83 Khz Antenna (compact wand) for test equipment

[baxterdmutt]

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.

 

[mtwieg]

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...

 

[baxterdmutt]

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...

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

 

[jiripolivka]

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.

 

[betwixt]

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.

 

[biff44]

https://www.ets-lindgren.com/pdf/7405.pdf

 

[baxterdmutt]

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.

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.

 

[baxterdmutt]

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 - - -

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?

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

 

[betwixt]

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.

 

[KerimF]

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.