433MHz Radio Links in Australia

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westaust55

Moderator
Initially some theory that may be of interest to others, and then a question at the end for our more radio orientated members.

Having late last year purchased some 433.92MHz Keymark Tx and RX modules from Jaycar, I did some research and Googling to find out a bit more about any limitations of use.

While there are a number of threads on this forum, most discuss the maximum range for their modules and maybe the length of a simple piece of wire as an antenna.

I did find an Instructables article by Dr Acula who set up a dipole antenna for greater distance with a PICAXE project. Research suggested that a 1/2 wave dipole has a gain of 2.15 dBi (in free space – read as "well above the ground").

Manuka (Stan) also has an article in the Silicon Chip Magazine for Jan 2006 on this topic. In this article Stan mentions:
YES! – it’s legal, as the only Australian/NZ 433.92MHz LIPD ISM regulatory restriction is that the transmitter should not exceed 25mW EIRP (Effective Isotropic Radiated Power).
Click to expand...
In January 2009, The Australian Govt issued a new variation to the Class License as:
“Radiocommunications (Low Interference Potential Devices) Class Licence Variation Notice 2008 (No. 1)”.
Under item 17, for the 434MHz band, the same 25mW EIRP still applies.

Started thinking about possible extension of the dipole antenna to a small Yagi antenna with say 3 elements (add a reflector and director) to be able to cover some distance and penetrate several brick walls.

The mandatory EIRP is calculated using this formula:
EIRP = Pout + Gt – Ct
Where:
Pout = transmitter power output (dBm)
Ct = signal loss in cable (dB)
Gt = gain of the antenna (dBi)​

The Jaycar sold 433MHZ transmitter module has a rated Output power of 3 dBm with Vcc = 3 V into a 50 Ohm load.

Lets say I have a few metres of Low loss RG-213, 50 Ohm coaxial cable (available from Dick Smith). Attenuation will be around 0.5 dB for 3 metres.

Conversion from mW to dBm gives: 25 mW = 13.97940008672 dBm

Therefore, from EIRP = Pout + Gt – Ct
we get Gt = EIRP – Pout + Ct
so, Gt = 13.9 – 3 + 0.5 = 11.5 dBi

Reference to some Amateur (ARRL) type/member sites suggest the a 3 element yagi antenna has a theoretical gain of around 8 to 9 dBi in free space, but other sources/calc suggest typical as ~ 7 dBi and as low as ~5 dBi.

So in theory, a small(ish) 3 element Yagi antenna could be used and still remain within the relevant regulations. By smallish the overall width would be around ~360mm (reflector) and the beam length around ~140mm which is still very portable (to me at least).

For those who are interested, here are some Australian Govt based links on the topic.
http://www.acma.gov.au/WEB/STANDARD/pc=PC_2643

http://www.acma.gov.au/WEB/STANDARD/1001/pc=PC_2633


http://users.bigpond.net.au/vk3yng/lipd/aca_resp01.htm
Note that Australia is part of ITU Region 3.
The band 433.05 to 434.79 MHz is not a designated ISM band in Australia.


Noting that some others have amateur radio experience, here is the question:

Can anyone see any flaws in my thoughts/calcs before I dash out and buy some hardware to make a “better” antenna ? :confused:




EDIT:
some further information for those in Australia (from Australian Communications Authority correspondence):
The band 433.05 MHz to 434.79 MHz is shared by amateur radio, low-powered applications and the
radiolocation service. The radiolocation service is the only primary service in this band. Other services
operating in this band must not cause harmful interference to the primary service, and are not afforded
protection should they receive harmful interference from that primary service.


also for reference:
ISM Band = The Industrial, Scientific and Medical (ISM) radio bands were originally reserved internationally for non-commercial use of RF electromagnetic fields for industrial, scientific and medical purposes.
 
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D

Dippy

Moderator
A note to UK Amateur hobbyists.
AFAIK is it illegal to use 'gain' antennas on little TRANSMITTER modules.
Perfectly fine for Rx.
Always read the module Data Sheets re: power output and recommended antennae.
Only take notice from reputable manufacturers and the DTI.

So, put your Yagis away.
OK Boo Boo.

PS. If the law has changed or there are exemptions then please add notes - as I'd like to know too.
 
G

Gavinn

Member
Dippy,

You are right, the UK law doesn't allow any gain antennas on these devices. Some do come with external antennas but they really shouldn't.

Being a licensed amateur radio op in the UK we sometimes have fun with these devices, upto 200 watts (license allows 400 watts) of fun and big antennas!

The problem we normally find though is their lack of filtering on RX and therefore rejection to amateur transmissions. Even transmitting at 5w into a 1/4 vertical can block remote central locking to most cars upto 200m, with a new wave of amateur D-Star (digital) repeaters being deployed in the UK around those frequencies we have already experienced issues and have had to move repeater input frequencies as a consequence.

