uhf - receiver and or transmitter problems

You can make the bytes as long as you like and certainly 16 bits is fine using b0/b1 as w0 etc. My data packets are 10 bytes but any number will do.

Re Manchester coding, this code does use up a fair bit of memory, especially on an 08M. Clearly sending a row of low value numbers (1,2,3 etc) is not good as the binary has a bias towards zeros (00000001, 00000010, 00000011). One system that uses less code is just to send the inverse of each byte eg 255- the value. So if sending 00000001 then send 11111110 as the next byte and discard alternate bytes (or use these bytes as part of a checksum system).

Re Rigidig's 9 digit problem, see <A href='http://www.geocities.com/drvernacula/315_mhz_solar_powered_radio_rptr.htm' Target=_Blank>External Web Link</a> for some code (near the bottom of the page). Sends all the registers of the picaxe. Note lots of &quot;U&quot;s as the higher power modules seem to need more. The multiple &quot;U&quot;s also ought to please our NZ friends (sorry, couldn't resist the pun). Checksums are also very helpful if there are several modules transmitting nearby. It helps to define if the unreliability problem is due to interference or due to the digit string being too long. I haven't been game to go much longer than these strings, though they do seem 100% reliable over 100 metres with the higher power modules.

Edited by - Dr_Acula on 21/08/2007 14:40:16
I have not been folling this post, but I noticed today in the local Mitre 10 (hardwear chain) they had Twin (x2) 40-Ch UHF CB radios in a blister pack for $19.95 AUD.


Senior Member
OK &amp; good work on coding. These Mitre 10 specials will no doubt be the usual 38/40 ch. ~470MHz UHF CBs. Although powerful (500mW) Aus/NZ regs. only permita crippling 3 seconds an hour ch. 21/22 telecontrol/telemetry.

What brand are they however? As mentioned above under UK PMR mods,these sets are pretty generic &amp; suitable internal diode matrix tweaking may persuade them to work both on other freqs. &amp; at legally low 433.92 MHz power.

Dr-A: Do you have any UHF radio gear? If so, then Rx sensitivity easily checked by comparison with the performance of a UHF ham set or scanner. Such sets usually have ~0.2&#181;V sensitivities, which is ~an order of magnitude better than 433.92MHz cheapies. Stan

Edited by - manuka on 21/08/2007 21:02:36


Senior Member
Are these cheapie Mitre 10 sets the Oricom units shown =&gt; <A href='http://www.mitre10.com.au/products/search/desc/oricom ' Target=_Blank>External Web Link</a> and <A href='http://www.dealsdirect.com.au/p/oricom-3km-38ch-radio-handsets-2-uhf-cb-radio-units/' Target=_Blank>External Web Link</a> ? Here in NZ both The Warehouse &amp; Mitre 10 chains are presently selling a twin pak Teac PMR-100 for NZ$50-60. The PMR (Private Mobile Radio)title of course is a give away to UK origins. With SiChip articles in mind I'm naturally keen to nail down items readily available in both Oz &amp; NZ.

Footnote: Virtually duty free NZ these days often seems a convenient test bed for new products pre wider Western release,&amp; items at times super abundant here may never see the light of day in Oz/UK/USA. Ex. Laptops

i recently had a drama with a company that practices this practice of not listing prices openly, needless to say it was a wast of 25 mins of my time setting up an account and making an order only to find out that the linear rail i was hopefully going to get was priced at $375/metre i promptly cancelled the order , i have never returned to them, and probably won't

i think it's a very bad buisness practice, the worst bit was it was a long distance call so it cost me a bit too
Hi Manuka, no I don't own professional quality UHF gear (Shades of Monty Python's nudge nudge sketch).

These cheapie UHF radios seem to be everywhere. I pulled some to bits and hacked into the microphone circuit, the speaker and replaced the push to talk button with a relay. It is very fiddly work and one needs a torx screwdriver set to open the case. However, the waveforms were very distorted and the best I could manage was a morse code sort of speed. Needless to say, it is hard to comply by the 3 second rule.

Have gone back to the little UHF modules from China. They work out cheaper. Am moving towards getting some boards made up for the solar powered wireless mesh. A friend had an idea of using the mesh to sense microclimates in vineyards. There is a company in the US doing this so it is not a crazy idea.


