Re: [Discuss-gnuradio] a simple qustion about the attenuator for the SMA cable

[Philip Balister]

On Wed, Nov 5, 2008 at 1:02 PM, Bill Stevenson
<address@hidden> wrote:
>
>
> ________________________________
> From: Dan Halperin <address@hidden>
> To: Bill Stevenson <address@hidden>
> Cc: address@hidden
> 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 Stevenson 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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> 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?

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


>
> Thank you!
>
> Bill
>
>
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