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From: | Nemanja Savic |
Subject: | Re: [Discuss-gnuradio] [USRP-users] WBX Lo leakage to LFRX |
Date: | Mon, 16 Dec 2013 18:03:45 +0100 |
First of all you need to _know_ (not _guess_), where it comes from, where it goes to…
Ralph.
From: Nemanja Savic [mailto:address@hidden]
Sent: Monday, 16 December, 2013 16:48
To: Ralph A. Schmid, dk5ras
Cc: Patrik Tast; address@hidden; GNURadio Discussion List
Subject: Re: [USRP-users] [Discuss-gnuradio] WBX Lo leakage to LFRX
Well, maybe I can use spectrum analyser with proper antenna, but what can I achieve with that. If I see peak, I still have a problem to attenuate it.
On Mon, Dec 16, 2013 at 4:36 PM, Ralph A. Schmid, dk5ras <address@hidden> wrote:
Take a handheld scanner or a UHF walkie talkie, tune it to the LO frequency, use a paperclip or some similar 2cm piece of wire as antenna, and start sniffing with this improvised probe for the leakage.
Ralph.
From: USRP-users [mailto:address@hidden] On Behalf Of Nemanja Savic
Sent: Monday, December 16, 2013 4:26 PM
To: Patrik Tast
Cc: address@hidden; GNURadio Discussion List
Subject: Re: [USRP-users] [Discuss-gnuradio] WBX Lo leakage to LFRX
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
--
Nemanja Savić
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