Need advice on repeater selection and mobile radios

My organization works overseas in dangerous areas. We currently use MTS2000 450-520 MHz UHF radios with DES-XL encryption. Most of our work is done in urban areas where the buildings are mostly 2-3 stories tall.
The MTS2000s do not have enough power to transmit even close to a mile in these urban environments, and we need a minimum of 3 miles range. The more, the better.
Setting up a repeater and antenna on a tower is not really an option because we move so much. We would like to mount a repeater and mobile radio in our pickup truck that will give us at least 3 miles range in these towns/cities with low buildings. Our personnel are always going to be within 3 miles of the truck when we use the radios anyway.
We believe that the best mobile radio for us is the high-power XTL5000 380-470 MHz UHF 100 watt model with a DES-XL encryption module. This meets our mobile radio budget of around $1,000 used. Our budget for a used (or new) repeater is also around $1,000. There are some additional funds available for the antenna, duplexer, etc.
Here are the problems/issues that we really need help with:

- We are considering the Futurecom DVRS repeater, but are not convinced that 10 watts output power is sufficient, nor can we find affordable cables to connect it to a XTL5000 radio anyway
- We are considering using a MTR2000 435-470 MHz UHF 100 watt repeater, powered using a DC to AC inverter in the truck. Paired with the 100 watt XTL5000, won't this give us plenty of power and range?
- We are open to other repeaters also like Bridgecom, Kenwood, Vertex, Pyramid, etc. if one would be better suited for our application.

We would greatly appreciate any advice on how to design a system that meets our requirements and is close to our budget. This is a time-sensitive request for help as we need to put this system together in the next 10 days. Thank you.

A 100 Watt repeater is not going to help, you may increase the talk out range to 3 miles but your talk back range will be no better than you have now. With your simplex system you currently have the ability to station someone in between the two stations that can relay any messages, with a repeater if the distant station cannot hit the repeater nobody is going to hear them. Perhaps you would be better served with a VHF system instead of a UHF system.

"rfradioconsult" is correct. You still have to be able to "talk back" to the repeater. You might be able to increase the talk back range if the repeater antenna were on a tall building or tower.
BB

As you've already heard, the biggest limitation to mobile repeaters is the antenna. The primary concept of a repeater is to put a remote radio (and its associated antenna) at the highest, most prominent location available, so as to increase the coverage footprint.

Most mobile repeaters are mobile in the sense that the repeater-equipped vehicle can be positioned in a prominent location (perhaps with a larger antenna) to serve a given area on a temporary basis. Having the repeater-equipped vehicle (with a typical - almost ground level - antenna) at the same general level as the hand-held users won't do much for increased coverage.

I think the only way your idea might work is to use a portable, suitcase-type repeater that can be temporarily relocated to a tall building (or a vehicle repeater that can be driven to prominent terrain) in the general area where your team is operating.

John

VHF high band would be your best bet from the sound of it.

The big issue occurs with the fact you are currently running on UHF and using DES-XL encryption. There is not very many low cost options to migrate one to VHF while retaining encryption.

Indeed having the DES-XL requirement pretty much limits your repeater options. Motorola made a portable DES-XL repeater based on Spectra mobiles . Finding one in your frequency range may be difficult however. You might be better off racking a Quantar repeater in a fly away case.

How many portable radios does your team require? Moving to P25 might give a bit of a coverage boost. Also your repeater options will be many more. You dont need more than 10 or 25 watts. You do need a mast to get the antenna up, though in an urban area, power lines will be a constant danger.
.

Why do you feel you need a 100w mobile AND a UHF mobile repeater? Are you linking the mobile repeater back to another network?

Regardless, a 100w UHF mobile operating with in a metre or less of an in band UHF mobile repeater is not going to work very well with out some very pricey filtering. You will want to link on a different band for best results if that is something you want/need to do.

A 10w Futurecom repeater will provide the coverage you are looking for IF you have a good feed line and antenna system. You will likely need a 20m mast though. I doubt you will get 3 miles talk in range with a roof mounted antenna. And likely well under a mile if you have a 100w mobile transmitting in the same band as your repeater.

For reference, I have used UHf repeaters, on a 100m tower, fed with 7/8 Alucel hardline, putting 12.5w into the duplexer, and been able to work it with a 35w mobile over a 70-80KM radius.

A 100w MTR-2000 repeater, in a mobile environment is OVERKILL and will make duplexer choices much, much more expensive.

Besides, you are limited to your 4w portable talk in power. Analogue DES-XL is likely not helping, you would be better to be operating P25/DMR/NXDN with DES-OFB or AES256. Analogue DES suffers from degraded range over unencrypted analogue voice.

Edit: in order to use the Futurecom repeater with a XTL5000 mobile, it must have the DVRS(can't remember what the option number is) option enabled in its flashport. The XTL5000 is, AFAIK the only radio that will control the Futurecom repeaters.

What's the building construction like?
Are we talking mud huts or steel reinforced concrete?

I've got an 800MHz system and a mix of high density steel and steel reinforced concrete buildings as well as rolling hills/forest. The higher frequencies tend to do a better job of building penetration. 3 watt hand helds work well. Repeaters are 84watts ERP.

Also, what are your encryption requirements? Is this federal contract work where you have certain requirements, or is it just to reduce the chances of eavesdropping?

Throwing huge amounts of RF power at these sorts of things usually only results in drained batteries.

Personally for the application, I'd go with P25 and either ADP (Motorola or Tait) or AES 256 (D, all of the above).

Both Motorola and Tait have portable repeater options but last I checked they were not cheap.

