Choosing wireless

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Dippy

Moderator
I've never heard of them. There are so many.

The trouble is that people (including me) read the spec and believe it.

There are so many things that can/will affect performance.

For a start, 433 to 434 MHz is very popluar. At the extreme of range the signal will be iffy and easlly intefered with.
In my location I'd avoid 433/434. I did a survey with a scanner and it's a little busy around me.

Then we have non-omnidirectional performance, so you may get 1000m in one direction but not another.

Range claims from manufacturers/vendors are often the absolute best range when tested on the dark side of the moon... and going downhill.

Then, finally, there is YOUR ability to optimise an RF design....
If you make a mish of it then you'll ruin the potential.


Those modules may have a proprietry comms chip like a MRF49 or TI1101 or whatever , so a lot of the tricky stuff is done for you.


I'm not going to start blathering on about how I got 1007metres using a Faith transmitter with half my kitchen cutlery attached to it, but all I'll say is don't be surprised if your actual range is a lot different to what it says on the tin.

Just buy a few and have a go. It's only (your) money ;)
You may be disappointed or you may get greater range than claimed.

Are the sites fixed? Can you have a yagi on the Rx?
 
S

srnet

Senior Member
cdngunner said:
Well I am doing a little project and need to select a wireless unit that can transmit to 1km
Click to expand...
2nd what dippy says.

433/434 is a noisy part of the spectrum although its a lot quieter out in the countryside.

I have tested a 434Mhz module as a lost model alarm locator, not transmitting data per se, just listening for audio tones, on a amateur 70cm tranciever (which is quite sensitive)

The flat, relativlely unobstructed range of the loacator was maybe 750M.

I would guess the (reliable) data transmission range to be substantially less than that, and even shorter in any type of built up area.

The main issue is the power restriction, which is 10mW for licence excempt devices IIRC.

Although if the TX is in an elevated location and you use a large yagi (ZL specials are shorter) you might get 1km.
 
hippy

hippy

Ex-Staff (retired)
If choosing between two modules I'd set aside whether it will work or not, and judge each module on their comparative strengths. (A) would be the winner for me because it does more on-module whereas with (B) you'll have to do all that yourself and you may not do it as well as they have. Though twice as expensive, that cost would likely be eaten up in time and effort of adding what they already provide.

Whether either module is any good, lives up to expectations, or there's something better I couldn't really say. An answer really depends on what aspect you want the module assessing; ease of use, capabilities or performance.
 
C

cdngunner

Senior Member
This would be used on a firing line. So it will both be isolated and unobstructed. All I need is to have one unit transmit and the other recieve. I will be transmitting 3 bits; left, right and stop.(for now)

Easily enough done with a pic except I have done very, very little with RF.

So so much to learn and so little time left......
 
D

Dippy

Moderator
Aha! Late with the proverbial homework are we? Tsk Tsk ;)


Have you:-
a) Searched this, or other, micro Forums to see if the modules have been used?
b) (if so) have you got people's comments on performance and how to squeeze out the best.
c) Looked on an any Forums anywhere to see if these units have been used reliably?
d) Contacted the vendor or manufacturer for ideas on range claim reliability and optimising?

If you haven't then it's worth a look. If there is no info around, then, well, you can be the first.... :)


If the project is crucial and with a looming deadline then, if you haven't time to play, then you will have to dig your wallet out and buy modules which are KNOWN to work over those ranges.


I'm sure you'll get some replies saying I've used a Yingtong plus the wife's underwired bra at over 1km on a sunny day, but unless you have time (and budget) to experiment then it ain't much use.
And, as you know, your physical arrangement (ground planes, antennas) will play a huge role.

Of course there are devices around that will EASILY achieve what you want - but I guess you have a tight budget. Most PICAXE Forumites do. ;)

Again, if your sites are fixed, then a yagi antenna (or a.n.other gain design) can make a huge difference. (Direction, gain, s/n etc.)
Yagi's are usually only allowed on the Rx end .
It could solve your problem.


I've used RF Solutions T7G and R7G reliably at 400m with hedges, trees and fat people in the way. I used simple whips and the data was reliable. They claim 1000m range on their Data Sheets. Maybe with greater care in matching and using a fancy gain antenna and PCB design I could have achieved that.
The nice thing about RF Solutions (and other pukka Manufs) is that they have brains, speak English and don't bullship.
An email to them could extract some useful info.
Go to the Horse's Mouth (regardless of manufacturer).
Good luck (or spend the money!)
 
C

cdngunner

Senior Member
Dippy said:
Aha! Late with the proverbial homework are we? Tsk Tsk ;)

Not really just have so many pokers in the fire I dont know which one to pull out first

If the project is crucial and with a looming deadline then, if you haven't time to play, then you will have to dig your wallet out and buy modules which are KNOWN to work over those ranges.

