A few things to consider when providing communications for public events. Written for the Non Technical Planning Staff.
Batteries – Batteries come in several Chemical Types, Its is not recommended that a mix of batteries be put into service in the same event, unless the chargers used are rated for all battery types.
- Nickle Cadmium (Ni-Cad) – Notorious for cyclic memory issues which no longer a problem but are subject to crystalline deposits of cadmium collecting on the negative electrode plate that lowers battery performance. This crystalline material collects when the battery is overcharged or not fully discharged before a full recharge.
- Lithium Ion (Li-Ion) (Recommended) Low maintenance, no memory, no recycling required. Life span is 2-3 years. Fast Charge is OK, Lower weight per power ratio. Newest Technology.
- Nickle Metal Hydride (NiMH) Requires special charger, Does not like fast charge or overcharge. Recharging requires oversight. Most intolerant of abuse
- Chargers – Most radios available today come with either a usb cable/charger or a drop in single charger. Bank chargers are available for multiple radios in groups including but not exclusive to 4, 6, 12, 24. For events with multiple radios, bank chargers are highly recommended. All radios should be returned to a central location at the end of each day for overnight charging.
- Speaker Microphone/Headsets
Radio accessories include the following external speaker microphone combinations
- Microphone – The PTT is in the microphone while the speaker is in the radio (not too common for portables)
- Speaker Microphone – Hand microphone with built in speaker and PTT- usually a coiled cord (most popular)
- Boom Mic Headset – Over the head, head set with speaker and boom microphone. PTT usually in the straight cord.
- Headset with wired ear bud. The Microphone and PTT are usually in a module on the straight cable
- Headset with air tube ear bud. The Microphone and PTT are usually in a module on the straight cable(my personal favourite)
- Bluetooth Headset. The microphone and speaker are usually in the bluetooth ear piece. The PTT could be on the bluetooth ear piece or on the radio.
Different Operating Modes
- Simplex Radio – Point to Point, Line of Site . The radio units transmit(Tx) and Receive(Rx) to/from each other on the same frequency. (Limited Local Coverage Only)(~5Km)
- Repeater Mode – Point to Point through a repeater. A repeater receives a signal on one frequency and simultaneously transmits it on another frequency. The stations using the repeater transmit on the repeater Rx Freq. and then listen on the repeater TX Frequency for a reply. (~100Km) (Wider Area Local Coverage)
- Trunking Radio – Trunked Radios establish a channel to individual radios or groups of radios called Talk Groups. Each radio can select which talk group to listen to or talk to. This mode can make use of special repeater links into the phone system or internet at each geographical location that requires communication to the system network. Any radio anywhere on the network can communicate with any other radio anywhere on the network.(Unlimited Range). There is typically a delay from the time a ptt is depressed until the full circuit is established to the receiver, so the person transmitting must delay speaking for a brief moment.
a) Portable to base is simplex
b) Base to Mobile is through the repeater.
- Squelch Modes
- Carrier Squelch – The receiver opens ea signal is received that is strong enough to over ride the squelch setting in the radio.This setting is adjusted to quiet the radio in noisy locations. (not recommended)
- CTCSS – Continuous Tone Coded Squelch System. All network transmitters and receivers are set to the same tone frequency. When a receiver receives a signal with the correct tone, the receiver opens to accept the signal, and stays open as long as the signal with the tone is received. The signal only needs to be strong enough to decode the tone. CTCSS does not inhibit other radios from listening to radios on your network. It will inhibit your radios from hearing any radios that are not transmitting with the designated tone.
- DCS – Digital Coded Squelch (Motorola DPL) is a slow speed binary data stream. Works similar to CTCSS
- Tone Burst – A sequence of tones is sent once, as soon as the PTT is depressed. The receiver decodes the sequence and opens the receiver. There is a short delay to decode the tones so the sending radio must delay speaking for a brief moment.
- Cross Talk / Adjacent Channel Interference (Multiple radios on different frequencies in the same location)
- In electronics, crosstalk is any phenomenon by which a signal transmitted on one circuit or channel of a transmission system creates an undesired effect in another circuit or channel.
- ie: Radio A listening on Frequency 1 to a weak signal from Radio B hears distorted audio because Radio C is broadcasting on Frequency 2 in close proximity to Radio A (Where Frequency 1 and Frequency 2 are fairly close together.) The power output from Radio C swamps the receiver in Radio A with unwanted signal.
