We seek to understand and document all radio transmissions, legal and otherwise, as part of the radio listening hobby. We do not encourage any radio operations contrary to regulations. Always consult with the appropriate authorities if you have questions concerning what is permissable in your locale.

Author Topic: Using two SDRs with two aerials for steerable array?  (Read 3301 times)

Offline Billy the Mountain

  • Jr. Member
  • **
  • Posts: 46
  • MO
    • View Profile
    • Email
Using two SDRs with two aerials for steerable array?
« on: November 02, 2012, 2058 UTC »
Anybody thought of doing this?  I see two methods that might be interesting:

A) two identical vertical aerials[1] spaced >0.1 wavelength apart, each connected to a separate SDR. 
Use software to continuously change the phase between the two SDRs, then mix it
Voila!  Electronically steerable array.  Essentially what you get here is a steerable null.

2) One vertical and one horizontal aerial, each connected to an SDR.
Do that phasing thing from above.
Voila!  Diversity reception.

Obviously, I haven't clearly thought this all out.  Once upon a time I thought it might be neat to try something like this with two softrocks (or other cheap SDR), with two sound cards (tied to the same xtal clock).  I'm still thinking about it.  This has got to be easier than running phasing lines, etc., out in the yard for the dogs to "comment" upon.

Was denkst du?
--
Somewhere in MO.
TR7/Sony 2010/SDRPlay/40m dipole/Various other aerials.
Ubuntu 14.04, FreeBSD 10.2, why am I putting OSs in my sig?

Offline ChrisSmolinski

  • Administrator
  • Marconi Class DXer
  • *****
  • Posts: 23337
  • Westminster, MD USA
    • View Profile
    • Black Cat Systems
Re: Using two SDRs with two aerials for steerable array?
« Reply #1 on: November 02, 2012, 2118 UTC »
RF Space may offer a second RF input for the netSDR (it's a module listed on their site but not yet available). This would allow you to do exactly what you're describing.
Chris Smolinski
Westminster, MD
eQSLs appreciated! csmolinski@blackcatsystems.com
NRD 545 / netSDR / AFE822x / AirSpy HF+ / KiwiSDR / 670 ft horizontal loop / 500 ft northeast beverage / 58 ft T2FD / 300 ft south beverage / 43m / 20m / 10m  dipoles / Crossed Parallel Loop

Offline Token

  • Global Moderator
  • DX Legend
  • *****
  • Posts: 1791
    • View Profile
Re: Using two SDRs with two aerials for steerable array?
« Reply #2 on: November 03, 2012, 1259 UTC »
Anybody thought of doing this?  I see two methods that might be interesting:

A) two identical vertical aerials[1] spaced >0.1 wavelength apart, each connected to a separate SDR.  
Use software to continuously change the phase between the two SDRs, then mix it
Voila!  Electronically steerable array.  Essentially what you get here is a steerable null.


This has been discussed a few times on a few forums.

Comparing the phase of a signal received by both gives you angle of arrival, for very quick RF DF capability.  Adjusting the phase relationship between the two SDRs steers the beam.

Of course, with only two SDRs/antennas you have a bi-directional system, meaning two main lobes/nulls 180 degrees apart, and two possible directions of arrival, also 180 degrees apart.  Adding a third SDR and antenna could reduce that to a single main lobe/null.  A fourth would be better yet.

T!
T!
Mojave Desert, California USA

Offline Billy the Mountain

  • Jr. Member
  • **
  • Posts: 46
  • MO
    • View Profile
    • Email
Re: Using two SDRs with two aerials for steerable array?
« Reply #3 on: November 03, 2012, 1459 UTC »
Anybody thought of doing this?  I see two methods that might be interesting:

A) two identical vertical aerials[1] spaced >0.1 wavelength apart, each connected to a separate SDR.  
Use software to continuously change the phase between the two SDRs, then mix it
Voila!  Electronically steerable array.  Essentially what you get here is a steerable null.


This has been discussed a few times on a few forums.

Comparing the phase of a signal received by both gives you angle of arrival, for very quick RF DF capability.  Adjusting the phase relationship between the two SDRs steers the beam.

Of course, with only two SDRs/antennas you have a bi-directional system, meaning two main lobes/nulls 180 degrees apart, and two possible directions of arrival, also 180 degrees apart.  Adding a third SDR and antenna could reduce that to a single main lobe/null.  A fourth would be better yet.

T!




