Grid Dip Meters

[Paul Burridge]

Hi gang,

I've never had a lot of luck with GDMs for some reason. Even with a
decent meter, it seems such a drag tuning across such a vast range
looking for a tiny, easily-missed dip which you have to screw out of
the meter by forcing the sensing coil so far into the circuit
concerned you practically break the circuit board. Am I alone in
finding this potentially invaluable device practically useless in
practice? Is there a more viable alternative?

p.

[Bill Turner]

On Sat, 15 Nov 2003 18:56:05 +0000, Paul Burridge

Post by Paul Burridge
Hi gang,
I've never had a lot of luck with GDMs for some reason. Even with a
decent meter, it seems such a drag tuning across such a vast range
looking for a tiny, easily-missed dip which you have to screw out of
the meter by forcing the sensing coil so far into the circuit
concerned you practically break the circuit board. Am I alone in
finding this potentially invaluable device practically useless in
practice? Is there a more viable alternative?

_________________________________________________________

I can't quite decide if this is a troll or not. Let's assume it isn't.

OF COURSE the grid dip meter is a valuable tool. I wouldn't be without
one. There is a certain technique involved and a bit of knowledge.

1. The dip is sharpest and deepest if the circuit is unloaded by any
resistive components. In this sense, a low Q ferrite can act as a
parallel resistor and may completely obscure the dip.

2. Tune slowly.

3. Ride the meter sensitivity control, keeping it near full scale as
much as possible.

4. Practice on known tank circuits.

5. Parallel circuits only, not series (you knew that, right?).

6. Keep the GDO coil parallel to the tank under test, not at right
angles.

Hope this helps.

--
Bill, W6WRT

[Uncle Peter]

Post by Paul Burridge
Hi gang,
I've never had a lot of luck with GDMs for some reason. Even with a
decent meter, it seems such a drag tuning across such a vast range
looking for a tiny, easily-missed dip which you have to screw out of
the meter by forcing the sensing coil so far into the circuit
concerned you practically break the circuit board. Am I alone in
finding this potentially invaluable device practically useless in
practice? Is there a more viable alternative?
p.
--

It is kind of hard to get the proper coupling on PCB style coils.
You may have to use a link coupling system (came with some
of the Millens); also solid state circuits can have fairly low Q
circuits, again making it hard to see the dip.

Those were intended for larger tube circuit designs, not PCB
based gear.

Pete

[J M Noeding]

On Sat, 15 Nov 2003 17:06:34 -0500, " Uncle Peter"

Post by Uncle Peter
It is kind of hard to get the proper coupling on PCB style coils.
You may have to use a link coupling system (came with some
of the Millens); also solid state circuits can have fairly low Q
circuits, again making it hard to see the dip.
Those were intended for larger tube circuit designs, not PCB
based gear.

Item 2.4 described on http://home.online.no/~la8ak/5c.htm
is the solution for dipping pcb coils, and you don't need a
griddipmeter, at all. Another problem with the pcb coil is low
Q-value, and if the coil is loaded too much it won't dip with any
arrangement tried.
also described some GDMs on http://home.online.no/~la8ak/5a.htm -
haven't got the time to re-edit these pages

Jan-Martin
LA8AK
--
remove ,xnd to reply (Spam precaution!)

[Dana Myers]

Post by Uncle Peter
It is kind of hard to get the proper coupling on PCB style coils.

Bingo.

Post by Uncle Peter
Those were intended for larger tube circuit designs, not PCB
based gear.

Daily Double!

Dana

[Dale Parfitt]

Post by Paul Burridge
Hi gang,
I've never had a lot of luck with GDMs for some reason. Even with a
decent meter, it seems such a drag tuning across such a vast range
looking for a tiny, easily-missed dip which you have to screw out of
the meter by forcing the sensing coil so far into the circuit
concerned you practically break the circuit board. Am I alone in
finding this potentially invaluable device practically useless in
practice? Is there a more viable alternative?
p.
--

First rule is to get a good dip meter- the stuff made for the amateur
community is very poor- the Eicos, Heath Millen etc. Pick up a Measurments
model 59. With this meter you can take a 1/2 wave wire- say at 2M and hold
the meter a couple inches from the center and see a huge dip. Other meters
don't even respond when held to the wire. Dips on conventional L-C circuits
can easily be full scale.

Dale W4OP

[Bill Turner]

THERE MUST HAVE BEEN SOMETHING WRONG WITH YOUR MILLEN. BILL T.

[Tracy Fort]

Yep...He probably bought it from you.

Tracy

Post by Bill Turner
THERE MUST HAVE BEEN SOMETHING WRONG WITH YOUR MILLEN. BILL T.

[Ashhar Farhan]

GDOs are sort of dated by now. i build one last year when i was just
getting back into hamming. i found very little use for it over the
last 3 months that i have actively been homebrewing. let me explain
why ...

a gdo is primarily used to check for resonance of a tuned circuit. if
you knew the inductance and the capacitance, you could easily compute
the resonanating frequency youself.

as another poster mentioned, getting a dip is a fight. so, what i do
use is a combination of three things: an rf probe with a high
impedance voltmeter, a test oscillator and a frequency counter. all
these things are in themselves pretty useful. but i seldom go wrong in
getting properly tuned circuits.

i have a test oscillator (see the schematic
Loading Image...). i plug in a coil with a 330pf
capcitance in series between the base of the vfo transistor and the
ground. and measure the frequency on the counter. that gives me a
pretty accurate (within 1%) measure of the coil's inductance. it
involves a bit of calculating, but once i have cast the values, there
is seldom need to change them. i tend to do simple maths in my head
using 10MHz as starting value for resonance (100pf with 2.5uH). I can
now scale up or down without resorting to a calculator.

