# Re: Mixing two signals for Radar application **URL:** \ **Category:** GNU Radio\ **Created:** [March 27, 2014, 10:16am UTC](https://www.ruby-forum.com/t/re-mixing-two-signals-for-radar-application/240096 "2014-03-27T10:16:04Z")\ **Posts on this page:** 3\ **Page:** 1
**Author:** ![musicdenotation](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/m/ea666f/32.png) [@musicdenotation](https://www.ruby-forum.com/u/musicdenotation)\ **Post date:** [March 27, 2014, 10:16am UTC](https://www.ruby-forum.com/t/re-mixing-two-signals-for-radar-application/240096/1 "2014-03-27T10:16:04Z")
Hi Marcus,here is the flow graph and the output signals with movement across the antennae and without.[http://tinypic.com/r/a5et5k/8](http://tinypic.com/r/a5et5k/8) (GRC flow)[http://tinypic.com/r/nbeq0k/8](http://tinypic.com/r/nbeq0k/8) (without movement)[http://tinypic.com/r/2s7dnye/8](http://tinypic.com/r/2s7dnye/8) (with movement)Thank you.Dimitris. On 26.03.2014 15:28, Marcus M. wrote:\> Hi Dimitris, > Greetings, > Marcus ---
**Author:** ![Dimitris\_Siafarikas](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/d/9fc29f/32.png) [@Dimitris\_Siafarikas](https://www.ruby-forum.com/u/Dimitris_Siafarikas)\ **Post date:** [March 27, 2014, 12:06pm UTC](https://www.ruby-forum.com/t/re-mixing-two-signals-for-radar-application/240096/2 "2014-03-27T12:06:40Z")
-----BEGIN PGP SIGNED MESSAGE----- Hash: SHA1 Hi Dimitris, I thought you might be supplying us with some background on the flow graph, hardware, expected Doppler Shift, target range etc. You’re just posting the effect, without even referring to what you’re expecting. Greetings, Marcus On 27.03.2014 10:11, Dimitris Siafarikas wrote: > > > Hi list, I am in the process of building an FMCW radar. For > > \_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_ Discuss-gnuradio > mailing list [removed\_email\_address@domain.invalid](mailto:removed_email_address@domain.invalid) > [Discuss-gnuradio Info Page](https://lists.gnu.org/mailman/listinfo/discuss-gnuradio) -----BEGIN PGP SIGNATURE----- Version: GnuPG v1 Comment: Using GnuPG with Thunderbird - [http://www.enigmail.net/](http://www.enigmail.net/) iQEcBAEBAgAGBQJTNAX7AAoJEBQ6EdjyzlHtKtwH/j3+UQTmMdq/Er1w2MNKiV2Q whmWV1loocvDvE5dXfSMZYFCM2SkxT9zaMp9caLMLmrwcndCSL4e58i+ytnkS7BG jcGzU5XcZW8wXSRqR6cRe/41cvEAgSHpnRLoc/+R7TDVxER4NyDExE+M5F3mU2dH XLOgun5yRuRGMv+4UOBgBAbVivgQIdg6zOXo5y/4VBxJLSzBoDWOUid+VdaNtTkD QtCJVaNhb48ORSyapqUgHU8LHTfIpYIsHY31IxicONkxgIUqVqvo5B/s9woKIN+O 5ZOcFjhH1oHJN/eL/1dFgmLjEZ8MoVZbCBQfEm9vCKGYk9BhOzvtnE+mEnx2oo4= =82DC -----END PGP SIGNATURE----- ---
**Author:** ![Dimitris\_Siafarikas](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/d/9fc29f/32.png) [@Dimitris\_Siafarikas](https://www.ruby-forum.com/u/Dimitris_Siafarikas)\ **Post date:** [March 27, 2014, 2:17pm UTC](https://www.ruby-forum.com/t/re-mixing-two-signals-for-radar-application/240096/3 "2014-03-27T14:17:59Z")
> Hi Marcus, > here is the flow graph and the output signals with movement across the antennae > and without. > [http://tinypic.com/r/a5et5k/8](http://tinypic.com/r/a5et5k/8) (GRC flow) > [http://tinypic.com/r/nbeq0k/8](http://tinypic.com/r/nbeq0k/8) (without movement) > [http://tinypic.com/r/2s7dnye/8](http://tinypic.com/r/2s7dnye/8) (with movement) > Thank you. > Dimitris. > OK, so I looked at the flow-graph you posted. There’s a lot of > confusion in there, it has a lot of “confusion per unit area” of > flow-graph, so there’s > a list: o You’re mixing sample-rates without doing any interpolation or decimation. For example, slamming your 100ksps signal source into a USRP hardware source that will try to suck samples out at 20Msps. o You’re trying to mix this 100ksps source with a USRP source running at 25ksps (which isn’t a valid rate for any USRP that I’m aware of). o You’re using a throttle block in a chain that includes hardware – I’m _guessing_ that you thought maybe it would do sample-rate conversion or something, but it isn’t clear what your intention is here. o You’re trying to generate a 1MHz signal source with a sample-rate of only 100ksps. This violates Nyquist rather badly. I think you need to understand what your bandwidth requirements are, and let that guide your sample-rate decisions. If this is a CW radar, you don’t need a lot of bandwidth, and thus, sample-rate. You don’t mention what USRP hardware you have, but in general, the sample-rate must be a proper integer fraction of the master-clock rate, and generally, the resulting decimation can be no higher than 512. Some USRPs (B100, E1xx, B2xx) have variable master-clocks, so you can achieve a variety of different rates. Further, my suspicion from all the above is that your current grasp of DSP techniques isn’t all that solid–I could be wrong, but it _seems_ that way from the flow-graph. My suggestion would be to step back, trying to really understand what you want to do, and maybe curl up with a book on DSP _first_. While “stumbling around” when you’re just building RX flow-graphs with real hardware doesn’t do any harm, doing the same with TX flow-graphs can get unwanted visits from the Federal Authorities in some countries…