Ramsey PM50 High Range RF Power Meter Kit Manual PDF (EN)

Ramsey Electronics Model No. PM50 Ever need to tune up RF equipment, but didn’t have the money for expensive watt meters and spectrum analyzers? Want to be able to measure low-level signals and high-level signals without changing slugs and flipping switches? This versatile piece of test equipment should be standard on every RF experimenter’s bench. • Can accurately measure signals from –30dBm to +47dBm, that’s PM50 Page 1

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RAMSEY TRANSMITTER KITS • FM100B Professional FM Stereo Transmitter • FM25B Synthesized Stereo FM Transmitter • MR6 Model Rocket Tracking Transmitter • TV6 Television Transmitter RAMSEY RECEIVER KITS • FR1 FM Broadcast Receiver • AR1 Aircraft Band Receiver • SR2 Shortwave Receiver • SC1 Shortwave Converter RAMSEY HOBBY KITS • SG7 Personal Speed Radar • SS70A Speech Scrambler • BS1 “Bullshooter” Digital Voice Storage Unit • AVS10 Automatic Sequential Video Switcher • WCT20 Cable Wizard Cable Tracer • LABC1 Lead Acid Battery Charger • LC1 Inductance-Capacitance Meter RAMSEY AMATEUR RADIO KITS • DDF1 Doppler Direction Finder • HR Series HF All Mode Receivers • QRP Series HF CW Transmitters • CW7 CW Keyer • CPO3 Code Practice Oscillator • QRP Power Amplifiers RAMSEY MINI-KITS Many other kits are available for hobby, school, Scouts and just kits are always under development.

Write or call for our free Ram PM50 HIGH RANGE RF POWER METERKIT MANUAL Ramsey Electronics publication No. MPM50 Revision 1 First printing: 2002 COPYRIGHT 2002 by Ramsey Electronics, Inc. 590 Fishers Station Drive, Vi 14564. All rights reserved. No portion of this publication may be copied or dup written permission of Ramsey Electronics, Inc. Printed in the United States of PM50 Page 2

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Ramsey Publication No.

MPM50 Price $5.00 KIT ASSEMBLY AND INSTRUCTION MANUAL FOR PM50 HIGH RANGE RF POWER METER TABLE OF CONTENTS Introduction ...........................................4 Theory of Operation ..............................4 Learn As You Build ...............................8 Parts List .............................................12 Display Assembly ................................14 Main Board Assembly .........................16 Detector Board Assembly ...................20 Heatsink Assembly ..............................22 Front and Main Board Mounting ..........24 Testing .................................................26 Using ...................................................27 Operation .............................................28 Troubleshooting ..................................29 Layouts ...........................................30,31 Schematics .....................................32,33 Warranty ..............................................35 RAMSEY ELECTRONICS, INC.

590 Fishers Station Drive Victor, New York 14564 Phone (585) 924-4560 Fax (585) 924-4555 www.ramseykits.com PM50 Page 3

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PM50 INTRODUCTION Welcome to the PM50 kit (and if you didn’t have time to build a kit, the wired and tested version!). This great little product works so well our technicians are using them here at the shop as their bench-top power meter of choice. The kit is based around an AD8307 log detector which has a 90dB dynamic range for signal strength measurements. Tie that with a nice 50 watt dummy load and a fan-cooled heatsink and you have yourself a very easy to build and calibrate power meter! The handiest part of the power meter is its ability to measure very small signals, such as the RF from low-power transmitters such as our FM10A.

This meter allows you to accurately tune the last stages of a transmitter’s filter or gain stages for maximum efficiency and transmission range. Without this power meter you might have to simply go with your best guess. For larger high-power fields you can put a calibrated antenna on the input and measure signals as small as –30dBm; from this you can easily calculate field strength, the very thing the FCC would do if they tested your radio station. You can now check your transmitter for compliance. You’ll need to find a calibrated antenna to rent but they are available. We hope you enjoy building this kit as we had a lot of fun designing it for you.

To keep costs down we have miniaturized the kit to fit in our standard plastic case and panels and left the detector board separate so its heatsink can get plenty of ventilation to keep it cool when you are applying heavy loads. In the interest of preserving battery power we chose to use a CPU heatsink and fan combination. Then we motor speed control the fan so that it only runs when there is power to be dissipated. For power measurements under 5 watts there is no need to run the fan so your battery life is extended. Over 5 watts the fan speed will vary from about 1/4 speed to full speed depending on power applied.

PM50 THEORY OF OPERATION Our goal in this section is that you will come away from this theory with a greater understanding of electronics, dBm, and how power is measured from transmitters. You may also learn why this power meter has such a fantastic range and you will find out why our engineer (me) has such a bad headache after writing a routine to convert an analog to digital value to dBm and then to watts using nothing but assembly language on an 8-bit processor. The C language equivalent just wouldn’t fit in such a small microcontroller. The heart of the power meter is the combination of the 50 Watt thin-film 50 ohm resistor.

This is a nifty part in that it has excellent characteristics for being used as a dummy load saving us a lot of expense of more complex solutions and making this kit more affordable. This 50 ohm load is tied directly across the PM50 Page 4

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