Author Topic: Has anyone used a 915MHz RFM69 to shift down to 433MHz?  (Read 906 times)

TomWS

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Has anyone used a 915MHz RFM69 to shift down to 433MHz?
« on: June 11, 2015, 12:36:28 PM »
I have an application that uses 433MHz to control some AC relays (similar to those cited in: https://lowpowerlab.com/forum/index.php/topic,1115.msg7221.html#msg7221) but the Moteino network will use 915MHz radios.  I know that the radio parameters can be changed to set the frequency to 433, but I wonder how much signal loss there is in doing so.

The application only calls for transmit at 433MHz so I don't care about receive performance at that frequency and my thought was to use a 1/2wave dipole for 915MHz so that it wouldn't be 'too far off' a 1/4wave at 433MHz (where 'close enough' = works, but with wasted power).

Let me know if you have any experience in trying this...

Thanks in advance,
Tom

Felix

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Re: Has anyone used a 915MHz RFM69 to shift down to 433MHz?
« Reply #1 on: June 11, 2015, 01:46:42 PM »
I think I tried, or the other way around. The loss is pretty massive, because of the matching network is tuned to a certain freq band and it wont like going outside of that, the farther off the worse the loss.

TomWS

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Re: Has anyone used a 915MHz RFM69 to shift down to 433MHz?
« Reply #2 on: June 11, 2015, 02:02:36 PM »
I think I tried, or the other way around. The loss is pretty massive, because of the matching network is tuned to a certain freq band and it wont like going outside of that, the farther off the worse the loss.
Well, I can believe that an antenna network tuned to 433 is going to really tank a 915MHz signal, but maybe not the other way around.  Still it is a data point...  I suppose I could go the 'second radio' route - yuck  ;)

Actually this may not be too horrendous since the AC Control function doesn't rely on the interrupt (since it's transmit only, the status bit is polled) and could be easily shifted to a different SPI select...

T