‰  NOW 35 WPM  ‰  TEXT IS FROM MAY 2019 QST  PAGE 58‰

QRPGUYS DIGITAL FIELD STRENGTH METER KIT  REVIEWED Y PAUL DANZER, N1II N1II
ARRL.  NET  A FIELD STRENGTH METER DOES EXACTLY WHAT THE NAME IMPLIES
SENSES THE STRENGTH OF AN RF FIELD AND GIVES A RELATIVE VALUE ON THE
DISPLAY.  FIGURE 10 SHOWS THE SCEMATIC FOR A CLASSIC FIELD STRENGTH METER
THAT IS SIMPLY A DIODE DETECTOR CONNECTED TO AN ANALOG METER.  THE STRONGER
THE FIELD, THE HIGHER THE METER WILL READ.  AS YOU MIGHT GUESS, THE DESIGN
WAS NOT VERY SENSITIVE.  THE METER WOULD NOT READ ALMOST UNTIL THE INHERENT
VOLTAGE DROP ON THE GERMANIUM DIODE 0R25 TO 0R3 V WAS RECEIVED.  FROM
THERE, YOU COULD GET A METER READING.  ALTHOUGH IT WAS USEFUL IN STRONG
FIELDS, IT GAVE NO INFORMATION IN WEAK FIELDS.  A MODERN DESIGN  THE
QRPGUYS FIELD STRENGTH METER KIT REVIEWED HERE USES AN ANALOG DEVICES
AD8307 LOGARITHMIC AMPLIFIER, AN LM358 OP AMP, AND A DIGITAL DISPLAY TO
CREATE A SENSITIVE, MODERN FIELD STRENGTH METER.  IT IS RATED TO SENSE A
SIGNAL AS WEAK AS 80 DBM, WHICH IS THE EQUIVALENT TO AN INPUT, IF DIRECTLY
CONNECTED AS A 50 LOAD, OF 10 PICOWATTS 0R00001 MICROWATTS.  AT THE HIGH
END OF THE RANGE, THE MAXIMUM SIGNAL INPUT IS 16 DBM 40 MILLIWATTS OR 1R41
V, BUT THE UNIT SHOULD NOT BE USED AS A POWER METER.  YOU MIGHT DAMAGE IT
IF CONNECTED DIRECTLY TO AN RF VOLTAGE AT THE HIGH END OF ITS RANGE.
PACKAGED ON A 2R4 X 2R7 INCH PRINTED CIRCUIT BOARD, THIS DEVICE IS POWERED
‰  END OF 35 WPM TEXT  ‰  QST DE W1AW  ƒ