As for peaking a circuit, it is best done by the ear or using an
oscilloscope. peaking by the ear is probably the best, if u can manage
it. now, i dont mean to be rude, but frankly very few people have the
ear to be able to tune for best fidelity rather than loudness. it
takes patience and care (i have very little of either). so, i depend
upon a scope. it is a little like knowing morse. it is the best mode
of communicating, but not all want to use it.

a poor man's alternative is using the RF probe. the RF probe will
never show distortions. But it can show clear peaks while tuning up a
circuit. be sure that you also terminate the output of the tuned stage
properly! otherwise you maybe be tuning away from the sweet point.

i would rather that you invested into building a simple PIC based
counter. It is pretty accurate, you will never need to caliberate it.
(I never got around to caliberating mine, it is off by 1.5KHz at
10MHz). That with the test oscillator, you would be completely
informed about your coils. An RF probe is a 10 minute project and if
you already have a good VOM, you might not need a High impedance
voltmeter. I brewed my own voltmeter to keep things completely
homebrewed.

the counter can always be used with all your projects as a standard
read out. The rf probe will the most useful tool in tuning up any
transmitter. The voltmeter is indispensable.

- farhan

[Bill Turner]

Post by Ashhar Farhan
a gdo is primarily used to check for resonance of a tuned circuit. if
you knew the inductance and the capacitance, you could easily compute
the resonanating frequency youself.

Correct, but if you *know* both the capacitance and inductance, you
don't need a GDO in the first place. IMO, a GDO is most useful when one
of the variables is known and the other must be determined.

Post by Ashhar Farhan
as another poster mentioned, getting a dip is a fight.

You just need more practice. I have no problem finding the dip, but
I've been doing it a long time.

Post by Ashhar Farhan
so, what i do
use is a combination of three things: an rf probe with a high
impedance voltmeter, a test oscillator and a frequency counter. all
these things are in themselves pretty useful. but i seldom go wrong in
getting properly tuned circuits.

That method can work ok *if* you take into account the loading effect of
the probe. Using a GDO avoids this problem entirely, and is the primary
benefit, IMO. I've done it both ways and find the GDO faster and less
prone to errors. Either method will work; it's mostly a matter of
personal preference. Also, a GDO is likely to be much less expensive
than the three separate items.

--
Bill, W6WRT

[Michael Black]

Post by Bill Turner
Also, a GDO is likely to be much less expensive
than the three separate items.
Bill, W6WRT

That's always been some of its appeal. Throw one together, or buy one,
and you get a tool for finding the rough frequency of a coil. But you
also get that ability to figure out an unknown L or C, you get a signal
generator, you get a wavemeter (which also still has potential use),
you get a general purpose oscillator that you can connect a crystal to,
and you get likely some other uses that don't immediately come to mind.

They date from a time, late forties is when they started becoming popular
but I'm uncertain if the concept was there before, when the average ham
had little test equipment, and even labs and repair places might not
have all that much of it. It was a handy little unit, relatively easy
to build, that did give good returns.

Of course, a lot of recent equipment isn't conducive to as easy use
with a GDO, with self-shielding toroids and the rest shielded in cans.
Construction isn't nearly as wide open as in the days of tubes.

But whether it's worth having likely depends on a mindset. If someone
wants to load down on tons of test equipment, then a GDO is likely
redundant. But a GDO can have its uses, especially if one doesn't have
a wide-range signal generator.

Michael VE2BVW

[Paul Burridge]

Post by Bill Turner
THERE MUST HAVE BEEN SOMETHING WRONG WITH YOUR MILLEN. BILL T.

I'm not using a Millen and this post isn't a troll as someone else
suggested. The meter I use started out life as a Tradiper (Japanese)
but because it was hopelessly outdated and used old germanium trannies
with enough lead inductance to tune a VoA transmitter, I decided to
rip its guts out and rebuild from scratch.The actual
chassis/meter/facia etc was quite high quality, so it made sense.
I got this nice circuit from the UK equivalent of the ARRL Handbook
and set about building it. It used 2 SK88 FETs and the output of this
oscillator could be adjusted to keep its impedence as high as poss for
each test, thereby giving really good dips when even quite heavily
loaded low Q circuits were tested *provided* they were physically big
enough to shove the sense coil into. The sense coils are about 3/4" in
diameter, which although fine for large, out-of-circuit component
measurements, is *hopeless* for getting in close on a circuit board
with subminature components a fraction of the size. That's the main
problem I face with all GDMs, though: they all seem to have relatively
huge sense coils relative to today's component sizes :-(

[oh2baw]

i use my GD-meter when building antennas and tuning
antennas and traps to frequency. Although
the calibration is quite inexact, it's always possible
to listen to the GD-meters frequency on the
receiver.

"Paul Burridge"

On Sat, 15 Nov 2003 17:23:50 -0600 (CST),

Post by Bill Turner
THERE MUST HAVE BEEN SOMETHING WRONG WITH YOUR

MILLEN. BILL T.

