VHF-Mid Band Use

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Perth.SWL
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VHF-Mid Band Use

Post by Perth.SWL » Thu Nov 23, 2017 5:12 am

Just wondering why fire-fighting Agencies still hold on to frequencies in the VHF-MID band. A lot of repeaters in that segment are linked with VHF-HIGH repeaters located on site. Also, given a lot of VHF–High band sites have multiple repeaters in the same segment (back-up option), what are the benefits of continuing a VHF-Low presence? Perhaps to talk to Local Govt….

Does it offer better propagation properties in hilly terrain? Or is it being slowly phased out?

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Re: VHF-Mid Band Use

Post by yorky » Thu Nov 23, 2017 8:20 am

It's still useful. Yes Some areas mid band can be better than high band but that's a topographical thing.

Main use is sector channels, where the control channel is now almost always high band it's easier to have mid band sector channels. This is because most appliances have one high band and one mid band radio but usually not two high bands (have to use a portable for second high band). Using both vehicle radios be it separate handsets or dual band receive mid/high is far more effective than using a dinky little high band portable for simplex.

Not to mention there are a ton of mid band radios still out there, where phasing them out would reduce capability not improve it.
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Re: VHF-Mid Band Use

Post by Zebedee » Thu Nov 23, 2017 9:36 am

Long term I believe the intention is to phase out VHF Mid Band from the fire and emergency services.

But until that day comes, the repeaters are there, the channels are programmed and allocated, so we may as well use them.

Mid band channels are allocated in pre-formed communications plans, so to take them out of the equation would limit our options. However, I do know that some appliances out there don't always have mid-band capability, so communications planning has to take this into account. There's various ways of knowing what appliances have what radios. One example is by using little coloured dot stickers on T-cards. If you had an appliance without a mid-band radio, you wouldn't send it into a are where they were using mid-band as their sector channel for example.

In my brigade, we make use of VHF mid, VHF high, DFES UHF and even UHF CB depending on where we go and who we need to talk to.
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Re: VHF-Mid Band Use

Post by Perth.SWL » Thu Nov 23, 2017 4:41 pm

Thank you to both - I appreciate your comments.

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Re: VHF-Mid Band Use

Post by vk6hgr » Fri Nov 24, 2017 9:24 am

I don't think mid-band will be going anywhere as it's useful for dual-watch, given that most simplex channels are VHF high-band.

On a fireground, a sector commander to need to listen to two channels: The simplex channel the vehicles under his command are using, and the duplex channel that he uses to talk to other sectors, the incident command, etc. Without scanning (which means you could miss something), or dual radios on the same band (which will interfere with each other), operating on dual bands is the easiest. Until recently, DFES UHF didn't have enough channels available to do this using VHF/UHF and the capabilities of simplex UHF vs VHF on a fireground perhaps aren't as well known.

Also, it seems a number of non-DFES and private fire vehicles (i.e. Whiteman park and the airport) have VHF mid-band only.
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