The new police, ambulance and fire brigade Airwave system is just below 430MHz and has the same effect - they won't move their frequencies if there are issues!

The joys of a shared band.
 
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manuka

Senior Member
6dB antenna gain with 3-4 element Yagi is pretty normal at UHF freqs. While not as compact or critical as 2.4GHz, 433 MHz antenna are tolerant & cheap to work with, & feed line losses modest. UHF TV antenna can be hacked to suit of course too. N.B. Although at ~ -105dBi they have a superior Rx to many 433 MHz cheapies, for serious use go for something better than those Jaycar "Keymarks". Consider HopeRF tx/rx units perhaps?

When PICAXE + 433 MHz showed itself feasible, to stimulate wireless interest I rustled up a simple educational "coatanga" => www.picaxe.orconhosting.net.nz/yagi433.jpg, with diverse versions also built around compacting telescopic whips. Such simple DIY creations can be tweaked endlessly, & decent Z matching organised as well - even consider attaching the tx on the antenna boom itself?

Have you checked ham "70 cm" antenna designs? Rather than just rushing out & buying a stash of hardware,I 'd first suggest reading/browsing about overall UHF propagation features as well. Man-made noise may be less, but path losses increase. Although not as picky as microwaves, UHF signals are enhanced with elevated antenna & few path obstructions too. Many UHF features can be quickly verified with a pair of hand held 470MHz "PRS" UHF CB sets by the way. "Hello 1 this is 2. I am speaking to you from beside a metal shipping container, & am X mm away from the reflective walls. How does my signal alter with reflective distance changes?"

And speaking of 470MHz -did those new Oz. regs. mention changes to the crazy "3 secs an hour" UHF CB data restriction? Stan (ZL2APS)

EXTRA: Those Jaycar tx/rx units need ~5V on the receiver, & will not operate under 4.5V, but the tx supply is flexible from ~3V-12V. I've not bothered pushing it myself, as I usually run them from a 3 xAA PICAXE supply, but reports indicate tx output can be significantly boosted at higher supply voltages. This may be worth some careful testing!! Jaycar had these supply figures shown incorrectly for some years, both catalog. & web site.
 
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W

westaust55

Moderator
Thanks for the feedback/comments Manuka.

Have subsequently found a few more ACMA related documets while searching further but did not spot anything about the
"3 secs an hour UHF CB data restriction? "

Likewise in view of Dippy's comments I did some more searching on LIPD devices and permissible antenna. Virtually nothing found on the topic of allowed antenna - it all seems to come down to the maximum output of 25mW EIRP.


Have downloaded during last week several free programs that cover antenna design. Also some others on the web with Javascript interfaces for on line calcs.

Some minor variation but seems it is as much a function of spacing and element diameter from my reading. Your "coatanga" antenna using terminal strip for securing elements to the beam is a good idea.

As I have the Jaycar Keymark modules, I will start with those and will move to the HopeRF modules at a later date.
 
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westaust55

Moderator
433MHz and other UHF radio module tips

Here are some tips I spied at the website of UK based RF module supplier RF Solutions

http://support.rfsolutions.co.uk/faq/content/4/58/en/rf-design-tips.html

RF Design Tips
Here are some design tips to bear in mind when using RF modules in circuits.

1. Whenever possible avoid using bread-board or strip-board with RF modules
The long tracks inside these types of prototyping board introduce large capacitances /inductances to the circuit which can badly distort / detune RF signals.
Ideally prototype or evaluation PCB’s should be used.

2. Tracks connected to the antenna (RF input / output) pin of transmitter and receiver modules should be as short as possible.
Any conductor connected to this track will act as an antenna, so it will lengthen and detune the actual antenna.

3. Design PCBs with an adequate ground plane.
A ground plane is an area of conductive PCB connected to the circuits ground. It helps with RF propagation and is generally better when placed perpendicular to the antenna.
It should be placed on the PCB in a large area, however it should not be placed directly underneath the RF module.

4. Use decoupling capacitors on the power supply circuitry to prevents RF interference passing through the power lines.
Low power modules work on high frequencies, eg. 433MHz, so the capacitors should be of small value, eg 10nF, to cut out high frequency interference.

5. Use smoothing capacitors and a regulator to ensure a stable constant supply.
Click to expand...
 
D

Dippy

Moderator
Re: Gain antennas. Yes, I guess that is more precise way of putting it. I haven't got the time to search for the original data.

