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Saturday, January 10, 2015

7 GHz Digital RF Milli Wattmeter

On the bench..... (Updated on time...) I redo my old digital RF wattmeter.
Prototype model of the front face

The laboratory instruments such HP, Giga-tronics, etc... are used by some microwave experimenters.
But this stuff is not yet affordable on the surplus market because their prices still high, and sometimes questionable operation! For our amateur bench, it is inexpensive enough to be careless with a handy device with many uses without shame performances compared to large laboratory equipment.
A Wattmeter can be used to measure gain in amplifiers, bandwidth in filters, field strength from antennas, transmitter power, SWR, return loss and more.
This digital RF Milli Wattmeter is not an innovation. Many Ham's have already done this kind of equipment for their laboratory.  It is only a modest compilation of Digital Wattmeter from OZ2PCU (1KHz to 500MHz) and the Portable RF Sniffer and Power Meter from  W1GHZ VHF to 10 GHz.
Based of chips  LTC5508 Linear Technologies (300MHz to 7GHz range), AD8307 Analog devices (500 MHz),  PIC 16F876, Displaytech 202A Series (20 Characters x 2 Lines).

In this arrangement, instead of having dual input ports of 500 MHz with AD8307 on the original OZ2PCU display  to the PIC 16F876, Frequency coverage: 1 kHz to 500 MHz (calibrated),1 kHz to 1000 MHz (uncalibrated, for relative power measurements only), the portion of WIGHZ  10GHz with the LTC5508 was added to the CPU. The first Milli wattmeter was built with the probe outside the box. The second version is built with the two boards for SMD Fwith LTC5508 and AD8307 inside.

According from Paul W1GHZ the LTC5508 can be used until 10GHz.
While the frequency response is not as flat as a laboratory power meter, it still works even at 12 GHz. For the time being, I’m QRV only to 2320 MHz Max, but I hope to go higher!! And be ready to experiment my new SHF equipments.

With couple of attenuators, 50 ohms /10 GHz, this digital RF Milli wattmeter can be used for different measurements powers input.
 0 dB, no attenuator mounted, 1 W max.
10 dB attenuator mounted, 10 W max.
20 dB attenuator mounted, 100 W max.

WIGHZ Microwave Integrated Power Detectors - Portable RF Sniffer and Power Meter.
OZ2PCU Digital RF wattmeter.
Pic of old one.