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Author Topic: Interference filter  (Read 28210 times)

woody

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Interference filter
« on: August 09, 2014, 07:55:27 am »
I just finished a video on the interference filter i have been developing over the last few months.
https://www.youtube.com/watch?v=oqnhEW7yWUk

Haveadig

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Re: Interference filter
« Reply #1 on: August 09, 2014, 01:50:38 pm »
How much ?

woody

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Re: Interference filter
« Reply #2 on: August 09, 2014, 02:00:02 pm »
The filter is $180 on Ebay  Can do $20 cheaper by escaping the Ebay fee's....come with the correct litz cable interconnect..

Haveadig

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Re: Interference filter
« Reply #3 on: August 09, 2014, 03:00:57 pm »
Thanks for that , will be in touch soon

m3sca1

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Re: Interference filter
« Reply #4 on: August 09, 2014, 08:43:45 pm »
Watched your video-looks like an excellent addition to the front end...is there enough room to build it in as a mod or does it have sit outside?
Is there any dB losses in gain across those 5 pin microphone sockets?



woody

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Re: Interference filter
« Reply #5 on: August 09, 2014, 09:09:13 pm »
Hi Mescal,

I tested for any signal loss and I cannot find any loss at all, I tried with a customers GPX5000 in fine gold and the performance was better with the filter in all circumstances, it goes to show that the input opamps are subjected to all types of radio wave derived interference that impact on the detectors performance. Even in quiet areas the depth and sensitivity was better when the filter was installed. These filters cannot be used inside the detector, there are reasons for this, i have seen a filter of sorts in some early detectors and it did not work.  I had to get very special materials made to get these to work. The R&D costs have been substantial.

m3sca1

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Re: Interference filter
« Reply #6 on: August 10, 2014, 11:20:12 am »
Would that filter help an F1A4?
I can boot up the F1A4 in the house and it runs smooth and quiet.
Can't say the same for the modded SD2100-it goes nuts...i think that would be good for the 2100 but i think the F1A4 doesn't need it.
Your thoughts?

woody

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Re: Interference filter
« Reply #7 on: August 10, 2014, 01:53:38 pm »
The F1A4 i have here also runs quiet, there is a big chip inside the detector that removes impulse noise, i wonder why it was not included into the design of all their newer detectors?  I would think that the f1A4 would still be desensitized by any hf signals falling into the passband of the input amplifiers.  The input stage is a replica of a SD2100 .

m3sca1

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Re: Interference filter
« Reply #8 on: August 10, 2014, 06:16:38 pm »
Maybe that big chip that removes the impulse noises is there to allow it to run side by side with other F1A4's.
The instructions mention booting them up in sequence one after the other so that a line of men can walk in close proximity and demine large strips at once.
Might be too expensive to throw them into gold detectors, or maybe it Mil-Spec stuff.
Anyhow i think you might be right on that it would help the F1A4 too-the science of filter traps is sound.
Just like an audio crossover stops the wrong frequency getting into a speaker, your filter stops the noises getting into the detector front end.
Great idea.

debongos

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Re: Interference filter
« Reply #9 on: August 25, 2014, 10:26:10 pm »
Have you watched the YouTube version of Jack Lange's testing of a modified F1A4. Quite a stable unit and performed well against his fav 3500.

https://www.youtube.com/watch?v=hmAq7WRl-O8


woody

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Re: Interference filter
« Reply #10 on: August 25, 2014, 11:31:29 pm »
Here is my fully modded version of the F1A4 inside.

https://www.youtube.com/watch?v=5KEXSpWU-U0

debongos

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Re: Interference filter
« Reply #11 on: August 26, 2014, 10:55:16 pm »
I didn't know they were so popular Woody.

I got to ask though, how do you get these units you work on to be so stable in your work shop? If I fire up my SD2100 in the yard the thing goes beserk.

debongos

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Re: Interference filter
« Reply #12 on: September 11, 2014, 09:44:39 pm »
Tried the Interference filter on the weekend and yes the unit was much smoother. I found myself concentrating solely on the ground balance as there was no warble or other interference even with a 5000 and a SDC 2300 near by.

Woody I normally use your recommended settings for the modified 4500 and manually tuned the unit which on the weekend was around 110 with the filter in use. As an exercise I tried the auto tune as well with the filter and it settled around 210. I was puzzled why there was such a variation as both seemed to provide the same result.


Peter

woody

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Re: Interference filter
« Reply #13 on: September 23, 2014, 02:11:52 pm »
That is an interesting observation, the frequency setting seems to work with stock standard detectors but with the mods it changes the ratio shown as tuning numbers on the LCD, with the mods it is ok just to autotune it.


Here is a vid of the filter being tested.


www.youtube.com/embed/oqnhEW7yWUk
« Last Edit: September 23, 2014, 04:02:33 pm by woody »

vittima57

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Re: Interference filter
« Reply #14 on: November 06, 2014, 07:33:38 am »
ce qualcuno che si vende un minelab 2200v2