Blimey, I posted that link a week or two ago. Great minds think alike ;)
 
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vk6bgn

New Member
Oh, this will be interesting. Hanging Yagi antennas with gain off of these 433 Mhz. UHF modules. Fascinating.... not to stop anyone from having fun with them, but beware, if you unknowingly start interfering with UHF 70cm repeaters, Fast Scan TV, UHF weak signal SSB reception etc. etc. in the 70cm Amateur bands, you'll more then likely to have a car resembling a porcupine with a dozen antennas on it and two or three extremely knowledgeable but geeky looking gentlemen with black plastic rimmed coke bottle thick glasses and hand held radios hanging off their belts politely knocking on your front door to discuss possible ways to eliminate the interference. These gentlemen are not the Federales, but rather some of the Amateur Radio communities finest.

If you are interfering and leave your transmitter on for any length of time, they, the men with the thick glasses, will probably arrive at your HQ within a matter of minutes, rather then hours. Some of them are quite good at radio detection finding. This is actually part if their hobby. Some have even built their own Doppler radio detection systems. No need for two receivers to triangulate the source anymore!

Have Fun.
"The Addict"
 
K

KIGX

Member
One point that I haven't seen mentioned too much is matching the antenna to the transmitter frequency/feedline. Manuka points in that direction when he mentions Z matching. A mismatched antenna system will result in reflected power from the antenna and an SWR (standing wave ratio) greater than one. In that case you won't be emitting as much power as you would like. The antenna should be trimmed under real conditions to give an SWR near 1 but for most of us that's too much work or too difficult - need an SWR meter of some sort. Bottom line would be that if the antenna is waaaay off frequency then you could damage the transmitter but if you build it to reasonable theoretical specs you'll be close enough but probably not with an SWR = 1. You won't be radiating as much power as you think based on theory so I might just go ahead and add that extra element or 2 to the yagi to make up the difference and I'd wonder who would notice...
 
K

KIGX

Member
To: Hamradioaddict:

OK, so maybe in Australia you'll get noticed.

You beat me to the send button..
 
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vk6bgn

New Member
About 15 years ago I was "noticed" while living in Hesperia, California. Unknowingly to me, my 1 watt 900Mhz. Amateur Radio Fast Scan TV transmitter, 10 watt 2C39 valve amplifier and 15 element Yagi antenna were not up to scratch and eventually two well dressed gentlemen (radio technicians) from Edwards Air Force base visited my QTH and ever so politely asked me to cease transmission until I cleaned up my transmission. :( Seems I was interfering with some sort of RADAR or ground RADAR or something there of, even though my antenna was 20 miles away from the USAF base and pointed almost 180 degrees in the opposite direction.

So it is possible to interfere with other services sharing the same spectrum and have visitors to you home. ;)

"Hammy"
 
W

westaust55

Moderator
KIGX said:
One point that I haven't seen mentioned too much is matching the antenna to the transmitter frequency/feedline. Manuka points in that direction when he mentions Z matching. A mismatched antenna system will result in reflected power from the antenna and an SWR (standing wave ratio) greater than one. In that case you won't be emitting as much power as you would like. The antenna should be trimmed under real conditions to give an SWR near 1 but for most of us that's too much work or too difficult - need an SWR meter of some sort. Bottom line would be that if the antenna is waaaay off frequency then you could damage the transmitter but if you build it to reasonable theoretical specs you'll be close enough but probably not with an SWR = 1. You won't be radiating as much power as you think based on theory so I might just go ahead and add that extra element or 2 to the yagi to make up the difference and I'd wonder who would notice...
Click to expand...
KIGX,

Yes you are right. I do have the antenna matching side in hand with a balun.

While I have done nothing in over 20 years in radio some past exploits included:

1. As a hobby, legal 27MHz back in late 1970's using a 100m x 50m inverted "V" metal sheet as a ground plane with a whip antenna on the edge of a 130m high cliff looking over the ocean and daily talking into Japan, Queensland, Northern Territory and USA .

2. Set up a 1GHz link over 120km with no intermediate repeaters driving 250Watts into each of two (from memory) 5m x 3m gridpak dish at each end. Bouncing the signal of the troposphere interface.
In fact had to inform the local light aircraft in the district not to fly within 500 metres of the forward side of the antenna as it was deemed that the fluid in their eyes would boil (microwaved) in the time it took to cross the radio beam.

But for now it is just some simple experiments with 433MHz and a couple of PICAXE. :)
 
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stocky

Senior Member
Still 3 sec per hour on UHF CB Manuka....but we are working on them!

Speculation is that it was *supposed* to be 3 sec per 60sec not 60min and a typo crept in - and none of the bureaucrats wanted to take responsibility for the mistake so it became law as it was!

ahhh the joy of government depts!
 
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manuka

Senior Member
Stocky- glad you've survived the recent big heat! I'd heard that PRS CB typo tale before & believe it's true, epecially since 3/60 = a neat 5%. Is your new workshop in place yet?

