Potomac Instruments PI 4100 - Completing the Save; Entering Save Screen Data before Measuring; The HOLD Key; View and Delete Saved Data

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4.2.4.2 Completing the Save: Press SAVE a second time to complete the Save process and
return to the field strength screen for the next measurement. The 4100 allows up to 250 measurement
records to be saved before some records must be downloaded to make space for more. At the top of the
Save screen the number of measurements that can be saved at any time is given as NNN Free. To reduce
the possibility of data loss it is advisable to download saved data as soon as possible, using the PI 4100
Data Downloader program supplied (see Sec. 4.5).
4.2.4.3 Entering Save screen data before measuring: Data can be entered on the Save screen
before starting measurements, which saves time during measurements. To do this press SAVE once,
enter the data, and press MENU to go back to the field strength screen. All Save screen data is held for
all measurements until the operator changes the data, except Data point, which automatically increases
by one as each measurement is saved. When measuring, press SAVE to hold the measurement data and
view the Save screen, which will show the previously entered data. Edit as necessary as described above
and press SAVE a second time to save the data.
4.2.4.4 The HOLD key: Press HOLD to ‘freeze’ everything on the field strength screen at the
instant the key is pressed; all values on the screen remain fixed until further action is taken. Press HOLD
again to return to normal operation without saving the data, or press SAVE to save the data and return to
normal operation. The operator may make a measurement and press HOLD when satisfied that the
measurement is accurate, and then decide whether to save it.
4.2.4.5 Viewing and deleting saved data: To view measurement data records saved in the
4100, press DELETE. The screen now shows the most recent record and gives on-screen instructions for
going to other records. Press the up arrow key to go to an earlier record or hold the key down to step
through the saved records. Press the left arrow key to go to the earliest record. To delete a record, make
it the one shown on the screen and press SELECT. To go back to the field strength screen press MENU.
4.2.5 Measuring Field Strength
4.2.5.1 Field strength units: FS1 and FS2 on the display express the same measurement in
different units, which are selected for each as follows: press MENU; press Fld Str 1 or Fld Str 2; press
SELECT; move the cursor to the desired units; press SELECT. The choices are voltage units, uV-mV-
V/m or mV/m only, or dB units, dBuV/m (dB above 1 uV/m). Although voltage units are standard in US
practice, dB units can be easier to interpret when the value is fluctuating because a one unit change in the
last digit always represents approximately a one percent change in value. When it is desired to find the
dB difference between two values, having dB units simplifies the calculation. FS1 and FS2 values are
both saved when a measurement is saved.
4.2.5.2 Loop antenna orientation: When measuring, the loop antenna can be oriented for the
highest reading, or it can be pointed at the transmitting antenna by making the compass reading equal the
displayed bearing value. When using the compass, be sure that no nearby iron or steel objects are
affecting the compass, and that declination (variation) is entered correctly. Pointing at the antenna may
give a lower value if there is significant reflection from conducting objects in the area. If this is the case,
both values can be saved for analysis after downloading. Standard practice is to keep the loop antenna
plane vertical; this also can be varied and the results saved.
4.2.5.3 LPF use: Low-pass filtering to reduce fluctuation in the displayed value is available by
using LPF to step through three choices. Approximate values of the time it takes for the reading to reach
its final value are for LPF1, 0.5 sec; for LPF2, 1.5 sec; and for LPF3, 5 sec. When the FS reading goes
below 35 dBuV/m the 4100 switches from LPF1 to LPF2. When cochannel interference is present, and
the frequency difference is 2 Hz or greater, use of LPF3 allows measurements when the desired signal
exceeds the undesired signal by 4 dB or more.
Another way to deal with varying readings is to save several readings and average them after
downloading.