Hello,
   I want to ask a basic question. Full-duplexity in time is understandable
but how is it achieved in frequency? I mean how is a simultaenous
transmission and reception at different frequencies achieved? I don't even
have a good idea of how the current flows in an antenna.
Thanks in advance for answers.

On Mon, 08 Aug 2011 10:45:31 -0500, "commsignal"
<commsignal@n_o_s_p_a_m.yahoo.com> wrote:

>Hello,
>   I want to ask a basic question. Full-duplexity in time is understandable
>but how is it achieved in frequency? I mean how is a simultaenous
>transmission and reception at different frequencies achieved? I don't even
>have a good idea of how the current flows in an antenna.
>Thanks in advance for answers.
>

Google "diplexer".



Eric Jacobsen
http://www.ericjacobsen.org
http://www.dsprelated.com/blogs-1//Eric_Jacobsen.php

commsignal wrote:

> Hello,
>    I want to ask a basic question. Full-duplexity in time is understandable
> but how is it achieved in frequency? I mean how is a simultaenous
> transmission and reception at different frequencies achieved? I don't even
> have a good idea of how the current flows in an antenna.
> Thanks in advance for answers.
> 
> 

commsignal <commsignal@n_o_s_p_a_m.yahoo.com> wrote:

>   I want to ask a basic question. Full-duplexity in time is 
> understandable but how is it achieved in frequency? 
> I mean how is a simultaenous transmission and reception at 
> different frequencies achieved? I don't even have a good 
> idea of how the current flows in an antenna.

On wired nets you can even do the same frequency at the same time.
For S/N reasons that is harder in wireless networks, so different
frequencies are used.  Consider the problem of listening to a
far away radio station while sitting under the tower of a different
station.   That is one of the difficulties in designing
radio receivers.

> Thanks in advance for answers.

-- glen

>commsignal <commsignal@n_o_s_p_a_m.yahoo.com> wrote:
>
>>   I want to ask a basic question. Full-duplexity in time is 
>> understandable but how is it achieved in frequency? 
>> I mean how is a simultaenous transmission and reception at 
>> different frequencies achieved? I don't even have a good 
>> idea of how the current flows in an antenna.
>
>On wired nets you can even do the same frequency at the same time.
>For S/N reasons that is harder in wireless networks, so different
>frequencies are used.  Consider the problem of listening to a
>far away radio station while sitting under the tower of a different
>station.   That is one of the difficulties in designing
>radio receivers.
>
>> Thanks in advance for answers.
>
>-- glen
>
>

"On wired nets you can even do the same frequency at the same time." How is
that done?

On Aug 10, 4:46=A0am, "qasimilyas" <qasim.mahmood@n_o_s_p_a_m.gmail.com>
wrote:
> >commsignal <commsignal@n_o_s_p_a_m.yahoo.com> wrote:
>
> >> =A0 I want to ask a basic question. Full-duplexity in time is
> >> understandable but how is it achieved in frequency?
> >> I mean how is a simultaenous transmission and reception at
> >> different frequencies achieved? I don't even have a good
> >> idea of how the current flows in an antenna.
>
> >On wired nets you can even do the same frequency at the same time.
> >For S/N reasons that is harder in wireless networks, so different
> >frequencies are used. =A0Consider the problem of listening to a
> >far away radio station while sitting under the tower of a different
> >station. =A0 That is one of the difficulties in designing
> >radio receivers.
>
> >> Thanks in advance for answers.
>
> >-- glen
>
> "On wired nets you can even do the same frequency at the same time." How =
is
> that done?

Read up on sidetone suppression. Also hybrid coils. The scheme depends
basically on balanced bridges. It was developed about 150 years ago to
send telegraph signals simultaneously in two directions in a single
wire (with earth return). Not much is really new.

Jerry
--
Engineering is the art of making what you want from things you can get.

Jerry Avins <jya@ieee.org> wrote:

(snip, someone wrote)
>> >> � I want to ask a basic question. Full-duplexity in time is
>> >> understandable but how is it achieved in frequency?
>> >> I mean how is a simultaenous transmission and reception at
>> >> different frequencies achieved? I don't even have a good
>> >> idea of how the current flows in an antenna.

(snip, then I wrote)
>> >On wired nets you can even do the same frequency at the same time.
>> >For S/N reasons that is harder in wireless networks, so different
>> >frequencies are used. �Consider the problem of listening to a
>> >far away radio station while sitting under the tower of a different
>> >station. � That is one of the difficulties in designing
>> >radio receivers.

(snip)
>> "On wired nets you can even do the same frequency at the same time." 
>> How is that done?

> Read up on sidetone suppression. Also hybrid coils. The scheme depends
> basically on balanced bridges. It was developed about 150 years ago to
> send telegraph signals simultaneously in two directions in a single
> wire (with earth return). Not much is really new.

It does get a little harder at high frequency.  Gigabit ethernet
uses all four pairs of a Cat 5 cable in both directions at the
same time.  (The standard allows for half-duplex, but, as far as
I know, no implementations.)  Cat 5 cable is spec'ed to 100MHz,
so getting 250Gb/s down a pair isn't so easy.  Doing it in both
directions at the same time is even harder.

At some point, it comes down to S/N.  You have to subtract the 
signal being sent out from what you see on the end of the cable
to detect the signal coming in.  Gigabit ethernet uses an adaptive
equalization and echo canceling system.  Among others, you have
to subtract the reflection from the far end due to impedance mismatch.

-- glen