FAQ: Can the LO frequency of the downconverter be modified (e.g., from 1750 MHz to 875 MHz or 750 MHz)?

Q: Hello, can the down converters we bought from you be modified to cut the LO frequency in half? They currently operate at 1750 MHz—can they work around 875 MHz or be set to 750 MHz?

A: Yes, the LO (Local Oscillator) frequency can be modified. However, we strongly recommend that the modification be carried out by our engineers, or that you return the unit to us for adjustment to ensure optimal performance and stability.

If you prefer to modify it yourself, it is also possible by following the procedure below.

🔧 Self-Modification Guide

Table of Contents

1. Hardware Setup

Open the metal enclosure of the FDC (Frequency Down Converter).
Connect the device to your computer using a USB-to-TTL adapter.

Wiring (3 connections only):

TX → RX
RX → TX
GND → GND

You may also make the cable yourself if needed.

IF frequency is set by tuning the LO frequency

Tune LO to modify the IF output frequency

Changing LO shifts the IF frequency accordingly

IF depends on LO frequency in downconversion

2. Software Control via Serial Port

Use a serial terminal tool to send commands to the module.

Modifying LO Frequency From 1750 MHz to 875-750 MHz

3. Check Current Status

Command:

check?

Description:

Returns the current operating status and detected frequency values.

Important:

The command must end with a question mark (?), otherwise it will be invalid.

4. Modify LO Frequency

You can adjust the LO frequency by sending the following commands:

Target_FRE1=XXXX;
Target_FRE2=XXXX;
Target_FRE3=XXXX;

Explanation:

XXXX = desired frequency value (unit: MHz)
Each command corresponds to a specific LO module (LE1 / LE2 / LE3)
The system will automatically relock to the new frequency after setting

Examples:

Set LO to 875 MHz:

Target_FRE1=875;

Set LO to 750 MHz:

Target_FRE1=750;

Important:

Each command must end with a semicolon (;), otherwise it will be invalid.

⚠️ Important Notes

Ensure the target LO frequency is within the supported operating range of the hardware.
Changing the LO may affect IF output frequency and system performance.
Improper configuration may lead to signal instability or loss of lock.