Jeremy Leach
Senior Member
I know there has been a lot(!) of discussion on Antenna design in previous posts, but in basic terms: Is a 1/2 wavelength whip antenna likely to give better results than a 1/4 wave whip, for my receiver?
'Simple' 433MHz question
- Thread starter Jeremy Leach
- Start date
You should get better performance with a half-wave. In the centre fed half-wave design you essentially have two quarter wave whips where the 'bottom' whip acts as the ground plane. Must be kept away from conductive surroundings for best performance.
(You can get variants where the bottom half is helical to shorten overall length.)
The end fed designs (physically neater) have a matching network feeding a single whip. You can add a ground plane for extra effect. They are easier to install too.
Check http://www.rfsolutions.co.uk/acatalog/Flexi_Whip_Antenna.html
for prices and sizes - and download the data sheets to get specs.
You might like to contact their experts for professional 'proper' advice.
And remember, putting a gain antenna on your transmitting end means you are very naughty and you may get shouted at by anyone nearby who is watching DTT.
Is a Yagi out of the question?
( I got some reasonable results out of an old Band A yagi with 50 ohm cable - yeah, yeah Gurus I know [yawn], but it worked. Not as good a pukka one but a fifth of the price!)
Edited by - dippy on 24/05/2006 08:47:02
(You can get variants where the bottom half is helical to shorten overall length.)
The end fed designs (physically neater) have a matching network feeding a single whip. You can add a ground plane for extra effect. They are easier to install too.
Check http://www.rfsolutions.co.uk/acatalog/Flexi_Whip_Antenna.html
for prices and sizes - and download the data sheets to get specs.
You might like to contact their experts for professional 'proper' advice.
And remember, putting a gain antenna on your transmitting end means you are very naughty and you may get shouted at by anyone nearby who is watching DTT.
Is a Yagi out of the question?
( I got some reasonable results out of an old Band A yagi with 50 ohm cable - yeah, yeah Gurus I know [yawn], but it worked. Not as good a pukka one but a fifth of the price!)
Edited by - dippy on 24/05/2006 08:47:02
Bet Stan would have loved to have answered this one! (but he is probably ‘swanning’ around China somewhere ha ha).
From the basic theory I learned (but never practiced), quarter wave antennas can be fed from one end (while the surrounding area at its base acts like a ground plane). On the other hand half wave antennas need to be fed from a point in the middle, and this feed point needs to be a balanced line (i.e. not coax).
So half wave antennas are more fiddly to connect-to (& bigger, obviously), but also can be more efficient when implemented correctly.
Hope I have got that right
From the basic theory I learned (but never practiced), quarter wave antennas can be fed from one end (while the surrounding area at its base acts like a ground plane). On the other hand half wave antennas need to be fed from a point in the middle, and this feed point needs to be a balanced line (i.e. not coax).
So half wave antennas are more fiddly to connect-to (& bigger, obviously), but also can be more efficient when implemented correctly.
Hope I have got that right
Jeremy Leach
Senior Member
I knew I shouldn't have asked ;-)
So it's not as simple as just doubling the length of my whip antenna ! I'll try it anyway and see if it helps.
In my 'real world' situation I'm tranmitting through my house and my receiver is very near a wall ! It works but I get quite a few lost receptions (Ok, so that doesn't suprise you !).
So it's not as simple as just doubling the length of my whip antenna ! I'll try it anyway and see if it helps.
In my 'real world' situation I'm tranmitting through my house and my receiver is very near a wall ! It works but I get quite a few lost receptions (Ok, so that doesn't suprise you !).
Thanks for jolting my memory on that Dippy.
But since driving a half wave antenna from one end is going to encounter high impedance, I think that a tuned coupling transformer is required. But in the process, at least that can also allow 50 ohm coax to be used.
I bet that Andypro would love to be saying something on this subject also (if here were on-line); as I think I recall him saying he has a communications background.
BTW Dippy, I liked your suggestion of a yagi.
And also, what do your mean by ‘DTT’ –I haven’t come across that term before –are you referring to Digital Terrestrial Television?
Surely it doesn’t mean Department of Telephone Tapping, or even <i>less </i> likely, Dippy’s Temper Tantrums!
Oh dear, I’ve got a crazy sense of humour, It’ll get me in trouble one day! <img src="smile.gif" width=15 height=15 align=middle>
Regards
Edited by - whizzer on 24/05/2006 09:59:44
But since driving a half wave antenna from one end is going to encounter high impedance, I think that a tuned coupling transformer is required. But in the process, at least that can also allow 50 ohm coax to be used.
