Screeching noise from PI coils...

[Anonymous]

Hi all,
While recently detecting in the Rye Patch Nevada area, my ears suffered thru some of the most horrible screeching noises I have ever heard, anywhere...
The 6" x 18" coil I started with, was screeching about every 10 minutes in the morning and at least every minute in the afternoon. (and yes my battery was charged, plus I changed to another fully charged battery, thinking it was battery problems) Yes,I also tuned the detector properly, when using both coils... )
I then changed to a Coiltek 14" mono coil the same afternoon and had only 6 loud screeches in 2 & 1/2 hours time...
The other sd2200 and sd2100 users, experienced no screeching sounds what-so-ever...
First, why was the 6' x 18' Mono coil much worse than the 14" Mono Coiltek??
Secondly, will someone (Eric?) explain this strange phenomenon, so I will have some idea what to do, before I leave for Australia??
Many thanks,
SabraJim French

 

[Anonymous]

Hi Jim,
Identifying the source of noise and false signals is one of the most difficult things in metal detection. Electromagnetic noise changes not only from place to place but day by day and even hour by hour. PI detectors are somewhat more susceptible to noise picked up on the search coil because of the wide bandwidth of the system, but firstly it is important to determine if the noise is being picked up by the coil or if it is an internal electronic problem in the control unit. If there are other similar detectors in the area that do not appear to be affected by noise, the first step is to swap search coils and see if the noise transfers to the other detector. If it does, then the problem is with the search coil. If the original noisy detector is still noisy, then the control box is suspect. This test is not absolutely determinate as the transmitter and sampling frequencies may be different on the two detectors. The SD2200 has automatic frequency adjustment to minimise noise but personally I find a manual adjustment better as you can fine tune the system for minimum audio fluctuation. However, either system is only effective for continuous electromagnetic noise. Sporadic noise that occurs once every 10 minutes or once every hour is almost impossible to correct for.
From what I have heard and read, Nevada is a place where there are experimental defense establishments and other strange goings on, so who knows what electromagnetic signals come and go. Although PI coils and detectors normally are only affected by low radio frequencies, 1MHz and less, if the field strength is high enough then frequencies into 100

 

[Anonymous]

Hi Eric,
Thank you very much for your response. Dana & I tested the Minelab 11" Mono, 14" Coiltek Mono and the 6" x 18" just outside Hawthorne, NV today and only the 6 x 18 had the "screeching noise".. Tomorrow, we will put the 6 x 18 on Dana's new sd2100, to see if it has any noise problems with the coil. I am also sending the Control Box to Las Vegas and have them do some tests on it.
I will email you the results in a week or so.. It sounds like everything will be ok in Australia, which makes me feel much better...
Thanks again Eric,
SabraJim French

 

[Anonymous]

Just got back from Rye Patch. Used my 6 x 18 for 2 days. Found three hot spots where I got a lot of falsing. On the same spots, about 1 or 2 square yards each, I tried the 11" DD - it was quieter but still falsed a lot, and the XT18000 - it was impossible. Did not find out why those spots were hot.
Over all I am very happy with the 6 x 18. I believe it is more sensitive, goes deeper and is quieter then the Coiltek 14". I was really surprised at how sensitive it is.
Thanks Eric for a wonderful coil!!
Enjoy Hunting
Jim (Zaz)