Jun 2015 Repeater Talk

This months Repeater Talk article will focus on the migration from traditional repeater use towards the possibilities, benefits and implications of these new machines.

Let’s start with a discussion on Tones.

Initial (traditional) repeater operations evolved over time to include more and more features intended to allow the users and operators to set up machines closer to each other and more “private” or controlled access. In the earliest days machines could experience overlaps due to hearing other users from near or sometimes far because only the squelch gate was available to prevent the machine from repeating any signal on the input frequency. Over time the use of tones of various types and frequency became the norm to help a local machine repeat only signals from their locale or users. Still though some of the equipment didn’t have this capability and the use of tone boards where needed.

Thankfully we have grown past those limitations and even though there are “tone less” radios still serving well in non repeater use – most , rather all modern radios come equipped with full tone support.

The most well known would be “PL” this name was coined by a well known manufacturer to represent their feature known as “Privacy Line”. Simply put if the radio receiver didn’t detect a certain tone it wasn’t going to be heard or in the case of a repeater it wouldn’t be repeated on the output frequency. This allowed more users to carry a radio that was ready to hear calls without hearing those that they weren’t interested in or intended for repeating.

Tone can be used on the input and/or output frequencies, they can be the same or different tones and more so recently it can be a digital signal that controls the function of hearing and or repeating. These options are driven by the club and the capability of its equipments . (The W2ZQ 2 meter repeater uses 131.8 as our tone)

Incidentally the reason some traditional analog radios may not hear the initial word spoken could be the “fast trigger” of the operator that speaks as soon as they key the mic – which may prevent the repeating radios circuits from switching over to transmit – OR – it could be a slow decoding circuit in the receiving radios PL decoder.

So the traditional “PL” tone scheme has served the community well and will do so going forward for analog machines. What about the newer digital protocols such as our Yaesu System Fusion machines coming on line?

This leads the conversation to that of new digital radios and the mix of analog decoding of PL tones with the modern digital formats such as C4FM. Since the digital technique involves the conversion of analog voice to a digital signal, the protocols have defined segments of their patterns reserved. In the case of C4FM for three main parts – the Header, the Communication and the Terminator. (Note how the duration is aligned with the bit rate and tied to the bandwidth used.)


Within the header and the terminator segment is the following data structure that your message / signal is encoded into during transmission and later decoded on the receiver’s side. See the segments numbered 0-6 and 7 they serve to address the legacy “PL” like controls.


The digital segment 7 is used to indicate if squelch is enabled or not – and if so then the segments 0-6 are used to express the squelch code 0 – 126 being used.

So what does that mean for the users and optimizing the needs and features of Squelch control in the new world? Well for one, the best way to avoid redundancy and the possibility of that annoying delay in decoding your PL tone is to use a Digital Continuous Squelch ( DCS ) which is expected and embedded into the stream of digitally encoded C4FM signal. I would encourage you to check out your radio’s manual (gasp !) to see how and what it can do.

We will continue to explore the benefits of digital HAM radio in coming issues of Repeater Talk – taking on more and more of the technical side and breaking it down for easy understanding.

Stay tuned to this feature column RepeaterTalk for the latest on our DVRA/W2ZQ System Fusion repeater upgrade.

Credit – fig 4.6 & 4.9 “Amateur Radio Digital Standards”, Yaesu Musen Co., Ltd April 18, 2013.

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