PIC-PIC RF Comms

[Ioannis]

These modules you are using should get further but long time ago, I run a test on these and was disappointed by their behaviour. Then switch to Aurels and after that I am building my own modules for superegenarative and hyperodyne ones.

I would suggest if you don't need many, to try some other brand.

Ioannis

[mikem]

I'm using the same receiver transmitter combo and I reliably obtain 200 feet indoors and over 300 outdoors running the transmitter at 5 volts using 1/4 wave antennas at each end.

Here is what I found; in 2 installations that I did I found that the receiver needed to be tuned to the particular transmitter.

As a result I wrote a short program to continuously send a simple serial signal consisting of a pre-amble character, the letter H for example, and a data value such as a string of 01010101.

I sent these basic commands only to Keep things simple at first when tuning the receiver.

I then moved the receiver board away from the transmitter until the signal level as indicated by a flashing LED on the receiver board went away. Next I slowy adjusted the tuning coil on the receiver board until the LED came back on. This is a very very sensitive adjustment so do not move the tuning slug more than 1/2 turn in either direction.

I repeated this each time increasing the distance between the transmitter board and the receiver board until the LED went out. I found the tuning to be very very sensitive, even a 1/8 turn of the tuning slug resulted in a loss of the demodulated signal.

Next I took 2 untuned receivers to work and measured their input impedance on my HP network analyzer and I found a very narrow match on each one.

Both of the unalaigned receivers as they came from the factory were either tuned below 432.85MHz or above 434.5 Mhz. between 433.2 to 434 .25 Mhz they had a match of over 2.5 :1 VSWR which is a poor match for these modules.

I compared these to the 2 that were tuned using the method above and the 2 tuned receivers were showing a near 50 + J0 match at 433.75 and 433 .95 Mhz respectively.

When I get some more playing time I plan on running some further test using My HP spectrum analyzer to try and determine, dB wise, how sensitive the receivers tuning adjustment actually is.

Mike

[Kamikaze47]

ahh cool, thanks for that mikem... i'll give it a try

[Squibcakes]

Kamikaze,

I've just started palying with these RF modules too and might have some info that may help you.

I found that reception was very flakey when using serout instructions, fortunately I use 16F628 chips that have a built in USART. ie use the HSEROUT/HSERIN instructions.

Straight away i found a marked improvement.

The other thing I noticed, was that if the TX/RX modules are too close, ie less than a couple of inches, the RX module just doesn't work.

I have been able to get good range up to 30m indoors without using any antennas at all.

I haven't yet experimented with the max range but sure it will improve when an antenna is added.

BTW I have had no problems with 4800 baud or lower. Lately I have been playing with manchester codeing, which should be used for RF data... but still trying to get that to work. See code examples.

Cheers
J