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
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