I bet that Andypro would love to be saying something on this subject also (if here were on-line); as I think I recall him saying he has a communications background.
BTW Dippy, I liked your suggestion of a yagi.
And also, what do your mean by ‘DTT’ –I haven’t come across that term before –are you referring to Digital Terrestrial Television?
Surely it doesn’t mean Department of Telephone Tapping, or even <i>less </i> likely, Dippy’s Temper Tantrums!
Oh dear, I’ve got a crazy sense of humour, It’ll get me in trouble one day! <img src="smile.gif" width=15 height=15 align=middle>
Regards
Edited by - whizzer on 24/05/2006 09:59:44
Me? Tantrums? Never! I enjoy reading this forum too much. I was just remembering how I was reminded to read posts a couple of weeks ago. Can't remember who that was now...
Yes, I was rambling about Digital T TV.
My fiddling with 434 modules a while ago completely obliterated mine and the neighbours TV when I was closeby.< 10m. It was a bit of a joke really... after the shouting died down.
Though one thing I would mention is the benefit of ground planes. A case of No-Sh**-Sherlock to experienced users but often forgotten by many.
If you're using modules with RSSI then experiment.
And there's nothing like a nice big whip... or built-in matching networks on end-fed half-waves.
Edited by - dippy on 24/05/2006 11:26:24
Yes, I was rambling about Digital T TV.
My fiddling with 434 modules a while ago completely obliterated mine and the neighbours TV when I was closeby.< 10m. It was a bit of a joke really... after the shouting died down.
Though one thing I would mention is the benefit of ground planes. A case of No-Sh**-Sherlock to experienced users but often forgotten by many.
If you're using modules with RSSI then experiment.
And there's nothing like a nice big whip... or built-in matching networks on end-fed half-waves.
Edited by - dippy on 24/05/2006 11:26:24
BeanieBots
Moderator
Jeremy, the answer to your opening question is YES. Everything else is of course valid as well.
Jeremy Leach
Senior Member
Thanks Beaniebots, the concise answer I was looking for ;-)
BeanieBots
Moderator
Ahha, somebody has mentioned the elusive 5/8ths!
Please, please, please, could somebody explain to me how the 5/8ths works?
It certainly does, and very well too, but for the last 30 ish years I've never been able to work out how or why.
Please, please, please, could somebody explain to me how the 5/8ths works?
It certainly does, and very well too, but for the last 30 ish years I've never been able to work out how or why.
Before we nip off at another tangent...
I hope a 'better' antenna works, but within a building have you considered that loss of data may be caused by other things? e.g. Interference, multipath etc.
IF 'other things' have caused the problem then a bigger antenna may not cure it.
Have you cheched your RSSI for instance?
Have you tried a simple ground plane?
Edited by - Dippy on 24/05/2006 17:53:24
I hope a 'better' antenna works, but within a building have you considered that loss of data may be caused by other things? e.g. Interference, multipath etc.
IF 'other things' have caused the problem then a bigger antenna may not cure it.
Have you cheched your RSSI for instance?
Have you tried a simple ground plane?
Edited by - Dippy on 24/05/2006 17:53:24
Jeremy Leach
Senior Member
Dippy, I'm a real beginner when it comes to radio. So can you ,in a nutshell, describe a groundplane? I've just got my stripboard circuit in a wooden box with therefore no earthed chassis, which I would imagine would be the groundplane in most things??
So is my 'groundplane' at the moment the tracks of 0V in my stripboard? Would it help to have, say, a small metal sheet as a larger groundplane?
I'm content to avoid all the intricacies of radio as it isn't really my thing - well not at the moment - and I'm happy if these modules just 'work' ... although I'm prepared to do a simple mod if it helps !
So is my 'groundplane' at the moment the tracks of 0V in my stripboard? Would it help to have, say, a small metal sheet as a larger groundplane?
I'm content to avoid all the intricacies of radio as it isn't really my thing - well not at the moment - and I'm happy if these modules just 'work' ... although I'm prepared to do a simple mod if it helps !
Antennas work better if they can radiate against a ground plain.
A metal disk of 1/4 wave radius around the base of your 1/4 whip is ideal - although just about anything is better than nothing.
Your RF wire from module to your whip should be as short as possible unless you're using coax/microstrip (which is a better way to get the RF out of your product).
