Grid Dip Meter

It's now called a GDO (grid dip oscillator). Here's a page of various manufacturers and models:

I have three Heathkit HD-1250 GDO's. Not the best. You can get what might be a clone of a Heathkit HD-1250 from MFJ: Also, check out the sold listings on eBay for approximate pricing:

Sorry, no recommendations as all my stuff is ancient.

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Jeff Liebermann     jeffl@cruzio.com 
150 Felker St #D    http://www.LearnByDestroying.com 
Santa Cruz CA 95060 http://802.11junk.com 
Skype: JeffLiebermann     AE6KS    831-336-2558

So's a lot of my stuff. But there's nothing wrong with old gear IMO it's the quality of it and whether it's in calibration that counts. The only issues with GDOs IME are that they're not too bad for the lower frequency RF stuff, but hopeless for anything higher.

In google (images) about 10 solutions.

This looks very interesting: No clue how to purchase one and it's only 1 to 42 MHz.

May 2003 QST article on building a "modern" GDO:

Feb 2013 Circuit Cellar article on building a GDO:

Goes to 1GHz by changing both the oscillator and the coil with frequency range. See "Plug in Oscillators" section:

July 2014 QST. Using an MFJ-259/269 as a GDO: MFJ sells these as MFJ-66C:

More:

--
Jeff Liebermann     jeffl@cruzio.com 
150 Felker St #D    http://www.LearnByDestroying.com 
Santa Cruz CA 95060 http://802.11junk.com 
Skype: JeffLiebermann     AE6KS    831-336-2558

Huh? VHF and UHF is where they really worked well, because at lower frequencies, a lot of the coils were shielded. There were GDOs that worked well at VHF and UHF.

Michael

On Sun, 29 Nov 2015, OldGuy wrote:

You can build simple or you can build complicated. With semiconductors, the cost of extra transistors and the space they take up doesn't amount to much, but you can end up with a better device, and one that can be used for more things.

The biggest problem seems to be false dips, coming from an rf choke feeding the oscillator that resonates in the wrong place, or just the layout of the circuit. I suppose it's made worse if the oscillator doesn't oscillate very well as you move up in frequency.

Calibration was always kind of vague, but nowadays with so many having frequency counters, one can build something that has a buffer to feed a frequency counter, so you can either have vague calibration on the dial, or none at all.

It's probably also worth adding a buffer and output jack so you can use it as a rudimentary signal generator.

SOme circuits are better than others. Something that uses a two terminal coil is simpler (Heathkit used phono plugs in at least one of their GDOs) but I suppose you get more control with more contacts. If nothing else, you can pre-adjust the level of the oscillator from band to band. Of course a circuit that uses only two terminals can then be useful in other ways, put a crystal where the coil goes and you can test that crystal, connect a shielded coil where the coil goes and with the variable capacitor at minimum, you get the general frequency of that shielded coil if you listen for it in a receiver, or have the frequency counter hooked up. Since coupling to shielded coils can be a problem, this works out well.

Like regen receivers, for a long time a GDO was a minimal circuit, yet nowadays you can complicate it. Why not have a nice 3terminal voltage regulator? Why not use an exotic oscillator circuit that uses more than one transistor?

For a long time, most GDOs were about the same, the difference being that anytime someone wrote about their GDO, they'd built it just like someone else's, except changed the coils a bit or used a tube socket instead of a phono jack for the coils, or vice versa. Even the Measurements Corporation or the Millen GDO were fairly simple circuits, though I gather Millen put a lot of effort into a nice flat output. It was the move to solid state that shook things up, technically those were no longer GDOs but everyone knew what was meant. So Heathkit used a tunnel diode in an early sixties one, not sure if it gave any advantage. In some circuits there wasn't anything that really dipped, so they'd measure the signal strenght of the oscillator and see where it dipped. Bipolar transistors often didn't work so well, at least not if someone was basically transcribing a tube GDO to a bipolar oscillator. Later FETs and mosfets came along, more like tube GDOs. IN the seventies, Heathkit and some others used mosfets, and more peripheral devices, still fairly simple. The December 1971 issue of QST (I'm pretty sure it was that issue) had an article by someone from Millen talking about their effort to come out with a solid state GDO. I think they set out to use the same variable capacitor and coil set used by their tube one, but I remember one thing was they had to use ferrite beads and RF chokes in series to get rid of false dips.

GDOs can still be found at hamfests on the used market. I think someone is still making new ones, but I'm not sure who. There was period when people were taking tube GDOs and solid stating them, the magazines had articles about that.

Michael

Best one I ever used was the tube version of the Millen. I switched to the solid state version and regretted it. Much less sensitive and more fiddly than the tube version. Tunnel dipper was the worst for sensitivity.

If ham swapmeets are any indicator, most GDO's available second hand are missing some or all of the coils.

Find an old Measurements (Boonton) 59 'Megacycle Meter' on eBay. I used to have a Heath 12something that I used for years. On Joerg's recommendation, I got a Measurements 59, and soon afterwards the Heath went in the trash.

The 59 has accurate frequency calibration. Mine is still within 2% over the full range, by actual measurement, and it hasn't been trimmed in a loooong time. It also gives a nice deep dip even with quite weak coupling--much weaker than the Heath, especially on low-Q resonances. I've used it to measure the coupling coefficient of toroidal transformers, for instance. (An ISDN unit had a CC of 0.99986.)

