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Re: [Discuss-gnuradio] DC component and daughter-boards
From: |
Matt Ettus |
Subject: |
Re: [Discuss-gnuradio] DC component and daughter-boards |
Date: |
Thu, 28 Apr 2005 10:48:33 -0700 |
User-agent: |
Mozilla Thunderbird 1.0 (X11/20041206) |
Damien B. wrote:
> Matt in a previous thread you were talking about making d/b that let
> DC component pass:
>
>
>>If there is enough interest, I might make such a set of boards. If someone
>>else
>>is interested in the design, the BasicRX/TX are a great starting point, and I
>>can offer guidance.
I have seen very little interest in that.
> When i'm inspecting the my FIR output, it's really difficult to
> measure a 30ns (one sample) delay if the signal is not clean.
This is unrelated to the DC component issue.
> Would it
> be possible to make a quick but not perfect hack of the basicTX and
> RX, something like:
> - removing transformer
> - Short-cut pin 3 to 6 and 1 to 4
> the resulting impedance would be 40 Ohms (50 // 50+200+50), but is it
> really bad for low freq square wave < 2MHz ?
Sort of. You would remove the transformer first. Then you have 2
options --
1> Feed your signal to the + input, and send the reference voltage
(Vdd/2, 1.65V, available on the board) to the - input. The problem here
is that the ADC expects the signals to be +/- 1V from the reference,
1.65V. Your signal will need to be properly biased.
The better option is:
2> Put an AD8132 or similar differential amplifier in the circuit. You
can find the appropriate connections in the AD8132 datasheet. This is
what I would do if I did make a DC version of the BasicRX
Matt