JD700B Series User’s Guide
655
4
Press the
dB
soft key to complete the entry.
Setting external offset
You can turn the
External Offset
on and manually set the external offset value. An offset consists of a cable
loss and a user offset, and the measurement result shows the value reflecting both offset values. When the
external offset value is set at 40 dB, the measurement result compensates 40 dB.
Procedure
To set the external offset:
1
Press the
AMP/SCALE
hard key.
2
Toggle the
External Offset
soft key and select
On
.
3
Enter a value by using the numeric keys.
4
Press the
dB
soft key to complete the entry.
To turn the external offset off:
1
Press the
AMP/SCALE
hard key.
2
Toggle the
External Offset
soft key and select
Off
.
Enabling auto leveling
It is normal that you see higher level of RSSI in OBSAI spectrum than you have seen in RF spectrum
because the digital signal has a different gain level from RF’s. If you use the Auto Leveling feature and enter
the Noise Figure (NF) for the system to be tested, the instrument calculates an offset that compensates the
digital gain of RRH and applies it to the spectrum automatically to displace the level of spectrum to a known
RSSI power even though its accuracy cannot be guaranteed. Offset calculation for Auto Leveling is based
on the following:
Auto Level offset = (Noise Floor of RFoOBSAI) – (Ideal Noise Floor of RRH), where (Idea Noise Floor) =
N.F (RRH) + Thermal Noise + 10log (RBW)
Procedure
1
Press the
AMP/SCALE
hard key.
2
Press the
Auto Leveling
soft key.
A calculated level of offset without NF is applied as the external offset and the user input field is
activated for entry of the noise figure value.
3
Enter a noise figure value by using the numeric keys.
NOTE
Having the noise figure factored in the offset calculation for Auto Leveling will enable you
to view the OBSAI spectrum closer to what you can view in the RF spectrum, but if you
do not know the noise figure, you can skip this noise figure setting.
4
Press the
dB
soft key to complete the entry.
New external offset value appears in the
External Offset
menu box.
Setting RBW
You can set the RBW and VBW in the Spectrum, Spectrogram, and RSSI modes. The RBW range is limited
as per the bandwidth of the signal under test.