• Most VHF/UHF transceivers are configured to limit continuous transmissions to a count of 60 - 90 seconds. This counter is automatically reset to 0 when transmitting stops.
  In many cases a continuous data transmission will periodically receive acknowledgement back from the destination before continuing the transmission. Since this short RX automatically resets the transmission timer counter, overall transmission can easily be nearly 100% - which may cause the transceiver to overheat.
  
  

• Improving heat dissipation is an important factor to extending a transceivers duty cycle. If it is positioned correctly and power consumption is no issue, having a fan continuously cooling a transceiver will probably help significantly.
  
  

• Heat soak is the effect of residual temperatures moving from a hot source towards a cooler place. Heat soak occurs over time and temperatures measured at one physical location may not accurately reflect the overall temperature of the part.
  Experiment:
  Turn your car off when it is hot, taking note of the temperature gauge position. Wait 2 minutes and turn on the ignition. The temperature gauge reads higher now than when the engine was running. The heat accumulated in the metals of the motor has moved into the now disabled cooling system.

• Not necessarily - residual heat may still be flowing towards the cooling surface of the transmitter after transmission ceases. See 'What is Heat Soak ?'.
  
  

• Mobile transceivers are probably not suitable for your application. Base units with 100% rated duty cycles will need to be considered.
  
  

• A1. Among other things, the duty cycle of a transmitter is related to the heat generated by the unit whilst transmitting. The manufacturer has listed a maximum operating temperature for the transceiver in the specifications list and this figure must never be exceeded. Keeping the transmitter well under the listed heat threshold is an important step to increasing the units duty cycle.
• 
  A2. If the base is relatively close by, try experimenting with reducing the transceivers output power. Most high power mobile transceivers can be programmed to operate at lower output levels. Less transmit level directly equates to less heat.
  
  

• Different between manufacturers - please check the documentation for your radio. A common duty cycle is 25-30%.

• Duty cycle is the relative proportion of time during which the transmitter is operational. A 20% duty cycle means a transceiver must be in receive mode or idle for 8 minutes for every 2 minutes spent in continuous transmission.
  
  

• Yes - if they can guess your 'FGU' address. Nexion Data Systems recommends changing the FGU from the default of 001,002,003. For higher security requirements a 48/128bit encryption module is under development.
  
  

• Digital data entering a Nexion modem is first converted into analogue signals before transmission by a unique conversion algorithm. Without a second Nexion modem to decode a received audio data stream the signal appears as noise or interference on the radio channel.
  
  

• Firmware is updated frequently to resolve issues and to add new features. The latest code firmware is NOT downloadable but IS available on request.
  Please be aware that firmware code versions prior to 3.39 are not compatible with later versions. Firmware in all modems in use must be updated.
  Contact us for update procedure and to request your new code .

• Yes.
  UUPlus offers flexible emailing client and server packages optimised for slow connections. UUPlus is ideal for email over any radio link.
  Alternately, please refer to the following document for information on setting up a Linux dial-in server. 

• A 'quirk' of Kenwood radios is that during a data transmission the microphone remains active having the potential to corrupt data in a noisy environment - please remove the microphone when sending data.

• Kenwoods use inverted logic for the busy, hence the constantly illuminated busy LED. Fix this with S107 to 1.

• In a mixed environment the weakest link is the slowest radio (i.e. highest S111 setting) or older transceiver's that do not have a good audio circuit. These radio / modem combinations may have to be speed limited to 4,800bps and are slow with data transfer due to long lead in delays. When you're setting up a network all units must operate at the lowest common level to ensure service to all.

• Nexion VHF radio modems will work with most modern 2 way radios with minimal modification to the radios. Please contact us for advice regarding how to interface Nexion modems with your radio. Contact Us

• The current NX1500 series has been optimised for 25Khz wide band operation, however customers are successfully using the NX1510 modem on 12.5Khz narrow band systems.

Normal telephone modems are designed to use a single standard connection which varies minimally across the globe.
Nexion Data Systems radio modems are designed to interface with the widest possible range of transceivers - each of which vary in their interface requirements from model to model. Even different transceiver units of the same model can sometimes require vastly different settings for optimal performance. The flexibility of the Nexion modems configurations caters to these variations in radio transceivers allowing optimal (data) use of virtually any radio unit.
Basic modem settings to suit a range of transceiver units:

• Icom IC-F410 with OPC617 
• Maxon SD-125
• Motorola GM338

• In a typical 25Khz wide band system, 3Khz deviation is preferred. However make sure that the transmitted data is not distorted or 'clipped' as this will affect or prevent data communications.

• Nexion Data Systems will not be releasing a data repeater for the NX1500 series modems. Whilst the modems are designed for direct Point-To-Point or Point-To Multipoint operation, we have successfully used the NX1510 modems through properly configured voice repeaters (i.e. repeaters set for equal deviation Flat Audio In / Out transmissions.

• In some cases, operation through a 25KHz repeater may not be possible. Whilst voice communications may seem OK through the repeater, high-speed data communications requires a flat audio response through the repeater and no audio distortion / clipping.

• Registers S114 and S115 adjust the amplitude of the audio signal. Low audio levels will result in inconsistent data transmission and an overdriven signal will cause data corruption. To configure S114 and S115, see the document  How do I set S114 and S115?  

• Yes - however ... In some environments the noise level may be higher than available signal and automatic setting (S114=0) may auto calibrate in the wrong direction. Automatic setting is recommended for only clean, fixed site environments with a good signal to noise ratio.
  S114=0 should never be used in mobile environments.

• The interfacing requirements to the two-way radio are also simple, requiring a minimum of 6 connections, namely...

1. 10-30V DC power @ 50ma
2. Ground
3. PTT to the transceiver
4. Busy / Mute indication from the Transceiver
5. Modem audio to the Transceiver (post pre-emphasis)
6. Discriminator audio from the Transceiver (i.e. pre de-emphasis)

• In most cases, we will endeavour to produce an application data sheet, detailing the exact interface requirements for all brands of 2-way radio that have been submitted to us.

• Please first check if there is already an application note for your model radio.
  
  Without access to proper communications test equipment many parameters cannot be easily measured for fine tuning the integration process. The following method however, while not optimal, will often give acceptable results: How to Set up Nexion 1500 series modems to a radio.

• The interfacing requirements to the two-way radio are also simple, requiring a minimum of 6 connections, namely...

1. 10-30V DC power @ 50ma
2. Ground
3. PTT to the transceiver
4. Busy / Mute indication from the Transceiver
5. Modem audio to the Transceiver (post pre-emphasis)
6. Discriminator audio from the Transceiver (i.e. pre de-emphasis)

• No. The NX1500 series modems work with your existing radios, providing an economical method of implementing data services into your existing radio network.

• One major advantage of the Nexion modem is its use of in-band (300Hz to 3000Hz) audio tones to achieve data transfer. This effectively means that the Nexion modem can be utilised over virtually any modern day conventional radio system requiring virtually no system modifications.

• Most modern day 2-way radios have the capabilities to support the NX1500 over-air protocols.

• A radio modem is used in conjunction with separate 2-way radio transceiver to transfer data over distance.