I suggest scanning the CREG articles on my website before starting construction in order to understand how the units work and what you can do with them. The schematics and parts lists in the CREG articles are out of date, but the rest of the info is good. Refer to the schematics, layouts, parts lists, and notes included here for the final word. Also look at the picture gallery on the website to see the various loops etc. READ THE "README" FILE on the WEBSITE and THE NOTES HERE BEFORE BUYING PARTS OR STARTING CONSTRUCTION!

NOTE:  7/30/03.  These notes have been updated for the latest boards with the dates 2002 or 2003 printed on them.  All earlier boards were shipped with printed notes which mention corrections that are no longer needed.


Detector Board notes

RF Amp Board Notes
Receive Loop Notes
Beacon Notes
Locating Ground Zero

Radiolocation requires practice. Even though this gear often gives a useable signal close to 1 km away, always try to position yourself as close as possible to the expected location by using topographic overlays, GPS, compass course and distance from an entrance, etc. Try to always be higher than the cave passage, ie wait uphill rather than downhill. If you are within a horizontal distance of about 1.4 times the expected depth of the beacon, the locating will be very easy.

Depth Measurement
"Ratiometric" and "absolute"(signal strength) depth measurements are discussed in "Operation" in the CREG article "Constructing the 3496 Hz DQ Beacon Receiver" on my website, and are discussed in more detail in "Depth by Radiolocation: an Extreme Case". Using 2 independent depth measurement methods helps to give confidence (or lack of it) in the results. The only missing information is the receiver amplitude calibration for depth by absolute signal strength. The procedure given here is based on a calibration table (which follows) generated for the first receiver I built using the new circuit boards. It allows one to adjust the receiver RF gain for a reasonable DVM reading, without overload, with the receive loop horizontal at ground zero, and calculate depth by absolute signal strength later.
Calculating Ratiometric Depth

RF Gain                                  RF Gain
Pot Setting     Inverse Ratio     Pot Setting     Inverse Ratio

10.0                 1.000                 4.5                 50.12

9.5                  3.273                 4.0                 60.26

9.0                  5.754                 3.5                 73.28

8.5                  8.610                 3.0                 90.16

8.0                  11.61                 2.5                 112.2

7.5                  14.96                 2.0                 146.2

7.0                  18.84                 1.5                 197.2

6.5                  23.44                 1.0                 285.1

6.0                  28.51                 0.5                 478.6

5.5                  34.28                 0.0                 1259

5.0                  41.69

Calibration for Depth by Signal Strength (Absolute Depth)
Calculating Absolute Depth


For a start, you can do the Ratiometric measurement without any calibration at all.  With the receive loop horizontal on ground zero, just set the receiver dial to give a reading of 1000 or more (if you can), then raise the horizontal loop a known distance for the second reading, without changing any receiver settings.  You then use the equation to calculate ratiometric depth.  For shallow depths (say <100 ft [30m]), this is all that you need to do.
    For the Absolute measurement, simply record the precise receiver gain settings and DVM reading that you obtained with the loop resting on ground zero.