Besides, it has such a nice retro look and feel.

Cheers

Phil Hobbs

--
Dr Philip C D Hobbs 
Principal Consultant 
ElectroOptical Innovations LLC 
Optics, Electro-optics, Photonics, Analog Electronics 

160 North State Road #203 
Briarcliff Manor NY 10510 

hobbs at electrooptical dot net 
http://electrooptical.net

Just downloaded an archive of Radio Constructor from Americanradiohistory.com - in the course of browsing through them, I found a valve design that uses untapped coils.

It would probably adapt well to a JFET.

Can't remember which issue, but it was before mid 50s.

A while back I acquired a small Tektronix component envelope containing very tiny "top hat" style diodes that there's a faint possibility they could be TDs.

Copying the Heathkit TD dipper had crossed my mind - now I probably won't.

It seemed like the Tunnel Diode got a lot of press in the sixties in the hobby magazines, but much of it wsa novelty. I can't remember anything where some other device couldn't be used. I suppose when the Heathkit GDO came out, the Tunnel Diode might have had better bandwidth, though I don't remember that GDO has having great VHF and UHF coverage. But while neat things were shown, that tunnel diode FM broadcast receiver was more unique becuase of the low IF and pulse counting detector than that it used a tunnel diode as a mixer/oscillator down to that low IF.

There were uses for tunnel diodes that hobbyists generally didn't see, and those at least took advantage of the device at the time, but the time passed pretty fast before other things didn't do most of what a tunnel diode could do.

So I think the Heathkit tunnel diode dipper was mostly for novelty sake.

Michael

For good reason. Tunnel diodes flew in most of the early satellites up to about 1990 because it was the only reliable microwave device available at the time.

I believe you're referring to the HW-10 GDO: No pulse counting detector but rather a simple half wave RF rectifier followed by 3 stages of DC amplification. As I vaguely recall, I had difficulties getting a clean dip because the tunnel diode was probably oscillating on multiple frequencies at the same time.

I may have an HW-10 GDO somewhere in my junk pile. I dropped it from about 60ft up during an antenna raising party. It landed in some bushes and did not appear to be damaged, but failed to function afterwards. I also have a few new TEK tunnel diodes.

Tektronix also used tunnel diodes in their oscilloscope trigger circuitry: I use one testing scope rise time: GE Tunnel Diode Manual (1961): Today, Aeroflex/Cobham/Metelics currently sell tunnel diode detectors and use them in their instruments: Sorry, but tunnel diodes are not quite dead and obsolete.

Nope. During the 1960's, the big draw for Heathkit was that kits were much cheaper than labor intensive assembled products. Heathkit had to do something to keep the price down on their products. Cheap was the order of the day and tunnel diodes were CHEEEEEEP.

--
Jeff Liebermann     jeffl@cruzio.com 
150 Felker St #D    http://www.LearnByDestroying.com 
Santa Cruz CA 95060 http://802.11junk.com 
Skype: JeffLiebermann     AE6KS    831-336-2558

I've never used one, but I suspect that part of the reason that tunnel diode dippers are inferior is that you can't run a high-Z tank without tapping the TD way way down, so that you need an impractically large split variable capacitor.

Nuvistors are really good for that, over a pretty wide frequency range.

Cheers

Phil Hobbs

--
Dr Philip C D Hobbs 
Principal Consultant 
ElectroOptical Innovations LLC 
Optics, Electro-optics, Photonics, Analog Electronics 

160 North State Road #203 
Briarcliff Manor NY 10510 

hobbs at electrooptical dot net 
http://electrooptical.net

Back then there was a fanatical craze for FM bug transmitters - with a tunnel diode, the circuitry was always smaller than the battery.

There's a low voltage 8056 Nuvistor in my bits box waiting for a *VERY* elusive round-tuit.

I'd forgotten about those. The only time I remember seeing them mentioned (and this was after the fact) was one or two converters that used them, no need to have a high voltage power supply.

Nuvistors came in just on the cusp of transistors taking off. So other than tv set front ends, they didn't see a lot of use, people going after transistors instead.

I remember one review for a nuvistor converter (I think it was for

144MHz), where someone compared it to their existing converter and said "the noise figure is better, which probably means my old converter needs returning). The Nuvistor did give good noise figure without the fussing needed with previous devices. Or the cost, the previous converter in the article was either a 416 or 417.

Michael

Mine came from an old Sealy TV that someone left in the bin room at the flats.

It didn't suit the UK standard so I just pulled the back off to look for interesting bits.

Apparently there was a time that most remote garage door openers had a Nuvistor of some description.

The problem was that TDs had such a lot of capacitance that it was only the ones with the huge peak currents (200 mA!) that were really fast. I have a bunch of 2 mA TDs with 200 pF of capacitance. Fast? Not so much.

Cheers

Phil Hobbs

--
Dr Philip C D Hobbs 
Principal Consultant 
ElectroOptical Innovations LLC 
Optics, Electro-optics, Photonics, Analog Electronics 

160 North State Road #203 
Briarcliff Manor NY 10510 

hobbs at electrooptical dot net 
http://electrooptical.net

I've never heard of that, but it's possible. There were those subminiature tubes (the leads were generally laid out in parallel with each other, and the leads were relatively low gauge wire) seen in hearing aids and some portable radios. I think those came early enough that they had a longer span, but they too were whiped out by transistors.

Michael