- Increase physical distance between Radio A and Radio C
- Select frequencies that are further apart.
- VHF to UHF would have no appreciable interference
- All commercial radio equipment must be licensed, usually held by the radio owner or leasing vendor. A leasing vendor holds licenses for multiple radios on specific frequencies, to be used in a specific geographical area. Other vendors will be licensed for different frequencies. If multiple vendors are involved, where communications is required between the different vendors equipment, a special license must be obtained from Industry Canada. The Trunking system can be used to circumvent these restrictions. Vendors can be selected in the different locations to provide radio’s licensed for their local geographical area with a trunking link via long distance telephone circuits or internet, to all other local cells or locations.
- All radio equipment should be obtained from one vendor, unless not required to communicate into the network(Network: System of locations which communicate with each other), or the trunking option is selected.
- Do NOT rely on the cell phone network for time critical communications in Large Events. The cell phone networks were not designed for, nor can adequately handle the thousands of cell phones congregated in a in a small area during an event. Take the Vancouver 2010 Olympics as a prime example.
- Hands Free Rules for Radio Equipment.
- A mobile radio mounted in a vehicle is exempt from the hands free rule.
- A portable radio may be used in a vehicle provided that a separate microphone is used and the radio is fastened down.
- Cell phones MUST use hands free hardware: ie: bluetooth modules or wired headsets.
Considerations for Mobile Antennas & Mounts
a) The location of the antenna and how it is mounted make a big difference on the radio’s performance.
b) Mag mount antennas are a poor compromise, especially if something is used under the mag mount to protect the paint.
c) A good trunk clip mount works well for temporary installations(Recommended) Comet CP-5M, or Diamond K400SNMO – Articulating mounts to better align antenna.
d) A high gain antenna provides the best performance.
e) Take care to match the antenna to the mount. Several connection types are available. (NMO, UHF-SO239)
Band Allocations VHF vs UHF (Lower Frequency = Longer Wavelength)
- VHF(150-160Mhz), UHF(450-470Mhz, 800Mhz, & 900Mhz)
- Longer wavelength gives longer range under ideal conditions(VHF)
- The shorter wavelength goes through trees and buildings better.(800/900 Mhz)
- VHF works best outdoors except in heavily wooded areas
- 800Mhz, 900Mhz work best through buildings.(shortest wavelength)
- UHF Good all round performance and less likely to experience interference from non event radios in other areas.
- All radio frequencies in Canada and the USA are SHARED, and are usually allocated in different geographical areas such that they do not interfere with each other.
- Programming –
- Most radios available today are programmed via computer software..
During warm summer days, an event referred to as an atmospheric temperature inversion may occur that will bring in radio stations for a thousand kilometers. This is more likely to occur on vhf or lower frequency uhf. An atmospheric temperature inversion in layman’s terms is a duct in the atmosphere which allows a radio signal to travel a great distance, and releases it into a geographical area where it may interfere with a local radio network.
Best of All worlds – Radio that does it all .
Very Large distributed events may require all units to have trunking. However if a mix of the various frequencies and or modes is required then a few radios capable of communicating across the network may be required.
The Motorola APX 7000 is a portable radio capable of working all possible modes, and frequencies including trunking. ( VHF 136-174), UHF(380-470, 450-520), UHF(763-776,793-806,806-824,851-870)
Similar units are available for Mobile and Field locations.
16. Event Radio Logistics
- A central control or dispatch is manadatory to control activity on the channel and provide for logistical support.
- Safety is the primary responsiblity of everyone concerned with the event.
- The design of the radio system should be such that it can cover the whole event location.
- In land based events, radios should be positioned at all water stops, or dangerous locations,or turn around locations
- In water based events radios should be on safety boats with an adequate number of safety boats for the event size and number of participant boats.
- Different water sports have quite a discrepancy in event size, from Canoe/Kayak (200-1000M), Dragon Boat (200-500M) Rowing (500-2000M)
A) In Land or water sports where distance or line of sight is concerned, radios that can cover the entire course are manadatory.
B) Radios should be located at all convenient turns, water stops
Reference Material :
Practical Guide for two Way Radios – Rescue Dynamics
Benefits of Trunked Radio Technology