On Sun, 16 Nov 2003 22:33:38 GMT, (J M Noeding)
wrote:


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.
--

"I expect history will be kind to me, since I intend to write it."
- Winston Churchill

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

"Bill Turner" wrote in message
...
On Sun, 16 Nov 2003 16:14:04 +0200, "oh2baw" wrote:

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

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

"Bill Turner" wrote in message
...
On Sun, 16 Nov 2003 16:14:04 +0200, "oh2baw" wrote:

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

Paul Burridge wrote:
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 wrote:
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.

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

On Sun, 16 Nov 2003 22:33:38 GMT, (J M Noeding)
wrote:

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

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

On Sun, 16 Nov 2003 22:33:38 GMT, (J M Noeding)
wrote:

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

J M Noeding wrote:

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

On Sun, 16 Nov 2003 22:33:38 GMT, (J M Noeding)
wrote:

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

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.
--
I say, the boy is so stupid that he tried to make a back up copy of his
hard drive on the Xerox machine!

Michael A. Terrell
Central Florida

J M Noeding wrote:

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

On Sun, 16 Nov 2003 22:33:38 GMT, (J M Noeding)
wrote:

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

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.
--
I say, the boy is so stupid that he tried to make a back up copy of his
hard drive on the Xerox machine!

Michael A. Terrell
Central Florida

On Fri, 21 Nov 2003 21:29:19 -0500, Kenneth
%wa2mze%@%bellsouth%.%net% wrote:

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?

--

"I expect history will be kind to me, since I intend to write it."
- Winston Churchill