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From: | Marcus D. Leech |
Subject: | Re: [Discuss-gnuradio] Modify the Basic RX Daughterboard |
Date: | Thu, 08 Sep 2011 13:17:50 -0400 |
User-agent: | Mozilla/5.0 (X11; U; Linux x86_64; en-US; rv:1.9.2.20) Gecko/20110817 Fedora/3.1.12-1.fc14 Thunderbird/3.1.12 |
On 09/08/2011 01:08 PM, valentac wrote:
I'd say consult the data-sheet for the AD8132. But just to clear things up, you're discussing the *LF_RX* daughtercard, *NOT* the BASIC_RX, which has no op-amp on it at all, just aI have my own RF front end i'm using with the USRP, but it requires a High impedance load to operate correctly. Since the basic RX daughterboard has a 50 ohm impedance, I have to modify it or add a separate voltage buffer before the input. However, since the basic RX daughter board in the USRP has an op-amp in its first stage, perhaps I could modify this. I've tried removing R3 and R9 (http://code.ettus.com/redmine/ettus/documents/4), but this did not seem to load the RF front end sufficiently. Would changing the 348 ohm resistors to a higher value help increase the input impedance into the basic RX daughterboard? If so, how would this affect the output going into the A/D (besides the obvious filtering effects).
transformer.If your input impedance isn't insanely high, you could use a transformer. 4:1 broadband impedance
transformers are available fairly cheaply from Mini-circuits, etc. -- Marcus Leech Principal Investigator Shirleys Bay Radio Astronomy Consortium http://www.sbrac.org
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