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Increasing Range of 868Mhz system

Increasing Range of 868Mhz system

Increasing Range of 868Mhz system

We need to increase the range of 868Mhz intruder/fire systems to allow us to cover multiple buildings or floors within construction sites using a single control panel with paired wireless smoke/intruder detectors. Would I be correct in thinking that increasing the size of the antenna at the control panel would do just that?

RE: Increasing Range of 868Mhz system

It probably wouldn't hurt...but there are other things to consider.

You need to take into account the building construction, as steel buildings will attenuate the signal more that wood/composite buildings would.

You also need to take into account antenna placement. If it is possible to elevate the antenna into an overhead space while adding a higher gain antenna (larger antenna) you can increase your range.

It is near impossible to say how great an increase you can expect without knowing all the details of the system. Some of the factors that will affect the overall range are:
TX power at the panel
RX sensitivity at the panel
TX power at remote
RX sensitivity at the remote
modulation scheme & data rate
height of the main antenna
Height of the remotes
distance of the remotes
building construction
other obstacles between


RE: Increasing Range of 868Mhz system


...wireless smoke/intruder detectors...

Are these the usual consumer version intended to be used within a single family dwelling? If so, then they're probably designed to provide reliable radio range of perhaps 30m. It's almost certainly 'too big an ask' to expect them to cover "multiple buildings or floors within construction sites" over perhaps hundreds of meters. There's a square function to face when trying to increase radio range.

If they're something different (designed for this application), then (as above) much more information is required.


RE: Increasing Range of 868Mhz system

Yes these are normal domestic intruder and fire detection devices. We have adapted these for use in the construction environment and they will be relocated once the fire risk has reduced (plasterboard and Ames Taping completed).
The problem we currently face is that although the trials were successful, it can be seen that we will need multiple control panels, batteries, signalling systems as the wireless detectors can currently only operate at best in a single block of say three town houses. I have begun a dialogue with the manufacturers to see if they can give us an interface to which we can screw in a suitable external antenna and I posted my question to see if this is likely to help.

From what I gather, if we were to install at the highest point and have a larger antenna then we may be able to increase range enough to perhaps halve the number of control panels we need which would be a good result.

While I have your attention, if manufacturer can not give us the interface for external antenna, is there any other way I could take the existing signal and boost it?


RE: Increasing Range of 868Mhz system

What's possible and what's practical are two different things. If one is trying to double the radio range, then one needs 6dB improvement; that magnitude of improvement might be practical. If one is seeking 10x the radio range, then one needs an extra 20dB. A 20dB high gain antenna is inherently directional, so it will need to be installed remotely; so you'll also need to make allowance for another ~6dB of cable loss. So 20dB perhaps becomes 26dB. All this is possible, but it's not really practical. It becomes a tangle of RF cables and is obviously unsuitable for practical use.

A better solution would be to employ a different technology for the 'Wide Area' side of the link. The alarm system panels must each have a discrete output for the alert (intended to be wired to a siren). This could wired to a more-suitable radio system to send the signal for several miles.  Some alarm systems have built-in cell phones that can be programmed to call out. But they incur a monthly cell phone fee.

RE: Increasing Range of 868Mhz system

One method for you to check max range is to get on top of your structures at their farthest points using your control panel and your sensor and see if a straight shot over the airwaves will work. Be able to physically move your units a little bit (sideways, up/down, rotating them) to see if the range is improvable.

what is your brand of intruder fire detection system? If we can access a specification of transmit power and receive sensitivity, it'd be simple to estimate what improvement you need.


RE: Increasing Range of 868Mhz system

The product we have adapted for use in this environment is made by HKC (www.hkc.ie)

The product code is SW-1070.

What I am keen to learn is if the manufacturer is not prepared to provide an interface for connecting bigger antennas then could we have this work carried out ourselves by commissioning an RF/electronic engineer assuming that a larger antenna would increase range?


RE: Increasing Range of 868Mhz system

Generally, it's not permitted to modify an unlicensed radio system to provide increased range. One sign of this policy is that such products typically either have permanently installed antennas, or the little antenna connector is intentionally made non-standard or unique.

The OEM / importer is very unlikely to participate in such changes.

Suggest you look again at the other options suggested above.

RE: Increasing Range of 868Mhz system

Thanks for the feedback, it has been invaluable. I think we will stick to installing multiple units to compensate for low range.



RE: Increasing Range of 868Mhz system

The sw 1070 says it uses 868 Mhz radio's for communications.

