Quality of RF transmitters

Hello,

I'm looking to buy some transmitters and I was thinking of this:

http://www.purlance.com/product/product51.html

They are very cheap and I was wondering if the quality is any good. Can anyone with experience of buying RF transmitters let me know what they think is good quality? By this I mean a decent range, long life and the fact that they will transmit/receive :slight_smile: I am willing to pay extra if needed, but if the cheap ones are ok then why not.

the part you mention is a small Receiver on 433 MHz, there is a companion Transmitter. the Radios Chosen are suitable for "Simple" communication between two locations that can "See" each other and are less than 10 meters in range and there are libraries to support those devices. The RF pair is capable of sending and receiving small data packets. If your requirements are larger please consider a more sophisticated device.

Bob

I am willing to pay extra if needed, but if the cheap ones are ok then why not.

What you pay extra for is automatic retransmission in the event of an error, error checking, reliability, range, etc.

I just got a pair of these in the mail today.
I tried to use Serial.print and the txrx ports of Arduino, but that was not a success.

Then I tried VirtualWire, and now I have over 5m range through a concrete wall.
So for my project, a simple outdoor temp. sensor I am pretty sattisfied.

200 feet @ 12 volts

200 feet @ 12 volts

1 mile @ 4000 volts.

What are you talking about?

Used the same unit and got a useful range of 200 feet using 12 volts on xmtr.

Used the same unit and got a useful range of 200 feet using 12 volts on xmtr.

12 volts supplied by your Arduino? If not, then that tidbit is useless information. You need to define HOW you supplied 12 volts to the transmitter for it to be useful information.

I used 12 volts from the Arduino power adaptor connector. jack.

The power output of some of these cheap SAW radios is partly a function of the supply voltage, so using a higher voltage yields a (slightly) longer range. I've had problems with the reliability of the cheap ones at the full, or a shade above, the max 12V. I've been sticking with 5V since then. The ones the O/P linked are definitely cheepies. I haven't found an alternate supplier for these ones, but there must be one.
http://www.robotshop.com/433mhz-high-sensitivity-transmitter-receiver-pair-rxa30-3.html
These have a really convincing superhet receiver with fancy IF filtering. Probably the top of the heap for simple on-off-keying.

FWIW, just today a friend of mine emailed me with the following. He had previously
tried many of the really cheapo units mentioned in this thread ...

When I was building the ..... [robots] I bought a lot of radio modules and
everybody seemed to say it was easy to transmit data, Personally I found the
results depended more on the weather in some random place rather than the
data I fed in. It was a nightmare. Even using NiCam's Manchester
encoder/decoder chip results were very poor and I had to do a lot of error
checking. Until I changed to the EasyRadio modules, that is, and their
encoder/decoder worked flawlessly. Ok so they are dearer but they work and
no pairing rigmarole required.

For my part, I have recently been playing with the HopeRF RFM12B transceivers, which
have become fairly popular, along with the higher powered RFM22B units. I would like
to be able to say something positive about them, as they are fairly cheap, but they
are also very sophisticated electronics, and I am so far finding the 3rd party libraries to
be a nightmare to use. Maybe someone else has had better experience with these.

Also, for years previously, I have been using XBee and XBeePro transceivers, and these
have always been very reliable devices, although not cheap.

OK, I'll think I'll try the cheap one and see how it goes. My project involves me using one of these to communicate with a RF controlled power socket switch at 433,92 MHz, which turns on/off a water pump indoors at max~10m. I am using RF and not a relay as it adds some flexibility in my design. I am guessing with one of these I could learn the advanced protocol of the socket(s) and make a pair, so I turn on always the right socket?

RF controlled power socket switch at 433,92 MHz

Well, this is a completely different problem from what you seemed to be suggesting
originally. Not only do you need reliable transmission, but you have to know the
protocol on the receiver side. First off, you need to be sure the transmitter is on the
right frequency, and secondly if the receiver uses anything other than simple on/off,
how will you ever learn the protocol? It could be anything at all. Obviously, it would help
to get the receiver spec sheet.

Many of the Radio controlled power points use the SC2262 / SC 2272 chips for the encoder and decoder.
The protocol is very simple and easy to reverse engineer.
You need to pull apart one of the power points to see what the decoder chip inside is.
Some clues that help are the number of power points that can be switched from the encoder.
If its 4 or less, its likley to be the above chips, but if the encoder supports more than 4 , then its a differant chip.
Ive had no success reverse engineering the power points where more than 4 are supported as the manufacturer rubs
the numbers off the decoder chip, and the protocol is very complex.

Yes reverse engineering will be a challenge, that is half the point in doing it. Currently I know very little about RF and hoping I'll know more after doing this. I live in Finland and it seems the Nexa brand is popular, I have heard that this can be hacked. Good to know about those chips, do you know if Nexa uses them? How did you figure out which socket uses which frequency and ID? Will I need a probe?

What do you mean by reliable transmission? Why won't those cheap ones be reliable?

Thanks.

Actually it seems that the X-10 protocol might be a good option. They seem to have what I need too.

http://www.x10europe.com/pdf/AM12E.pdf

I got some cheap 433MHz radios like that. They were ASK radios. RX/TX pair. I found the automatic gain control (AGC) on the RX would respond rather quickly--so if the signal from the TX stayed in one place for long, the AGC would saturate and I'd get a lot of noise. I did some testing between garage and basement and ran into more noise than I expected. I'm sure there are ways around it.

But I threw in the towel and got a pair of JeeNodes from Modern Devices. They are RFM12-B based and and I'm quite pleased. They are Arduino compatible and have decent library support written by the creator.
You can set a radio id and group id so you can have more than a pair going. They are transceivers too so you can do bidirectional. The Arduino library comes with tons of examples. I wished the getting started documentation was a little simpler (I am writing one as a blog post soon) but it's entirely possible to figure it out in a few hours.

I don't usually spend lots on hobby parts as I can make them cheaper but here there's a lot of heavy lifting already taken care of so this is one of those rare occasions where I succumb to the great value rather than seeking dirt cheap.

Hope this helps.

All of the remote power points Ive purchased all use 433.92 Mhz ASK and the channels are simply
selected based on the data stream.
The easiest way to reverse the protocol is to pull an encoder apart , and connect a CRO to the data input pin
of the Transmitter, and then simply capture the data stream.

bot-thoughts:
But I threw in the towel and got a pair of JeeNodes from Modern Devices. They are RFM12-B based and and I'm quite pleased. They are Arduino compatible and have decent library support written by the creator.
You can set a radio id and group id so you can have more than a pair going. They are transceivers too so you can do bidirectional. The Arduino library comes with tons of examples. I wished the getting started documentation was a little simpler (I am writing one as a blog post soon) but it's entirely possible to figure it out in a few hours.

I've been playing with the JeeNodes this past week, but have a totally different experience
so far. I find the libraries and examples to be poorly commented, plus the RF12demo sketch
pumps characters to the screen endlessly, whether or not the other node is powered up,
and the rf12serial sketch loses almost all of the transmitted characters. The first sketch is
long and complex, and I haven't had time to debug it, and the 2nd sketch is so simple there
is nothing to debug. It's just not reliable. So, still scratching.