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There will no doubt be folks who will say "yes" to this question, but the "real" answer is:
There is no way to tell.
There are a number of factors that affect the range of any transmitter. Here are a few:
Whether or not it is horizontal in the line
Interference from other adjacent underground utilities
Type of pipe
That being said, I have picked up a signal from my SeeSnakes from that depth with Radiodetection receivers, BUT depth readings at that depth were NOT correct. I could tell where the transmitter was, but the "push button depth" was way off - likely due to lack of signal.
When you don't have accurate push-button depths, you have to go back to the old school find nulls & calculate method.
as vance has mentioned. it's not the reciever that's the issue, it's the transmitter that needs the power.
look at it from this perspective.
you can take a $5.00 am/fm radio and pick up a good signal from 100 miles away, as long as the transmitter is putting out the power.
Look at it this way: you could have a $500 receiver and be 20 miles away but if you have a sh!t antenna you ain't hearing nothing.
The sensitivity (ability to discern low level signals) and selectability (ability to reject unwanted signals and/or interference) of the receiver is just as important as the transmitters' output power.
"It's a table saw, do you know where your fingers are?" Bob D. 2006
One day, I have NO problem at all locating a 20 ft. deep sewer in an open field with no other utilities and/or interference.
The next day, I can't pick up a 18" deep sewer because it's in a mechanical room right next to a VFD (variable frequency drive - the absolute WORST device I have ever encountered for generating huge amounts of broadband hash) for a 100HP chilled water pump.
So, three things matter:
Rcvr sensitivity & selectivity
I would personally add another:
Regardless what the mgfrs. of the equipment tell you about "Push button simple!!!", you WILL get better at using the stuff over time. I have been running all kinds of subsurface detection gear for over 20 years, and not a week goes by that I don't learn something new.
Have you tried using other frequencies? There should be one or two that offer better reception (stronger signal to noise ratio) than the rest.
You can't change the xmtr freq. - it's fixed at 512Hz.
But to answer your question - yes, I have tried diff. freqs. when locating other stuff around VFD's - it didn't matter much. All that current, being switched off & on, just generates hash and the frequency spectrum of it is VERY wide. Can't do much about it. If someone wants something critical located near an interference source like that, they just have to schedule a shutdown (yes, it has happened, twice in 20 years).
Thanks for the advice guys. I went ahead and bought received the scout. I ran a few winter tests and everthing seems ok for now. I will recheck when the snow goes or if I need it for a service call. F.Y.I. pipe is typically 6" clay and transmitters are the sewer cable sonde and camera sonde.
I have tried diff. freqs. when locating other stuff around VFD's - it didn't matter much. All that current, being switched off & on, just generates hash and the frequency spectrum of it is VERY wide. Can't do much about it. If someone wants something critical located near an interference source like that, they just have to schedule a shutdown (yes, it has happened, twice in 20 years).
You guys are all correct. The variables are endless, from soil, to pipe, mositure in the soil, surrounding electrical freq., What transmitter are you using etc.... The deepest I have located and verified the line once it was dug up was 19'. That does not happen very often. If you are questiong the location use two locaters and double check them.