I'm not using a Millen and this post isn't a troll as

someone else

suggested. The meter I use started out life as a

Tradiper (Japanese)

but because it was hopelessly outdated and used old

germanium trannies

with enough lead inductance to tune a VoA transmitter,

I decided to

rip its guts out and rebuild from scratch.The actual
chassis/meter/facia etc was quite high quality, so it

made sense.

I got this nice circuit from the UK equivalent of the

ARRL Handbook

and set about building it. It used 2 SK88 FETs and the

output of this

oscillator could be adjusted to keep its impedence as

high as poss for

each test, thereby giving really good dips when even

quite heavily

loaded low Q circuits were tested *provided* they were

physically big

enough to shove the sense coil into. The sense coils

are about 3/4" in

diameter, which although fine for large,

out-of-circuit component

measurements, is *hopeless* for getting in close on a

circuit board

with subminature components a fraction of the size.

That's the main

problem I face with all GDMs, though: they all seem to

have relatively

huge sense coils relative to today's component sizes

:-(

[Bill Turner]

Post by oh2baw
Although
the calibration is quite inexact, it's always possible
to listen to the GD-meters frequency on the
receiver.

_________________________________________________________

Here's another fun thing you can do while listening to your GDO on a
receiver.

Tune the receiver carefully when the GDO is at or near the dip. You
will find it is oscillating on two separate (but close) frequencies.
One from it's own tank circuit, one from the tank circuit under test.
Probably the tank circuit under test isn't oscillating in the true sense
of the word, but rather "ringing" due to the power induced into it.

I would not have believed it if I hadn't heard it myself.

--
Bill, W6WRT

[ON5MJ]

This double frequency could possibly come from the coupling of two tuned
circuits (like in the good old IF). In this case two frequencies are
natural. Am I ok ?
I wonder if the coupling between GDO and the measured circuit would be done
with a closed loop.

73 de ON5MJ - Jacques.

[Steve Nosko]

Something strange going on here...
Steve k,9,d.c,i,

Post by Bill Turner

Post by oh2baw
Although
the calibration is quite inexact, it's always possible
to listen to the GD-meters frequency on the
receiver.

_________________________________________________________
Here's another fun thing you can do while listening to your GDO on a
receiver.
Tune the receiver carefully when the GDO is at or near the dip. You
will find it is oscillating on two separate (but close) frequencies.
One from it's own tank circuit, one from the tank circuit under test.
Probably the tank circuit under test isn't oscillating in the true sense
of the word, but rather "ringing" due to the power induced into it.
I would not have believed it if I hadn't heard it myself.
--
Bill, W6WRT

[james]

Hi Paul,

ARRL QST had nice article on a modern GDO

May 2003 QST page 54 A Modern GDO--The "Gate" Dip Oscillator Bloom, Alan, N1AL


73 jimbo

Post by Paul Burridge
I'm not using a Millen and this post isn't a troll as someone else
suggested. The meter I use started out life as a Tradiper (Japanese)
but because it was hopelessly outdated and used old germanium trannies
with enough lead inductance to tune a VoA transmitter, I decided to
rip its guts out and rebuild from scratch.The actual
chassis/meter/facia etc was quite high quality, so it made sense.
I got this nice circuit from the UK equivalent of the ARRL Handbook
and set about building it. It used 2 SK88 FETs and the output of this
oscillator could be adjusted to keep its impedence as high as poss for
each test, thereby giving really good dips when even quite heavily
loaded low Q circuits were tested *provided* they were physically big
enough to shove the sense coil into. The sense coils are about 3/4" in
diameter, which although fine for large, out-of-circuit component
measurements, is *hopeless* for getting in close on a circuit board
with subminature components a fraction of the size. That's the main
problem I face with all GDMs, though: they all seem to have relatively
huge sense coils relative to today's component sizes :-(
--
"I expect history will be kind to me, since I intend to write it."
- Winston Churchill

[Michael Black]

Post by james
Hi Paul,
ARRL QST had nice article on a modern GDO
May 2003 QST page 54 A Modern GDO--The "Gate" Dip Oscillator Bloom, Alan, N1AL
73 jimbo

But is it really modern, or just a rehash of what's come before?

I haven't seen the article, but in thirty years of reading the magazines
(and I've seen plenty of back issues from before that), there has been
very little change. Most of the articles are a small variant on a previous
article, with any real change being about coil forms ("I didn't have what
the previous article used", or "I noticed these things that would make a GDO,
so I built one around them") or variable capacitor.

Admittedly, when solid state devices came along, there had to be some change
since people did want to make use of them. The original ones were likely
pretty bad, using bipolar transistors, and of course there was the Tunnel
diode one from Heathkit. Once FETs came along, the GDOs were back to
basically a tube circuit, albeit with low supply voltage.

There have been the occasional outrageous scheme, switchable coils,
or making use of an existing signal generator or building a whole GDO along
such lines, but they never really held. Next time a GDO article was
published, it was back to simplicity.

If I was building one, I'd make sure it had a good reduction drive. I'd
certainly put in a buffer for an output, as a signal generator or to feed
a frequency counter. The latter then means the dial doesn't require much
effort, and the readout will be much much better than any GDO from before.
Maybe I'd even build a plug-in that has switchable coils, but the whole
thing is shielded, for those times when you just wanted a signal generator.

But I'd also be looking at the circuitry of the Millen Solid-state GDO,
from the early seventies. It was a more extensive design, but of course
it costs virtually nothing for those extra active devices. They found they
had to put a variety of chokes in the thing to isolate the oscillator from
the B+ line, so there weren't false dips.

