RF Wattmeter with PIC 16F876
Software info
/ user guide for version 1.04
The main startup screen shows:
dBm, status, RF-voltage
Bar-graf, RF-powerwatts
The status readout show the selected frequency band, and attenuator mode
Use the band dial to change between LF, HF, VHF, UHF and SHF calibration memories
I have calibrated my wattmeter 0 dBm at: LF=3.5MHz, HF=14MHz, VHF=145MHz, UHF=430MHz, SHF=440MHz
But you can calibrate at your own favorite frequencies for best performance.
In the RF-powermeter screen, use the SELECT button the enter RELATIVE mode.
In this mode dBm and bar-graf is shown, when entering this mode the dB read out for Channel A is zero'ed and all subsequent readings are relative to this reference value.
The menu:
To enter the menu / settings use the MENU button
when in menu, use the band dial (or Up/Down) to get the desired setting,
at the right setting use SELECT to activate, this is also shown in the display.
Here is all the menu layout:
0: Set attenuator value from -1 to -59dB. Use Up/Down to set the value, SELECT to set it
1: Toggle the attenuator ON/OFF using SELECT
2: DC Voltmeter, actual and min. and max.
3: RF Powermeter, the default startup screen.
4: SSB PEP Wattmeter, with peak hold and variable decay
5: Return loss with SWR readout for a single channel. Press SELECT to set the reference value on Channel A
6: Dual Channel Ratio Measurement with SWR
7: Calibrate 0 dBm at the selected band for Channel A
8: Calibrate 0 dBm at the selected band for Channel B
9: Read all calibration values
10: Zero all calibration memories
11: Display update delay 2-80mS, and Peak hold and decay speed
12: About Info, shows software version and so on.
DC voltmeter:
The DC voltmeter can measure from 0 to 20 volt only positive, with a resolution of 20mV.
Nothing is burned if input is reversed, it just can not measure !
Calibration is done in hardware: use one or two 10meg resistors to parallel R28 or R18 until correct voltage is shown.
In the DC voltmeter screen, actual voltage, minimum and maximum is displayed. To reset min and max press select button
The voltmeter can be used to monitor the battery voltage if a battery supply is used, or what ever you want to measure,
but remember the input impedance is about 80 kOhm.
Dual Channel Mode:
The system now uses Channel B in the Dual Channel mode.
Connect the reference value to Channel B and the varying value to Channel A.
The system will then return the difference between A and B in dB (ie the ratio of A/B).
If a return loss bridge is used, connected the reference (forward) port to Channel B
and the reflected port to Channel A.
Note – in the Dual Channel Mode, there is no check to see if either Channel is at the noise floor. Also, there could be cross talk between the channels – again, check basic levels before taking measurements.
Here are 2 video demonstration of the Wattmeter assembly: Videos