A half wave dipole would be 6.8" long.

Guessing they didn't want too much range, and used a simple inefficient antenna.


RE: Increasing Range of 868Mhz system

It seems so. They have also come back and said that they cannot retro-fit another antenna interface to device as it would require a complete re-design of the PCB. That's life.

Thanks for your assistance in this matter.


RE: Increasing Range of 868Mhz system

"Complete redesign" means they just don't want to bother.

If you have a spare sensor, and you're interested, since I'm a bored antenna engineer, send it to me and I'll add a free antenna to it. You could try it out.


RE: Increasing Range of 868Mhz system

Higgler, Just to be clear, we have the main panel which has the built in antenna then we have multiple battery operated smoke detectors with I'm assuming their own receivers. There is a wired "repeater" which connects to the main panel as well which can be used to extend the range of the main panel but the problem with it is that we need to run a cable to it through a build project which would get cut/damaged at some point. The repeater I'm assuming just contains the same antenna and circuit for the RF comms without any of the other control circuits in the main panel.

I could send you the repeater which if this works could then just be mounted next to the main panel thus negating the need for running a cable through the houses under construction.

Where can I send it?


RE: Increasing Range of 868Mhz system

It says in the documentation on the repeater these sentences;
"Up to 2 wired/wireless repeaters" and "wired or wireless"
per the bottom of this link (click on RF-Interface) http://secure.go2.ie/hkc/main/Products_Wireless.htm  

That means you don't need to wire it to your panel I believe. Just get it power somewhere else and it should extend your range.

It says antenna diversity too, so I'd guess they use two antennas at 868 Mhz. If you have the unit, peak if they gave you two antenna that are cylindrical and about 8" long. The unit would need two external connectors protruding from the box to attach the antennas. If not, the antennas are built onto the circuit board.  

There must be a brochure on how to use the repeater?


RE: Increasing Range of 868Mhz system

I can't remember why but using repeater in wireless rather than wired mode was not suitable for some reason and the manufacturer recommended we use the wired repeaters.

They do have two short thin straight antennas built in to the circuit board arranged vertically and horizontally.


RE: Increasing Range of 868Mhz system

The short thin vertical and horizontal antennas should be about 3.4 inches (or a little shorter) each (1/4 wavelength = 1/4 * (11.803"/0.868 ghz frequency). If for some reason they aren't that long, say they're one inch, that's a very inefficient antenna and you could improve it by making it longer. It's always possible someone just added some etched lines that fit on the circuit card and didn't do a real antenna design.

It might be worth a try to call the manufacturer and ask for technical support on how to setup the wireless repeater.

If they sell a repeater that is wireless, then it should work wirelessly. The only reason it wouldn't function is that the signals don't get to each antenna. i.e. inside metal building to outside of building, when it's very well sealed.

Don't trust a salesman to save you money.  

RE: Increasing Range of 868Mhz system

I will speak to them again. However, if my memory serves me correctly I think there were a couple of issues with the wireless option. The first was power consumption as the wireless had to constantly poll the main panel and the sensors resulting in battery needing replaced more often (we could just increase battery capacity). The second, although I could be wrong, was that the sensors were no longer visible/directly addressable. It's been a while since we discounted the option to use the repeater in wireless mode so I will check again as to why we came to this decision.

If it is not viable to use the repeater in wireless mode to extend range, can the additional antennas you mentioned earlier  be added to this type of device or is that not an option?


RE: Increasing Range of 868Mhz system

It might be worth trying the wireless repeater. After all, if they built it to extend range, it ought to do something.

Antennas can be added, but only if current antennas are proven not very good, otherwise you'd be wasting effort and get the same range.

In any link, transmit to receive, both directions, both antennas and both transmitter powers affect range. You really have two ranges mostly because power transmitted is different from each end.

To maximize coverage, you can try to improve one antenna (base station) and see if it helps. Both antennas improved gives max range. I expect the antennas in the sensors, if very small, may not be good antennas.

Are you going from inside metallized buildings to the outside of the building? What is you physical layout?

RE: Increasing Range of 868Mhz system

Layouts change as these are fire detection systems installed in buildings (flats and houses) under construction. The properties have devices installed in them after roof is put on and remain protected until the plasterboard and Ames Taping is done at which point the devices are relocated to next area and eventually another site where the cycle continues.

Construction material varies but more often than not its timber frame (foil backed), brick outside and often scaffolding to get through as well.


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