The Heathkit from the eighties seemed rather interesting. Again, it
was a more complicated design. I can't remember what the extra circuitry
amounted to. That design did generate some similar home made circuits
at the time.

Michael VE2BVW

[Bill Turner]

Post by Michael Black
I'd
certainly put in a buffer for an output, as a signal generator or to feed
a frequency counter. The latter then means the dial doesn't require much
effort, and the readout will be much much better than any GDO from before.

_________________________________________________________

This would be a good way to go in the sense of not requiring a
calibrated dial, but a GDO is necessarily a broadly tuned device simply
because a single tank circuit is a broadly tuned device. A high degree
of precision is neither needed nor even possible.

Still, I like the concept.

--
Bill, W6WRT

[J M Noeding]

Post by Bill Turner

Post by Michael Black
I'd
certainly put in a buffer for an output, as a signal generator or to feed
a frequency counter. The latter then means the dial doesn't require much
effort, and the readout will be much much better than any GDO from before.

_________________________________________________________
This would be a good way to go in the sense of not requiring a
calibrated dial, but a GDO is necessarily a broadly tuned device simply
because a single tank circuit is a broadly tuned device. A high degree
of precision is neither needed nor even possible.

...because frequency it is pulled when dip occurs and when you adjust
excitation for best reading on the meter

Post by Bill Turner
Still, I like the concept.
--
Bill, W6WRT

73
LA8AK
--
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[james]

hi

This gdo uses three fet and runs off two aa batteries, nice project.
The coils are built with bnc connectors.

jimbo

Post by Michael Black

Post by james
Hi Paul,
ARRL QST had nice article on a modern GDO
May 2003 QST page 54 A Modern GDO--The "Gate" Dip Oscillator Bloom, Alan, N1AL
73 jimbo

But is it really modern, or just a rehash of what's come before?
I haven't seen the article, but in thirty years of reading the magazines
(and I've seen plenty of back issues from before that), there has been
very little change. Most of the articles are a small variant on a previous
article, with any real change being about coil forms ("I didn't have what
the previous article used", or "I noticed these things that would make a GDO,
so I built one around them") or variable capacitor.
Admittedly, when solid state devices came along, there had to be some change
since people did want to make use of them. The original ones were likely
pretty bad, using bipolar transistors, and of course there was the Tunnel
diode one from Heathkit. Once FETs came along, the GDOs were back to
basically a tube circuit, albeit with low supply voltage.
There have been the occasional outrageous scheme, switchable coils,
or making use of an existing signal generator or building a whole GDO along
such lines, but they never really held. Next time a GDO article was
published, it was back to simplicity.
If I was building one, I'd make sure it had a good reduction drive. I'd
certainly put in a buffer for an output, as a signal generator or to feed
a frequency counter. The latter then means the dial doesn't require much
effort, and the readout will be much much better than any GDO from before.
Maybe I'd even build a plug-in that has switchable coils, but the whole
thing is shielded, for those times when you just wanted a signal generator.
But I'd also be looking at the circuitry of the Millen Solid-state GDO,
from the early seventies. It was a more extensive design, but of course
it costs virtually nothing for those extra active devices. They found they
had to put a variety of chokes in the thing to isolate the oscillator from
the B+ line, so there weren't false dips.
The Heathkit from the eighties seemed rather interesting. Again, it
was a more complicated design. I can't remember what the extra circuitry
amounted to. That design did generate some similar home made circuits
at the time.
Michael VE2BVW

[J M Noeding]

On Sun, 16 Nov 2003 13:27:49 +0000, Paul Burridge

Post by Paul Burridge

Post by Bill Turner
THERE MUST HAVE BEEN SOMETHING WRONG WITH YOUR MILLEN. BILL T.

I'm not using a Millen and this post isn't a troll as someone else
suggested. The meter I use started out life as a Tradiper (Japanese)
but because it was hopelessly outdated and used old germanium trannies
with enough lead inductance to tune a VoA transmitter, I decided to
rip its guts out and rebuild from scratch.

sorry I don't really see your point. I bought my Tradipper in 67, and
it has been very useful since then, I may not use it so often now
because I've also got a Philips GM3121.
Mine operatet satisfactorily - as original - up to 140MHz, but the 2M
coil is no coil at all, only a short between to pins on the connector.
Have described how to improve on this on
http://home.online.no/~la8ak/m2.htm

The other modification is to use external +12V since the battery would
normally be flat when needed, but the original version had "positive-
ground", and some minor changes had to be done

LA3JA later bought the same model, but this had a very bad
intermittent contact in the tuning capacitor, so I couldn't repair it.

DL7QY described a dipmeter covering up to 1GHz, but I haven't really
felt I needed it because it is other ways to check ressonance than
using a GDM, and 1GHz is still not the highest frequency I need to
cover

73
Jan-Martin, LA8AK
http://home.online.no/~la8ak/c.htm
--
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[Paul Burridge]

Post by J M Noeding
sorry I don't really see your point. I bought my Tradipper in 67, and
it has been very useful since then, I may not use it so often now
because I've also got a Philips GM3121.
Mine operatet satisfactorily - as original - up to 140MHz, but the 2M
coil is no coil at all, only a short between to pins on the connector.

Maybe you have a different model. Mine purports to cover up to 360Mhz,
but there is *no way* AFAICS that the thing would be capable of
anything remotely close to that upper range limit, on cursory
inspection of the internals. I'm glad I went for the wholesale
re-build but still find it hopelessly impractical to use on minature,
in-circuit components.

