Marcus, Thanks for the advice on the filter pairs. This would seem to be a quick and cheap way to solve this issue. Unfortunately, this is a bit above my understanding. I forgot to mention I am a software guy…which will probably explain a lot to you regarding my question…lol. I will pass this on to my EE work colleague. She will understand this much better than I.
Cheers, Ken > On Sep 5, 2017, at 6:33 PM, Marcus D. Leech via USRP-users > <usrp-users@lists.ettus.com> wrote: > > On 09/05/2017 05:07 PM, Humphries, James R. via USRP-users wrote: >> And I guess the other question would be if there is a circulator that you >> can buy at that low of frequency. I'm not sure that I have seen one, but >> never actually looked. >> >> -Trip >> >> >> -----Original Message----- >> From: USRP-users [mailto:usrp-users-boun...@lists.ettus.com] On Behalf Of >> Humphries, James R. via USRP-users >> Sent: Tuesday, September 5, 2017 5:00 PM >> To: Ken M Erney <gsmmobile...@gmail.com> >> Cc: usrp-users@lists.ettus.com >> Subject: Re: [USRP-users] 50 Ohm terminator on LFTX board >> >> Hey Ken, >> >> Are you thinking of something like a circulator? >> >> https://www.microwaves101.com/encyclopedias/circulators >> >> -Trip >> >> >> -----Original Message----- >> From: USRP-users [mailto:usrp-users-boun...@lists.ettus.com] On Behalf Of >> Ken M Erney via USRP-users >> Sent: Tuesday, September 5, 2017 4:47 PM >> To: usrp-users@lists.ettus.com >> Subject: Re: [USRP-users] 50 Ohm terminator on LFTX board >> >> Here is another question for the RF folks out there. I have a device that >> is sending a signal over a coax cable at about 8 MHz while receiving a >> signal over the same cable at around 3 MHz (both HF). I have an N210 with >> both LFRX and LFTX boards installed. Attached to the coax is a filter and >> DC block. The filter blocks 0 to 1.7 MHz and passes 1.8 to 54 MHz. >> >> What I wanted to do is take the output from the filter, split it, and send >> one feed to the LFRX and one feed to the LFTX. I am then going to use >> gnu-radio to send (at 3 MHz) and receive (at 8 MHz). My initial thought was >> to use a splitter but this setup would basically create a loop-back between >> the TX and RX boards on the N210. I next thought of a duplexer, but I could >> not find anything that would split out 3 and 8 Mhz. >> >> My question is… is this even possible? If it is, what do I need to put >> between the TX and RX side of the N210 to prevent the TX signal going >> directly into the RX port? >> >> The setup looks something like this: >> >> >> |—— (LFRX) ———(8 Mhz)———| >> N210 | |——(y-cable)——| >> (filter/block) |——— (signal coax 50 ohm) >> |—— (LFTX) ———(3 Mhz)———| >> >> >> In this diagram, what would I used on the RX and TX ports on the N210 to >> prevent the loop-back condition? The frequencies (i.e. 8 and 3) are not >> exact, so I can’t really use a hardware filter (I assume). I could use a >> software filter in gnu-radio, but I was not sure about what might happen in >> this scenario (i.e. loopback). One possible idea is to put an attenuator >> just before the LFRX board like the one supplied in the N210 loopback kit >> (i.e. 30db, 0-6Ghz) but I assume this would reduce the power of the receive >> signal as well. Noob here, so my apologies if these are simple questions. >> I could not find much via google on this. >> >> Thanks > Ideally, you want a duplexor. > > But you may be able to get away with a pair of filters--one for your TX > frequency and the other for RX. > > Stick a deep NOTCH for your TX frequency into the RX path, and then a > bandpass for your RX frequency into the RX path. > > Stick a stiff bandpass for your TX frequency into the TX path, and then a > stiff *NOTCH* for your TX frequency into the TX path. > > At these frequencies, ordinary L-C filters work quite well, and "off the > shelf" SMD inductors/Cs can be used at low power levels (below +20dBm or so). > > Check out: > > http://www.wa4dsy.net/filter/filterdesign.html > > > > > _______________________________________________ > USRP-users mailing list > USRP-users@lists.ettus.com > http://lists.ettus.com/mailman/listinfo/usrp-users_lists.ettus.com _______________________________________________ USRP-users mailing list USRP-users@lists.ettus.com http://lists.ettus.com/mailman/listinfo/usrp-users_lists.ettus.com
