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Re: [Discuss-gnuradio] Low TX Power when performing frequency hopping

From: Marcus Müller
Subject: Re: [Discuss-gnuradio] Low TX Power when performing frequency hopping
Date: Mon, 02 Mar 2015 12:39:56 +0100
User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:31.0) Gecko/20100101 Thunderbird/31.4.0

Hi Vaibhav,

tuning is an issue, here. The problem is not that you're only retuning the LO, the whole signal chain has to be correctly locked in again after each tune.
If the total bandwidth you're spanning is less than 40MHz, which is the baseband bandwidth of the daughterboard's you're using, try setting your LO frequency to the center of that band, and hop via frequency shifting in the FPGA only[0]. To do that, you'll need to use tune_request_t[1] objects rather than simple using the target frequency when tuning using set_tx_freq in your USRP sink.

Further things of interest: How do you measure the power of a 6ms burst? How wide is your signal?


On 03/02/2015 12:24 PM, vaibhav kulkarni wrote:
Dear All, 

I am trying to implement some frequency hopping schemes in the ISM band with USRP N210 with RFX 2400 board ( I also tried the same with the SBX 40MHz board). I hop to the next channel (channel seperation : 5MHz) after every 6ms (tuning time for RFX board is 250usec) so tuning is not an issue. I set max gain (20dB in case of RFX board) and 30 dB in case of (SBX Board) and send random modulated (BPSK) bits. 

However, I get very low power at the receiver (another USRP, RX gain 20dB)  around -70 to -80 dB 1 meter away from the tx USRP. When I dont perfrom frequency hopping I get a rx power of -10 dB. I am not able to understand why the tx power reduces by such an extent while perfroming fx hopping, although I give enough settling time. 

Also is there any firmware which allows to further increase the tx power ?

Any help to resolve this issue is appreciated.  

ETH Zurich

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