No, no deadlines. i'm looking into this as a favour for one of my gun buddies

Of course there are devices around that will EASILY achieve what you want - but I guess you have a tight budget. Most PICAXE Forumites do. ;)

Ah, its never my budget thats the problem, its the tightwads that ask me to do things :)
Again, if your sites are fixed, then a yagi antenna (or a.n.other gain design) can make a huge difference. (Direction, gain, s/n etc.)
Yagi's are usually only allowed on the Rx end .
It could solve your problem.

Yes it may very well....
Click to expand...
Thanks for all your input.
 
M

manuka

Senior Member
I've made many past posts on 433 MHz options, & yet again stress that this is VERY big field with numerous trade offs. Furthermore local 433 MHz interference may blanket the band, while rural sites may be cursed with terrain obstacles. However the very nature of a rifle range should at least mean the RF link is essentially line of sight!

It's STRONGLY advised that serious projects evaluate offerings (including technical data sheets,others experiences & personal real world testing) before bolting them into a design. Aside from ones budget,such issues arise as Tx power (25 mW usually allowed), modulation type (GFSK considered best),adjustable data rates (slower usually gives superior ranges), receiver sensitivity (aim for at least -110 to 115 dBm),stand by current drain, physical size, supply versatility (some insist on 5V),inbuilt error correction & ESPECIALLY configuation ease. The latter can be a NIGHTMARE...

Many Asian sourced modules can be rebadged under other names,so it's worth checking the original makers specs & prices. Both these SparkFun offerings are from Shenzhen (over the border from Hongkong) & A. looks from HAC while B. Appcon. Although I'd no real hassles (yeah-magic touch) these Appcon modules have been reported as buggy with return rates high. The HAC UM12 is known to have a very sensitive receiver,but it's now an older module.

In fact this makes a point- crowded Asian cities find sub GHz bands (usually 433 MHz) better than 2.4 GHz for utility monitoring & newer modules with superior specs. & easier config (inbuilt USB) are continually being produced. Hence ensure offerings being promoted here in the West are not just factory runouts!

FWIW I'm increasingly tending to 850-950 MHz slots, as these higher freqs.(usually ~868MHz or 915 MHz) allow greater TX powers, more B/W, reduced spectrum noise and compact higher gain antenna. HopeRF, MicroChip,Nordic,ChipCon (CC=TI) & SiLabs & the like all have raw offerings in the US$10 range.
Stan.

Footnote: This picture free post respects Dippy's sensibilities.
 
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moxhamj

New Member
That second one has an interesting feature where they say it tries at 19200 but if it fails it drops back to 1200. That is the way fax machines work, where they test the line first to see what is the best speed they can get.

There are many modules around now. Whatever you buy, the same RF rules apply, ie line of sight, and the higher the antenna the better.

Please keep us posted with the results of your experiments.
 
J

john2051

New Member
Hi,
As quite a few people here point out, range using 430mhz is very quirky. As a licenced radio amateur I regularly use 433.050mhz at 5 watts into a helical antenna. Sometimes I cannot speak to someone much more than a mile away, and moving about in the room can make a difference. In general, and to a point, the lower the frequency theres less chance of buildings affecting performance. The other option is to use directional antennae.
The other problem with 433mhz is that most car keys use this frequency (433.92).
Hope this helps...
best regards john
 
C

ciseco

Senior Member
4 suggestions for you in 968/900Mhz

The XRF in tests will do 570m at 250Kbps, if you slow the over the air data rate down (software setting) the recieve sensitivity goes up, so that might do it in one hop.

Another way which will certainly work is have 3, the one in the middle, you can in software, switch to repeater mode.

Last way on an XRF is replace the wire whip with sma connectors and use a directional antenna with higher gain, you'll not need a great deal to clear 1Km

Last suggestion would be the maxstream xbee pro 868/900, they claim something really high in 10's of km's with appopriate antennas.

Miles
 
P

papaof2

Senior Member
srnet said:
I was testing the Lost Model Alarm I built on 434.075Mhz, and had and left it on in my pocket.

Car door would not open.
Click to expand...
I tested some "generic" 443MHz units from ebay and found that having the transmitter on n the basement would block the garage door receiver (about 30 feet away horizontally and 15 feet away vertically, through a couple of walls and a floor). The original garage door remote had to be less than a foot away from the garage opener receiver to be recognized.

I only use these transmitters when they are to be turned on for a transission and then turned back off. For some reason, my wife didn't appreciate the range tests I was running ;-)

John
 
M

manuka

Senior Member
FWIW: Naturally local band noise can threaten to desensitise a receiver,but I've had numerous 433 MHz devices running here over the last decade without experiencing such behaviour!
 
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