Hello everyone. My name is Daniel Arranz and I am looking for someone on possesion of an Electro Metrics Active Loop Antenna (EM 6874). For some reason, the antenna is not working and I don´t know why. I hope someone can show me the inside electronics to compare and find what is wrong. Thank you in advance and have a nice day!
Hi Daniel Arranz López ,
sorry, I'm not in possesion of an EM6874. But since the datasheet gives a load of 600 nH in series with a resistance of less than 1 Ohm, and the inductance of a loop of 321 mm diameter and about 17 mm diameter of the cross-section of the conductor is about 600 nH, I guess that the N connector is directly connected to the loop, without any intermediate electronics.
In this case, you could just rule out a short circuit by visual inspection, and a disconnection by measuring the resistance at the connector. Or, better still, you could run a current of a few A (40 A max), 50 Hz, for example, through the loop, and use a clamp ampere meter to confirm the current.
Did this antenna work already in your actual setup, and ceased working later on? If not, I suspect that your signal source isn't able to drive 600 nH directly. E.g., at 1 MHz, the impedance is less than 4 Ohm.
PS The EM-6874 is not active, obviously. But Electro Metrics also offers active antennas, like the EM-6876. Are you sure you have the EM-6874?
If Joerg Fricke is right, then your antenna may well be working perfectly but it looks like a short circuit, and you need to design a matching circuit for it, like a big parallel capacitor, e.g. 40 nF, so that it resonates at your working frequency. This will also multiply the (radiation) resistance by the Q of the resonance, so it may approach 50 ohms, or 75 ohms. You will probably need to be fairly close with the capacitance because the Q may be around 100 so the bandwidth will only be 10 kHz or so.
Hai,
Most of the manufactures will assist such issues.Try by dropping a e mail to them.
Most common problem is impedence mismatch.
Hello everyone!
First of all, I would want to thank you for your responses.
Joerg, you were rigth, the antenna we have is the EM-6876.
The problem we seem to have is that for some reason the power the batteries have to provide to the active circuit doesn't arrive. The battery is connected to a circuit board that eventually have 3 pins were the active circuit is conected. We have checked the battery power directly and ther is no problem with that. The problem has to be on the board. Any idea?
Thank you people!
The easiest solution would be, as Elangovan Sundaram wrote, to contact the manufacturer. Although the board looks like it was designed in the late 70s or the early 80s (I like the MC1723 in the 10-pin metal case :-) it seems that the EM-6876 is still offered by Electro Metrics, perhaps with a newer version of the board. If they provide the schematic, locating the fault should be easy.
If not, reverse engineering (i.e. drawing the circuit diagram according to the board) does not seem too difficult with about 20 parts and a two-sided PCB, after unscrewing the board, of course. Some parts might be only available via eBay.
BTW, is the intended use either battery powered measurement or charging of the battery without using the antenna? This way, a "clean" supply voltage would be guaranteed.
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