SVARC’s Implementation of Yaesu System Fusion Digital Capability

What is Yaesu System Fusion Anyway?

SVARC is not the leading expert on Yaesu System Fusion technology. So, if you’re not sure what this is, SVARC is happy to leave the explanation to the real experts:
Understanding what Yaesu System Fusion is and what capabilities it offers may be helpful in understanding SVARC’s implementation, so please refer to Yaesu’s explanations as needed.

SVARC’s Yaesu System Fusion Repeater Configuration

In 2015, SVARC decided to replace both of the its aging (2 meter and 70 centimeter) repeaters. SVARC’s decision to acquire and install Yaesu System Fusion repeaters was compelled by very attractive pricing on the Yaesu DR-1X repeaters offered at that time.

Beyond the financial incentives, Yaesu incorporated the AMS (Automatic Mode Select) feature in these repeaters, enabling the capability of mixed-mode operation. Using the AMS feature could mean that operators with FM-only equipment can continue to make calls on the repeaters with their existing equipment, AND there would also be support for operators having purchased Yaesu System Fusion compatible equipment. The nature of the receiver AMS feature is based on each transmission received. This means that once the received modulation is detected and selected, it remains the same through the duration of the received signal. Conversely, modulation mode can change on the very next transmission. This allows true mixed-mode input, on one repeater. The implications here are support for digital and analog modulation methods on one repeater. This means a drop-in replacement for an analog-only repeater enables digital modes without the expense of adding a dedicated digital mode repeater, nor is it necessary to go through the process of obtaining an additional channel pair.

So, now that we can hear either C4FM digital or FM analog transmissions, the decision has to be made on what to do to generate an appropriate output signal from the repeater. Yaesu’s AMS feature can also be selected for transmitting the output matching the received input type. This is the default, out-of-the-box behavior of all Yaesu System Fusion repeaters. However, both receive and transmit modes can be forced to digital-only or analog-only. A Yaesu System Fusion repeater can be configured to do either digital only, analog only, or AMS in, with fixed digital or fixed analog out. Yes, it could even be configured to  translate what it receives from one modulation to the other.

A Tale of Two Repeaters

SVARC has long had the good fortune to have both a 2 meter VHF repeater, and a 70 centimeter UHF repeater on the air. Currently, both repeaters are co-located at an excellent location to provide very good coverage across the northern Shenandoah River Valley. So, SVARC has some additional flexibility in deciding how to configure the Yaesu System Fusion repeaters.


There is a slight difference in how the two repeaters behave based on how they are configured –

  1. The 2 meter repeater is configured to transmit fixed FM output signals regardless of whether it received an FM (analog) or C4FM (digital) on the input receiver (AMS/Analog mode)
  2. The 70 centimeter repeater is configured such that the transmitter output mode follows whichever modulation mode that the receiver is seeing at the input (AMS/AMS mode)

Explaining What You May Be Hearing On The Air

The configuration of the 70 centimeter repeater allows maximum flexibility by supporting both analog-to-analog calls, as well as Yaesu System Fusion C4FM-to-C4FM calls on the same repeater. This creates the scenario where an operator with FM-analog-only equipment could be received C4FM signals on their receiver, without the ability to demodulate that digital signal into something intelligible out of their radio’s speaker. The sound of a C4FM signal on a radio set for FM analog reception is analogous to loud white noise coming from the speaker of the receiver.

On the 2 meter repeater, only analog FM output is transmitted, regardless of whether the input signal to the repeater is analog FM, or digital C4FM. Users with analog-only equipment should only ever hear the digital noise described above when monitoring the repeater input of a station transmitting in C4FM mode. The repeater output is always analog FM.

Saving Your Hearing and Sanity

For this reason, FM analog-only users, particularly on the 70 centimeter repeater, may be best served to set their radio to use CTCSS / PL decode mode, in addition to the required CTCSS / PL tone encode mode. When the repeater is transmitting an FM analog signal, it is also configured to transmit the CTCSS / PL tone on the output. This way, FM-only users can use the receipt of the CTCSS / PL tone to selectively block when the squelch opens, and consequently, the noisy digital transmissions that do not incorporate the CTCSS / PL tone in transmission. This allows the user to still effectively monitor the 70 Centimeter repeater for FM analog calls, without all of the mind-numbing digital noise. Nearly all amateur radio equipment designed to operate on 70 centimeter FM modes built in the last 20 years support enabling tone decode features.

Something To Remember

The one potential downside to operating this way is that it becomes important to look at the rig before transmitting, and see if there are indications of an output from the repeater, even though the squelch isn’t opening. The possibility exists that a digital call could be in progress, but nothing is being heard from the receiver (the desired case). Beyond the embarrassment of unwittingly causing interference by keying up on top of a QSO in progress, transmitting an analog FM signal on top of the digital QSO in progress can, in some cases, cause the repeater to lock up. When we say lock up, we mean that it won’t recover without the repeater being powered off then back on again to recover normal operation.

This secondary problem is widely thought to be a bug in the Yaesu System Fusion controller in the repeater that Yaesu has yet to successfully squash. The indications that the bug has been triggered include the repeater going into a state where it transmitting an unmodulated continuous carrier, and further input has no effect on it.

Other anomalies have been observed triggering the problem, and we would ask that if you do find either of the SVARC repeaters in this locked-up state, that you attempt to reach us on the other repeater and let us know, so we can check it out and attempt to resolve it with remote power control to the repeater experiencing the lock-up.

Lastly, the SVARC repeater committee would ask that you please use and enjoy the repeaters, but that you exercise reasonable courtesy and caution (often recognized to be the manifestation of the FCC’s required ‘good operating practices’) to check for the possibility of an on-going digital QSO on the 70 centimeter repeater before you attempt to key it up in FM mode.