[USRP-users] Safety Calculation

Kevin McGuire kmcg3413 at gmail.com
Thu Oct 12 21:29:47 EDT 2017


You guys can ignore this but your welcome to reply. I found the archives
for this list and was able to locate a couple subjects that are giving me
some information.

But, feel free to reply, but also feel free to ignore it because I believe
I am asking the same question you guys have likely answers about 40 times,
lol.

On Thu, Oct 12, 2017 at 7:34 PM, Kevin McGuire <kmcg3413 at gmail.com> wrote:

> Guys,
>
> I got to doing some calculations and I realized that exceeding -15dBm on
> the receiver circuitry could be a lot easy than it seems to amateurs like
> me. So, I wanted to run this by some of you because I know that you guys
> have far more radio engineering knowledge than me.
>
> So, lets take a situation for me. Lets say there is a 100-watt transmitter
> within proximity of me. And, I never thought much about it but obviously
> that could be a problem. When I use the link budget calculation I enter in
> 50dBm for the transmitter power, set zero for transmitter loses, set zero
> for receiver loses, set 5db for both TX and RX antennas. Then for the
> distance I have to put in about 3200 feet in order to only see a link
> budget of -15dBm.
>
> I know that is only for perfect world conditions and then its even more
> complicated in reality but I figure that should give me a fairly good idea.
> It is actually scary because I used to tinker with my B200 less than 500
> feet from an antenna that was 50-foot up around 154mhz.
>
> Now, I am not sure what part of the RX chain is sensitive. It could be
> after filtering which means that -15dBm is only for a signal that gets
> through but I suppose also to be on the safe side I might need to consider
> anything. Anyway, it just took me by surprise when I realized how much and
> how easily I could exceed -15dBm. I know too it depends on time so that 1ns
> of -5dBm might not burn something up but you know in my case this 100-watt
> FM transmitter would transmit for a few seconds at a time.
>
> What are your thoughts, suggestions, or ideas?
>
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