A big trend in ham radio activity is the use of internet-connected transceivers commonly referred to as hotspots. These devices often use one (or more) of the popular VHF/UHF digital formats (DMR, D-STAR, Fusion) but analog FM is also used. They allow a radio amateur to have a local RF connection into one of the extensive radio networks (e.g., Brandmeister).
Unfortunately, there have been situations where radio amateurs arbitrarily chose hotspot frequencies that caused interference with existing radio activity. For example, a hotspot showed up on the 70 cm SSB calling frequency, 432.100 MHz. One of the worst examples of interference was a hotspot sitting on the input frequency of a satellite transponder. Not good.
The Colorado Council of Amateur Radio Clubs (CCARC) is the VHF/UHF frequency coordination body for the state of Colorado. Included in its spectrum management role, the CCARC maintains a detailed set of band plans (called Frequency Use Plans) for the 144 MHz, 222 MHz, 420 MHz, 902 MHz and 1200 MHz bands.
The CCARC recently decided to provide some guidance on what frequencies should be used for hotspot operation. Previously, the operator of a hotspot had to scan through the Frequency Use Plan and figure out where hotspots fit in. It wasn’t very obvious, so the CCARC now recommends 10 specific frequencies on the 70 cm band for hotspot use.
| Hotspot Channel | Frequency |
|---|---|
| 1 | 438.4500 MHz |
| 2 | 438.4750 MHz |
| 3 | 438.5000 MHz |
| 4 | 438.5250 MHz |
| 5 | 438.5500 MHz |
| 6 | 438.5750 MHz |
| 7 | 438.6000 MHz |
| 8 | 438.6250 MHz |
| 9 | 438.6500 MHz |
| 10 | 438.6750 MHz |
These frequencies are available for simplex hotspot use. However, for each of these simplex frequencies, there is also a corresponding frequency 5 MHz lower that can be used for hotspots that operate duplex.
Unlike repeaters, hotspots are not coordinated by the CCARC. With 10 frequencies available, it should be easy to find one that doesn’t have any co-channel interference from other users. See the complete CCARC hotspot guidance here.
These guidelines won’t solve every problem but it will help people find a hotspot frequency that plays well with others. These frequencies are valid for Colorado only. Check your local VHF/UHF band plans for more information.
73 Bob K0NR
Disclosure: I contributed to these CCARC guidelines but I don’t speak for the CCARC.
Jim/NC0JW pointed out to me that because these frequencies are Colorado specific, they are not necessarily useful for mobile hotspots. Many people use hotspots as they are traveling across state lines, usually connected to the internet via a mobile phone. Given that VHF/UHF band plans are local, it would be difficult to come up with an approach that works everywhere. Most of the mobile hotspots run very low power, so hopefully the interference potential is low.