Why the push towards higher frequency?

[78k10]

As I’ve wandered through the forums, I’ve noticed what seemed to be a push for the public safety radio systems to go to higher frequencies. For example, I’ve seen it posted that in the early 20th century, police comms were in the 1400-1600 AM range. Then it seems they moved to vhf Low, 40-50 MHz. Later they pushed to 150-160, and now are pushing to 700-800. So, is there a legitimate reason? I figured technology played a part, but at the same time it must have been a significant cost to keep buying radios and equipment for the new channels, and constantly having to change out the systems. I figured there is a logical explanation, but I can’t come up with one on my own. Any ideas?

 

[jtwalker]

VHF signals travel farther in open areas, while UHF signals penetrate buildings better, making "800" a good choice for urban environments with many obstacles.

 

[avery_k]

A side benefit of higher frequencies is that the antenna is shorter and less conspicuous.

 

[GlobalNorth]

Lower noise floor.

 

[k9wkj]

can sell a whole new set of antennas.towers.repeaters,duplexers,combiners,coax,user radios and infrastructure every few years

 

[mmckenna]

As mentioned above, noise floor, also: more available spectrum with nice evenly spaced channel pairs, less co-channel users, etc.

Keep in mind that public safety equipment gets used pretty hard, so replacement cycles on hand held radios is often on a 5-7 year cycle. Even with good preventative maintenance, they wear out.
Systems often are on a depreciation cycle, so replacement funding is often built in to the budget.
Repair parts can get hard to come by, and doing component level repairs isn't always cost effective in the long run.

And, the same reason officers are not still driving around in 1960 Ford Fairlane's like Sheriff Taylor and Barney Fife. Stuff wears out, better technology comes along, needs change.
Comparing a hand held radio from the late 1970's to what is available now will explain a lot why we are not running old equipment.

 

[N4DES]

Another reason in 700/800 MHz is the ability to better control the antenna patterns to keep the majority of the coverage within the agency's jurisdictional boundaries. Every state has at least one local entity that manages the spectrum (acts as the 1st coordinator) to review the applications and is a requirement for FCC licensing. https://docs.fcc.gov/public/attachments/DA-22-643A1.pdf

Controlling the patterns also reduces interference complaints and allows for better frequency reuse based on the specific state plan.

 

[buddrousa]

The most important thing is all the VHF and UHF frequencies are all taken up.
The antenna system Combiners Can Filters and or Duplexers to make a 10 Frequency 20 pair system to work like a 700/800 system would be more expensive bigger and draw more power and generate more heat requiring more HVAC cooling.

 

[MTS2000des]

The biggest reason as others have mentioned in addition to controlling coverage contours is the noise floor. VHF is absolute trash in many urban and suburban areas thanks to modern electronics not being held to any standard as "incidental radiators".

 

[nokones]

My new Street Lights in front of my house are LED that emit noise on the 2 Meter and VHF Bands particularly the 151 Meg freqs and the LED Street Lights at an intersection with the Freeway near my house emits noise on GMRS Ch. 22 (462.725 MHz). Of course, this only occurs when the lights are on.

My Ditch Lights on my 23 Wrangler Rubi affect my VHF channels when turned on.

 

[78k10]

Ok, all of the above reasons make sense now. I figured that some of it may have been just the number of frequencies available. I didn’t take into account things like LED lights, which are everywhere now, creating electrical noise. I also didn’t think about agencies aging old equipment out before moving to newer, high frequency equipment. My mind went more to “this is the newest, greatest technology and you should upgrade immediately”. That’s why I had questions.

 

[k9wkj]

cool I poked the bear and got great responses

lowband and VHF high are nearly useless driving around in even my small town
and even UHF (460Mhz) is troubling inside some of the county buildings
causing BCLO to happen in places where you would not want it happening
time moves on and stuff wears out and support for old stuff disappears

 

[mmckenna]

Ok, all of the above reasons make sense now. I figured that some of it may have been just the number of frequencies available.

One of the downfalls of the lower frequencies is non-standard repeater offsets. Getting a VHF pair may be impossible in some areas, and getting a pair in others may come with real challenges regarding spacing. If you need more than one pair, it gets very complex and expensive.

