Xterra low frequency coil

[MXTerer]

Has anyone noticed if the Low Frequency concentric coil is more susceptible to EMI than the 7.5 or 18.75 Khz coils

 

[Old Longhair]

Not that I've noticed.

 

[Digger]

In the places I've hunted, I've actually found the HF coils to be more prone to interference than the MF or LF coils. I don't know whether the HF is more susceptible to EMF& RFI or if it is because it is just more sensitive to everything? I say that because I have to lower the Sensitivity on my HF coils, compared to the other two freqs. Around here, the 3 kHz is my most stable coil. JMHO HH Randy

 

[MXTerer]

A lot of my hunting is very close to high voltage transmission lines-230,000 volts. I have a teJon that works perfectly,high sensitivity under these lines The tejon runs in the 17 khz range. I also have a Mxt and they run in 14 kHz range, high sensitivity with no problem. What brings up this question is that I have had several minelab advantages that I believe ran in the 5 khz range and I couldn't get within 100 yds of these lines before they were unusable. It seems that the lower the frequency the worse the interference. Any more comments appreciated.

 

[Old Longhair]

The noise cancel feature on the XT705 takes care of most of that for me. Tracking helps keep it even calmer. And target stabilization helps too.

The only thing that I've noticed with my LF running hot, is higher TID's on shallower targets. And it's amplified when hunting wet ground. It takes some getting used to, but if you listen to the quality of the tone you can still avoid trash, and the extra depth is worth it.

 

[Mtnmn]

My XT-70 has very little problem with EMI no matter if a med. or high freq. coil is being used.

 

[Digger]

If you encounter an "outside source", such as the power lines you mentioned, which operates at or produces harmonic frequencies matching one or more of the detectors harmonic frequencies, you will get chatter and falsing. These harmonic frequencies of the detector are multiples of the fundamental frequency (transmit frequency). For example, an X-TERRA equipped with the 7.5 khz coil would create harmonic frequencies of 15 khz, 22.5 kHz, 30 kHz, 37.5 kHz, 45 kHz, 52.5 khz 60 kHz etc. etc. etc... The 3 kHz coil would create harmonic frequencies of 6 kHz, 9 kHz, 12 kHz, 15 kHz, 18 kHz, 21 kHz, 24 kHz etc. etc. etc...... The HF coil would produce harmonics of 37.5 kHz, 56.25 kHz, 75 kHz, 93.75 kHz, 112.5 kHz etc,.etc, etc. As you can see, regardless of which coil you chose for the X-TERRA, none of them create the same harmonics as your 17 kHz Tejon or your 14 kHz MXT. So the power lines must be creating harmonic frequenices "outside" of the Tejon and MXT harmonics. However, if you noticed the harmonics of the 7.5 kHz coil, you see that every other one is a harmonic that is also produced by the 5 kHz Advantage. (10 kHz, 15 kHz, 20 kHz, 25 kHz, 30 kHz etc) So if I were to guess, if you were going to use an X-TERRA at that site, I'd say the 7.5 kHz coil would be more likely to be influenced in the same locations as your Advantage. Coming in "second" would be the 3 kHz (6kHz, 9kHz, 12kHz, 15kHz, 18kHz, 21kHz, 24kHz, 27kHz, 30kHz, 33kHz etc. etc. etc) where it is in sync with the 5 kHz Musky with each fifth harmonic. In my opinion, the HF would be the least likely to chatter, due to the power influence. The LF would be second. And the MF will be more likely. I've usually found that when I do get some slight interference, I am able to shift the operating frequency by changing the Noise Cancel Channel. JMHO HH Randy

 

[Mick in Dubbo]

That explains why I have been frustrated with the medium frequency coil and have preferred the high frequency DD's. Here in Australia, our mains single phase power is 240 volts, while in the States you run 110 volts. that goes a long way to explain why there can be differences in our experiences, in the field. I have not wanted to go with the low frequency coil as my thinking was along the same lines as MXTer. Although the noise cancel does help somewhat, I have found that the different frequency coil gave a much more solid reliable TID reading.
Having the harmonics explained like you just did, really helps to understand how EMI issues can be successfully resolved.
Cheers and thanks Randy.
Mick Evans.

 

[Bullpine]

My biggest problem with that coil are the cheesy rod attachment ears. They crack very easily if you even slightly tighten the plastic wingnut. But having the ears crack gave me an excuse to buy a new Coiltek 15 incher. It arrives next week. I will epoxy the ears back on the concentric later and then sell it.

 

[MXTerer]

n/t

 

[pilot]

What coil are you selling ? I may be interested if it's the 3 Khz.

HH
Kim

 

[Bullpine]

It is the 7.5, concentric but thanks anyway,