Users manual
FA845
version 1.5
Envionic
26
3.6 Single frequency measurement
After the "Sngl" button is used, the device will only measure at a single frequency.
Why is this useful ? Suppose a scan takes 3 seconds. If you want to keep the antenna in
different directions to see in which direction the signal is the strongest, you must wait 3
seconds in each direction before the same frequency is measured again. In the single frequency
mode, this waiting is not needed.
The single frequency button (called "Sngl") in SCAN BAND mode stops the scan and
continuously measures the frequency of the peak (the peak was detected during scanning). In
this way, the changes in signal level are displayed almost immediately.
If you use the "Sngl" button in the MKR (Marker) mode, you can continuously measure any
frequency in this band. By moving the marker (with the arrow buttons), you can freely choose
which frequency to measure.
If the measurement result changes strongly every second (in SNGL mode), this means that this
is a mirror image frequency. A mirror image frequency is an "unwanted" signal that is not
really present at the specified frequency.
The device acts as a "superheterodyne" receiver (see Wikipedia), which means you could see
mirror image frequencies.
In the FA845, the mirror frequencies are recognizable as follows: In SNGL mode, the device
uses two different intermediate frequencies ("IF" Intermediate Frequency). Every second, it
changes the IF frequency and the local oscillator between two values. This means that mirror
frequencies appear or disappear every second while the "real" frequency signals remain visible
all the time.
In XPRT mode, you can switch between the two intermediate frequencies with the IF-A, IF-B
function to check for mirror image frequencies.
The above section seems to imply that the intermediate frequency can be one of two fixed
values. However, these two frequencies are also dependent on the frequency that is received.
The single-frequency mode is switched off when you press "Sngl" again or when you switch to
another band. In SNGL mode, there is no data logging.