UHF, 700 and 800MHz have common repeater offsets with (more or less) uplink and downlink portions of the band that have sufficient offset to allow using duplexers that can be less expensive.

Trying to coordinate VHF pairs, even for public safety use, is a stone cold bi†¢h in many areas. So as an agency's needs change, adding an additional channel can be a huge pain in the arse. On the other hand, I have 5 800MHz pairs in a section of the band that is restricted to public safety use and the closest co-channel user is about 100 miles away with a mountain range between us.

I didn’t take into account things like LED lights, which are everywhere now, creating electrical noise. I also didn’t think about agencies aging old equipment out before moving to newer, high frequency equipment.

Yeah, radios in public safety use take a beating and periodic replacement is necessary in most agencies. We usually work on a 5-7 year cycle. Equipment gets replaced.
Plus having more features, like GPS location of radios, better encryption, etc. is a valuable upgrade.

My mind went more to “this is the newest, greatest technology and you should upgrade immediately”. That’s why I had questions.

Yeah, common for those not familiar with the industry, you are not the first to look at it from that point of view.
Reality is that technology moves on, needs change, and equipment wears out.

Most of us take the taxpayers money seriously. After all, I'm a taxpayer, too. I do look for reasonable cost savings wherever possible. But there are requirements placed on agencies that require updating equipment periodically.

 

[consys]

Also driving it is the amount of data sent now- higher frequency’s allow higher data rates. Voice is data now, plus all the radio IDs ect. I knew the formula in a prior life, can’t quote it now sorry. That part of the brain has retired.

 

[12dbsinad]

VHF "used" to work really good, but not anymore. With all the radiating garbage, unless you're in the middle of no mans land, you'll be dealing with a noise floor that just deafens your radio and system receivers. Heck, try putting a VHF mobile radio in a new vehicle, school bus, garbage truck, etc, etc.. the radio will probably hear garbage (no pun intended) from the vehicle itself. You need to get into at least 450Mhz and up to start to get away from it as most electronic junk will radiate up to at least 300Mhz and sometimes higher. I sweep stuff with spectrum analyzer daily and it amazes me the garbage floating around that doesn't need to be if stuff was built to a higher standard.

 

[rf_patriot200]

My new Street Lights in front of my house are LED that emit noise on the 2 Meter and VHF Bands particularly the 151 Meg freqs and the LED Street Lights at an intersection with the Freeway near my house emits noise on GMRS Ch. 22 (462.725 MHz). Of course, this only occurs when the lights are on.

My Ditch Lights on my 23 Wrangler Rubi affect my VHF channels when turned on.

Install rg58 size Ferrite Cores at connection points to your ditch lights, and/or to your antenna input to your radio. This will decrease the rf noise from LEDs .

 

[freddaniel]

All of the above reasons are valid, but the primary reason was technology, or lack of it. I started in Land Mobile in 1962 and all radios were tube type and most businesses used 30-50 MHz. In urban areas, 150-174 MHz was really starting to take hold. There were some state-of-the-art UHF radios like the T44 or MC306, but they only really worked well, if you had a repeater. Most new radios used vibrators in the power supply, which replaced dyamotors [motor-generators] from earlier designs.

Tube technology was the limiting factor as better tubes were required for use of higher frequencies. As reliable radios were built at higher frequencies, they were first made using low power, such as 10-25 watts. Later higher power products became available. Every business or government agency wanted more frequencies and everyone wanted private frequencies. Like today, wishful thinking. So the FCC made ever higher frequencies available, to satisfy demand. Then they decided to narrow-band to 5 KHz bandwidth from 15 KHz.

In the early 1970s solid-state receivers became the norm, with tube type finals in the transmitters. Then later, all solid-state came along. In the late 70s, I remember testing a prototype 800 MHz radio and repeater in the LA area and was amazed how much better it covered the metro area, with lower noise floor.

Today, anyone can build an amazing network or system using the Internet for transport with satellite receivers and simulcast transmitters. Even $25 crap analog radios from China will work well on a well designed system.

We can even buy cheap data bandwidth on cellular networks and operate nationwide push-to-talk handhelds costing under $99. This is a different world from 1962 as the communications options are endless. With the IoT [Internet of Things], endless possibilities exist for young radio savvy engineers.