[J M Noeding]

On Mon, 17 Nov 2003 13:55:19 +0000, Paul Burridge

Post by Paul Burridge
Maybe you have a different model. Mine purports to cover up to 360Mhz,
but there is *no way* AFAICS that the thing would be capable of
anything remotely close to that upper range limit, on cursory
inspection of the internals. I'm glad I went for the wholesale
re-build but still find it hopelessly impractical to use on minature,
in-circuit components.

Can only agree very much to your comment "there is *no way* AFAICS
that the thing would be capable of anything remotely close to that
upper range limit", whether the upper limit is 280 or 360MHz becomes
less important when it actually don't operate properly above 140MHz

But I don't see that an instrument intended to cover down to 500kHz
could have practical variable capacitor for UHF, so somewhere should
be another construction. Perhaps an idea to look at DL7QY microwave
dipmeter.... I might consider copying some of his details to a web
page

73
Jan-Martin
LA8AK
Instruments: http://home.online.no/~la8ak/m1.htm (and -.m2.htm)
Homebrew instruments: http://home.online.no/~la8ak/m3.htm
Homebrew audio instruments: http://home.online.no/~la8ak/m31.htm
--
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[Michael A. Terrell]

Post by J M Noeding
On Mon, 17 Nov 2003 13:55:19 +0000, Paul Burridge

Post by Paul Burridge
Maybe you have a different model. Mine purports to cover up to 360Mhz,
but there is *no way* AFAICS that the thing would be capable of
anything remotely close to that upper range limit, on cursory
inspection of the internals. I'm glad I went for the wholesale
re-build but still find it hopelessly impractical to use on minature,
in-circuit components.

Can only agree very much to your comment "there is *no way* AFAICS
that the thing would be capable of anything remotely close to that
upper range limit", whether the upper limit is 280 or 360MHz becomes
less important when it actually don't operate properly above 140MHz
But I don't see that an instrument intended to cover down to 500kHz
could have practical variable capacitor for UHF, so somewhere should
be another construction. Perhaps an idea to look at DL7QY microwave
dipmeter.... I might consider copying some of his details to a web
page
73
Jan-Martin
LA8AK
Instruments: http://home.online.no/~la8ak/m1.htm (and -.m2.htm)
Homebrew instruments: http://home.online.no/~la8ak/m3.htm
Homebrew audio instruments: http://home.online.no/~la8ak/m31.htm
--
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You can use a capacitor in series with the variable capacitor to reduce
the tuning range, but you would need a switch to select the high or low
capacitance range, and to move the coil connection to the active
components. That, or use a dual capacitor, build two circuits, and
select one oscillator at a time.

[J M Noeding]

On Sat, 22 Nov 2003 13:50:38 GMT, "Michael A. Terrell"

Post by Michael A. Terrell
You can use a capacitor in series with the variable capacitor to reduce
the tuning range, but you would need a switch to select the high or low
capacitance range, and to move the coil connection to the active
components. That, or use a dual capacitor, build two circuits, and
select one oscillator at a time.

in practice - a not so good idea!
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[Wes Stewart]

On Sat, 15 Nov 2003 22:05:45 GMT, "Dale Parfitt"
<***@parelectronics.com> wrote:

|
|"Paul Burridge" <***@osiris1.notthisbit.co.uk> wrote in message
|news:***@4ax.com...
|>
|> Hi gang,
|>
|> I've never had a lot of luck with GDMs for some reason. Even with a
|> decent meter, it seems such a drag tuning across such a vast range
|> looking for a tiny, easily-missed dip which you have to screw out of
|> the meter by forcing the sensing coil so far into the circuit
|> concerned you practically break the circuit board. Am I alone in
|> finding this potentially invaluable device practically useless in
|> practice? Is there a more viable alternative?
|>
|> p.
|> --
|>
| First rule is to get a good dip meter- the stuff made for the amateur
|community is very poor- the Eicos, Heath Millen etc. Pick up a Measurments
|model 59. With this meter you can take a 1/2 wave wire- say at 2M and hold
|the meter a couple inches from the center and see a huge dip. Other meters
|don't even respond when held to the wire. Dips on conventional L-C circuits
|can easily be full scale.

Yep. I have two 59s and they are great. I got rid of two Millens.
They are better than anything else but the 59.

As to usefulness, a short war story. Another engineer and I were
working on an AGC problem in the early Phoenix missile i-f amplifier.
Phoenix being a monopulse radar had a three channel receiver with very
tight agc tracking requirments (both gain and phase). The agc voltage
was fed to each of the three channels via feedthru caps in the walls
of a very well shielded and gasketed chassis. Nevertheless, there was
obvious crosstalk.

The other guy said to me, "Wes, do you have a GDO?"

I said, "Sure."

A couple of younger engineers who were watching this asked, "What's a
GDO?"

So we poke the coil of the Model 59 into the chassis and find a nice
resonance at the i-f in the agc wiring. The feedthru capacitance and
wiring inductance were resonating at i-f. We had millions of dollars
worth of test equipment in our lab and I doubt that we could have
devised a test for this without heroic efforts.

The only problem was keeping the GDO hidden from the metrology guys
since they couldn't "calibrate" and service them so they wanted them
gone.