Easiest way, though not perfect, is get a bit of pcb or metal sheet, drill a big (>15mm) 'ole in it and get a bit of plastic and stick it over hole. Then drill a hole in the plastic to mount your antenna (is it a 4mm mount thread?).
Obv. if you can be bothered to etch pcb you can do this isolating ring.
Then circuit/module round to sheet/pcb and RF to whip. On Tx and Rx.
The 'hot' end of your antenna should be kept away from anything metallic.
Honest Guv, even a little GP will make a difference. The last time I was experimenting even a 2" square pcb ground-plane increased my RSSI by over 20% at 50 metres and I'm no radio genius.
And its cheap and easy.
Have you got RSSI o/p on your modules? Its a real quick way to check signal strength and then use your scope to look at quality and noise levels.
There are better antenna/gp alternatives which you can see on that little link I placed earlier.
http://www.radiometrix.co.uk/products/bim1/antenna_gnd.gif
Also, for bedtime reading have a look at:
http://www.radiometrix.co.uk/apps/apnt000.htm
These are application notes about RF modules that are highly readable.
A metal disk of 1/4 wave radius around the base of your 1/4 whip is ideal - although just about anything is better than nothing.
Your RF wire from module to your whip should be as short as possible unless you're using coax/microstrip (which is a better way to get the RF out of your product).
Easiest way, though not perfect, is get a bit of pcb or metal sheet, drill a big (>15mm) 'ole in it and get a bit of plastic and stick it over hole. Then drill a hole in the plastic to mount your antenna (is it a 4mm mount thread?).
Obv. if you can be bothered to etch pcb you can do this isolating ring.
Then circuit/module round to sheet/pcb and RF to whip. On Tx and Rx.
The 'hot' end of your antenna should be kept away from anything metallic.
Honest Guv, even a little GP will make a difference. The last time I was experimenting even a 2" square pcb ground-plane increased my RSSI by over 20% at 50 metres and I'm no radio genius.
And its cheap and easy.
Have you got RSSI o/p on your modules? Its a real quick way to check signal strength and then use your scope to look at quality and noise levels.
There are better antenna/gp alternatives which you can see on that little link I placed earlier.
http://www.radiometrix.co.uk/products/bim1/antenna_gnd.gif
Also, for bedtime reading have a look at:
http://www.radiometrix.co.uk/apps/apnt000.htm
These are application notes about RF modules that are highly readable.
Jeremy Leach
Senior Member
Thanks Dippy. I'l take a read of those links soon. Fyi here's the module I'm using (which is the standard Maplin Tx/Rx pair that a lot of people will be using) <A href='http://www.rfsolutions.co.uk/acatalog/DS016-12_AM-HRR.pdf' Target=_Blank>External Web Link</a>
RE Groundplanes: Tey can turn a bad antenna into a mediocre one, and a good antenna into a fantabulous antenna! You really dont even need a solid disk (though it IS the most efficient). At least 4 radial pieces of wire (each 90 degrees apart) at the bottom of your antenna should help. The more you put in, the better off you are.
RE the 5/8 wave: well...I honestly have no REAL idea. If I had to fathom a guess...a 5/8 wave is exactly twice the aperture of a true isotropic antenna (I'm pretty sure that's a circle 5/16 of a wave wide), so it would reason that it should have at least some gain over an isotropic antenna. Kinda like making a 1/4 wave whip into a 1/2 wave vertical dipole? I may just be grasping at straws, but it seems to make sense to me.
--Andy P
RE the 5/8 wave: well...I honestly have no REAL idea. If I had to fathom a guess...a 5/8 wave is exactly twice the aperture of a true isotropic antenna (I'm pretty sure that's a circle 5/16 of a wave wide), so it would reason that it should have at least some gain over an isotropic antenna. Kinda like making a 1/4 wave whip into a 1/2 wave vertical dipole? I may just be grasping at straws, but it seems to make sense to me.
--Andy P
Uhm...ok. I can edit my own post..grrr. It keeps timing out, but I can make a new one, so here it goes. I found this website:
<A href='http://k9erg.tripod.com/theory.htm' Target=_Blank>External Web Link</a>
Scroll down and find where it says "7. Elevated vertical antennas:" and the first thing it goes into is the 5/8 wave vertical.
--Andy P
<A href='http://k9erg.tripod.com/theory.htm' Target=_Blank>External Web Link</a>
Scroll down and find where it says "7. Elevated vertical antennas:" and the first thing it goes into is the 5/8 wave vertical.
