Looking for real life experience, UHF or 800 MHz inbuilding,

[RFguy]

I have a user that runs 4-watt UHF (455 mHz) simplex radios. Standard 1/4 wave whips. Some use speaker mics, so the radio is on the belt and will have body shielding. Others don't use speaker mics, so will have the radio at head level while transmitting.

The building they are in is dense concrete, quite large and about 15 floors high. They experience spotty coverage in some locations.

A repeater will solve the problem, but they have been told (not sure by who) that if they switch to 800 MHz from UHF (455 mHz) will "fix" the problem.

I've never done a side-by-side test between 4-watt UHF and 3-watt 800 mHz portables in-building, simplex, but am planning to do so.

I was curious if anyone has direct experience from UHF to 800 MHz in-building. What about belt worn UHF compared to 800? Is there similar body shielding effect between the bands?

[Jim202]

I have a user that runs 4-watt UHF (455 mHz) simplex radios. Standard 1/4 wave whips. Some use speaker mics, so the radio is on the belt and will have body shielding. Others don't use speaker mics, so will have the radio at head level while transmitting.

The building they are in is dense concrete, quite large and about 15 floors high. They experience spotty coverage in some locations.

A repeater will solve the problem, but they have been told (not sure by who) that if they switch to 800 MHz from UHF (455 mHz) will "fix" the problem.

I've never done a side-by-side test between 4-watt UHF and 3-watt 800 mHz portables in-building, simplex, but am planning to do so.

I was curious if anyone has direct experience from UHF to 800 MHz in-building. What about belt worn UHF compared to 800? Is there similar body shielding effect between the bands?

You will get all sorts of suggestions and comments on one frequency band is better than the other. My suggestion is to try both and see which one works better than the other. I don't mean install a repeater and do the test. You can get a good feel by using a couple of portable radios and see what type of coverage you get. No two buildings are constructed the same. You need to know what radio band will work with your building, not an average building construction. A single antenna on the roof will probably not work well at all for your application.

A 15 story building will probably require installing an in building antenna system. By this I mean using leaky coax and splitters. It may even take a bi directional active amplifier system and a multiple antenna system on several floors or each floor. Without doing some testing, I don't think anyone could come up with any concrete recommendations. If you get a vendor that says they can provide a system without doing any testing, I would tell them thanks, but no thanks. Look for another consultant or vendor that will work with you.

Jim

[Will]

I would from experience recommend UHF.

[MT2000 man]

Going simplex in a building, UHF would hands down be better than an 800MHZ portable just for the 4 watt vs. 3 watt factor alone.

[Satelite]

Hello :
I will 3rd the above recommendations on UHF over 800 MHz for simplex operation in bulidings.
I personaly dealt with 800 MHz in a cement grain elevator operation and it was unacceptable at best.
I then gave them a few uhf handhelds and they were very happy with the results.
That was at least 10 years ago and they narrow banded to still uhf at the first of the year and no complaints.
The 800 did not do well in the cement structures but UHF did well .
My thought is that uhf bounced around and found the other radios where as 800 MHz didn't.
Cant say for certain why uhf worked better than 800mhz but UHF is the way to go.
I also had a scrap iron salvage yard complain about communicating from buildings into other buildings with vhf hand helds but when I gave them uhf loaners to try they loved them and purchased the uhf loaner hand helds and they too narrow banded and stayed uhf with no complaints on coverage.
Its like UHF bounces where others didn't .
Ive often wondered why uhf did well where the others didn't but never really dug into the theory on it as it worked in the real world and I accepted it from happy end users and no more complaints.
Otherwise yeah you might need the repeater but uhf beats 800 in my experience.
Satelite

[Bill_G]

Ditto UHF. Much better building penetration than 800. A lot easier to make a poor man's radiax with RG8 too. 100ft run up and another 100ft run down with simple antennas terminating each end, and you're golden. That 90% shield becomes your friend, and turns both runs into antennas through the building. At UHF. Not so much at 800.

[MTS2000des]

My experience is with a mutli-building hospital campus, four main reinforced concrete structures (typical hospital construction) and several smaller outbuildings. Four main patient towers are 7 stories. Most outbuilding are 1-3 stories.

