It utilized to be a major rite of passage for a hardware hacker to obtain an oscilloscope. up until recently, new instruments were seldom in typical people’s budgets, so you most likely made finish with a utilized scope. Now, there are great deals of low-cost options, particularly if you include low-end PC scopes as well as “scope meters.” digital meters are likewise now low-cost (often totally free at some major stores), together with signal generators, frequency counters, as well as even logic analyzers.
But there is one piece of test devices you don’t see as commonly as you utilized to as well as its a shame, since it is a extremely flexible piece of kit. Admittedly, if you aren’t doing wireless work, it may not be high on your desire list, however if you do anything with RF, it is not only a flexible tool, however a great value, too. What’s it called? Depinde. Historically, they went by the name “Grid Dip Oscillator” or GDO. in some cases you’d hear it called a “Grid Dip Meter” instead. However, contemporary versions don’t have tubes (and, thus, no grid) so in some cases you hear them now called dip meters or perhaps just dippers.
Why Does it Dip?
Regardless of what you phone call them, the theory of operation is the exact same as well as it is quite simple. The instrument is nothing much more than a extremely broad band oscillator with a method to couple the output to an outside circuit. There will likewise be some method to screen exactly how much power is being taken out of the oscillator. This is many commonly done by taking a look at the top amplitude of the oscillator.
The reason for the dip has to finish with the method inductors as well as capacitors behave at different frequencies. just about any type of circuit or element has three sources of impedance: the resistance, which shouldn’t modification based on frequency; the capacitive reactance, which is due to–of course–capacitance; as well as the inductive reactance from inductive elements. In some cases, you only have a considerable amount of one of these. For example, in a carbon resistor, you shouldn’t have extremely much of either type of reactance. A capacitor ought to be predominantly capacitive reactance.
Reactance as well as Impedance
For a provided capacitor, the reactance is extremely high at low frequencies as well as extremely low at high frequencies. Inductance is the opposite: low frequencies create a lower reactance than higher frequencies. It is quite simple to keep in mind this if you believe of a DC present as a zero Hertz wave. An inductor (a coil of wire) will clearly pass DC (low reactance) as well as a capacitor (two parallel plates) will clearly not pass DC (high reactance).
Even though the overall impedance of the circuit depends upon these three elements, it isn’t as easy as just adding up the values. That’s since resistance as well as reactance aren’t the exact same type of quantity. If you have a 1V signal going into a 2 ohm tons with 3 ohms of reactance, you’d like to understand it would behave the exact same as 1V going into an normal resistor. If the resistance as well as the reactance are in series, the value of that efficient resistor is the impededance as well as it is the vector sum of the resistance as well as the reactance.
In the example, then, 22+32=13. The square root of 13 is just around 3.6, so the magnitude of the impedance is 3.6 ohms. To complicate things further, inductive reactance as well as capactive reactance tend to cancel each other out. It is customary to treat capacitve reactance as negative, although because we will square it, it truly doesn’t matter which one you think about unfavorable to do this specific calculation. For the math inclined, you are truly treating the resistance as the genuine part as well as the reactance as the imaginary part of a complex number. The conversion to polar type provides the magnitude as well as the phase angle.
In parallel it is kind of the exact same thing however the reactances add just like resistors in parallel. Here’s the point though: At some frequency, the inductive reactance as well as the capacitive reactance equal. In a series circuit, that implies the reactance goes to zero as well as all you have left is the resistance. In a parallel circuit, the zero winds up in the denominator of a fraction, as well as so the efficient reactance is unlimited (and, in parallel with a pure resistor, doesn’t modification the value of the resistor). Either way, reactance cancels out leaving pure resistance.
Rezonanţă
The point where the reactances cancel each other out is resonance. The dip meter works since at the resonance point, the meter’s oscillator will have the greatest tons on it (lowest impedance), as well as therefore the voltage will decrease (or dip). At any type of other frequency, some reactance will be left as well as the overall impedence of the circuit under test will be higher than atrezonanţă.
Clearly, the most fundamental function of the dip meter is to determine the resonant frequency of a circuit. If that were all there was to it, it would be quite useful. however with just a bit additional effort, the dip meter can do so much more.
What Can you Measure?