HRA: I've done my share of foxhunting RDF signal tracking as a ham of 40 years standing, much of it at HF & VHF, & especially recall TVI issues back in the early colour days. At just 25mW the power levels on 433.92MHz gear are so puny that few hams would bother hobby users, & as that ISM spectrum slice is often so festooned with "dawn chorus" signals, regular 70cm hams tend to stay clear of it. Stan (ZL2APS)
 
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manuka

Senior Member
Only 16 years- I've over twice that awaiting my attention! At least digital cameras can now readily snap pix of old paperwork.
 
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westaust55

Moderator
433MHz transmitter on AXE021 board

Have assembled a circuit on the proto area of an AXE021 board,
circuit includes:
- LDR for light level
- DS18B20 temp sensor
- pushbutton switch
- 433 MHz transmitter module

Have pre-tested input devices and switching the 433MHz Tx on but yet to assemble the receiver end. Using header sockets for sensors so they can ultimately be mounted on outside of an enclosure.

Attached is the schematic and layout for the AXE021 proto section for those who may be interested.
 

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manuka

Senior Member
Looks OK, but the ~25mA source current of a PICAXE output pin will usually alone be able to handle direct TX switching. These 433 MHz TX often are off unless data is being sent as well- that NPN may not be needed. Which 433 units are you using again- those Jaycar ones?

The voltage reg. may be cutting your output power, as most TX can run on anything from 3V-12V, with higher supply voltages giving more TX power. I've found the broad TX output freq. pretty "stable" as supply changes anyway. The DS18B20 is a significant mA level "power hog" by the way, so worth turning it on/off via a PICAXE pin between readings.

The 3 x AA powered barebones DS18B20-08M-433TX approach I normally use is shown => http://www.picaxe.orconhosting.net.nz/all3.jpg
 
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westaust55

Moderator
Thanks for the comments Manuka.

There is always food for thought in feedback.

Yes I am for now at least using the Jaycar TX and RX modules.

The Keymark data sheet from Jayvcar states 3V as typical Vcc for the Tx and others here have emphasised previously this should not be exceeded but then have also seen reference to using up to 6Vdc as well.
Datasheet for the Rx unit is 5V +/- 0.25V

Have you operated these Jaycar Tx modules at higher voltages satisfactorily?

========

25mA is the absolute max pin output/input current and we really should promote an operating max of 20mA per pin (and a max of 95mA per port/chip)

I elected to use the transistor approach as a PICAXE output can be around ~0.6V (max) when pulled low whereas by driving the transistor into saturation, Vce is only around 0.07 Volts at Ic = 10mA (which happens to be the Tx current).

DS18B20 standby current from the datasheet is typiically only 750 nA (= 0.75uA) and a max of 1.5mA when active. Would not consider that a power hog relative to 10mA for the 433MHZ Tx module.
 
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manuka

Senior Member
I run all circuitry from 4½V (3 x AA) to 5V ("USB") these days, so haven't pushed those Jaycar TX higher tyhan this,although others certainly have- to good effect. IMHO the limiting link factor is often the "deaf" 433 RX however. OK on other points- you'll learn by doing, so good luck !

NB- Jaycar had the supply voltages incorrectly shown for some years on both their 433 TX & RX. I ran both from 4½V - 5V OK, but suggest you check the actual values from the Keymark site. Stan
 
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westaust55

Moderator
While the Keymark datasheets from Jaycar and other sources show that the transmitter module works with a typical voltage of 3Vdc, I found that I needed to remove the 3V regulator and operate the transmitter module at approx 4.3V (4.5V form 3 x AA cells - 0.2V for switching transistor).
Only then did I get a signal.

I also measured the current draw and have the following results:

~2mA when in pause - not reading temp or transmitting
~3mA when reading the DS18B20. (DS18B20 data sheet indicates a TYP of 1mA and a MAX of 1.5mA)
~5mA when transmitting data and not simultaneously reading the DS18B20
(Search of internet had found measurements by others suggesting the Keymark Tx module has a peak current of 9mA but an average of around 3.9mA)
Note that I am using a transistor to switch off the Tx module except when transmitting data.

So now, amongst house moving etc, its away to mount the modules in a couple of plastic boxes and do some trials on distance with various antenna types.


Edit: Another finding this morning while testing . . .
Keep the module and antenna above items such elevated concrete slabs. The concrete is obviously acting as a ground plane and with the initial antenna wire parallel to the concrete surface effectively blocked/cancelled the sognal..
The concrete in question was part of the working surface at the side of an old brick type BBQ.
No signal recevied each time the antenna and module were only a few mm above the concrete (on a newspaper) but works perfectly when elevated 150mm on a cardboard box.
 
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westaust55

Moderator
433HMz Radio link

I have assembed my 433MHz receiver module into a box that fits onto the expansion port/conenctor on my PICAXE experimenters box.

