Peak Reading Wattmeter Board FAQ
How does the peak board operate?
A brief, simplified explaination, will show you how the Peak Board functions.
The peak board is connected to the directional coupler or line section just like the
meter was originally. The peak board amplifies the incoming varying voltage level so it can
apply the higher voltage to a peak / hold circuit. The peak circuit charges a capacitor,
which holds the peak voltage level. The second part of the peak circuit reads the peak
voltage and converts the voltage level back to the correct level to drive the meter movement.
A variable resistor discharges the peak hold capacitor, which determines how long the pointer will remain at the peak measurment level.
What is the difference between the PR-80 and the PR-80M, PR80-MS, PR90M?
The Peak / hold circuit for all boards is the same. The only difference is the mounting method, and accesories supplied. The PR-80 is a smaller board, which is desgined for installation into RF amplifiers, wattmeters or other equipment with a 30ua meter movement (standard). The PR-80M board is designed to mount on 1.45-1.55inch (38.1mm) center to center meter studs, .195" (5mm) diameter maximum . The user can decide if they want to add a DPDT switch for peak and average readings. If they don't want to switch modes, the PR-80M comes with a jumper installed, that allows it to go right to work in the Peak mode. Just mount it on the studs, connect the original wires to the studs on the PR-80M, apply power (9-15vdc) and it is ready to run. (calibration is required)
The PR-80MS comes with a DPDT switch on 3 inch leads, and a 9v battery connector.
It is wired and ready to install. No other parts are required. It is up to the user to decide
where to drill a mounting hole for the switch, and whether they want to use a battery, or
an external DC power supply.
I have a very old (25+ years) Bird Model 43 wattmeter. Will the PR-80M or the PR-90M mount?
The PR-90 is the "top of the line" unit. The peak / average switch, battery holder, external
power jack, common mode RF choke, and limiter circuit are all included. No drilling,
modifications, or soldering is necessary.** Just install the board, and perform a quick
calibration. Note: The side openings will not be useable after installation of the PR-90M.
** Older "vintage" unit stud spacing may be smaller than 1.45" minimum for the PR-80M and PR-90. Check spacing before ordering. If the stud spacing is less than 1.45", you can use the PR-80, and mount it using the four mounting holes. Click for more information and dimensions.
The boards may not fit into some older units due to meter stud spacing and meter positioning
changes. You may have to "home brew" the installation of a PR-90, or better yet, choose the PR 80 universal mount, and wire it into the meter circuit with a DPDT switch.
Check for proper fit here
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