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CC1350: terrible sub 1Ghz range

Bill Cullen
Prodigy 140 points
Part Number: CC1350

I have been struggling to get more than a 1000 feet or so of range using my cc1350 launchpads with an external 1/4 wave 50ohm  antenna. I attached an external antenna booster that amplifies about 10x and was able to get about a 1/2 mile. I am looking at the RF voltage output from  the mcu going into 50 ohms and it looks like it is only around 20 millivolts. That equates to -20 dBm or so which is pretty much what I see as the RSSI value when receiving with another launchpad if it is right next to the one transmitting. I have programmed the simplelink power to 10. Is this not dBm? Does anyone know what the expected voltage peak is for a cc1350 at 915Mhz into 50 ohms when TX power is set to 10? I expected waveform peaks of 1V. Is there something I don't understand? Thanks for any insights.

  • 0
    TI__Guru**** 317180 points
    - I have never measured the voltage swing with a 50 ohm load since I always measure output power conducted with a spectrum analyzer. But 10 dBm should give ~0.7 V swing. (P = UxI over 50 ohm)
    - When you write 1/4 wave antenna, I assume that this is a antenna you have bought and you know is 50 ohm?
    - I assume you have changed direction of the cap on the LP ensuring that the signal is routed to the JSC contact and that you have a cable between this and your antenna?
    - I assume you have used the excel sheet in e2e.ti.com/.../375556 to calculate the expected range given your settings and placement of the LPs?
  • 0 in reply to TER
    Prodigy 140 points
    Everything you mention I did. I have an unmodified set of launchpads also and they are showing RSSI -50 when sitting 2 feet apart. I am wondering if I damaged all my boards. I do understand I should have .7V, not 1V. I'm going to play in RF studio and see what I can find. I'm planning an upgrade to the 1352 so I can start with some fresh hardware. I wish it wasn't so hard to switch to an external antenna. They make switched SMA connectors which would really help. Thanks for your help.
  • 0 in reply to Bill Cullen
    TI__Guru**** 317180 points
    -50 dBm sounds a bit low. For which datarate and frequency do you measure this for?
  • 0 in reply to TER
    Prodigy 140 points

    I am at 915Mhz and using the 50K long range mode. I'm just trying to figure out why I don't see .7 volts. It seriously looks like 20mv and I have a scope that samples at 5Ghz. I think I will move on to the 1352, be careful and measure early. I don't want to waste anyone's time. I do appreciate your replies and I have a feeling I'll be back soon . Thanks.

  • 0 in reply to Bill Cullen
    TI__Guru**** 317180 points
    I tested with two CC1350 LPs ~70 cm apart and I got -30 dBm RSSI with the standard 50 kbps setting using SmartRF Studio.
  • 0 in reply to TER
    TI__Guru**** 317180 points
    Closing this thread do to inactivity. You can reopen the case by adding a new reply.