UHF, by far, has the best coverage (without a repeater, there are many dead spots). Our hospital security uses 800MHz XTS series portables on the county DTRS, who has a prime site about 3 miles away directly behind campus. There are MANY and I mean MANY dead spots for the 800 radios on the system. On talkaround using I-TAC channels, they barely cover 2-3 floors if that.
UHF radios can reach from the lobby level to the 7th floor in many areas WITHOUT a repeater.

UHF is the undisputed KING of coverage for on-site, in building use. 800MHz pales in comparison.

It's no wonder why the two largest cities in the USA use UHF and UHF "T" band for their public safety voice systems. It's a no brainer.

[wavetar]

My main comparison story is we switched a major university from an 800MHz GE trunked system to a UHF MotoTRBO system. System antenna at the same location. The UHF coverage in all campus buildings was far superior. So much so, that plans for a couple of buildings to have bi-directional enhancement were scrapped.

[Jim1348]

How much does going from analog to digital format help?

[RadioSouth]

I worked for a large urban agency during a UHF to 800 rollout. Although there were more sites for the 800 system there were many more dead spots especially at indoor locations. In one example there was a building that you could see a site from, go around the other side of the building and no coverage from the ground floor.
I had a conversation with at tech that was maintining a 800 system in FL, they were having problems with a site every time it rained but could find no site water intrusion. They attributed it to pine needles becoming conductive with moisture and being a resonant length they were absorbing RF.
So what's the botton line with 800, why has it been so widely adopted ?

[Jim1348]

.....So what's the bottom line with 800, why has it been so widely adopted ?

I think in the case of the Minnesota ARMER system it was the availability of frequencies. I think UHF 450-470 mHz was considered, but it was determined that there would not be enough frequencies available for a statewide trunked system.

[RFguy]

Thanks for all the responses. I hope to be doing a test in the next week or so. I will test VHF, UHF, 800 mHz. Analog and MOTOTRBO digital in each band. I will also test belt-worn with a speaker mic and hand held at mouth level.

All these tests are for in-building coverage. I'll report back on my findings (I already know VHF will suck).

[Bill_G]

How much does going from analog to digital format help?

RF doesn't go any further in either mode cuz power is power, and range is still range. However, there is the "apparent" gain of a few db from the error correction offered in digital. So, in that signal fringe area where 3db makes the difference, digital comes through where analog may not. And this seems to play out better in buildings than in a mobile environment because people move slower, and can more accurately find a sweet spot better when they are walking. ie: in analog, a parking structure has numerous dead spots, but in digital it is entirely served with some "bubble voices" in a lot of places. It's not magic. It's still the fringe, and the radios are right on the edge of signal failure.

[Bill_G]

So what's the botton line with 800, why has it been so widely adopted ?

First, there was a lot of spectrum made available, with a good chunk reserved for public safety. Combined with trunking and simulcast, you could design a system with plenty of bandwidth and the coverage you wanted.

Second, because of the advanced features in trunking, you could separate traffic, and increase loading. Thus, several agencies could build a system together to serve an entire metro area giving everyone greater coverage with the advantages of mutual aid and independent channels at a reduced cost of building something on their own.

Third, because propagation was so poor, the frequencies could be reused in well under 50 mile radius depending on the HAAT of the primary sites thus ensuring most major metros could have plenty of channels to work with. The shorter wavelength also allowed smaller directional antennas so you could land a signal where you wanted especially to avoid overlap and interference.

Fourth, again because the wavelength is shorter, portable antennas actually approximated quarter wave performance rather than a fraction of one that lower bands did. So, portable and mobile performance became more equal.

Fifth, since large systems are designed around portable performance, mobiles no longer needed to be 100W drawer units. They could be 10 to 15 watt dash mounts cutting unit costs.

Sixth, as BDA's, and later DAS's, became available, you could improve indoor coverage easily. They come with a cost, but are cheaper than building new sites.

[Jim1348]

Bill,

Obviously you speak from experience because those are all excellent points. Thank you for adding that!

Jim