Andy G4HUE sent me his Arduino code for measuring low power and shows on a liquid crystal display the power in dBm Peak to Peak
volts, millivolts and uV. It makes a nice unit displaying lots of data
Return Loss Measurement kindly conducted and provided by Pierre Binggeli, HB9IAM
Please note that as described in the datasheet,
"Note that while the AD8307 can operate down to supply voltages of 2.7 V, the output voltage limit is reduced when the supply drops below 4 V. This characteristic is the result of necessary headroom requirements, approximately two VBE drops, in the design of the output stage."
the chip will not be able to produce its output voltage for large RF input signal (tested to be around -15 dBm). The 3.3V ultra-low-noise voltage regulator really helps on AD8307 performance with low-level RF signals. The current version of the boards has a new jumper J3 to select 3.3 or 5V operation. You can use 3.3V and use an external attenuator for extending its dynamic range. Of course if you would like to stay at +5V DC for its operation voltage you can place the jumper J3 to the to +5V position.
The RF input SMA is terminated to a 52.3 - 0.1% Ohms resistor (R1) to match the AD8307 input resistance to 50 Ohms.
It draws under 12 mA at 12 VDC and has two internal voltage regulators.
For low noise operation, a special ultra low-noise 3.3 V voltage regulator is used. The TPS79333 is made by Texas Instruments and is optimized for RF circuits. This one powers the AD8307 chip. Its input is connected to an on-board 5 V voltage regulator (LM78L05) to facilitate wide range for the input voltage. The AD8307 is now much more sensitive. The AD8307 output voltage is routed to the output connector pin 5 for 25mV/dB measurements (O3).
On that route, two 100 nF capacitors are connected to the ground and can be removed or modified.
Space for installing optional scaling resistors (R3 and R4 of 1206 size) is provided.
Two op-amp DC amplifiers (LM358) multiply the output voltage to 2x (50 mV/dB) routed to pin 4 (O2) and to 4x (100 mV/dB) routed to pin 3 (O1).
If used, the op-amp chip should be powered by a higher voltage supply (say 12V) in order to be able to deliver higher voltages at higher RF levels.
Again, the op-amp gain scaling resistors are of 1206 size for easier handling if should be changed.
The PCB dimensions are 30 x 45 mm and a special gold-plated band is provided on the edges to help soldering any shielding material (copper clad board, tin etc).
The KIT includes a high-quality ENIG FR4 PCB (30 x 45 mm) that comes with all SMD components pre-soldered.
RF capacitors are used for all the circuits. A 52.3 Ohm resistor is used for R1.
One SMA female connector is also supplied.
The shipping is with registered mail (your signature is required upon delivery).
I usually ship the next day and it takes about a week to 10 days for USA or Australia, less than a week for Europe..
Copyright © Makis Katsouris, SV1AFN. All Rights Reserved.