First, it can likewise determine other tuned circuits, not just capacitors as well as inductors made of components. For example, antennas, crystals, as well as transmission lines can all have a specific resonance points, as well as the meter can determine them. For a crystal, the frequency is the one the crystal ought to oscillate at (with a bit error based on packing capacitance as well as other factors). Antennas may be resonant at much more than one frequency, not just the one you are interested in, so some judgement is required. Anything that doesn’t have a coil (like an antenna or a crystal) will requirement a bit cable loop to couple energy from the meter to the circuit.
For transmission lines, you can determine by making a little loop to couple the dip meter (the smaller the better). browse for the lowest dip, as well as that will show the 1/4 wavelength frequency of the transmission line. For example, if the cable television is resonant at 7.5 Mhz (40 meter wavelength) then the cable television is about 10 meters long. Don’t forget, however, to element in the transmission line’s velocity factor. That is, a quarter wave transmission line with a velocity element of 0.66 will be shorter than the theoretical length (it will only be 66% as long, in this case).
Of course, you can utilize the transmission line relation either way. That is, you can get the resonant frequency to determine the cable, or you can set the frequency as well as trim the line for a dip. In fact, utilizing what you understand to get what you don’t know is typically a great principle with the grid dip meter. want to determine an unknown capacitor? resonate it with a understood inductor. Or begin with a understood capacitor as well as discover the value of an unknown coil.
One of the primary problems, though, is reading the frequency accurately enough. Some contemporary meters have digital screens (like the DipIt shown on the right). many typical meters, though, don’t. On the other hand, you can quickly couple them to a frequency counter or utilize a receiver to identify the frequency accurately.
If you don’t mind a bit estimation, you can do even much more measurements. Coils have a Q (quality factor) that suggest exactly how much resistance they have family member to their reactance. utilizing a great recommendation capacitor, type a resonant circuit as well as dip the meter. note the frequency. then tune the dip meter down up until you discover the frequency where the meter reads about 30% higher than it did at the dip. now tune the dip meter up, with the dip again, up until you discover the 30% mark once again on the other side. The Q will be approximately equal to the dip frequency split by the difference between the two 30% frequencies.
It may be obvious, however the dipper can likewise just be utilized as a signal source. For example, to repair work a radio, you may put the dip meter at a frequency the radio ought to be able to hear as well as trace it with the circuit. numerous dip meters likewise have a mode where they will turn off their oscillator as well as utilize the coil (and tuning capacitor) together with a diode to act as a wavemeter. The meter, then, shows the stamina of RF energy at the tuned frequency. Some meters even have a headphone jack so you can listen to the signal (making it practically a crystal radio).
Finding a Dip Meter
One reason numerous people don’t have dip meters today is that they aren’t as easily offered as they utilized to be. Heathkit was a extremely prominent provider for dip meters as well as had a number of models. other prominent older designs (often discovered on eBay) were Eico, Millen, Boonton, as well as measurements company (be careful, though; the ones with tubes are most likely not a great offer unless you are a collector). You can discover a listing with photos of numerous GDOs at [n4xy’s] web site (the photos are a few clicks of the next button away from the primary page). To the left is a photo of one of my old measurements GDOs (and, yes, it does utilize tubes).
You can still discover new dip meters from MFJ (they offer the MFJ-201 shown on the right, as well as you can likewise convert a few of their antenna analyzers into a serviceable dip meter). There are likewise lots of plans on the Internet. If you want a genuine tube design (not recommended) [w4cwg] has plans. A much more contemporary FET style that has a book bridge to assist make the dip deeper is offered from [SM0VPO].
On the other hand, it seems a pity to develop a new system without a digital display. You can add one, of course, or you can choose one that is integrated like the DipIt or the ELM. There are lots of other job as well ca kituri chiar acolo. Uită-te in jur. Cea mai grea parte, de obicei, înfășoară bobinele, deși unii vor apela telefonul pentru condensatoare variabile care pot fi dificil de a se potrivi. Într-adevăr, totuși, orice tip de oscilator care poate fi făcut constant va funcționa. De fapt, am două dopuri vechi de heathkit care utilizează o diodă de tunel de rezistență nefavorabilă ca oscilator (unul dintre ele este în fotografie la stânga).
Dacă doriți o prezentare video de utilizare a unui contor DIP, nu am putut face mult mai bine decât [W2AEW] a făcut deja, astfel încât să puteți descoperi videoclipul de mai jos.