--Andy P
I can't see why you're fascinated with verticals for 433MHz use, since at this UHF frequency directional antenna are compact & a breeze to make!<A href='http://www.picaxe.orcon.net.nz/yagi433.jpg' Target=_Blank>External Web Link</a> Although praised for VHF omnidirectional work, 5/8 whips just have lower angle radiation & "waste" your modest tx output by radiating it in all directions -when receiving they'll also pick up unwanted interference. Most of these 433MHz Tx are 5-10mW & as ISM regs. allow 25mW ERIP then a boosting Yagi style antenna is legal & far preferred if point to point. You could even use a parabola, although it'd have to be large (~1m) since a 70cm wavelength! UHF signals punch thru' modest wooden/plaster walls OK, so is there any blocking metal in yours? Maybe other ISM devices nearby -garage door openers etc?
Typically simple breadboarded DS18B20/08M setups yield ranges to 50m (doubled with cotanga Yagi) in NZ suburbs. A simple "store & forward " repeater gets around dead spots & gave 200m even with simple 1/4 wave whips => www.picaxe.orcon.net.nz/433rpt.jpg <A href='http://www.picaxe.orcon.net.nz/433rpt.jpg ' Target=_Blank>External Web Link</a>. The "rubber duckie" antenna on the Tx shown in fact came inbuilt, & worked a treat. These units were only ~£2 each from a NZ schools supplier as well!
Elevated cotanga Yagis both ends can push ranges to ~1km. Perhaps solar power the repeater? If at all possible borrow a UHF scanner with a signal strength meter to assist in antenna tweaking & positioning. Naturally <b> s l o w </b> the data rate (300bps?)if signals are weak.
A very important range issue is that some of these cheapie 433 units have deaf receivers! READ THEIR SPECS! The Maplin Rx seems a puny -90dBm RF sensitivity, meaning only strong nearby signals will be heard. I've worked with many 433 offerings & some are much more sensitive than others. Tx output varies too. Many Rx modules are VERY picky about the supply voltage range, typically only working with 4.5-5.5V. The usual Picaxe 4.5V is hence marginal, with 4 x NiCds (4.8V) better.
I penned several Silicon Chip articles (Dec.05/Jan.06) covering 433/08M applications. These concentrated on Jaycar's KeyMark offering (RXB1)<A href='http://www.jaycar.co.nz/products_uploaded/ZW3102(mod).pdf ' Target=_Blank>External Web Link</a>which, although more costly (~£4), has a superior -104dBi Rx sensitivity. Even that is puny beside some (Chipcon etc ~-120dBi) which can work over miles. Every 6dB gain is equiv. to range doubling, so hence 18dB system gain yields 2x2x2 =8 times the range. Article teasers =><A href='http://www.siliconchip.com.au/cms/A_105581/article.html' Target=_Blank>External Web Link</a> and <A href='http://www.siliconchip.com.au/cms/A_105744/article.html ' Target=_Blank>External Web Link</a>
Stan-ham since 1966(ZL2AJZ), back when antenna (3.5MHz)were the size of trees...
Edited by - stan. swan on 25/05/2006 00:19:49
Typically simple breadboarded DS18B20/08M setups yield ranges to 50m (doubled with cotanga Yagi) in NZ suburbs. A simple "store & forward " repeater gets around dead spots & gave 200m even with simple 1/4 wave whips => www.picaxe.orcon.net.nz/433rpt.jpg <A href='http://www.picaxe.orcon.net.nz/433rpt.jpg ' Target=_Blank>External Web Link</a>. The "rubber duckie" antenna on the Tx shown in fact came inbuilt, & worked a treat. These units were only ~£2 each from a NZ schools supplier as well!
Elevated cotanga Yagis both ends can push ranges to ~1km. Perhaps solar power the repeater? If at all possible borrow a UHF scanner with a signal strength meter to assist in antenna tweaking & positioning. Naturally <b> s l o w </b> the data rate (300bps?)if signals are weak.
A very important range issue is that some of these cheapie 433 units have deaf receivers! READ THEIR SPECS! The Maplin Rx seems a puny -90dBm RF sensitivity, meaning only strong nearby signals will be heard. I've worked with many 433 offerings & some are much more sensitive than others. Tx output varies too. Many Rx modules are VERY picky about the supply voltage range, typically only working with 4.5-5.5V. The usual Picaxe 4.5V is hence marginal, with 4 x NiCds (4.8V) better.
