flop
equivalent, and had the same problem.  

Using a large value resistor was one of the first things we tried. The
problem was that any offset in the loop amplifier would dramatically
increase the reference oscillator feedthrough.

The 1M resistor is also a problem in marine radios.  One just does not
use large value resistors in a marine environment.  The largest value
I used was 470K for a microphone amp, where PCB leakage was not
important.  Otherwise, about 100K was as large as I would consider
safe.  Someone will surely suggest conformal coating.  We did some of
that but the inability to apply it consistently, even with UV
additives, caused problems.  Connectors had to be masked, and rework
was difficult and messy.  No thanks.  Incidentally, we also pioneered
(with Piezo Technologies) the use of low impedance crystal filters for
much the same reasons.

What we did to "solve" the low frequency noise and rumble problem was
rather uninspiring.  We discovered that 11C44 chips from one country
would have a smaller dead band than other.  Those were selected for
the more critical HF radio synthesizers.  It turned out that only one
loop was really critical making selecting parts tolerable.  Next, the
audible noise was removed by high pass filters in the audio circuitry.
The trick was keeping the noise below 300 Hz, which proved fairly easy
by tweaking the PLL constants.  This also had the added benefits of
reducing the audible "clunk" whenever the frequency was changed and
reducing microphonics[1].  Lastly, the selection of the loudspeaker
and the acoustic design of the box, was designed to reduce the low
frequencies, mostly to prevent oscillations due to microphonics.


[1] Microphonics are produced by beating on the case, or yelling into
the enclosure, which modulates the PLL.  This can be heard on the TX
and RX audio.  In extreme cases, the loudspeaker audio modulates the
VCO, causing audio oscillation.

--  
Jeff Liebermann     snipped-for-privacy@cruzio.com
150 Felker St #D    http://www.LearnByDestroying.com
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Re: Max Frequency of SM 118A counter?
snipped-for-privacy@cruzio.com says...
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 I had an amp that had a microphonic problem. It turned out to  
be a through hole transistor of a common variety that had a
loose element inside and it just happen to be in the preamp
section.
    
 It was a guitar amplifier head and it would squeal like
hell as soon as you turned it up..

Jamie


Re: Max Frequency of SM 118A counter?
On 1/26/2014 5:50 PM, Jeff Liebermann wrote:
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There are a variety of ways of getting round it.  The Motorola way is to  
have separate up and down outputs, both of which have a nonzero width  
when the phase error is zero.  With that approach, there are two regions  
where the slope is reduced, but neither of them is where the loop wants  
to servo.  Pulling the loop slightly to one side makes it easier.

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If you're relying on the pulse width going to zero to meet your ripple  
spec, then yes, you're going to have to servo on the flat spot.  That's  
a design error, however.

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There's nothing special about 1M.  It just has to be enough to pull the  
servo point a few nanoseconds off the flat spot.  If the rest of the  
loop filter is lower-Z, 100k would probably do it.  You just have to  
design it.

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That's pretty much turd-polishing.  If you come into a project late,  
sometimes you have to do that sort of thing, but nobody likes it.

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Mechanical sensitivity of oscillators is a pretty well known problem, I  
agree.  Bumping up the loop bandwidth helps a lot.

Cheers

Phil Hobbs


--  
Dr Philip C D Hobbs
Principal Consultant
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Re: Max Frequency of SM 118A counter?
On Sun, 26 Jan 2014 18:47:05 -0500, Phil Hobbs

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I hadn't heard of that method.  Good idea and sounds like it would
work.  I wish I had thought of it.  (Note:  I was about 25 years old
at the time and thought I knew everything there was to know).

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Guilty as charged for using the 11C44 in the manufacturers prescribed
manner.  I wanted to replace it with a double balanced mixer (SBL-1)
as a phase detector, but never could get rid of the DC offset or keep
it linear.  The SBL-1 was chosen mostly because it was already being
used in the dual loop synthesizer as a mixer.  When I was done with
that diversion, patching the problem with high pass filters was the
best I could contrive in the time remaining.  If I had known about the
Motorola trick, I would certainly have tried it.

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I just took a closer look at the schematic.  The low frequency PLL
that supplied the 2nd LO frequency is a 4046 with a 10M resistor
pullup.  It's an early manual and that was later removed.

