Using the ICRI as a VHF to HF Radio Bridge/Crossbanding with Remote DTMF Control

Last week, I described the importance of RF shielding, and a few ways to protect electronic devices from electromagnetic interference. The these concepts and techniques were applied during the recent production of a custom made ICRI-2PE unit for a customer.

VHF to HF Radio Bridge/Crossbanding

Map of VHF to HF Link

The customer’s goal was to link a conventional VHF mobile radio with a HF radio. A potential application for this configuration would a allow disaster response team, operating at an incident or work-site, to share a long range communications link to their headquarters. This link would allow the headquarters to monitor activity at the site and to provide resources and support to the response team. Alternatively, multiple disaster sites could be linked together, during a widespread or large-scale event, in a similar manner.


ICRI-2PE, VHF to HF Radio Bridge/Crossbanding

VHF to HF Bridge


Usually, we can easily supply this functionality with a standard, off the shelf product, the ICRI-2PE. However, our customer wanted additional functionality to allow a user to remotely control the bridging/connection between the mobile radios. That “bridging” would be enabled or disabled via a DTMF keypad on a remote radio.


Here is an example of how the device works. If a remote user was to dial, “12345” on their keypad, this would enable the bridge/crossbanding between the radios. Conversely “12346” (changing the last digit has changed in comparison to the previous string) would disable/isolate the connection between the radios. A few more key criteria are listed below:

  • When the enable bridge/crossbanding DTMF sequence is transmitted to the receiving radio, none of the tones will be retransmitted by the other radio. Retransmission of these tones would likely be undesirable to a remote user, monitoring the transmitting radio.
  • A handset could be connected to the ICRI-2PE, allowing the “local” user to simultaneously talk and monitor over both radios
  • The bridging/crossbanding is enabled by default when the ICRI-2PE is turned on.

In addition to extending the range of a “line of sight radio”, via a “beyond line of sight radio”, the ICRI-2PE can be used strictly for radio interoperability. In the event that two disaster response agencies need to communicate in a localized area, rather than with headquarters, the ICRI-2PE could be used to connect a VHF to UHF radio, two VHF radios, a VHF radio to a telephone, or any other frequency bands.


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