Senior Member
Vineyard micro-climates = NOW we're talking! Your mate may become so overwhelmed by the volume of climatic data that it'll drive him to drink the stuff rather than selling it.

I'll keep my eyes open for a UHF scanner for you. Stan
I have been looking at the price list of Linx Technologies RF modules.(at least these guys have a pdf price list) seem pretty good value ,, i looked at were 315-433MHZ with data transfer 5kbps to 56kbps !! With some pretty good marketing blurb on their price lists. reliability over a 3000ft distance,all you need is the module a microchip and antenna . $5.60 to $12.00 (transceivers at $12) I will try and order some I think.
Hi Stan, Yes those units in the link look like the units I saw. They were in the clearance bin, prolly 10 sets, so I don't know if $19.95 is the regular price, I wouldn't have thought so.

I've had a set of Uniden 1 Watters, I think ?,(3xAAA cells) for years. I don't imagine these China units will be quite the performance of the Uniden models.

If you want a set of these cheapies to experiment with let me know.

Has anyone got/used these units ?



Senior Member
Linx RF units certainly look appealing, especially their very recently released TRM-433 LT transceiver. Aside from US Renton <A href='http:///www.rentron.com/PicBasic/RemoteControl.htm ' Target=_Blank>External Web Link</a> there are Oz. agents as well =&gt; www.clarke.com.au <A href='http://www.clarke.com.au ' Target=_Blank>External Web Link</a>, although their web site freezes up for me. Mmm- Rentron even have pinned versions <A href='http:///www.rentron.com/PicBasic/RemoteControl.htm ' Target=_Blank>External Web Link</a>. Anyone had anything to do with these ?

I'd a good workout with these Asian UHF CB sets 2003-5 (Hellschrieber etc <A href='http://www.siliconchip.com.au/cms/A_104391/article.html ' Target=_Blank>External Web Link</a>)&amp; amazingly found even the cheapies superb performers. It rather backfired on them in fact,since potential users dismissed them as just toys only capable of across the yard comms. In contrast we easily managed 12km LOS (cross harbour) links with DSE &amp; Jaycar units of that era. Stan

Edited by - manuka on 23/08/2007 00:19:57


Senior Member
TECHNICAL recently said &quot;We are still here, and yes we are working hard on new exciting PICAXE developments&quot;. I hope they are considering adding support for Manchester encoding/decoding, because it seems there is a lot of interest in using low cost radio for low speed telemetry.



Senior Member
DIY Manchester coding got the &quot;Hippy treatment&quot; ~2 years back =&gt; <A href='http://www.rev-ed.co.uk/picaxe/forum/Topic.asp?topic_id=2925&amp;forum_id=17&amp;Topic_Title=radio%2Bmodules%2Bmanchester%2Bencoding&amp;forum_title=No+new+posts+please%21+11 !
I'll settle for on board DTMF generation,which even the early BS had,as it's robustness is legendary &amp; the dual tone technique quite suitable for slow data telecontrol etc. ' Target=_Blank>External Web Link</a>
thanks for the link to your code Dr_A. I am getting there.
That reynolds site looked good but only for USA. Clarke site pretty uninformative and it always locks up. I will shortly get them from somewhere and let you know how it goes. Got more prices from the Aussie mob who advertise in a popular mag. Boy they are serious, must be from the prices I get. Obviously some very magic smoke inside them beyond my level 1 status.

I'd like 30 TRANSCEIVERS in sync????????????
To transmit to the base?
If you could share any ideas on this.

To be more specific : They are all in range of the PC receiver/transmitter.

I kind of was thinking of having the base just say &quot;ok number 'TRxy' send data&quot; and i was pretty content- until I realised it will hang/stop doing its job while waiting for a serin(uuuuu,&quot;abc&quot;,sdata1) .
That just wouldn't work.
The network could even be self learning to a degree if I get past this. Getting a little ahead of myself :)
So now I am thinking of having to have two picaxe chips on each station, just to listen out for a request.!! And my mail order rocket science degree hasn't arrived so it'd really perk me up if you can help :)
The serin problem strikes again. For most protocols you really want the PC driving things, otherwise the airwaves can get overloaded with conflicting signals. So for sensing data the PC sends out a request for a value and the sensor sends it back (eg soil moisture) For turning something on or off again the PC controls this (eg a sprinkler). The third scenario is when a sensor detects a change and has to send the message through. For these sensors, just have a wireless Tx unit and they spend their time in a loop waiting for a condition to change and then transmit (eg a sensor next to the front porch light that detects the light came on and sends this data to the PC to turn on other lights).