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Also guilty as charged.  Nobody liked it including me.  However, the
deadline (San Mateo Cow Palace Boat Show) was looming and marketing
wanted to demonstrate a working radio.  As it turned out, the
marketing manager took it with him on an airplane flight to Florida to
show some dealers and managed to misplace it for a while at a hotel.
When the prototype finally returned to California, it was too late for
the boat show.  A fair number of people in engineering gave up
weekends and evenings for that fiasco and were not amused.  As it
turned out, I did get another chance to fix things as there were also
production problems.  However, they were in other areas and the phase
detector problems were not addressed.

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That helps as long as I don't have to FM modulate the PLL.  The PLL
should NOT follow the modulation which means that the loop bandwidth
has to be lower than the lowest expected modulation frequency (about
300 Hz).  The initial design of the synthesizer was not my project, so
I don't have any design notes with which to check.  I could probably
calculate the loop bandwidth from the schematic.  

Microphonics is much less of a problem today because of crystal can
and SMT VCO's, which are far less susceptible to vibration than the
old discrete versions.


--  
Jeff Liebermann     snipped-for-privacy@cruzio.com
150 Felker St #D    http://www.LearnByDestroying.com
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Re: Max Frequency of SM 118A counter?
On 01/26/2014 10:17 PM, Jeff Liebermann wrote:
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I remember it well.  It was fun being that smart, wasn't it? ;)

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Back when I was making PLLs for a living, I used to be really fond of  
the MCL RPD-1 phase detector.  It has about 10 dB higher output than a  
level-7 mixer (2V p-p), and had much lower offset as well.  They still  
make it, or something like it (MPD-1).

I was probably saved from making a very similar mistake by having a very  
tight noise spec to meet, so that I was pretty sure I couldn't make it  
work using a PLL chip.  (The first thing I tried was a Motorola  
MC145152, which had that two-output phase detector.)  I wound up with a  
weird fractional-N loop based on a dual modulus prescaler and two  
decades of synchronous counters, with a chain of two BCD rate  
multipliers jiggling the carry input to get the bottom two decades.  
That way I got 8.333... kHz tunability with an 833.3... kHz comparison  
frequency.  (I didn't know about the Digiphase technique, but it would  
have been under patent still anyway.)  The rate multiplier jitter was  
pretty much out of band, but I still needed to use a VCXO to get good  
enough close-in phase noise.  (The 100-112 MHz output was being  
multiplied by an additional 120 times to make the LO for a direct  
broadcast satellite system.)

I really got chucked in the deep end on that one. Fortunately my boss  
was a noise geek. (Josef Fikart, his name was.  Escaped from  
Czechoslovakia in 1968 on a freight train.  Really a good guy.)

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I remember grousing about how much reference frequency ripple it caused,  
and how much nicer a 4046 would be.

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The alternative is to put preemphasis on the audio and stuff it into the  
loop filter along with the phase detector output.  That way you can get  
decent stability as well as good FM.

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That's certainly one thing I don't miss about the old days.  You just  
have to remember not to use high-K ceramics in the loop filter, because  
otherwise the old days are liable to return!

Fun stuff.

Cheers

Phil Hobbs


--  
Dr Philip C D Hobbs
Principal Consultant
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Re: Max Frequency of SM 118A counter?
On Mon, 27 Jan 2014 11:08:18 -0500, Phil Hobbs

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Yep.  I thought I could do no wrong and nothing was impossible.  I
later noticed that other engineers were bailing me out of trouble a
bit too often, and that at least one of my assigned projects really
was impossible.  It took me about 10 more years to make all the
necessary mistakes, and to learn tact, humility, company politics,
basic management skills, and when to ask for help.  The last was the
most difficult.

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<http://www.minicircuits.com/pdfs/MPD-1+.pdf
DC offset of +0.1 to +0.2mv would certainly have fixed my offset
problem.  However, the MPD-1 lists for $23.70.  I don't think that
would have been acceptable.  The SBL-1 is about half the price
<http://www.minicircuits.com/pdfs/SBL-1+.pdf
but has no guaranteed DC offset spec.  As I recall, the SBL-1 varied
from -2mv to +4.0mv offset.  Yep... this is for the similar SBL-1-1LH:
<http://www.datasheetarchive.com/files/mini-circuits/html2/sbl-1-1lh.htm
Yech.  -0.5 to +2.3mv.

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The same radio with the 11C44 problem also used the MC145152 for both
the 2nd LO synthesizer and the BFO synthesizer.  Other than stupidly
putting the VCO on the top of a plug in PCB, I don't recall any
problems with the chip.  We also used it in some VHF radios.  At a
different company, I later used it for 952MHz electric utility radio.
Nice chip.

