83 Khz Antenna (compact wand) for test equipment

Hello all,
I have a wire tracer that transmits a signal on about 83khz. The antenna (a small wand) is missing. The company does not support the unit any longer and I have been unable to find a replacement anywhere. I have made some antennas on my own for my HAM equipment in the past but never for anything down that low and never for anything this small. My calculation suggests a full wave antenna would need around 1000 feet of wire. A 1/4 wave is still over 200 feet. I thought I could make some sort of active antenna but the antenna port has no way to provide power and so I am at a loss.

I don't want anything much larger than the original which was a little less than a foot long and about 3/4" in diameter. I guess I could do an active antenna with a AA or AAA battery but don't know if that's possible. Any help would be greatly appreciated.
Thanks in advance.

At that your frequency is just going to be a coil of wire rather than a real antenna. Active or passive doesn't really make a difference, except for maybe some improvement in SNR...

mtwieg said:

At that your frequency is just going to be a coil of wire rather than a real antenna. Active or passive doesn't really make a difference, except for maybe some improvement in SNR...

Click to expand...

Ok, I was kinda figuring that but is length of wire in the coil going to make a lot of difference. Should I try to make it as long as possible or try to keep to an even fraction of the full wave. For instance 67 inches is a half wave /100. Would that be better than 100 inches which isn't at all part of the wave or does it really matter once I get down to that small of a percentage of the wave length? It is important to try and get as much out of it as I can. It needs to be able to pickup the signal through walls and from underground as best as it possibly can given it's restrictions as far a size goes.

Also would I be better with a longer coil of really fine gauge wire or a shorter coil of thicker gauge. I was thinking the longer coil of fine gauge because it's not like the antenna is receiving a lot of energy that it needs to conduct.

Thanks

For a search wand, I would use a ferrite antenna with the coil tuned to your 83 kHz. It can be enclosed in a hand-held plastic case and it has a good directivity useful to search. Many wireless-controlled watches use such ferrite antennas, tuned to 60 kHz in U.S. and 77 kHz in EU. Easy to tune by moving the coil along the core.

Roger, you are missing an essential point - the antenna is almost certainly a tuned circuit comprising the 'antenna' coil and a parallel capacitor so it would be tuned to resonance rather than being a single ended antenna. With a tuning capacitor you would be looking at the inductance needed rather than the length of full/quarter waves.

Brian.

betwixt said:

Roger, you are missing an essential point - the antenna is almost certainly a tuned circuit comprising the 'antenna' coil and a parallel capacitor so it would be tuned to resonance rather than being a single ended antenna. With a tuning capacitor you would be looking at the inductance needed rather than the length of full/quarter waves.

Brian.

Click to expand...

Thanks Brian,
I came to that realization last night just before crawling into bed. I was thinking about something totally different related to inductance and frequency calculations. It struck me that that was probably what I needed here.
Thanks.

So, I just realized that to calculate the required inductance I need for this I also need a capacitor in the circuit (for an resonant inductance calculation). I didn't think these loopsticks had capacitors so how do I calculate what inductance to aim for the frequency that I need it for?

- - - Updated - - -

baxterdmutt said:

So, I just realized that to calculate the required inductance I need for this I also need a capacitor in the circuit (for an resonant inductance calculation). I didn't think these loopsticks had capacitors so how do I calculate what inductance to aim for the frequency that I need it for?

Click to expand...

Never mind! Stupid question. Of course it needs a tuning cap. I don't know what I was thinking:lol:

Intuitively, I would aim for 1nF as the tuning capacitor and an inductance of 3.6mH, they may not be optimal but they are ball park figures that are easy to buy/make and wouldn't be too bulky.

Brian.

Please note that the optimum antenna (on ferrite core here) is the one that matches the impedance of the terminal connected to it. At this very low frequency, a suitable coil tap could be used to achieve this goal. In this case, the transferred power is at its maximum.