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Re: [Discuss-gnuradio] LFRX board gain problems in usrp_oscope?

From: Martin Dvh
Subject: Re: [Discuss-gnuradio] LFRX board gain problems in usrp_oscope?
Date: Sat, 06 May 2006 18:49:53 +0200
User-agent: Debian Thunderbird 1.0.2 (X11/20051002)

Brett L Trotter wrote:
> When I try and use usrp_oscope.py on my USRP board with an LFRX board,
> setting gain at 4 or above results in a non-updating display. Setting
> below 3 works OK-
Did you try setting Trigger to auto (instead of pos or neg)

Default the trigger is set to pos.
Which means it looks for positive zero passings.
If the input never gets zero, it will never update.
If the input is not exactly balanced around zero you get a DC bias in gnuradio.
When you increase the gain, at some point all samples will be above zero so 
trigger pos will never go of and your display stops updating.

When you set trigger to auto, the display should start updating again.

The other options is that there is some bug in the LFRX code.
I haven't looked at that yet.

I do have an LFRX so if I ever find the time I will test this with the current 

I have worked with LFRX a some time ago and then it worked just fine.
(As long as you pay attention to DC-bias and DC/AC couplings)

> though still have not been able to find an appropriate
> antenna and/or high impedance buffer amp and have not yet listened to AM
> radio sucessfully. But the gain issue seems like something is wrong. Any
> thoughts?
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