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Ummm... that's complexicated.

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I don't know him.  My employer was Intech Inc (Santa Clara CA) which
was short for International Technologies.  Almost everyone in the
company was from outside the USA.  We had engineers and managers from
Switzerland, Spain, Lebanon, Denmark, Tennessee, Romania, Canary
Islands, South Africa and probably others that I've forgotten.

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With PLL, everything seems to be a tradeoff.

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That's exactly what we did, initially.  The problem was that the
radios were being used for SITOR (error correcting teletype), which
required extremely fast transmit-receive switching.  I vaguely recall
10 msec was the maximum allowed.
<http://en.wikipedia.org/wiki/SITOR
That meant that everything I had done to allow FM modulation inside
the loop went into the trash bin.  Fortunately, there was no
requirement for both FM and SITOR in the same radio, so two versions
of the synthesizer were deemed acceptable.

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I don't think there's much to be gained by redesigning a 40 year old
radio using modern technology.  Still it's interesting to look back
and speculate on how it might have been done if I had known what I was
doing.  Hindsight is always crystal clear.

I once cleaned up a radio design that was full of MLCC capacitors.  It
wasn't really microphonic, but nobody could figure out why the PLL
would go out of lock when the vibrator (eccentric cam motor) would
run.  It was fun to hang the radio on an improvised shake table (made
from a loudspeaker and some box cardboard) and watch the PLL go insane
from the vibration.

Enough nostalgia.  Back to work...

--  
Jeff Liebermann     snipped-for-privacy@cruzio.com
150 Felker St #D    http://www.LearnByDestroying.com
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Re: Max Frequency of SM 118A counter?

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** Yep.

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** Not so useful at 1 or more.

To interface with "ordinary" logic families, division by 128 or 256 is  
needed.

Like the Philips SAB6456 used in millions of CTV sets.

http://www.qsl.net/zl1wtt/pdf/SAB6456.pdf


....  Phil






Re: Max Frequency of SM 118A counter?

"Phil Allison"

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Re: Max Frequency of SM 118A counter?


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** Not so.

Philips described it as a Johnson ring in the app notes.

FYI:

With no input, SAB6456s oscillate at 1.35 GHz.

Rest of you smug, context shifting bullshit snipped.

Bye....


...   Phil






Re: Max Frequency of SM 118A counter?
On Sun, 26 Jan 2014 15:48:14 +0200, upsidedown wrote:

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Can't remember. It was nearly 50 years ago.
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Late 1960s/early 1970s. The ring counter was never a problem. All TO-18.
Never needed to touch that. The bad plastic was the succeeding dividers,
20MHz downwards,each on its own lille PCB. Early plastic stuff that were
notorious for bad passivation. We used BSX20 simply because it was on
inventory in bucket loads. After the first few fell over, we just changed
out the lot.

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Don't get hung up on ft. Device capacitances, tr, tf, tstorage, are where
it's won and lost. Bode plots aren't the whole story. There are plenty of
900MHz ft devices that suck as switches.

--  
"Design is the reverse of analysis"
                   (R.D. Middlebrook)

Re: Max Frequency of SM 118A counter?
wrote:


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Mixing is not that horrible.  That's the way my HP5246L and HP5248M
counters work.  The plugin has an input bandpass filter and a mixer
that down converts the input to 0 - 100 MHz.  The local oscillator
generates a comb line with 100 MHz spacing.  Basically, the counter
repeats the count every 100 MHz.  There's also a signal level meter to
help tune the preselector and set the input level.  The bad news is
that I can't sync either the counter clock or the local oscillator to
an external frequency reference.

It works quite nicely as a cheap microwave frequency counter as I have
8 of the 12 available plugins.  Also, Nixie tubes are cool.

<
http://www.barrytech.com/hewlett-packard/counters/hp5245m.jpg



--  
Jeff Liebermann     snipped-for-privacy@cruzio.com
150 Felker St #D    http://www.LearnByDestroying.com
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Re: Max Frequency of SM 118A counter?
amdx schrieb:
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It may be helpful to ask

here:
<http://groups.yahoo.com/neo/groups/heathkit/conversations/messages

HTH

Reinhard

Re: Max Frequency of SM 118A counter?
On 1/25/2014 1:51 PM, Reinhard Zwirner wrote:
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   I'm waiting for the administrator to decide I'm Ok, and let me in.
                                      Mikek


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