Using the Keymark Rx module as available from Jaycar.

While not a standard radio conenctor, I used a RCA (stereo type) plug and socket to enable removal of the antenna in case I wish to experiment with antenna later and to prevent the anetnna getting bent in storage.

I believe a straight wire is better than a coiled wire as an antenna but potentially harder to keep elevated.

To help keep a length of hook-up wire used as the antenna straight and vertical, I soldered it to the RCA plug then slid a length of plastic drinking straw over the wire and secured it to the plug with the tabs normally meant to secure the audio cable.

Pictures of the receiver module attached for those who may be interested.


I am awaiting a humidity sensor from Futurlec which when tested and runing I will complete my mini weather station (temp, humidity & light level) with 433MHz Tx module and upload a few more pics.
 

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Dippy

Moderator
Blimey, if you can't keep 17cm elevated you need some blue tablets mate :)

Most data sheets from proper RF manufacturers list the pros & cons of whip vs helical.
 
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westaust55

Moderator
Couldn't find blue wire ;) or straws :rolleyes:

Depends whether you are using hobby hookup wire or galvanised 3 or 4mm diameter coat-hanger wire :)
 
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manuka

Senior Member
Nothing wrong with the drinking straw Dippy- you've been sipping juice thru' worse I'd say. However I normally helix coil such UHF verticals a tad just for operator safety! When you've above a short stiff vertical wire,fiddling around with the circuitry below, it can be a tricky to judge the wire end's proximity to ones eyes. I've never had such an eye stab, but recall a ham radio mate back in the 1960s who DID,with extremely painful consequences.

An alternative is to add a top hat blob of hot melt glue (or a wire top twist over).

That's a pretty nifty "triple 4x4 key matrix" keyboard you've rustled up ! Why that approach?
 
hippy

hippy

Technical Support
Staff member
1" or so rubber balls ( and I expect golf balls would work ) with a hole drilled in and stuck on the end of the aerial are good to avoid poking an eye out. Similar things are used on bamboo posts in gardens to avoid the same damage so you'll probably find suitable 'balls' in garden centres.
 
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Dippy

Moderator
I reckon a golf ball on the end might make Westy wilt... unless those Ebay drinking straws are mega rigid.

Just 1 eye-poke per 40 years is a good safety record - but seriously, he has a point (!).

Maybe a cork out of a wine bottle. Or maybe just mount it out of the way where numpties can't get to ;)
 
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westaust55

Moderator
@ Dippy,

No Ebay fetish here dippy. Straws courtesy of the local IGA supermarket - grabbed a few new ones from the dispenser (for free). That price even beats Ebay :D


@ Manuka

As the main box is the base for most of my PICAXE experiments I was aiming to cover all bases from the start. The 3 x 16 keypads effectively give me 94 key combinations (one key acts as a shift key). Uses 3 standard 16 key keypads rubbed of the original text and used letraset to re mark then coated with spray on PCB sealer.

A look-up table and very small routine and I have access to almost complete PC type keyboard built in (and relatively compact). Have made a thread about this 11 months ago shortly after I started with PICAXE and this forum. See this thread for some more details:

http://www.picaxeforum.co.uk/showthread.php?t=9260
 
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manuka

Senior Member
I've recently been rustling up a 162MHz marine AIS (Automatic Identification Service) article, & have had great VHF reception with a 300 Ohm TV ribbon version of the esteemed "Slim JIM" (an acronym for “J-type Integrated Match”) – invented by the late Fred Judd, G2BCX in 1978. When mounted vertically (perhaps being hung from a tree inside a plastic tube well away from metal work etc) the design shows legendary low angle radiation (said to virtually parallel the ground), & is ideal for marine & flat terrain use. Forget it for aircraft,hilltop/valley links & satellites! Google for insights, including how they evolved from the classic "J" matched vertical.

Slim JIMs are scaleable, & thus they may have some mileage for 433 MHz low angle omnidirectional use. For the calculator challenged, take 1 wavelength at 433 MHz as 700mm - that's before considering VF (Velocity Factor) which is typically 0.9 for TV ribbon in such VHF/UHF applications. Hence ¾ "antenna" wavelength = 465mm, meaning a metre of cheap TV ribbon could nicely make a pair of them. Here in NZ DSE sell this ribbon at ~US$ 50c a metre, & almost any handy TV grade coax could be used with typical 433MHz modules. Yah-cheaper than "cotanga" Yagis, & they're far less visually obtrusive & bulky as well. A pocketable roll up version should be a breeze.