. . .and doing 4 receivers could be dirt cheap with softrocks or similar.  The piece I would be hung up on is how to execute it in software.
--
Somewhere in MO.
TR7/Sony 2010/SDRPlay/40m dipole/Various other aerials.
Ubuntu 14.04, FreeBSD 10.2, why am I putting OSs in my sig?

Offline ChrisSmolinski

  • Administrator
  • Marconi Class DXer
  • *****
  • Posts: 23337
  • Westminster, MD USA
    • View Profile
    • Black Cat Systems
Re: Using two SDRs with two aerials for steerable array?
« Reply #4 on: November 03, 2012, 1610 UTC »
. . .and doing 4 receivers could be dirt cheap with softrocks or similar.  The piece I would be hung up on is how to execute it in software.

You'd want to keep all the data sync'd. If you wanted to do it via softrocks or other sound card based SDRs, I suspect a multichannel sound input device might be best? An 8 channel device would let you bring in 4 pairs of I/Q data. You also might want/need to run all the SDRs off a common clock, so you don't get any relative drift (frequency or phase) between them.
Chris Smolinski
Westminster, MD
eQSLs appreciated! csmolinski@blackcatsystems.com
NRD 545 / netSDR / AFE822x / AirSpy HF+ / KiwiSDR / 670 ft horizontal loop / 500 ft northeast beverage / 58 ft T2FD / 300 ft south beverage / 43m / 20m / 10m  dipoles / Crossed Parallel Loop

Offline Token

  • Global Moderator
  • DX Legend
  • *****
  • Posts: 1791
    • View Profile
Re: Using two SDRs with two aerials for steerable array?
« Reply #5 on: November 03, 2012, 1749 UTC »
I like the idea, but you know, I assume, that steering a null/lobe is much easier to implement using a simple variable phase shifter and a single receiver.  The addition of the SDR brings not only steerability but also the ability to detect angle of arrival for even very short duration transmissions, such as single pulses.

T!
T!
Mojave Desert, California USA

Offline vinoul

  • Newbie
  • *
  • Posts: 19
  • Chicagoland - NW Suburbs
    • View Profile
Re: Using two SDRs with two aerials for steerable array?
« Reply #6 on: November 03, 2012, 1858 UTC »
Here's a ham that has used Softrocks to do it on 160m.  I'm guessing this would work for a small range of frequencies, since changing to a different frequency band would change all the phase relationships, and would have to be re-calculated.   :D

http://k1lt.com/


Offline Token

  • Global Moderator
  • DX Legend
  • *****
  • Posts: 1791
    • View Profile
Re: Using two SDRs with two aerials for steerable array?
« Reply #7 on: November 03, 2012, 2231 UTC »
K1LT's application is aimed at forming a decent beam to enhance received perfomance, that is the reason he uses 8 elements in 4 pairs of end-fire arrays.  He has also added the ability to reverse direction to those elements.  So yes, it would be frequency sensitive and have a relatively narrow range for a well shaped beam (and even at that you can see, in the QEX article, grating lobes affecting his beam shapes as he gets off boresite of the array).  However, for RFDF and applying a null to QRM/QRN you do not need that complex an array (gain is not necessarily the goal, only a well formed null), and the system would be more forgiving of bandwidth.  Don't get me wrong, you might still need several sets to get frequency coverage that might be most usefull, but each would be more simple than his setup.

For RFDF and QRM/QRN nulling a broadside array might be preferable.

T!
T!
Mojave Desert, California USA

Offline Pigmeat

  • DX Legend
  • ******
  • Posts: 4159
    • View Profile
Re: Using two SDRs with two aerials for steerable array?
« Reply #8 on: November 05, 2012, 0110 UTC »
Fansome is usually full of bright ideas and free advice on receivers and antennas. I wonder why he hasn't chimed in?

Offline Billy the Mountain

  • Jr. Member
  • **
  • Posts: 46
  • MO
    • View Profile
    • Email
Re: Using two SDRs with two aerials for steerable array?
« Reply #9 on: November 05, 2012, 1339 UTC »
Here's a ham that has used Softrocks to do it on 160m.  I'm guessing this would work for a small range of frequencies, since changing to a different frequency band would change all the phase relationships, and would have to be re-calculated.   :D

http://k1lt.com/



Now it's looking like a whole lot of work.  I'll still have to keep mulling this one. . .
--
Somewhere in MO.
TR7/Sony 2010/SDRPlay/40m dipole/Various other aerials.
Ubuntu 14.04, FreeBSD 10.2, why am I putting OSs in my sig?