See if you can figure this one out.....

[ifinditunderground]

I have two separate scenarios that both end with the same result. Do you know how to solve this problem? This is a real problem we are having.
Scenario 1: Military Base in Maryland, working around a fairly secluded building, but not high security so there is probably very little "Secret Stuff" going on inside. Working behind the building around the chiller unit, if you don't know what a chiller unit is, it's too long to explain here. Several high voltage ductbanks, cabinets and transformers around. Nothing extremely high voltage. Our crew was getting a great deal of interference all around this chiller unit, make locating anything near impossible. Crew was using a Metrotech 810 and a Metrotech 9890XT unit. recognizing a problem, the lead tech (of 19 years) turned both transmitters off. Using just the recievers (both of them) each of the two techs could get high signals (650 to 850), on all of the electric cabling, ductwork and grounding systems. Those signals were recieved on 9.8kHz, 82.5kHz, and 83.3kHz.
Here are the kickers......
No, there is nothing wrong with the transmitters, both were checked.
No, it has nothing to do with 60Hz, the 810 doesn't even have a passive mode.
No, the military doesn't transmit radio for locating over their ducts.
Yes, both units worked fine once removed from the immediate area.
No, it's not any secret military experimentation. Scenario 2 will blow that out of the water.

Scenario 2: Sewer treatment plant in Maryland, 150 miles North of the Military base. Crew was working around a large pump building housing several motors and pumps for circulation of water throughout the plant. Several ductbanks, cabinets and transformers in the area. Power confirmed to be at 60Hz per a facilities manager. Same interference encountered, transmitters turned off, same high signals on all of the power ducts at the following frequencies, 9.8kHz, 82.5kHz, 83.3kHz, 332kHz., 810, 9890XT 530. Pipehorn not tried. Once the equipment was removed from the area they worked normally.

Now, some of you would say great, I don't even have to hook up to locate this stuff, but we don't have that leisure. Sure, it's easy to get the power but how do you know you got all of it? We also have to find all of the other utilities that are much deeper and much harder to locate. These are all masked by the high interference levels on the ductbanks which are relatively shallow. We have to find all of these deep utilities to dig test holes on them......but can't find them because all of our frequencies are "jammed". The plant is fairly secluded and not in a highly urban area, just a few warehouses nearby.

Now what? How do you get around this? And no, you can't shut off the power at a sewer treatment plant.

Now where the hell is NC115 when you need him.....it's too bad UDIC ran him off, he was a real asset to this forum.

[Dave72]

Too bad you didnt have a RD (or some other brand) there to try.. maybe those 2 Metro's share some common circuit design in which some part was getting flooded with some type of RF.

Odd that it happened in 2 totally unique site tho... and like you say not like they were some really high power sites (generating station etc).

[ifinditunderground]

Going to try an I5000 next week.......

[underground quester]

Going to try an I5000 next week.......

One of our guys is demo'ing an I5000 at the moment.
So far, he seems to really like it!.

[Metroman]

Massive EMF is the cause i bet.It sounds like you know what is needed so you should just tell them and see if you can schedule during a maintenance power down or something.

[TheCableVine]

Massive EMF is the cause i bet.It sounds like you know what is needed so you should just tell them and see if you can schedule during a maintenance power down or something.

Yeah. What he said.

Both of those scenarios involved electric motors. If the brushes are dirty then you will get a wide range of frequencies coming off of them. It is simply electric noise... a.k.a. EMF.

[testtech]

There is a very good chance that the pumping station motors were driven by variable speed drives. The chiller, or its condenser or chill water pumps may also have variable speed drives. These drives will generate numerous high frequency harmonics (multiples of 60 Hz) that could produce the interference that you found. The high frequencies can travel out of the drive into the supply. What can you do about it? If you use a locator and transmitter with very narrow band filters and can set a transmit freqency to an even multiple of 60 Hz (such as 240 Hz), you might succeed. The drives will not produce even numbered harmonics, only odd multiples of 60 Hz. The Seektech could do this. Otherwise, with the drives in operation, you are probably out of luck. You could try GPR. However, I am in Maryland and in general, I have found GPR to be nearly useless in the soils around here.

[GWJ_CAS]

There is a very good chance that the pumping station motors were driven by variable speed drives. The chiller, or its condenser or chill water pumps may also have variable speed drives. These drives will generate numerous high frequency harmonics (multiples of 60 Hz) that could produce the interference that you found. The high frequencies can travel out of the drive into the supply. What can you do about it? If you use a locator and transmitter with very narrow band filters and can set a transmit freqency to an even multiple of 60 Hz (such as 240 Hz), you might succeed. The drives will not produce even numbered harmonics, only odd multiples of 60 Hz. The Seektech could do this. Otherwise, with the drives in operation, you are probably out of luck. You could try GPR. However, I am in Maryland and in general, I have found GPR to be nearly useless in the soils around here.

IfintIt, the above is the same explanation I would have given. We have experienced similar scenarios with older EM locators at two military bases and one hospital in Florida. The i5000 was able to discriminate its transmitter from the background freqs, so I would bet it will help you in your situation.

Keep us posted.

[nxs]

I experienced the same thing in a particular substation, and the RD4000 seem to be the only instrument that worked well and appeared to be completely unaffected by the EMF distortion. I was told by RD that the RD4000 had a very sophisticated filtering system in its design which allowed it to remain operational even though the distortion was so bad. You may want to give it a try.

[testtech]

Concerning the RD, I cannot comment on receiver filtering. However, I have looked at the transmitter output on a spectrum analyzer--the output is very accurate and within a Hz of what it is supposed to be. The Seektech actually has filter width settings. Narrower settings slow the digital processing but make it much more likely to succeed in the situation you have.

[ifinditunderground]

Testtech is correct, Variable Frequency Drives. I did some research last night after posting this and I found several specific references to the use of VFD at Wastewater Treatment Plants, and in several components at chiller units. Now, the question is....will the i5000 help, or will I have to break down a look at an RD......yuk. There is no way in hell I am looking at the Seektech again.

[Hurricane9]

Well, that's better than my suggestion. Since you are in Maryland, I would guess that you are trying to locate at Aberdeen? If so, I would look around for a vehicle with a axe looking thing on the front of it about 4-5 feet tall. Or see if they are working on those in the buildings. Without going into alot of detail, those things are designed to block just about any transmission signal except what they want to get through. But that doesn't help you at the treatment plant.

[GWJ_CAS]

Testtech is correct, Variable Frequency Drives. I did some research last night after posting this and I found several specific references to the use of VFD at Wastewater Treatment Plants, and in several components at chiller units. Now, the question is....will the i5000 help, or will I have to break down a look at an RD......yuk. There is no way in hell I am looking at the Seektech again.

The i5000 will most likely do the trick.

Speaking of the i5000, check this Metrotech video out:

http://www.youtube.com/watch?v=C9Pc9xjkNbE

[ifinditunderground]

The two sites are Patuxent River Naval Air Station and Little Patuxent Wastewater Treatment Plant. I just got a great document about VFD's from our local Metrotech folks.....anybody want a copy of it via e-mail just PM me.

[Linden Riddle]

Not sure why you'd want to set a transmitter at 240 hz vs. 128 hz, 256 hz, etc. His problem was finding lines situated underneath the electic ducts.

Agree with narrowing receiving bandwith on Seektech. Don't believe there's another receiver with that ability.