HamSCI simplex frequency

We advocate for a 70 cm simplex frequency for HamSCI in North America (United States, Canada). For example when at Field Day, conferences or solar eclipses, HamSCI affiliates and friends can find each other.

We suggest this HamSCI simplex frequency and CTCSS / PL tone:

446.025 MHz FM

100.0 Hz CTCSS / PL

Generally we use “wide” 25 kHz bandwidth, as the performance is about 4 dB better than “narrow” 12.5 kHz spacing due to the nature of FM analog “processing” gain from wider bandwidth. That is, in the absence of interference, 25 kHz wide modulation performs significantly better than 12.5 kHz narrow modulation. Most of our scientist members have analog-only radios at this time, so we kept with analog FM.

Frequency rationale

It’s generally much better to use 440 MHz band instead of 144 MHz band for portable hand-held radios (walkie-talkies). The 440 MHz signal is able to pierce through openings in buildings better. The interference from computers, LED lights, phone chargers, etc. is generally 20 dB or more less on 440 MHz vs. 144 MHz.

We aren’t trying to “hide” from anyone; we didn’t use 446.0 MHz as that’s the 70 cm calling frequency. We moved one “channel” up to 446.025 MHz so that people can still find us if they’re “scanning the band”. In most of North America, 446.025 MHz is recognized as a simplex frequency.

In North America, hams generally should not use FM below 442 MHz, as there are other modes coordinated for that frequency range. Hams should first consider 445.975, 446.0, or 446.025 MHz for FM simplex to be “safe” in most of North America, to not interfere with data links or repeater backbone links.


CTCSS has become analogous with the Motorola PL trademark, so we use it interchangeably like Kleenex and face tissues. We suggest 100.0 Hz PL because it’s easy to remember and is the default on some ham radios. With modern radios after about year 2000 or so, there isn’t a significant advantage of one PL tone over another. 100.0 Hz is just simple to remember.

There is too much bursty interference on any FM frequency to run carrier squelch (no PL).