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

Paul wrote:



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but because it was hopelessly outdated and used old germanium trannies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

james ) writes:
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

Paul wrote:

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

hi

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

jimbo


Michael wrote:

james ) writes:
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

Paul wrote:

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

hi

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

jimbo


Michael wrote:

james ) writes:
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

Paul wrote:

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

james ) writes:
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

Paul wrote:

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