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Author Topic: Software Defined Radio Direction Finding  (Read 11835 times)

Posts: 5

« on: March 25, 2012, 04:26:44 PM »

Hello once again,

For those of you interested in Radio Direction Finding, I thought I would share my recent presentation on the subject:

where I talk about DF in general, and my homebrew (auto-)mobile SDRDF system using the open source USRP (Software Defined Radio) and GNU Radio signal processing framework.

Any questions/comments most welcome!
73 VK2FUNK Balint @spenchdotnet
« Last Edit: March 25, 2012, 04:35:24 PM by VK2FUNK » Logged

Posts: 1513

« Reply #1 on: April 06, 2012, 04:24:26 PM »

VHF and UHF Doppler direction finding.......within a new technology framework, not new!

When I saw the heading on your post I got exciting thinking that a ham has  developed a SDR based HF phase correlative interferometer.  I dont think an affordable HF  DSP HF direction finder  that uses COTS hardware will be available
from ham vendors any time soon. There are several  technical challenges that have to be thought about when the hardware is designed. The most important is accurate phased locked clocks. In reality you need at least 8 phased locked
HF receivers to do decent HF DSP DF work.

The most workable solution for ham radio use would single site location DF work. Unfortunately its only leading edge companies like Rohde and Schwartz  who  make hardware, software and antennas for this application.
Ham radio will probably not exist as a hobby if you  are expecting and waiting for  a ham equipment company to produce  a HF DSP based direction finder. The HPSDR group already is moving in this direction and already they have hurdles about the hardware suitability. HF direction DF receivers have very demanding requirements.

All the algorithms  such as MUSIC ESPRIT are in the public domain. I have been experiment with  a DF system  using Matlab  and 3 DSP receivers for a number of years. Yes it works however integrating the whole system into a plug and play  box is beyond my time and resources. The  system works so well, that on  the low bands  you can tell where a ham is within one block on the low bands. The higher bands require accurate ionospheric  data from a sounder if you want to do single site location. The Ideal SDR receiver would be system with 9  SDR receivers that are phased locked. These receivers would have no AGC's and are totally phase stable. With so many hams on the planet a simple network of DF stations using the Watson Watt method would be sufficient to  deter jammers because their locality could be pinpointed accurately.  Single Site location DF systems knocks on the jammers door, which would deter almost all casual jammers.

Good luck  with your HF DF life, you will need your wifes blessing. You will be buried in your shack reading DSP manuals for 5 years!

Posts: 8

« Reply #2 on: April 21, 2012, 06:32:19 AM »

Will using the available GPS 10MHz stable clock signal be sufficient to keep different physical sites phase locked with each other?

Would anyone care to comment regarding accuracy of a HF DF solution under conditions of multi-path reception?

Please excuse my ignorance as I haven't diddled in DF since the early days of home brew VHF dopplescan units with 8 antennas on top of our cars.

73 Patrick AF5CK

Posts: 5

« Reply #3 on: April 21, 2012, 08:03:51 AM »

Hi Patrick,

That's an excellent question - I would love to hear from people who have applied this to HF!

I know SDRs (such as the more advanced versions of the USRP) have the option to be sync'd to GPS so multiple physically-separated sites can remain phase-locked. Therefore I imagine a good GPSDO would probably enable things work well (haven't tried myself though!).
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