Wes N7WS

[Bill Turner]

On Sat, 15 Nov 2003 23:08:53 -0700, Wes Stewart <***@_arrl.net> wrote:
<snip>

Post by Wes Stewart
The only problem was keeping the GDO hidden from the metrology guys
since they couldn't "calibrate" and service them so they wanted them
gone.

_________________________________________________________

Great story, Wes. But why couldn't the metrology guys figure out a cal
procedure? I suspect the Not Invented Here syndrome, right?

--
Bill, W6WRT

[Michael A. Terrell]

Post by Bill Turner
<snip>

Post by Wes Stewart
The only problem was keeping the GDO hidden from the metrology guys
since they couldn't "calibrate" and service them so they wanted them
gone.

_________________________________________________________
Great story, Wes. But why couldn't the metrology guys figure out a cal
procedure? I suspect the Not Invented Here syndrome, right?
--
Bill, W6WRT

More likely the results of corporate policy. The last place I worked
kept the records on the mainframe, rather than use dedicated software to
track the ISO9001 data because, "®That's the way we've always done
it!©".

That is like some test fixtures have elaborate setup and calibration
instructions, wile others are labeled, "Calibration not required" I told
the cal lab the label should read, "Calibration not possible". ;-)

[Bill Turner]

On Sun, 16 Nov 2003 14:45:47 GMT, "Michael A. Terrell"

Post by Michael A. Terrell
I told
the cal lab the label should read, "Calibration not possible". ;-)
--

_________________________________________________________

LOL!

--
Bill, W6WRT

[J M Noeding]

Post by Bill Turner
On Sun, 16 Nov 2003 14:45:47 GMT, "Michael A. Terrell"

Post by Michael A. Terrell
I told
the cal lab the label should read, "Calibration not possible". ;-)
--

_________________________________________________________
LOL!
--
Bill, W6WRT

A decade ago I had a struggle with those instruments idiots referring
to ISO 9000, had an old fully working 30 years old Wande&Goltermann
SPM-1 instrument for telex channels, with mark and space marked, but
they would give me a new digital possibly from HP, costing in the
region of $10000 - without the channel marks, but solid state. After a
dispute they agreed to check the calibration, and it was better than
they could measure, so they had to let it pass, but I damaged their
day!

I was told that if any tubes broke down it was forbidden to change
them, and it was a political decision to discard such old instruments

73
Jan-Martin
LA8AK
http://home.online.no/~la8ak/c.htm
--
remove ,xnd to reply (Spam precaution!)

[Wes Stewart]

On Sun, 16 Nov 2003 05:09:01 -0800, Bill Turner <***@nohow.com>
wrote:

|On Sat, 15 Nov 2003 23:08:53 -0700, Wes Stewart <***@_arrl.net> wrote:
|<snip>
|>The only problem was keeping the GDO hidden from the metrology guys
|>since they couldn't "calibrate" and service them so they wanted them
|>gone.
|
|_________________________________________________________
|
|Great story, Wes. But why couldn't the metrology guys figure out a cal
|procedure? I suspect the Not Invented Here syndrome, right?


The worst thing that could happen to our equipment was for it to go to
"Calibration." I had more than one piece of equipment "accidentally"
dropped and broken when they tired of maintaining it. If they did
this to an HP/Boonton 250 Rx meter what do you think would happen to a
Model 59?

The best we could do was get an "inactive" sticker put on the
equipment. This took it out of the cal cycle but theoretically meant
that we couldn't use it for anything. Also there were the everpresent
management directives to get rid of inactive equipment to reduce
inventory costs. Imagine how much expense could be written off if
Hughes Aircraft Co (now Raytheon) got rid of a Model 59 GDO <g>.

Might have been enough to reinstate my retiree medical benefit that
was promised to me for 33 years and then taken away. But that's
another story.

Wes

[Avery Fineman]

Post by Wes Stewart
|<snip>
|>The only problem was keeping the GDO hidden from the metrology guys
|>since they couldn't "calibrate" and service them so they wanted them
|>gone.
|
|_________________________________________________________
|
|Great story, Wes. But why couldn't the metrology guys figure out a cal
|procedure? I suspect the Not Invented Here syndrome, right?
The worst thing that could happen to our equipment was for it to go to
"Calibration." I had more than one piece of equipment "accidentally"
dropped and broken when they tired of maintaining it. If they did
this to an HP/Boonton 250 Rx meter what do you think would happen to a
Model 59?
The best we could do was get an "inactive" sticker put on the
equipment. This took it out of the cal cycle but theoretically meant
that we couldn't use it for anything. Also there were the everpresent
management directives to get rid of inactive equipment to reduce
inventory costs. Imagine how much expense could be written off if
Hughes Aircraft Co (now Raytheon) got rid of a Model 59 GDO <g>.

Dunno why you guys want to pick on metrology departments.

It's up to CORPORATE to see that metrology departments do
their thing properly. Most of them do. I worked in one for a bit over
two years (Ramo-Wooldrige) and everything was done according to
factory information and procedures. RCA Corporation was done the
same way.

On the other hand, Electro-Optical Systems (a Xerox division) was
terribly lax that way and any department could tag something out of
service and have it stored. EOS Corporate put such loose controls
on it that anyone could go into the storage area and "requisition"
anything, no questions asked.

Len Anderson
retired (from regular hours) electronic engineer person

[Kenneth]

Post by Paul Burridge
Hi gang,
I've never had a lot of luck with GDMs for some reason. Even with a
decent meter, it seems such a drag tuning across such a vast range
looking for a tiny, easily-missed dip which you have to screw out of
the meter by forcing the sensing coil so far into the circuit
concerned you practically break the circuit board. Am I alone in
finding this potentially invaluable device practically useless in
practice? Is there a more viable alternative?
p.

