A Grid Dip Oscillator
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- เผยแพร่เมื่อ 18 ม.ค. 2025
- This is a brief overview to show a couple of uses for the Grid Dip Oscillator. A good tried and tested circuit and coil details are given at the end for anyone wishing to try their hand at making one.
Even with a number of cheaply acquired GGO's, I never got to test them! This video inspires me to get them out of my shed to play with. Thank you!
Glad to have been some help. Have fun!
I remember reading about grid dip oscillators in old electronics magazines when I was a kid. Always wanted to build one but never did. I'll have to make one sometime! Thanks for the video!
Go for it I say! And let's face it, it's quite a simple circuit to build as well.
@@lishaton You know, its the simplicity that makes it so special - one active device. Today we throw millions or billions of transistors to do simple tasks like this.
Thanks for another informative video. Regards Clare
Thanks Clare :-)
An interesting property about the grid dip meter -- at least in my experience -- is that the oscillator's frequency will be pulled away from its natural oscillation frequency when brought in the vicinity of an LC tank. You can see or hear this behavior simply by monitoring the dip meter's radiated signal on a nearby receiver, spectrum analyser, or frequency counter. What this means in practice is that when brought near an LC tank, the dial markings of the dip meter become inaccurate, because the dial markings were created with the oscillator in isolation, not when the oscillator is being affected by a nearby LC tank.
Furthermore, there's an interesting "frequency snapping" that occurs. If you strongly couple an LC tank to the dip meter's inductor (for a deep dip), then you will probably notice that as you slowly tune the dip meter in one direction, the dip gradually becomes deeper and deeper, until suddenly, when you tune just a bit further, suddenly the dip disappears (not gradually disappearing, but suddenly), and the meter needle snaps back up. If you monitor the radiated frequency of the dip meter while this is happening, you will see that at the instant the needle "snaps" back up, the dip meter's frequency also suddenly jumps in frequency -- jumping upward if you were tuning upwards in frequency, and downward if tuning downwards. I found out that the most accurate way of determining the LC tank's resonant frequency is to slowly tune upwards across the dip and to find the frequency just before the snapping, calling this frequency f1 (which must be measured by measuring the radiated signal of the dip meter, since the dial calibrations become inaccurate when an LC tank is brought near the dip meter). Then, you tune slowly downwards across the dip and find the frequency just before the snapping, calling this frequency f2. The true resonant frequency of the LC tank is then the average of f1 and f2. I confirming this by measuring the resonant frequency of the LC tank by measuring it with a NanoVNA.
I should also add that this was with a transistor-based dip meter. Maybe tube-based dip meters behave differently. You can read about some of my experiments here: www.theradioboard.org/forum/other-electronic-projects/grid-dip-meter-frequency-pulling-and-jumping .
Most interesting observations. All points notes and quite valid. I tend to start using it with the smallest noticeable movement on the meter, then slowly increase this to give a better accuracy until one reaches the setting at which the issue with the frequency suddenly 'snapping' as you say, manifests itself. Back off slightly from this setting and take the reading. Thanks for the feedback!
@@lishaton I think that maybe one way to prevent the undesirable frequency pulling is to add a buffer amplifier after the oscillator, and to connect the output of the buffer amplifier to an untuned coupling loop, which then goes through a diode and through a microammeter to ground. The buffer amplifier will drive the oscillator's output through the coupling loop, through the diode, through the meter, to ground, creating a current readout on the meter. Then, if an LC tank is brought near the coupling coil, it will suck out energy from the buffer amplifier (not directly from the oscillator's LC tank itself), causing less current to flow through the diode and the meter, thus showing a dip. This approach should prevent frequency pulling of the oscillator because the oscillator's LC tank is never coupled to directly; we only couple to the coupling loop on the buffer amplifier. I've seen a similar approach recommended in some articles, and I think the MFJ dip meter also uses this approach. I haven't had a chance to try it myself yet.
If you ever try an example, do let me know how well it worked.
i made a GDO too a pair of weeks ago, i have a video but it's in italian :D i didn't care for the passive mode cos i can use a scope that is much better for running circuits, but a GDO is pretty legit for resonant circuits or parts of circuits, it works on tesla coils too
Yes, it's surprising just how many useful measuring tasks one can do with a simple bit of circuitry like this!