Forum: GNU Radio LFRX board gain problems in usrp_oscope?

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Brett L Trotter (Guest)
on 2006-05-06 20:19
(Received via mailing list)
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- 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?
Martin D. (Guest)
on 2006-05-06 20:52
(Received via mailing list)
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 codebase.

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)

Greetings,
Martin
Eric B. (Guest)
on 2006-05-11 07:35
(Received via mailing list)
On Sat, May 06, 2006 at 11:18:31AM -0500, 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- 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?

Set it to "auto trigger mode" and/or press the 50% button (sets
trigger at 50% of what it sees.)

Eric
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