Hi, Try a 1/4 shorted stub at 434 MHz (at the antenna).
Patrik (who said many times *not my fault* but usually is...) On Mon, 2013-12-16 at 16:26 +0100, Nemanja Savic wrote: > Hi, > > > i don't understand what can I do in this way with balun. Antenna is > matched very well I think, since I copied reference design from TI. > > I am sure that spike comes from WBX LO because when I change center > frequency the spike also shifts. I'll remind about the configuration > again: > > USRP1 with WBX and LFRX. I want two 434 MHz receivers. One receiver is > made with WBX as RF frontend, while the second receiver uses TI > CC1000 transciever as RF frontend. CC1000 provides 10.7 M IF signal. > From USRP to CC1000 there are two cables, one is coax for IF signal > and another is UTP for power and controlling. I am pretty sure that > leakage signal comes through utp cable and disturbs ground or i don't > know what. Power supply is decoupled many times with caps. This now > the point where experience of the engineer comes into the came, but > unfortunately I am not that experienced. I would like to know what > would you do with the shield of coax cable and UTP cable? How probable > is that I will make a ground loop in that way? > > > Thanx > > > > On Mon, Dec 16, 2013 at 4:09 PM, Patrik Tast <pat...@poes-weather.com> > wrote: > Hi, > > Try finding ferrites for your frequency (11 MHz) and google on > BalUn > (balanced to unbalanced), http://en.wikipedia.org/wiki/Balun > > You could also do it with COAX, impedance match using the > Smith Chart, > if your antenna impedance is known eg > http://en.wikipedia.org/wiki/Smith_chart > > Very usual interference at low freqs are AC power > sources...and are > harmless (you wont see the *spike* when you see a proper > signal) > > Patrik > > > > On Mon, 2013-12-16 at 14:38 +0100, Nemanja Savic wrote: > > I have a following doubt here: there are two cables, one > that brings > > 10.7 MHz if signal from external rf frontend to the usrp, > and utp > > cable that provides power and control signals for rf > frontend. My > > first doubt was that WBX LO signal is directly induced in > the lines on > > LFRX board, but as soon as I disconnected signal cable from > rf > > frontend to usrp the spike dissapeared, so it comes for sure > from rf > > frontend. The problem is how. Should i put rc filters at the > endof > > every controll signal? The other question is how to connect > shields of > > both cables in proper way? I don't want to make ground loop. > > > > > > thanx > > > > > > > > On Tue, Dec 10, 2013 at 5:32 PM, Marcus D. Leech > <mle...@ripnet.com> > > wrote: > > On 12/10/2013 11:24 AM, Nemanja Savic wrote: > > > But I think that I have problem with RX LO of WBX, > because I > > > don't use TX in my application, I have two > receivers. > > > External RF frontend brings HF to IF and is > connected using > > > coax with usrp (LFRX). The other cable, UTP, > connects io > > > pins as well as power of LFRX to external > frontend. > > > Interesting thing is that when I unplug my > frontend the > > > spike doesn exist any more in the spectrum of LFRX > signal, > > > which means that maybe noise comes via UTP cable, > because > > > it's shield is not bonded to ground. > > > > > > > > > > > > > > Well, again, you can offset the RX LO. > > > > > > > > > On Tue, Dec 10, 2013 at 5:12 PM, Marcus D. Leech > > > <mle...@ripnet.com> wrote: > > > On 12/10/2013 10:41 AM, Nemanja Savic > wrote: > > > hi, > > > thank you Ralph. > > > It looks like I should have known > about not > > > packing two receivers in the same > band in > > > the sme box, but anyway, rf parts > are not in > > > the same box, and I intended to > keep them at > > > the distance of arround 5 to 10 > meters. > > > Antenna of 434MHz in is more or > less > > > conected directly do the pin, > there just > > > matching cuircuit between. The > 10.7 MHz out > > > will be with 5 - 10 meters long > cable > > > connected with USRP. Power supply > of > > > external frontend runs through > twisted pair > > > of a UTP CAT 2 cable, which is > kind of > > > shielded, and I have a few > capacitors on the > > > other end for filtering supply > line. As for > > > the LP filter on the 10.7 MHz, i > think that > > > LFRX itself has cuoff frequency of > arround > > > 50 MHz or so. Will it help a bit > if I put > > > some alu plates over WBX board? > > > > > > -- > > > Nemanja Savić > > > The problem is that even with 50dB LO > suppression in > > > the TX mixer, there will still be some LO > energy > > > leaking out the antenna port. > > > > > > But something you *can* do is use > offset-tuning on > > > the TX side to move the LO off to the > side. It'll > > > still be there, but outside of your RX > passband. > > > > > > In "built for a specific purpose" radios, > it's often > > > the case that the last conversion stage > uses a fixed > > > LO that is offset from the final > frequency, and > > > there's a deep notch filter on the > output of the > > > final mixer. That strategy isn't possible > in > > > designs like these that aren't "for a > specific > > > purpose", since > > > there's only a single conversion stage, > with > > > variable LO--you'd have to put in a notch > yourself. > > > > > > > > > > > > > > > -- > > > Marcus Leech > > > Principal Investigator > > > Shirleys Bay Radio Astronomy Consortium > > > http://www.sbrac.org > > > > > > > > > > > > > _______________________________________________ > > > Discuss-gnuradio mailing list > > > Discuss-gnuradio@gnu.org > > > > https://lists.gnu.org/mailman/listinfo/discuss-gnuradio > > > > > > > > > > > > > > > -- > > > Nemanja Savić > > > > > > _______________________________________________ > > > Discuss-gnuradio mailing list > > > Discuss-gnuradio@gnu.org > > > > https://lists.gnu.org/mailman/listinfo/discuss-gnuradio > > > > > > -- > > Marcus Leech > > Principal Investigator > > Shirleys Bay Radio Astronomy Consortium > > http://www.sbrac.org > > > > _______________________________________________ > > Discuss-gnuradio mailing list > > Discuss-gnuradio@gnu.org > > > https://lists.gnu.org/mailman/listinfo/discuss-gnuradio > > > > > > > > > > -- > > Nemanja Savić > > > _______________________________________________ > > USRP-users mailing list > > usrp-us...@lists.ettus.com > > > http://lists.ettus.com/mailman/listinfo/usrp-users_lists.ettus.com > > > > > > -- > Nemanja Savić _______________________________________________ Discuss-gnuradio mailing list Discuss-gnuradio@gnu.org https://lists.gnu.org/mailman/listinfo/discuss-gnuradio