# Modify the Basic RX Daughterboard **URL:** \ **Category:** GNU Radio\ **Created:** [September 8, 2011, 7:09pm UTC](https://www.ruby-forum.com/t/modify-the-basic-rx-daughterboard/211608 "2011-09-08T19:09:51Z")\ **Posts on this page:** 3\ **Page:** 1
**Author:** ![dubstep](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/d/cdc98d/32.png) [@dubstep](https://www.ruby-forum.com/u/dubstep)\ **Post date:** [September 8, 2011, 7:09pm UTC](https://www.ruby-forum.com/t/modify-the-basic-rx-daughterboard/211608/1 "2011-09-08T19:09:51Z")
I 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](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). View this message in context: [http://old.nabble.com/Modify-the-Basic-RX-Daughterboard-tp32425579p32425579.html](http://old.nabble.com/Modify-the-Basic-RX-Daughterboard-tp32425579p32425579.html) Sent from the GnuRadio mailing list archive at [Nabble.com](http://Nabble.com). ---
**Author:** ![valentac](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/v/5fc32e/32.png) [@valentac](https://www.ruby-forum.com/u/valentac)\ **Post date:** [September 8, 2011, 7:18pm UTC](https://www.ruby-forum.com/t/modify-the-basic-rx-daughterboard/211608/2 "2011-09-08T19:18:32Z")
On 09/08/2011 01:08 PM, valentac wrote: > daughterboard? If so, how would this affect the output going into the A/D > (besides the obvious filtering effects). > 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 a > 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 L. Principal Investigator Shirleys Bay Radio Astronomy Consortium > **[Live Draw HK Tercepat | Result HK | HK Pools | Live HK | HK Prize Hari Ini](https://www.sbrac.org/)** > > Temukan live draw hk tercepat melalui halaman hk pools yang resmi dan dapatkan result hk prize melalui live hk secara langsung di situs kami. ---
**Author:** ![valentac](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/v/5fc32e/32.png) [@valentac](https://www.ruby-forum.com/u/valentac)\ **Post date:** [September 8, 2011, 10:41pm UTC](https://www.ruby-forum.com/t/modify-the-basic-rx-daughterboard/211608/3 "2011-09-08T22:41:09Z")
My mistake, I am using the BasicRX with the transformer (I was looking at the wrong datasheet). I could go ahead and get a new transformer, but I would ideally like a higher impedance than is offered. I just tried to modify the transformers in the schematic ([http://code.ettus.com/redmine/ettus/documents/2](http://code.ettus.com/redmine/ettus/documents/2)) by removing R3 and R9, and then changing R6 and R7 to 1 MOhm, however, this didn’t seem to give me a large enough impedance. Is there a better way to modify the transformer that is on the BasicRX to give me a high impedance? Marcus D. Leech wrote: > > > > ## the _LF\_RX_ daughtercard, _NOT_ the BASIC\_RX, which has no op-amp on > > [Discuss-gnuradio Info Page](https://lists.gnu.org/mailman/listinfo/discuss-gnuradio) – View this message in context: [http://old.nabble.com/Modify-the-Basic-RX-Daughterboard-tp32425579p32426977.html](http://old.nabble.com/Modify-the-Basic-RX-Daughterboard-tp32425579p32426977.html) Sent from the GnuRadio mailing list archive at [Nabble.com](http://Nabble.com).