As they could be rustled up in minutes, & have (thanks to the squashed radiation profile) a gain over isotropic radiators of ~6dB,such Slim JIMs may well appeal for demanding 433MHz roving links. Feedback awaited! Stan
 

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BeanieBots

Moderator
Any suggestions how to "adjust for lowest SWR" without running out and buying an SWR meter?
Presumeably just tweak length between range tests?
 
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russbow

Senior Member
I have used a "slim jim" a lot on the 70cm ham band.

I didn't like the floppy ribbon cable approach. The simple remedy is to use a length of 00 scale model train track. It also fits snuggly into a length of waste pipe ( don't use black variety - you'll lose all your signal ). Bit of 50 ohm coax out the bottom bung and voila - champagne quality on a beer budget.

BB. not easy to measure SWR without a meter. It's too easy to get hung up on SWR. Slide the feedpoint up / down 'til you get acceptable results.

Also google " j pole antenna " similar idea.

Russ
 
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manuka

Senior Member
Russ: OO = top marks for lateral (-ah parallel?) thinking! Guess this means you've raided someones toy box?

Google informs 00 gauge track uses 16.5 mm spacing -TV ribbon is ~10mm. Are the tracks giving good electrical contact over time however? How did you join their ends- soldered links? What lengths do they come in anyway?

Of course the cost effectiveness of TV ribbon is without peer in such applications (& you don't have broken hearted kid hunting for his missing tracks!) Stan- ZL2APS (since 1966)

EXTRA: SWR insights can be gained via far field performance checks. I've had a lot of fun in the past using simple Field Strength meters across a soccer field, read using binoculars! Naturally a mate at the receiver can inform you as well. With just a few mW output 433 MHz gear is not going to cook a TX if SWR is poor anyway.
 
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russbow

Senior Member
ZL2 - your not supposed to run an engine on it, it's vertical - will fall off.

I use min crocs to get optimum feed points then solder. I think a purist would want to talk about baluns, but at these freqs, I find balun losses are greater than gains achieved.

73s (G4DDV)
 
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westaust55

Moderator
Albeit over a year since I assembled my 433 MHz radio link and have referred a few folks to this thread I realise that there are photos, schematics, layouts but not example code.

So to rectify (yes a pun of sorts :D) the situation here is the program listings:

08M code:
Code: 
; =================================================
;   File....... MiniWeather
;   Purpose.... PICAXE 08M based weather station to measure the temp, humidity and light level
;               and transmit the data over a 433MHz radio link back to a base PICAXE unit 
;   Author..... Westaust55
;   E-mail.....
;   Started.... 12-03-2009
;   Updated.... DD-MM-YYYY
;  ===============================================
;The formula for RH% is: RH(%) = (Offset-Soh) * Sens /(2^12)    2^12 = 4096
;
;
#PICAXE 08M
;
; IO DEFINITIONS
;
SYMBOL temp      = 4
SYMBOL humid     = 3
SYMBOL ldres     = 2
SYMBOL RFdat     = 1
SYMBOL RFon      = 0
;
; VARIABLE DEFINITIONS 
; 
SYMBOL light    = b0
SYMBOL degC     = b1
SYMBOL axefactr =	b2
SYMBOL Soh	    = w2	         ; w2 = b5:b2		
SYMBOL diff	    = w3	         ; w3 = b7:b6
SYMBOL RH	=	w4	         ; w4 = b9:b8
	
;
; CONSTANTS
;				
SYMBOL Offset   = 7709           ; HH10D module 1 calibration constant	
SYMBOL Sens	    = 341            ; HH10D module 1 calibration constant 
; 
; MAIN PROGRAM
;
Init:
      LOW RFon
;
;
Main:

      READADC ldres, light       ; read the relative light level value

      READTEMP temp, degC        ; read the temperature in Degrees C.

      COUNT humid, 1000, Soh      ; read the frequency (ie cycles in 1 second)
      
      diff = Offset - Soh

	axefactr = diff / 19 + 1   ; a factor to prevent number roll over error (ie >65535)
	RH = 10 * Diff / axefactr * Sens ; intermediate result (multiply by 10 is to enable 0,1 resolution later if required)
	axefactr = 4096 / axefactr ; a factor to prevent number roll over error
	RH = RH / axefactr         ; final value for RH%
      RH = RH / 10               ; divide by 10 (for now) as not transmitting fractional part only whole RH%

      
      HIGH RFon  ; switch ON the RF Transmitter module
      PAUSE 1000

      SEROUT RFdat, N600, ($55, $55, $55, $55, $55)
      ; now SEND NOTHING for a little more than one data byte (1 start bit, 8 data bits & 1 stop bit.
      ; i.e. 10 bits in total or e.g. 16ms at 600 Baud or 4.2ms at 2400 baud).
      ; This will make sure that wherever the receiver was at the end of the preamble,
      ; it is now idle and eagerly waiting for the next start bit.
      ; Just don't wait much longer than one byte, otherwise the receiver will lose lock again.