One can build a "simple" P25 repeater using two Simoco SRM9005 RF decks, will probably set back about $3000 USD but is significantly smaller in size compared to a Quantar (the repeater would easily fit behind/under the seats of a Hilux).


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W5PKY said:

Personally for the application, I'd go with P25 and either ADP (Motorola or Tait) or AES 256 (D, all of the above).

Both Motorola and Tait have portable repeater options but last I checked they were not cheap.

One can build a "simple" P25 repeater using two Simoco SRM9005 RF decks, will probably set back about $3000 USD but is significantly smaller in size compared to a Quantar (the repeater would easily fit behind/under the seats of a Hilux).


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I found this useful article:

http://mrmap.org.uk/forum/uploaded_files/rebroadcast_manual_14_01_09.pdf

I have to read further. I wonder if it rebroadcasts raw P25 data or if it re-clocks and performs error correction on the repeated stream? - Or is it simply Demod-Remod P25-Analog-P25 in which case the audio quality will suffer?

RFI-EMI-GUY said:

I found this useful article:



http://mrmap.org.uk/forum/uploaded_files/rebroadcast_manual_14_01_09.pdf



I have to read further. I wonder if it rebroadcasts raw P25 data or if it re-clocks and performs error correction on the repeated stream?

Click to expand...

Haven't seen that doc yet. That's getting saved to Dropbox.

The simoco solution can be configured for either analog, mixed mode, or straight P25. I know in P25 pass through, the P25 isn't decoded but passed via serial. It may apply FEC but I haven't had a chance to order some SRM9005s to try it yet.


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chief21 said:

As you've already heard, the biggest limitation to mobile repeaters is the antenna. The primary concept of a repeater is to put a remote radio (and its associated antenna) at the highest, most prominent location available, so as to increase the coverage footprint.

John

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That is important but equally as important is the portable radio. You could have a million watts in the repeater but if the portable can't talk back, it useless. If the portable radio can't acknowledge what it hears, it not communication.

The important part of any two-way communication (face-to-face or radio) is understanding between the two. If I talk to you and you don't understand me, I haven't communicated. I've only talked.

W5PKY said:

Haven't seen that doc yet. That's getting saved to Dropbox.

The simoco solution can be configured for either analog, mixed mode, or straight P25. I know in P25 pass through, the P25 isn't decoded but passed via serial. It may apply FEC but I haven't had a chance to order some SRM9005s to try it yet.


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I would like to hear more. If you can, please share what you find.

KK4JUG said:

That is important but equally as important is the portable radio. You could have a million watts in the repeater but if the portable can't talk back, it useless. If the portable radio can't acknowledge what it hears, it not communication.

The important part of any two-way communication (face-to-face or radio) is understanding between the two. If I talk to you and you don't understand me, I haven't communicated. I've only talked.

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The biggest gain is with respect to antenna height. If a mobile repeater is used, there needs to be an antenna mast which can be extended to gain height and it must be done so with consideration of dangerous overhead power lines. The broadcast ENG folks are expert on these type masts. If the vehicle is a permanent install, a pneumatic mast (Will-Burt) can be used. There are safety interlocks so that the vehicle cannot be driven off with the mast extended.

Regarding repeater power, yes 100W is overkill. However having some additional power at the repeater is helpful because in normal operation, the portable is worn at the hip (greater body loss) and may require a bit more power from the repeater in order to "hail" the wearer over a larger distance. Once the radio is brought to head level, the talk back of the 5 watt portable is sufficient at that range.

So having a 25 watt repeater isn't out of line, however it is important that the duplexer chosen is sufficient to prevent receiver desensitization.

RFI-EMI-GUY said:

I would like to hear more. If you can, please share what you find.

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Until I began reading the document you provided, I was not aware that the dual control head board could be added to utilize a control head on the radio as well.

I'll run it by one of my clients who is waiting on grant money for a few P25 capable interop repeaters. That would significantly lower the cost over the bases they've previously been quoted.

Your best bet is to do some testing. It's hard to throw answers when we are behind screens. First, I'd see what kind of coverage can be obtained by a properly installed mobile radio. I doubt you'll get 3 miles, but again it all depends on terrain and obstacles.

If you shoot from the hip you could be just wasting time and money. Start with coverage tests, never mind what radios or repeaters to buy at this stage in the game.

EDIT: I would test in regular analog mode in the clear, this will give a baseline and you can go on from there.

Wow, answers all over the map. Stick with UHF analog or digital.

Your real problem is talk-back to the repeater. Cellular companies found using a second receiver at the repeater location connected to an antenna with cross polarization would provide up to 20 dB [100x] improvement on talk-in. How do you think a crappy 0.1 watt cell phone is able to work.

Think about it, talking between buildings will not retain vertical polarization back to the repeater. All signals are multipath with many reflections, and some phase cancelation.

If that is not enough, consider several satellite receivers, on the talkback frequency, installed in other vehicles spread throughout your operating area, and linked back to the repeater on some other frequency.

Unless the VHF spectrum is empty compared to UHF, isn't going do squat in an urban area.

VHF is terrible for urban areas. If you only get a mile out of 400 mhz, youd'd be lucky to get half with vhf.

Would 800, 900 mhz, or somewhere in ghz be an option?

Evgeni said:

Unless the VHF spectrum is empty compared to UHF, isn't going do squat in an urban area.

VHF is terrible for urban areas. If you only get a mile out of 400 mhz, youd'd be lucky to get half with vhf.

Would 800, 900 mhz, or somewhere in ghz be an option?

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I think that is actually debatable for the actual use. VHF would be better for working streets and not entering buildings. UHF better for building entry. 7/800 would almost be too dependent on LOS in some situations (there is a reason cellular LTE is in the 700 range, makes DAS practical for both consumers and public safety).