Schema and producing of a GSM signal detector (MAX2015)

As part of my professional activity I have to go in GSM base stations. Some sites are so well integrated in the environment that we sometimes have difficulty locating them.

MAXIM has released an integrated circuit RF measurement, the MAX2015; customer being called home, I asked two samples. Having a background in one drawer 900MHz YAGI antenna, I decided to use it to make a "divining rod" GSM.

The MAX2015

Features:

Technical / Catalog	MAX2015ETA + T
Seller	Maxim Integrated Products
Category	Integrated Circuits, Modules, Units for RF and RFID
RF Type	GSM, EDGE, CDMA
Housing	8-TDFN
Series	MAX2015
Frequency	50MHz ~ 2.5GHz
Characteristic	Detector / Controller RF
Conditioning	Tape and Reel
Lead Free Status	Lead Free
RoHS Status	RoHS Compliant
Other Names	MAX2015ETA + T MAX2015ETA + T

Editing

This assembly is powered by a 9V battery followed by a 78L05 regulator. The output of the MAX2015 is connected to an LCD module 200mV voltmeter via two knobs that adjust the "zero" and gain. The LCD module is powered by a 9V battery second, it is not possible to feed it with the same stack as the assembly, otherwise destroy it. The plate supports an on / off switch, turn off the power responsible for the two 9V batteries, and "Off" position, to isolate the MAX2015 input and link it to the ground. This is to avoid grilling MAX2015 when the assembly is not used and it is close to a powerful antenna.

Here's the diagram:

the list of components with value:

C1 = 680pF ceramic
C2 = 680pF ceramic
C3 = Ceramic, 100NF
C4 = 100pF ceramic
C5 = 100pF ceramic
C6 100NF = ceramic
C7 = 220nF ceramic
C8 = 50V 1μf
IC1 = MAX2015
IC2 = 78L05 TO92 case with
Adjustable P1 = 220 Ohms
P2 = Adjustable 10KOhms
R1 = 1Kohms 1/4W
R2 = 47kohm 1/4W
R3 = 75 Ohms 1/4W
Radio switch SW1 = 4RT
+ 2 couplers 9V
+ 1 200mV LCD voltmeter

The implementation of the components:

 

The circuit after etching (acid etching):

In the previous picture we can clearly see the notch that must be performed to connect the antenna cable.

the circuit after welding components:

 

Here is the GSM detector after assembly and installation in the back of the antenna:

Settings

Weld R2 standing only a foot welded to P2 and the other in the air to be able to adjust the knobs. Solder one leg of resistance in place of the second leg of R2.
For calibration, connect R2 to IC1, bypass the antenna and adjust P1 for 0 on the display. Then disconnect R2 IC1 and apply a voltage of 1.8 V on the leg in the air from R2 to ground, and adjust P2 for 199 on the display.

Note:

 

I chose to set the knobs to use the maximum dynamic range of the display, the MAX2015 has an output voltage proportional to the input power in dBm, it is possible to adjust the knobs for direct display in dBm. The bandwidth of the circuit goes from 100MHz to 3GHz, the assembly can be used with a 1800MHz or 2200MHz antenna. Some retailers offer dual-band antennas YAGI 900/1800.