I've built several GDO's over the years. My favorite circuit is the old
standby using a split stator variable capacitor and a shunt fed coplets
oscillator. This capacitor can be 100-250 pf per section. My favorite
tube is the 6CW4 nuvistor, though a 6DV4 might
be a better choice at VHF. I put a TO-5 transistor heat sink over the
tube fearing it might run hot! I use a cathode resistor of about
150-330 ohms (un-bypassed) and connect a bnc connector to the cathode
via a 1000pf capacitor to steal a little signal to drive my frequency
counter. With the counter set for low level input I get good drive up
to about 100mhz or so. My coil socket is an RCA (phono) connector and
the coils use a matching plug. A better idea might be to use a 3 pin
DIN plug and socket, this allows for a ground connection to go to a coil
center tap. If you add the center tap the circuit will work below
1.5mhz with proper coils, otherwise it will not oscillate below this
frequency! (Having coils that go to 455khz would be nice to test if
stages). Power supply used two 6.3v 300ma filament transformers back to
back with a bridge rectifier. You can find transformers small enough to
fit the supply into a box small enough to house the instrument, yet not
too big to be hand hold-able. The coils can be wound on 1/4" or 3/8"
plastic water line intended for ice maker use. These will fit into
small places. Use of peaking chokes in the plate and filament lines can
help eliminate "drop outs" in frequency coverage. Sensitivity can be
adjusted with a plate pot, or put the pot in the meter circuit. I have
used sub-mini meters salvaged from old jap tape recorders (vu-meters).
These are typically around 500ua sensitivity. See my web site at
www.qsl.net/wa2mze.

[Paul Burridge]

On Fri, 21 Nov 2003 21:29:19 -0500, Kenneth

Post by Kenneth
I've built several GDO's over the years. My favorite circuit is the old
standby using a split stator variable capacitor and a shunt fed coplets
oscillator. This capacitor can be 100-250 pf per section. My favorite
tube is the 6CW4 nuvistor, though a 6DV4 might
be a better choice at VHF. I put a TO-5 transistor heat sink over the
tube fearing it might run hot! I use a cathode resistor of about
150-330 ohms (un-bypassed) and connect a bnc connector to the cathode
via a 1000pf capacitor to steal a little signal to drive my frequency
counter. With the counter set for low level input I get good drive up
to about 100mhz or so. My coil socket is an RCA (phono) connector and
the coils use a matching plug. A better idea might be to use a 3 pin
DIN plug and socket, this allows for a ground connection to go to a coil
center tap. If you add the center tap the circuit will work below
1.5mhz with proper coils, otherwise it will not oscillate below this
frequency! (Having coils that go to 455khz would be nice to test if
stages). Power supply used two 6.3v 300ma filament transformers back to
back with a bridge rectifier. You can find transformers small enough to
fit the supply into a box small enough to house the instrument, yet not
too big to be hand hold-able. The coils can be wound on 1/4" or 3/8"
plastic water line intended for ice maker use. These will fit into
small places. Use of peaking chokes in the plate and filament lines can
help eliminate "drop outs" in frequency coverage. Sensitivity can be
adjusted with a plate pot, or put the pot in the meter circuit. I have
used sub-mini meters salvaged from old jap tape recorders (vu-meters).
These are typically around 500ua sensitivity. See my web site at
www.qsl.net/wa2mze.

Thanks. Do you reckon there's any benefit in using toobz over FETs,
then?

[Kenneth]

Post by Paul Burridge
On Fri, 21 Nov 2003 21:29:19 -0500, Kenneth

Post by Kenneth
I've built several GDO's over the years. My favorite circuit is the old
standby using a split stator variable capacitor and a shunt fed coplets
oscillator. This capacitor can be 100-250 pf per section. My favorite
tube is the 6CW4 nuvistor, though a 6DV4 might
be a better choice at VHF. I put a TO-5 transistor heat sink over the
tube fearing it might run hot! I use a cathode resistor of about
150-330 ohms (un-bypassed) and connect a bnc connector to the cathode
via a 1000pf capacitor to steal a little signal to drive my frequency
counter. With the counter set for low level input I get good drive up
to about 100mhz or so. My coil socket is an RCA (phono) connector and
the coils use a matching plug. A better idea might be to use a 3 pin
DIN plug and socket, this allows for a ground connection to go to a coil
center tap. If you add the center tap the circuit will work below
1.5mhz with proper coils, otherwise it will not oscillate below this
frequency! (Having coils that go to 455khz would be nice to test if
stages). Power supply used two 6.3v 300ma filament transformers back to
back with a bridge rectifier. You can find transformers small enough to
fit the supply into a box small enough to house the instrument, yet not
too big to be hand hold-able. The coils can be wound on 1/4" or 3/8"
plastic water line intended for ice maker use. These will fit into
small places. Use of peaking chokes in the plate and filament lines can
help eliminate "drop outs" in frequency coverage. Sensitivity can be
adjusted with a plate pot, or put the pot in the meter circuit. I have
used sub-mini meters salvaged from old jap tape recorders (vu-meters).
These are typically around 500ua sensitivity. See my web site at
www.qsl.net/wa2mze.

Thanks. Do you reckon there's any benefit in using toobz over FETs,
then?

