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Which Freqs work best in built up areas
27 March 2017, 13:26,
RE: Which Freqs work best in built up areas
Customers that are new to business radios are confronted a several confusing options, one of which is the type of frequency to choose: UHF or VHF. These abbreviations make no sense to most people and without some research it is easy to choose a radio that is not right for your situation.

The quick answer is: choose VHF if you plan to only use the radios outdoors and in an area that is relatively free of obstructions, such as buildings. If you plan on using the radio indoors, both indoors and out, or outdoors but around buildings, choose UHF. UHF is the better all around signal and is by far the most popular, so if you are in doubt, choose UHF.

UHF signals don't travel quite as far outdoors as VHF signals, but they do a better job of penetrating wood, steel, and concrete, giving you better range and performance in urban environments and around buildings. VHF signals travel farther, absent obstructions, and tend to "hug" the earth better, providing better performance outdoors or in hilly terrain
27 March 2017, 15:06,
RE: Which Freqs work best in built up areas
In the US our public safety radios used by police, fire and emergency medical services typically use APCO25 digital protocol on the 800 Mhz band. When operating in a steel reinforced concrete and steel high-rise office building, if there is not a nearby remote receiver for the trunking repeater system, direct unit-to-unit simplex "talk-around" is limited to about 8-10 vertical floors, with a 3-watt portable.

The former analog FM "high-band VHF" radios in the 154 Mhz band operating under similar conditions would only be reliable for 4-6 vertical floors.

Outside the building and operating in the street, the P25 800 Mhz. radios, in talkaround mode are reliable in and around an incident site for about a 10-block radius, whereas the 154 Mhz analog portables were LC solid-copy for 6-8 block at very best, but in the worst case you would have "dead" spots where the receiver of the portable would be desensed by strong nearby transmitters from digital paging, etc. and you couldn't communicate at all.

Away from the city and out in the suburbs the 154 Mhz analog radios worked wonderfully. We used a linked network of six remote receivers, a Motorola SpectraTac voting system and one 200 watt main site transmitter to cover a metropolitan area of 500 square miles. To cover the same area using 800 Mhz APCO25 digital required SIX digital spread-spectrum repeaters and 26 remote receivers and a ten-fold expenditure for equipment rack space and infrastructure...

When I first got out of the US Navy in the mid 1970s and was employed with the public works dept. our work trucks used "low-band" VHF in the 44-48 Mhz FM band, having crystal-controlled 200-watt GE radios which required dual batteries, a marine alternator, an isolator and Perko switches to keep the headlights from dimming upon full key-down. No repeaters were required and mobile units out in the country could talk directly to the Virginia EOC in Richmond from the suburbs of Washington, DC around the 495 beltway.

The new technology is said to be an "improvement". In profit margin for the people selling LMR equipment and lobby for Federal Homeland Security Preparedness Grant funds, perhaps...

73 de KE4SKY
"Almost Heaven" West Virginia
27 March 2017, 17:41,
RE: Which Freqs work best in built up areas
Thanks Motorola for a sensible answer to this question.....

And backed up by what CH wrote too.

So conclusion is that UHF is the best choice in a built-up area. But its not a perfect solution, there will still be inevitable dead spots, particularly in major cities with large sky-scraper type buildings in close proximity.
72 de



STATUS: Bugged-In at the Bug-Out
27 March 2017, 19:36,
RE: Which Freqs work best in built up areas
Recommended practice for police, fire and EMS is to have portable repeaters for voice, data and imagery installed in the POD used for the incident command post. This way responders to an incident are not dependent upon the available channel loading of nearby repeaters used for routine traffic, and having the repeaters located nearby at the staging area for the ICP enables portables working the incident site to have reliable coverage, even using minimum transmit power, so as to maximize talk-time on a set of batteries.

This was a hard lesson learned on the pile in NYC after 9/11 as several of the public safety main site repeaters were located on the WTC towers which went down. At the Pentagon the Virginia Task Force One urban search & rescue team was already equipped with multiple, frequency agile repeaters in their command post, which permitted flexibility and interoperability between local, state, federal government and military assets all working the site, permitting simultaneous voice, data and imaging on multiple operations, logistics and administrative channels, updating the status boards in the WebEOC incident management software in real time and having real time imagery with voice contact on the ground available to leadership, using multiple bands and modes simultaneously.

Eventually NYC came up in the network once replacement truckloads of equipment arrived and were set up.

73 de KE4SKY
"Almost Heaven" West Virginia

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