|
From: | Matt Ettus |
Subject: | Re: [Discuss-gnuradio] multiband FM transmission reception problem |
Date: | Wed, 13 May 2009 11:02:59 -0700 |
User-agent: | Thunderbird 2.0.0.21 (X11/20090320) |
mayur_CEN wrote:
I am sorry for being so impatient.Actually I have been experimenting with this problem for a long time,so i am a bit eager to find the solution.You guys are doing a great job helping out people with their problems.I did not mean to offend anyone. I have uploaded the code.I will explain to you in detail how i am conducting the experiment. I am using 2 daughter boards for sending and receiving simultaneously.I am checking the output of the fm transmission by running a nbfm_tx receiver program simulated in grcWhen I send 1 channel ,the audio can be heard clearly As I increase the number of channels,the audio strength decreases which I think is due to interference. What I want to know is how do I increase the signal strength and reduce noise as I increase the number of channels.
What you are seeing as noise is most likely clipping.As you increase the number of transmitted signals, you need to decrease the power per signal since you need to stay maintain linearity.
For example, say you are transmitting 1 signal at max amplitude and power. When you move to 2 signals, you need to use 1/2 the max amplitude for each signal, which will give you 1/4 the max power in each signal. If you have X signals, you need to give each one 1/X the max amplitude, which will give each signal 1/X^2 of the max power.
If X is very big (more than 20 or so), you don't necessarily have to reduce the amplitude quite as much as 1/X, but for small X you do.
Matt
[Prev in Thread] | Current Thread | [Next in Thread] |