Presentation on theme: "Cross Band Operating Options for Wide Area Only and Wide Area and Local Area Operations Mike Duff NY2PM 716-773-2684."— Presentation transcript:
Cross Band Operating Options for Wide Area Only and Wide Area and Local Area Operations Mike Duff NY2PM
What is Cross Band Operation? Cross Band Operation is a function of a Dual Band Radio wherein the two radios are tied together such that a signal received on the first radio is re-transmitted by the second radio and vice versa. The name “Cross Band” comes from the fact that one radio must operate on a VHF frequency while the other must operate on a UHF frequency. Thus traffic through the dual band radio is crossing bands from VHF to UHF and back again from UHF to VHF. Passing signals in the same band would require a duplexer and would comprise the functions of a regular repeater.
Why Cross Band? Cross Band Operation creates a gateway for other radios to: –Access other frequencies –Access other modes –Access power ratings not available on the client (non-cross banding) radio.
Examples of Cross Banding A Mobile Rig may be put in Cross Band Operation with a HT to allow the driver to access a repeater unreachable from the HT when he / she is out of the vehicle. A HF Base Station Rig may be put in Cross Band Operation with a VHF Mobile Rig to allow access to a HF net while operating from a vehicle.
A Real World Example Many radios deployed in Western New York hospitals are not in the Command Post or Logistical / Communications areas. The radios are in mechanical penthouses and odd offices / closets. The Radio Operators need to be in an area where they can pick up and deliver messages to Incident Command personnel. Since the Radio Operators and their radios are separated, a link needs to be established between the two. This link is provided via HTs which do not have the power for Wide Area Simplex Communications nor the ability to reach the proper repeaters. A dual band radio in cross band mode provides a gateway for these HTs to reach the proper repeaters.
Wide Area Only Via Simplex If the only concern is to enable Radio Operators to connect to each other over a Wide Area circuit, then the following scheme can be used. UHF or VHF can be used on the HTs as desired. If there are no restrictions, then UHF tends to work better inside buildings while VHF experiences less “green” attenuation on long haul circuits if antennas cannot be raised above the tree canopy.
Wide Area Only Via Duplex If a repeater is available, it can be substituted for the long haul VHF Simplex circuit. The HTs operate in Simplex mode while the Cross Band Radios operate in both Simplex and Duplex modes. In a severe situation, repeaters may be unavailable.
Wide & Local Area Via Simplex If the Local Area of operation for each camp / base is too large to support direct local communications between HTs, then the HTs may be operated in a Dual Band configuration to provide reception of the Cross Band radio’s Wide Area transmit signal. In this way, the HTs are eavesdropping on the out going signaling of the Cross Band radio. This makes the Cross Band radio function as a Wide Area link and as a Local signal booster simultaneously.
Wide & Local Area Via Simplex Local in range conversations can be conducted strictly on the local area VHF channel. Wide area communications use the cross band radios to access the wide area UHF channel. Users in the same local area that are out of range of each other can communicate by monitoring the local cross band radio’s wide area UHF channel. Reception of the UHF channel should be muted during VHF transmission to avoid a feedback loop. If simultaneous reception of the VHF and UHF frequencies presents a problem, the VHF channel can be permanently muted. In this case, local communications are made over the local cross band radio’s “boost” channel; however, local HTs must be able to hear the distant cross band radio’s UHF channel to receive distant users.
A Local Only Repeater If there is no distant system involved in your scenario and you only wish to create a “local only repeater” to allow HT’s on a large single site to communicate with each other beyond their normal range, then you can use one half of the Wide & Local Area Via Simplex diagram.
Wide & Local Area Via Duplex The wide area circuit can also be a made via a repeater by setting one side of the cross band radios to duplex mode. We come to a difficulty though if simultaneous reception of the VHF and UHF frequencies presents a problem. In the Wide & Local via Simplex scenario we could mute the VHF channel permanently and receive both local and wide area communications over the UHF channel. In this duplex scenario though, the local UHF “boost” channel is different from the incoming UHF wide area channel. Muting the VHF channel would block incoming wide area communications. Therefore, if simultaneous reception presents a problem then the local “boost” option must be abandoned in duplex wide area applications.
Special Feedback Concerns When designing systems that allow multiple radios to interact together it is important to avoid any possibility of developing a feedback loop. Such loops will lock up the cross band repeater radios and any regular repeaters involved in the plan. This can disable a complex wide area system and the only way to end such loops is to turn off all of the cross band radios. The following slide illustrates the problem and provides a few solutions.
A Double Duplex Solution The following slide illustrates another way to avoid feedback loops without having to increase separation, reduce power or assign different frequencies to each site. The method uses a duplex circuit on each side of the cross band radio and works because the cross band radios are not listening to each others’ outputs. Instead, they are listening to the local area duplex input channels instead. The downfall of this method is that all local communications occur on the “boost” channel.
Which is Best? Each of the preceding scenarios may have benefits in different circumstances. A good strategy would be to program each of the scenarios into your particular radios and then test each one to verify expected operation. A cross band radio with “Hyper” memories that records both radios’ setups could be used to quickly call up any particular scenario.
A Few Words of Caution Whenever cross banding to another system, protect the input channels on the cross band radio with CTCSS or DCS control tones. Be careful of power settings and duty cycles on the cross band radio. It is not a commercial repeater. Stay in local control of the cross band repeater as remote control of a repeater requires a separate third channel which is not available on simple cross band radios.