Introduction to shortwave communication
Short wave radio is a communication device operating at frequencies below 30MHz, which relies on ground waves and airborne ionospheric reflection to propagate communication signals, achieving long-distance short wave communication across regions and oceans. Short wave equipment is relatively simple and easy to install, but due to its low operating frequency, large antenna volume, and unstable ionospheric reflection in the air, it causes significant communication fading, instability, and unstable frequency selection, making it a traditional long-distance communication method. The following figure shows examples of common Japanese ICOM shortwave radio stations such as IC-F8101 integrated receiver and related shortwave radio stations.
VFO operating mode of shortwave radio station
VFO working mode is a working mode that many professional and amateur radio stations have. Its working frequency communication panel knob or button can be set at any time, making frequency setting convenient.
Careful friends will find that in VFO mode, there are generally two frequency memories available for selection: VFO A and VFO B. For example, the professional radio station IC-F8101 of ICOM in Japan has two memories: VFO A and VFO B. After entering VFO mode, pressing the function key A/B can switch between VFO A and VFO B, as shown in the following figure.
The default VFO working mode in the above figure is VFO A working frequency. Pressing the A/B multifunction key can switch between A and B keys. The figure on the right shows that when the receiving and transmitting frequencies are different, the receiving frequency of VFO A is 14.100MHz; The transmission frequency is stored in VFO B and the frequency is 14.105MHz.
The role of VFO A and VFO B
Obviously, when the transmission and reception frequencies are the same, both VFO A and VFO B frequencies can be selected for operation. But what should I do when the frequency of sending and receiving work is inconsistent? At this point, VFO B plays a role in storing the transmission frequency, and a single VFOA or VFO B cannot be achieved. This is the common SPLIT working mode of VFO.
That is to say, VFO A and VFO B provide a solution for transmitting and receiving different frequencies through relay stations.