Bad reception range with emonTH

Submitted by Miko95 on Wed, 25/12/2013 - 08:30

Hi,

I bought an emonTH module to monitor temperature (using DS18B20). I use an RFM12Pi on my Raspberry as receiver.

However, I found that after a few meters line of sight from the receiver, I don't receive anything. I'm currently using two AA batteries of 1.5V each one.

Is it the maximum range I can expect with 3V? If yes, what is the maximum voltage that can be used on the emonTH?

Thanks,

Mickael

Re: Bad reception range with emonTH

Submitted by aideen on Wed, 25/12/2013 - 10:02.

Mickael, It should work fine with batteries and emonTH and RFM12Pi in different rooms.

Do the frequencies match (both h/w and s/w)?

Re: Bad reception range with emonTH

Submitted by Miko95 on Wed, 25/12/2013 - 16:36.

I guess the frequencies match. On the RFM12Pi side, I used minicom to configure it (when I press a button on the keyboard, the RFM12Pi returns me the menu and I can see it is set to 433Mhz). Regarding the emonTH, I ordered it with frequency 433Mhz, but I don't know if there is a way to check the frequency?

I thought that if the transmitter and receiver use different frequencies, nothing can be transmitted at all. Is it right?

Re: Bad reception range with emonTH

Submitted by Robert Wall on Wed, 25/12/2013 - 17:01.

No, you will get transmission over a very short range if the software frequency is correct but the module is physically tuned to the wrong band. You can tell the frequency that the RFM12B is tuned to from here. Is the aerial length correct for the frequency and are the aerials roughly perpendicular to the line of sight and parallel to each other?

Re: Bad reception range with emonTH

Submitted by Miko95 on Wed, 25/12/2013 - 17:59.

The hardware frequency of my emonTH is 433 Mhz (according to the link). Regarding the software frequency, I guess I need the UART-USB adapter in order to access the code, right?

Regarding the aerials, the conditions you mentioned were not met, I only thought the aerial length is important. I will retry.

Re: Bad reception range with emonTH

Submitted by Robert Wall on Wed, 25/12/2013 - 19:49.

I think if your RFM12Pi is working on 433 MHz, and you have checked that both the RFM12B modules are tuned to 433 MHz also, then it is certain that the emonTH must be working on 433 MHz.

Both a monopole aerial and a dipole aerial radiate the maximum power at right angles to the aerial. Of course, the aerial in the emonTH is only an approximation to both of these ideals because the circuit board is not a perfect ground plane, neither is it a mirror image of the aerial wire! So it would be nearly impossible to predict its performance with theory and as far as I know no-one has tried to measure its RF properties either. However it seems reasonable to think that if you push the wire through the slots and point it directly downwards and away from the circuit board, then the direction of maximum power will be nearer to the horizontal than the vertical.

Re: Bad reception range with emonTH

Submitted by Miko95 on Mon, 30/12/2013 - 20:31.

My question is what is the utility of the emonTH with the RFM12Pi if the range is so short?

Am I missing something here?

Mickael

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