System Menus
Giga-tronics 2500B Series Microwave Signal Generators
Page 80
Operation Manual, Part Number 34737, Rev C, June 30, 2011
7.2
Use the Ref Tune Function
Why use this procedure:
Use this function when you want to phase-lock the output frequency of the 2500B with a
stable, external frequency source. See Figure 42 below.
The Reference Tune (Ref Tune) function allows you to adjust the output frequency of the 2500B over a range of
approximately 20 ppm (2 ppm with option 28) when the phase-lock loop with external source applies a 0 to +10 V
control voltage to the REF TUNE input on the rear panel.
Figure 42: Reference Tune Setup
Note the following about the Ref Tune function:
It is expected that the unlock (UNLK) message will appear in the upper right-side of the display when the Ref Tune
function is enabled. The 2500B is “unlocked”. The user must determine the appropriate parameters necessary to
lock the 2500B to the external frequency source.
The tuning voltage must not 15 Volts and must not go more negative than -1 Volt.
The instrument's phase noise performance may be degraded when Ref Tune is enabled.
The Ref Tune input is a high impedance input and has a 3 dB bandwidth of approximately 1 kHz that is set by a pole
consisting of 150 Ω and 1 µF as shown in the Figure 43.
Figure 43: Ref Tune Input Circuit
Additional resistance in the driving source will lower the bandwidth accordingly. The tuning sensitivity at the
instrument's output frequency is approximately 2 ppm/Volt (0.2 ppm/V with option 28) but should be carefully
characterized for the specific DC Voltage range being applied. A nominal tuning voltage of 4.5 Volts corresponds to the
instrument's nominal frequency setting.