      PAUSE 10  ; less than 16 but seems to work okay.
      ;
      ;
      SEROUT RFdat, N600, ("ABC", degC, RH, light)
      
      LOW RFon   ; switch OFF the RF Transmitter module

      PAUSE 7000	; delay so we send data at approx 10 second intervals

      GOTO Main
and 40X1 receiving code:
Code: 
; =================================================
;   File....... 433MHz Receiver Program
;   Purpose.... Receive temperature and light level from a remote PICAXE via 433MHz radio link
;   Author..... Westaust55
;   E-mail.....
;   Started.... 25-02-2009
;   Updated.... 25-02-2009
;  ===============================================
;
; -----[ Program Description ]---------------------------------------------
;
; A program to receive temperature and light level from a remote PICAXE via 433MHz radio link
; data is received from Keymark Receiver module with the SERIN command and displayed on the
; LCD module with the SEROUT commands.
;  
; 
;
; -----[ Revision History ]------------------------------------------------
; A = First issue
; 
;


#PICAXE 40X1
#NO_TABLE
;
; -----[ I/O Definitions ]-------------------------------------------------
;
SYMBOL lcd_data = 1          ; serial data output to LCD module
SYMBOL Rx433_In = 5          ; serial data input from 433MHz module

; -----[ Variables ]-------------------------------------------------------
;
SYMBOL shflock = b25         ; Flag to indicate if shiftlock is ON/OFF
SYMBOL pattern = b23         ; 8 bit pattern to be sent to the 8 x LED's
SYMBOL counter = w10
; 
SYMBOL light = b0            ; value for light level   received from radio link
SYMBOL degC  = b1            ; temperature in Deg C    received from radio link
SYMBOL humid = b2            ; relative humidity level received from radio link

; 4 x 20 char LCD commands
SYMBOL lcd_bs  = $08
SYMBOL lcd_lf  = $0A
SYMBOL lcd_ff  = $0C
SYMBOL lcd_cr  = $0D
; 
SYMBOL lcdcmand = $FE         ; = 254 - send this before following commands
SYMBOL lcdclear = $01         ; clear screen and cursor to home position
SYMBOL lcdhome  = $02         ; move cursor to home position
SYMBOL lcdnocur = $0C         ; display on with no cursor
SYMBOL lcdcuron = $0E         ; display on with visible cursor
SYMBOL lcdcblnk = $0F         ; display on with blinking cursor
SYMBOL lcdline1 = $80         ; move to start of 1st line
SYMBOL lcdline2 = $C0         ; move to start of 2nd line
SYMBOL lcdline3 = $94         ; move to start of 3rd line
SYMBOL lcdline4 = $D4         ; move to start of 4th line
SYMBOL lcdlitof = $FC         ; turn backlight off
SYMBOL lcdLiton = $FD         ; turn backlight on

;
; MAIN PROGRAM
;
Init:  SEROUT lcd_data, N2400, (lcdcmand,lcdclear)
       PAUSE 10
;
Main:
       counter = counter + 1
       SERIN Rx433_In, N600, ("ABC"), degC, humid, light 
       SEROUT lcd_data, N2400, (lcdcmand,lcdline1)
       PAUSE 1
       SEROUT lcd_data, N2400, ("Counter = ", #counter,  "    ")
       PAUSE 1
       SEROUT lcd_data, N2400, (lcdcmand,lcdline2)
       PAUSE 1
       SEROUT lcd_data, N2400, ("Temp     = ", #degC,  " C ")
       PAUSE 1
       SEROUT lcd_data, N2400, (lcdcmand,lcdline3)
       PAUSE 1
       SEROUT lcd_data, N2400, ("Humidity = ", #humid,  " % ")
       PAUSE 1
       SEROUT lcd_data, N2400, (lcdcmand,lcdline4)
       PAUSE 1
       SEROUT lcd_data, N2400, ("Light    = ", #light, "  ")
 
 SERTXD (#counter, " ", degC, " ", humid, " ", light, " ",  #degC, " ",#humid, " ", #light, CR, LF)  
 ; must select Prog Editor terminal (F8) at 4800 baud to see this

GOTO Main
 
Last edited:
D

Dippy

Moderator
Yes, my processor is underclocked to save my sanity.
(In truth: I hadn't looked at the date :eek:)

There was a good programme on TV the other day about various funicular designs. In Switzerland I think. I didn't realise how old they were.
Anyway, I digress. So I'll stop . (Yes, I can hear the sighs of relief!)
 
T

teddy7

Member
westaust55 said:
Initially some theory that may be of interest to others, and then a question at the end for our more radio orientated members.

Having late last year purchased some 433.92MHz Keymark Tx and RX modules from Jaycar, I did some research and Googling to find out a bit more about any limitations of use.

