Forum: GNU Radio a simple qustion about the attenuator for the SMA cable

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Bill S. (Guest)
on 2008-11-05 00:32
(Received via mailing list)
Hello, all!!!

I have a rudimentary question about the attenuator. When I was searching
some questions in the archive, I found that some guys mentioned
whentesting the transmitter and receiver for daughter board,the antenna
should be connect by Tx/Rx SMA, the Tx and Rx can NOT be connected
directly by cable and we need a attenuator about
40-50 dB!! What is the meaning of attenuator here? Is it a hardware?
Thanks a lot for all!

Bill
Dan H. (Guest)
on 2008-11-05 20:09
(Received via mailing list)
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On Nov 4, 2008, at 2:31 PM, Bill S. wrote:

> I have a rudimentary question about the attenuator. When I was
> searching some questions in the archive, I found that some guys
> mentioned when testing the transmitter and receiver for daughter
> board, the antenna should be connect by Tx/Rx SMA, the Tx and Rx can
> NOT be connected directly by cable and we need a attenuator about
> 40-50 dB!! What is the meaning of attenuator here? Is it a hardware?
> Thanks a lot for all!

An attenuator is a piece of hardware that weakens ("attenuate" means
weaken) the power of a signal transmitted along a wire. When you
directly wire a TX board to an RX board, the power transmitted is much
stronger than receiver expects (even a tiny bit of air gap induces a
lot of attenuation) and can fry the circuitry. So we simulate this air
gap with an attenuator.

Fixed RF attenuators can be had for fairly cheap ($10-20) I think.

- -Dan
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Bill S. (Guest)
on 2008-11-05 22:03
(Received via mailing list)
________________________________
From: Dan H. <removed_email_address@domain.invalid>
To: Bill S. <removed_email_address@domain.invalid>
Cc: removed_email_address@domain.invalid
Sent: Wednesday, November 5, 2008 1:08:41 PM
Subject: Re: [Discuss-gnuradio] a simple qustion about the attenuator
for the SMA cable

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On Nov 4, 2008, at 2:31 PM, Bill S. wrote:

> I have a rudimentary question about the attenuator. When I was searching some questions 
in the archive, I found that some guys mentioned when testing the transmitter and receiver 
for daughter board, the antenna should be connect by Tx/Rx SMA, the Tx and Rx can NOT be 
connected directly by cable and we need a attenuator about 40-50 dB!! What is the meaning 
of attenuator here? Is it a hardware? Thanks a lot for all!

An attenuator is a piece of hardware that weakens ("attenuate" means
weaken) the power of a signal transmitted along a wire. When you
directly wire a TX board to an RX board, the power transmitted is much
stronger than receiver expects (even a tiny bit of air gap induces a lot
of attenuation) and can fry the circuitry. So we simulate this air gap
with an attenuator.

Fixed RF attenuators can be had for fairly cheap ($10-20) I think.

- -Dan
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=Satt
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Hello, Dan

I got it!Thank you so much! But I think we could also attenuate the
transmitted power by
setting --tx-amplitude to a reasonable value. Do you think so? What's
your idea?

Thank you!

Bill
Philip B. (Guest)
on 2008-11-05 22:22
(Received via mailing list)
On Wed, Nov 5, 2008 at 1:02 PM, Bill S.
<removed_email_address@domain.invalid> wrote:
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> setting --tx-amplitude to a reasonable value. Do you think so? What's your
> idea?

Running full output from the output of the daughter board to the input
my damage the daughterboard. Using an attenuator is safer, avoiding
the possibility of coding errors leading to full output power.

Depending on the ammount you lower the tx-amplitude, you also add
quantization noise.

Philip
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