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Re: [Discuss-gnuradio] [USRP-users] WBX Lo leakage to LFRX
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From: |
Patrik Tast |
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Subject: |
Re: [Discuss-gnuradio] [USRP-users] WBX Lo leakage to LFRX |
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Date: |
Mon, 16 Dec 2013 18:13:18 +0200 |
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 <address@hidden>
> 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
> <address@hidden>
> > 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
> > > <address@hidden> 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
> > > address@hidden
> > >
> https://lists.gnu.org/mailman/listinfo/discuss-gnuradio
> > >
> > >
> > >
> > >
> > > --
> > > Nemanja Savić
> > >
> > > _______________________________________________
> > > Discuss-gnuradio mailing list
> > > address@hidden
> > >
> 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
> > address@hidden
> >
> https://lists.gnu.org/mailman/listinfo/discuss-gnuradio
> >
> >
> >
> >
> > --
> > Nemanja Savić
>
> > _______________________________________________
> > USRP-users mailing list
> > address@hidden
> >
> http://lists.ettus.com/mailman/listinfo/usrp-users_lists.ettus.com
>
>
>
>
>
> --
> Nemanja Savić
- Re: [Discuss-gnuradio] WBX Lo leakage to LFRX, (continued)
- Re: [Discuss-gnuradio] WBX Lo leakage to LFRX, Marcus D. Leech, 2013/12/10
- Re: [Discuss-gnuradio] WBX Lo leakage to LFRX, Nemanja Savic, 2013/12/10
- Re: [Discuss-gnuradio] WBX Lo leakage to LFRX, Marcus D. Leech, 2013/12/10
- Re: [Discuss-gnuradio] WBX Lo leakage to LFRX, Nemanja Savic, 2013/12/16
- Re: [Discuss-gnuradio] [USRP-users] WBX Lo leakage to LFRX, Patrik Tast, 2013/12/16
- Re: [Discuss-gnuradio] [USRP-users] WBX Lo leakage to LFRX, Nemanja Savic, 2013/12/16
- Re: [Discuss-gnuradio] [USRP-users] WBX Lo leakage to LFRX, Ralph A. Schmid, dk5ras, 2013/12/16
- Re: [Discuss-gnuradio] [USRP-users] WBX Lo leakage to LFRX, Nemanja Savic, 2013/12/16
- Re: [Discuss-gnuradio] [USRP-users] WBX Lo leakage to LFRX, Ralph A. Schmid, dk5ras, 2013/12/16
- Re: [Discuss-gnuradio] [USRP-users] WBX Lo leakage to LFRX, Nemanja Savic, 2013/12/16
- Re: [Discuss-gnuradio] [USRP-users] WBX Lo leakage to LFRX,
Patrik Tast <=