While there are a number of threads on this forum, most discuss the maximum range for their modules and maybe the length of a simple piece of wire as an antenna.

I did find an Instructables article by Dr Acula who set up a dipole antenna for greater distance with a PICAXE project. Research suggested that a 1/2 wave dipole has a gain of 2.15 dBi (in free space – read as "well above the ground").

Manuka (Stan) also has an article in the Silicon Chip Magazine for Jan 2006 on this topic. In this article Stan mentions:


In January 2009, The Australian Govt issued a new variation to the Class License as:
“Radiocommunications (Low Interference Potential Devices) Class Licence Variation Notice 2008 (No. 1)”.
Under item 17, for the 434MHz band, the same 25mW EIRP still applies.

Started thinking about possible extension of the dipole antenna to a small Yagi antenna with say 3 elements (add a reflector and director) to be able to cover some distance and penetrate several brick walls.

The mandatory EIRP is calculated using this formula:
EIRP = Pout + Gt – Ct
Where:
Pout = transmitter power output (dBm)
Ct = signal loss in cable (dB)
Gt = gain of the antenna (dBi)​

The Jaycar sold 433MHZ transmitter module has a rated Output power of 3 dBm with Vcc = 3 V into a 50 Ohm load.

Lets say I have a few metres of Low loss RG-213, 50 Ohm coaxial cable (available from Dick Smith). Attenuation will be around 0.5 dB for 3 metres.

Conversion from mW to dBm gives: 25 mW = 13.97940008672 dBm

Therefore, from EIRP = Pout + Gt – Ct
we get Gt = EIRP – Pout + Ct
so, Gt = 13.9 – 3 + 0.5 = 11.5 dBi

Reference to some Amateur (ARRL) type/member sites suggest the a 3 element yagi antenna has a theoretical gain of around 8 to 9 dBi in free space, but other sources/calc suggest typical as ~ 7 dBi and as low as ~5 dBi.

So in theory, a small(ish) 3 element Yagi antenna could be used and still remain within the relevant regulations. By smallish the overall width would be around ~360mm (reflector) and the beam length around ~140mm which is still very portable (to me at least).

For those who are interested, here are some Australian Govt based links on the topic.
http://www.acma.gov.au/WEB/STANDARD/pc=PC_2643

http://www.acma.gov.au/WEB/STANDARD/1001/pc=PC_2633


http://users.bigpond.net.au/vk3yng/lipd/aca_resp01.htm
Note that Australia is part of ITU Region 3.
The band 433.05 to 434.79 MHz is not a designated ISM band in Australia.


Noting that some others have amateur radio experience, here is the question:

Can anyone see any flaws in my thoughts/calcs before I dash out and buy some hardware to make a “better” antenna ? :confused:




EDIT:
some further information for those in Australia (from Australian Communications Authority correspondence):
The band 433.05 MHz to 434.79 MHz is shared by amateur radio, low-powered applications and the
radiolocation service. The radiolocation service is the only primary service in this band. Other services
operating in this band must not cause harmful interference to the primary service, and are not afforded
protection should they receive harmful interference from that primary service.


also for reference:
ISM Band = The Industrial, Scientific and Medical (ISM) radio bands were originally reserved internationally for non-commercial use of RF electromagnetic fields for industrial, scientific and medical purposes.
Click to expand...
I know this is an old post, but I use 315Mhz here in the states.

-teddy7
 
B

bpowell

Senior Member
Hi Teddy,

I've set up a 315 mhz link that is pretty effective at about 30 meters and through two buildings...however, I'm finding a couple of "dead spots" in my house where I can't receive data, so I'm looking to remedy that. I'll be watching this thread.

The two antenna I use now are just 1/2 wave antenna (17.8 inches) made from hook-up wire, and then wrapped around a screwdriver...once tightly wrapped, I put silicone sealant around the whole job, let it dry, and then slid the antenna off and soldered one end to the TX and one to the RX.

This has worked to a point, but I have a feeling this is dumb luck. Just yesterday, I started experimenting with a better receiver antenna, and I got better performance with a 1/4 wave (8.9 inches) piece of hook-up wire formed into a loop and taped...so one end is soldered to the RX, the other end just loops around and is taped in place (no electrical connection)...that's cleared up one of the dead-spots in my house, but not the other.

I'm trying to learn how to optimize but it's complex stuff. I also think I might need to go out to the pump house (when it warms up) and swap out the helical wrapped antenna for a straight whip. I wonder if my wrapped antenna is actually not as efficient as a straight piece of wire (at the TX side).

I welcome any feedback!

FWIW, my current setup (with two wrapped antenna) has been shooting lets see....12 bytes every 15 seconds at 1200 baud with no problems!
 
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