Mobile VHF/UHF Voice Radio Considerations

Mobile VHF/UHF radios are commonly used in vehicles and as "base" stations at field locations or Emergency Operations Centers (EOCs). A high-level summary of key features is presented here in quick, bulleted form.  More details are provided below.

• A mobile radio capable of at least 25 Watts is recommended; 50 Watts is preferable.
  • When operating with a repeater with a decent antenna, 5 Watts is usually sufficient.
  • But when operating simplex, especially if operating across cities on a county net, a tall antenna and 25-50 Watts is usually needed. Remember, when operating simplex, it's not only about being heard by Net Control. To avoid the hidden node problem, you need to be able to hear all of other operators on the frequency and they need to be able to hear you.
• Dual VFOs, Dual Receive operation, and stereo (or dual mono) headphone jacks are important for operating two frequencies at once.
• Cross-band repeat can be useful in several situations.
• A "data" connection is important if the radio might also used for packet.

Transmitter Power

• Generally speaking, a 25-50 Watt radio is recommended
• When operating with a repeater, 5 Watts is usually sufficient.
• But when operating simplex, especially if operating across cities on a county net, 25-50 Watts is needed. Remember, when operating simplex, it's not only about being heard by Net Control. To avoid the hidden node problem, you need to be able to hear all of the other operators on the frequency and they must be able to hear you.

 

Frequency Bands

• The 2m (144-148 MHz), 1.25m (222-225 MHz) and 70cm (420-450 MHz) amateur radio bands are used for both simplex and repeater operations.
• A common configuration is a dual-band radio for 2m and 70cm and a single band radio for 1.25m operation.

 

Dual VFO

• Dual VFO (variable frequency oscillator) radios allow tuning two different frequencies at the same time, typically, one on the left and one on the right.
• Both VFOs should be able to be tuned to the same band (i.e. both left and right VFOs tuned to 2m band, or both left and right VFOs tuned to the 70cm band).
• Avoid radios that do not allow direct input of configuration via the front panel.
  • These radios are typically from the commercial market and require pre-programming, usually with vendor-specific software, often at an added cost.
  • This lack of flexibility can be a major operational impediment during an emergency, since the radio can't be tuned to frequencies that haven't already been pre-programmed.
• For operation in an EOC, command center, or similar environment, avoid installations that separate the control head in one room from the radio body in another room or building.
  • These radios are typically from the commercial market and can be very convenient for specific circumstances.
  • But the cable (or network) that provides the separation is another point of failure.
  • And during a failure, such a radio can't easily be swapped out by another radio, unless it is the same brand and model, because the antenna connection is in one place and the operator is in another place.

 

Dual Receive

• For dual VFO radios, the radio should be able to receive on both VFOs at the same time
• If the two VFOs are tuned to different bands, then it is recommended that the radio be able to receive on one band while transmitting on another band. This lets you continuously monitor a second frequency, even while you are talking. It is also necessary for cross-band operation.

 

Stereo Output

• A stereo headphone jack (or two mono jacks and a Y-cable) allows the use of stereo headphones. This makes it easy for the operator to know which VFO is being used without looking at the radio front panel. Sound in the left is is from the left VFO; sound in the right ear is from the right VFO.
• Without this feature, it is mostly impractical to use both VFOs at the same time because you have to keep looking at the meter to see which receiver you are hearing.

 

Cross-band Repeat

• Cross-band repeat capability can be helpful in situations such as:
  • Sole field operator at a remote site or sole EOC operator: The base/mobile is setup for cross-band repeat and the operator carries an HT. The operator can move about the location, such as to deliver messages, without having to leave the net.
  • Shadow at remote location: The HT does not have enough power or a good enough antenna to reach the others on the net. The base/mobile is setup for cross-band repeat, perhaps in a vehicle with a rooftop-mounted antenna. The operator still carries the HT, but now has much better coverage.
• A radio capable of CW ID during cross-band operations is preferable. Otherwise, the station operator will need to insure that users of the radio remember to ID the cross-band repeater station, in addition to their own stations.

 

Channel Name Display

• Many radios allow a channel name to be saved for each memory location and for that channel name to be displayed instead of the frequency.
  • Setting the radio to display the channel name is helpful for operators who may not remember specific frequencies.
  • But it can also hide an incorrectly programmed frequency. For example, the channel name shows the call sign of a repeater, but the frequency that was saved is some other frequency. The channel name misleads the operator into thinking he/she is on the correct frequency.
• Some radios (those with larger displays), allow both the channel name and frequency to be displayed.

 

Data Connector

• If the radio will also be used for packet operations, then a data connector is recommended.
• The audio and PTT signals between the TNC and the radio can be connected via either the microphone and speaker jacks or a separate "data" jack designed for that purpose.
• Not all radios have a data jack.
• The "data" jack is preferred because:
  • It delivers a consistent audio level to the TNC, regardless of where the volume control is set
  • It allows monitoring of the packet activity with the speaker
  • It allows plugging in a microphone in case the radio needs to occasionally be used on voice nets

 

Notes on Some Specific Radio Configurations

• The SCCo EOC, SCCo Alternate EOC, SCCo communications trailer, and many city EOCs use the Kenwood TM-V71 (or TM-D710) radios for 144 and 440 MHz and Alinco DR-235T MKIII radios for 220 MHz.
• The SCCo Packet BBSs use Kenwood TM-V71 radios for 144 MHz and Alinco DR-235T MKIII radios for 220 MHz.
• The Kenwood TM-D710G is the same radio as the TM-V71, but also contains an internal packet TNC, GPS, and APRS functions, and a larger display that can show both the channel name and frequency information at the same time.
• Some city EOCs use various models of Yaesu or Icom mobile radios.