Thus the serin hang problem does not matter any more.



Senior Member
manuka, I was thinking more along the lines of the MikroElektronika approach. To quote from,


&quot;In BASIC, Manchester encoding functions are implemented on top of the software UART library. Using them is similar to software UART&quot;.

ok but currently i'm thinking of having the 'data collecting picaxe' work continuously , then a second picaxe on the unit can receive a request, interrupt the other to get its data and let it go off again, while the first sends this data.
Or some variation of that.


Senior Member
Of course that &quot;Poor Man's Manchester&quot; mention above was just a workaround! I recall Hippy has managed even more,including error detection,so do a Forum search. I'd personally request inbuilt DTMF,which even the earliest BS came with,as the dual tone robustness is legendary.

Thanks for a confirmation that the Oz. Linx agent's site lockup is not just my end. I've emailed them.

Rigidigital-suggest you tell us MUCH more about your x30 setup. Such dead boring things as interference &amp; power supplies may greatly influence your design. Just how often is data being sent? What is your budget- it could suit ZigBee?

I've been pondering the legal (AS/NZS 4268:2003 ) Aus/NZ 151.3 MHz narrow band data slot in fact,as this allows 100mW &amp; being VHF will have better punch thru' vegetation &amp; koalas. Elsema in NSW <A href='http://www.elsema.com/t15105.htm ' Target=_Blank>External Web Link</a> have some tempting link programmable offerings. Anyone had experience with these?

For real vegetation punch however much lower telemetry/telecommand spectrum slots (13.560 MHz,27.120 MHz,35.700 MHz &amp; even 40.680 MHz) appeal. Compared with 433.920 MHz (&amp; 2.4GHz !)these are now almost DC frequencies,&amp; should suit DIY- if allowed! Stan

Edited by - manuka on 23/08/2007 23:56:32


Senior Member
The matching Elsema receiver <A href='http://www.elsema.com/r15105.htm' Target=_Blank>External Web Link</a> has 1uv sensitivity, but expects 50/50 duty cycle on the incoming data bits - sounds very much like the less expensive devices people have been experimenting with.

I have had and used Elsema 27 MHz gear for 10 years, they have quite a range of products and seem to be very reliable.
There are probably dozens of farmers within 100km or so of here using their gear for Pumps, Watertanks, auto Gates, Kiln Alarms, Security you name it, and their prices are very reasonable also.
(Don't work for them, I just like their gear)


Senior Member
Meanwhile,back at UHF,I've been continuing to do my 433 MHz homework &amp; increasingly consider US firm <b>LINX Technologies </b> new LT transceiver chip highly promising. See a combo info page I've just rustled up outlining it's features=&gt; <A href='http://www.picaxe.orcon.net.nz/linx433.jpg' Target=_Blank>External Web Link</a>. This TRM-433-LT appears sensitive, versatile, cheap (~US$12)&amp; VERY Picaxable. Opinions/experiences anyone? Stan

Edited by - manuka on 25/08/2007 01:36:06
manuka, pretty much novice pupil here. Its a lot to see if I can. To Have a whole bunch of remote keypad stations data logging at each operators whim and having this data get safly back to the PC.

This started out a simple farm gate problem.,
but I got hooked and am now waiting to order 18X's ,

I think I need 08's on an individual unit as well to get over the serin().
What I got happening tonight is two 08's on a board. Pic One is collecting data. At intervals Pic Two simulates a request from the PC ,switches a pin high on Pic One and induces P2(itself) into a deadly
serin() coma.... Pic One, is to the rescue with a direct data transfer which includes a flag.

Pic Two now sends this data via UHF to the PC where it is recieved by my program which filters out duplicate data and into an sqlexpress db.
Its all working except for some kind of seemingly random lock up now and then on Pic One I think its happening. By all means feel free to tell it to me straight, Ive enjoyed all the input thus far!


Edited by - rigidigital on 25/08/2007 14:13:08

Edited by - rigidigital on 25/08/2007 14:29:00