I penned several Silicon Chip articles (Dec.05/Jan.06) covering 433/08M applications. These concentrated on Jaycar's KeyMark offering (RXB1)<A href='http://www.jaycar.co.nz/products_uploaded/ZW3102(mod).pdf ' Target=_Blank>External Web Link</a>which, although more costly (~£4), has a superior -104dBi Rx sensitivity. Even that is puny beside some (Chipcon etc ~-120dBi) which can work over miles. Every 6dB gain is equiv. to range doubling, so hence 18dB system gain yields 2x2x2 =8 times the range. Article teasers =><A href='http://www.siliconchip.com.au/cms/A_105581/article.html' Target=_Blank>External Web Link</a> and <A href='http://www.siliconchip.com.au/cms/A_105744/article.html ' Target=_Blank>External Web Link</a>
Stan-ham since 1966(ZL2AJZ), back when antenna (3.5MHz)were the size of trees...
Edited by - stan. swan on 25/05/2006 00:19:49
Jeremy Leach
Senior Member
Thanks for all the info .... I'm sure it will be a good reference for people's Tx / Rx problems in the future too.
As I said at the start it's not that it doesn't work, I just miss a few receptions so was only after some simple tips to make things better. I don't think it warrants any major antenna design. And like I say, I'm not too into this side of things, at the moment, so I'm happy to treat this area as a 'black box' and if it works then fine ;-)
I'll try a ground-plane and experiment with different length antenna and see if it helps capture those lost transmissions ! Thanks again for all the input though. I may well get more into all this in the future.
As I said at the start it's not that it doesn't work, I just miss a few receptions so was only after some simple tips to make things better. I don't think it warrants any major antenna design. And like I say, I'm not too into this side of things, at the moment, so I'm happy to treat this area as a 'black box' and if it works then fine ;-)
I'll try a ground-plane and experiment with different length antenna and see if it helps capture those lost transmissions ! Thanks again for all the input though. I may well get more into all this in the future.
Hi Jeremy
A further thought as this thread reaches its conclusion.
Dippy suggestion was a good one –particularly as it keeps the antenna compact.
And if you firstly just want to experiment with trying different antenna lengths, give ¾ wavelength a go. It’s not entirely the same as ¼ wavelength, but has similar feed characteristics (impedance-wise), and will have the natural advantage inherent with longer lengths. Also, (I’m not sure if anyone mentioned this), but best results would be obtained if both your Tx & Rx antennas are upgraded. (i.e. not just one)
All the best on this!
Regards
A further thought as this thread reaches its conclusion.
Dippy suggestion was a good one –particularly as it keeps the antenna compact.
And if you firstly just want to experiment with trying different antenna lengths, give ¾ wavelength a go. It’s not entirely the same as ¼ wavelength, but has similar feed characteristics (impedance-wise), and will have the natural advantage inherent with longer lengths. Also, (I’m not sure if anyone mentioned this), but best results would be obtained if both your Tx & Rx antennas are upgraded. (i.e. not just one)
All the best on this!
Regards
BeanieBots
Moderator
andypro, thanks for the link. It has at last pointed me towards the theory behind the 5/8ths.
Thanks also to Stan for some practical tips on my personal favourite the "cotanga" yagi.
Thanks also to Stan for some practical tips on my personal favourite the "cotanga" yagi.
Might be a long way to go for Jeremy to get a Keymark. I think you're UK based Jeremy?
If J does do another project it might be worth looking at the offerings from RFSolutions / Radiometrix /LPRS.
Quite a good range with good specs and many of the FM modules have the RSSI output which is very handy for testing your antenna and for duty-cycling.
Check out the BIM modules for a legally healthy range at a reasonable cost. A bit more than 4 nicker though. Cheapskates need not apply.
Happy modulating.
If J does do another project it might be worth looking at the offerings from RFSolutions / Radiometrix /LPRS.
Quite a good range with good specs and many of the FM modules have the RSSI output which is very handy for testing your antenna and for duty-cycling.
Check out the BIM modules for a legally healthy range at a reasonable cost. A bit more than 4 nicker though. Cheapskates need not apply.
Happy modulating.
Jeremy Leach
Senior Member
Yes I'm UK based. I don't want to give the impression I'm not too interested in all this radio malarky .... I've just got too many PICAXE related interests to cope with at the moment ! So am limited to trying just a few simple things to see if there's improvement. I'll probably have a go soon.
Jeremy Leach
Senior Member
Finally got the chance to experiment, and happy to say that a 5/8 wavelength antenna and a rectangular bit of aluminium foil acting as a ground plane has made a big difference - so just saying a belated thanks for those simple tips.