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Excessive pulsing in air tests?

A

Anonymous

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I have two goldquest detectors with me right now. One is being sold to me (G1) and another is from a friend (G2)who had the batt connector replaced due to corrossion.
While air testing them in my car port, I noticed that the one being sold to me (G1) experienced excessive pulsing. I had to reduce the reject by 1/4 turn from minimum and still it would sometimes pulse. My friend's (G2) MD was stable at minimum reject. Both detect a gold ring at up to a foot from coil. The pulsing of G1 got so bad at times that I could not hear the ring over the pulse.
Swinging both detectors on the same coil on my cement driveway, both detectors became stable with no pulsing a smooth threshold. But then, both cannot detect a ring that I placed on the driveway.
Is this an indication that G1 broke? Or a hot detector? Or are these tests inconclusive.
I am unable to go to the beach and do actual tests for a few days but am pressured to make a decision as the seller is waiting on me.
Any help would be appreciated.
JT
 
Hi JT,
What happens when you turn the delay up on your friend's detector? Does it begin to pulse also? If it does, then the pulsing is probably caused by some external noise. Even a neighbor's TV can be a big offender.
If your friend's detector begins to pulse with the delay is turned up a little, then there could be a slight difference in the minimum delay time. It doesn't need much of a difference before certain external noise generators can wreak havoc. Sometimes, just a half of a usec can mean the difference between noise and no noise. At least, that is what I have found to be true.
I would also make sure that the detectors are separated by a reasonable distance when making the tests. The second detector's coil could be part of the problem.
I am not sure I completely understand your following statement: "Swinging both detectors on the same coil on my cement driveway, both detectors became stable with no pulsing a smooth threshold. But then, both cannot detect a ring that I placed on the driveway."
The fact that when you lowered the coil, the detector become stable indicates the problem is most likely noise. What I am not sure of is why you couldn't detect the ring, or if you meant it couldn't be detected at the same distance as the air test.
Reg
 
Hello JT,
Many reasons may be why both machines are not testing well, Maybe the delay is advanced to far to detect gold conductors "such as the ring" Or, Could be re-bar or wire mesh in the cement alnog with a few other reasons Reg mentioned.
You're going to have to operate the GQ at the beach as this is the intended place to perform an actual field test, After a few trips you'll learn from using the delay and Sat speed were your GQ performs best. It took me about three trips to fully understand the GQ to get maxium performance, I'm sure it's not any of the two machines, you're going to have to hit the beach <img src="/metal/html/smile.gif" border=0 width=15 height=15 alt=":)">
HH, Paul (Ca) P.S. Let me know when you're going and I'll try to be there.
 
Be aware that the low battery warning gives a pulse on the audio, which increases in rate as the voltage falls below 8.5V. I have had two customers contact me with pulsing on the audio, and with both it was defective batteries.
As has been pointed out, testing near the house is not the best. TV's or computer monitors emit high levels of interference. If you hold the coil in a vertical plane, you also tend to pick up more noise as EM noise is generally vertically polarised. Not sure why?
Eric.
 
I have a few observations about air pulsing as well. I live on the escarpment overlooking the Sydney basin. The TV signals are so strong I can get a resonable receiption just plugging in the aerial wire alone. If I switch on my GQ or my Excal with the coil held up the noise is shocking. Putting the coil on the ground helps but its still bad. One event that occurs with my GQ is an extremely strong pulsing signal which only lasts about 7 seconds when I am at the beach on the central coast or on the river sand near a Air Force Base closer to home at approx. 0.5 to 0.75 hour intervals. It has not happened elsewhere so I am guessing it must be some sort of directional beacon etc. If I have the reject control at 10us the pulsing noise is only slight but if its at 15-20us watch out.
 
I dont have a Goldquest,I have one of Eric's PI.Been fighting same probelem over a yr now, found main cause in my PI.A Faulty power fet j113 made by fairchild, replaced it to day.pulseing stoped.desided to replace all fets,replaced another,PI went dead,put second fet back in, PI worked, dept went from13" on a nickel to 2".I ordered 6 power fets from Mouser.I supect that some of the new fets are faulty,IF Eric is useing same power fet made by fairchild in the Goldqued, I Supect that more Goldquest will give the same problem.In the future,I hope that I am wrong.
Frank.
 
Hi Frank,
The J113 is a small signal FET generally used as an analog gate. All the FETs I use for the gates are tested and matched and I have never had a problem with them. If the pulsing changes with different positions of the search coil, then the interference is external.
Of course, occasional random failures do occur in any component but this does not mean that the future performance of the majority of my products is suspect. Mr Bill will back me up when I say that the reliability of Pulsepower detectors is very good.
Both Mr Bill and myself have offered to diagnose the problem on your CS6, which would be the best way to go rather than changing the components at random.
Eric.
 
<span style="background-color:#ffff00;">I hate to be the one to pop your bubble, but you don
 
Bill, I stand corrected,I have a SC6 PI made by New Force in UK, Who claim that Eric,designed the CS-6 PI and uses Eric Foster name as indorse-ment.
Bill, you have a print on the Goldquest,Does it have a j113 power fet in it, made by Fairchild.
Main Thing, thes people need help, les not turn this into a soap opera.
Frank. in FL.
 
Hi Frank,
The Goldquest has 4 J113's, but they are not power FET's. I get them from various manufacturers, including Fairchild. I have used J113's for around 20 years and have not had problems with them. Two require matching for ON resistance, which I do here, and if you change one of these, then that part of the circuit will be out of balance.
True, I designed the CS6PI electronics for CScope. I have one here and it performs just as it should. However, I have no control or influence over another manufacturers sourcing of parts or internal quality control. CScope have been in the detector business long enough to sort out their own systems. If I come across a problem with a component, or get reports of a particular problem, then I contact CScope about it and offer suggestions for overcoming it. I have had nothing to report on J113's or instability.
Eric.
 
These people may need help, but you generalizing the problem with one you have, just doesn
 
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