Probably not, but there isn't any disadvantage to using a tube, except
for having to use an AC operated supply. If you need a portable grid
dipper (to check antennas up on the tower for example) then you want a
solid state battery operated unit (which sure beats 100 feet of
extension cord dragging behind you when you climb the tower!).

Not all fets function well into the vhf range. If you want to build a
solid state dipper using fets make sure you get vhf units, not ones
intended for audio use. There are circuits using fets that simulate
negative resistance (like tunnel diodes) which make for an interesting
oscillator since no coil taps are needed and a single gang cap can be used.

[J M Noeding]

On Sat, 22 Nov 2003 18:20:46 -0500, Kenneth

Post by Kenneth
Not all fets function well into the vhf range. If you want to build a
solid state dipper using fets make sure you get vhf units, not ones
intended for audio use. There are circuits using fets that simulate
negative resistance (like tunnel diodes) which make for an interesting
oscillator since no coil taps are needed and a single gang cap can be used.

Right. I don't like fets, execpt as switches, RX RF amplifier and in
PA. We had a discussion in a radio club among designers 30 years ago
if it was any reason for using fets in oscillators instead of
bipolars, but couldn't really find any good reason, except they were
fancy.
It is also a circuit using a jfet and pnp-combination which works in a
negative impedance mode, but usually found on lower frequencies. Used
it for some time to check resonnant frequency of unknown tuned
circuits with a counter, but the problem is to control oscillation
level. It worked fine for 50% of the applications while the counter
indicated some higher (or lower) frequency for some circuits, so it
was abandomed. Believe I have seen it mentioned for griddipmeters,
too.
It seems to be a reason why PNP UHF transistors are used in most UHF
tuners found here, usually BF479, BF679, BF979. I've copied some of
the text for DL7QY's dip meter covering up to 1400MHz on
http://home.online.no/~la8ak/m3.htm

-JM


--
remove ,xnd to reply (Spam precaution!)

[Kenneth]

Post by J M Noeding
On Sat, 22 Nov 2003 18:20:46 -0500, Kenneth

Post by Kenneth
Not all fets function well into the vhf range. If you want to build a
solid state dipper using fets make sure you get vhf units, not ones
intended for audio use. There are circuits using fets that simulate
negative resistance (like tunnel diodes) which make for an interesting
oscillator since no coil taps are needed and a single gang cap can be used.

Right. I don't like fets, execpt as switches, RX RF amplifier and in
PA. We had a discussion in a radio club among designers 30 years ago
if it was any reason for using fets in oscillators instead of
bipolars, but couldn't really find any good reason, except they were
fancy.
It is also a circuit using a jfet and pnp-combination which works in a
negative impedance mode, but usually found on lower frequencies. Used
it for some time to check resonnant frequency of unknown tuned
circuits with a counter, but the problem is to control oscillation
level. It worked fine for 50% of the applications while the counter
indicated some higher (or lower) frequency for some circuits, so it
was abandomed. Believe I have seen it mentioned for griddipmeters,
too.
It seems to be a reason why PNP UHF transistors are used in most UHF
tuners found here, usually BF479, BF679, BF979. I've copied some of
the text for DL7QY's dip meter covering up to 1400MHz on
http://home.online.no/~la8ak/m3.htm
-JM
--
remove ,xnd to reply (Spam precaution!)

The negative resistance fet circuit I mentioned used a pair of jfets,
one P channel and one N channel with the sources tied together and the
gates of each transistor tied to the drain of the other. In this way
each transistor acts as the self bias resistor of the other. The
resulting voltage/current curve of the combo exhibits a region where the
current decreases as the voltage increases, looking much like the 'kink'
in the plate circuit curves of an old time tetrode tube (such as the
24A). The major disadvantage of this circuit for a gdo is that it is
such a strong oscillator that you don't get much of a dip (you need to
sample the output and feed it to a rectifier and meter) unless you load
the coil down with a shunt resistor....and you need a different value
for each range. Also P channel fets with good vhf performance are as
rare as hen's teeth.

[Paul Burridge]

On Sat, 22 Nov 2003 22:02:03 -0500, Kenneth

Post by Kenneth

Post by J M Noeding
remove ,xnd to reply (Spam precaution!)

The negative resistance fet circuit I mentioned used a pair of jfets,
one P channel and one N channel with the sources tied together and the
gates of each transistor tied to the drain of the other. In this way
each transistor acts as the self bias resistor of the other. The
resulting voltage/current curve of the combo exhibits a region where the
current decreases as the voltage increases, looking much like the 'kink'
in the plate circuit curves of an old time tetrode tube (such as the
24A). The major disadvantage of this circuit for a gdo is that it is
such a strong oscillator that you don't get much of a dip (you need to
sample the output and feed it to a rectifier and meter) unless you load
the coil down with a shunt resistor....and you need a different value
for each range. Also P channel fets with good vhf performance are as
rare as hen's teeth.

Interesting. The circuit I rebuilt my old Tradiper with used two
dual-gate MOSFETs., 3SK88s I believe they are. It gives a nice fragile
ouput which is easily pulled down by an external tuned circuit,
thereby giving rise to a good, deep dip. The only problem is the size
of the blasted snifffer coils! Whilst this is fine for big old valve
type constructions, it *is* totally impractical for today's ever
smaller PCB jobs. I guess the time is coming to abandon it in favour
of some other method of measurement, probably involving a scope and
sig-gen.