Fellow SDR enthusiasts: I have constructed an electronically steerable phased array antenna (and receiver) system using 8 short verticals, 4 softrock v6.1 radios, a DDS 6.0 synthesizer, a Delta 1010LT sound card, DttSP, SDR-Shell, and a blob of software that I wrote (and, of course, a computer running GNU/Linux). I'm also using WA6UFQ's DDS controller software on my laptop to tune the synthesizer. Each vertical is 23 feet tall with 4 23 foot top hat wires sloping at a 45 degree angle. Each vertical has 16 23 foot radial wires. Each vertical is brought to resonance on 1.83 MHz with a 30.5 uH coil and matched to 75 ohm RG6 feedlines with a 68 ohm resistor. Pairs of verticals are separated by 70 feet, and fed through 40 foot pieces of RG6 to a phasing box with a couple of transformers and a relay and a 56 foot piece of RG6 as a phasing line. So a pair of verticals constitutes an end-fire array that can be remotely switched in direction by sending 12 volts down the feedline. There are 4 pairs of verticals in a line, separated by 290 feet, which is just 54% of a wavelength at 1.83 MHz. The whole array has a bore-sight bearing of 65 degrees. Each end-fire element is fed with 1000 feet of (Dayton special) RG6 back to the shack. At the shack are 4 softrock v6.1 SDR receivers tied together from the first receiver's quadrature circuits. That first receiver is fed from the DDS 6.0 synthesizer. The receivers have been manually tweaked to have similar amplitude and phase responses. The band-pass filter at the input of the receiver appears to make the largest contribution to varying frequency response. The I/Q signal from each receiver is fed into a Delta 1010LT sound card. The Delta 1010LT is the same as the Delta 44, except that it has twice as many input and output channels (8 versus 4). It uses the same driver on Linux as the 44 as well. The first pair of channels is configure for microphone level inputs rather than line level, supposedly removed by jumpers. However, the first two channels are inverted in the process with respect to the other 6. My computer has enough horsepower along with the low-latency version of the 2.6.18 kernel to run 3 simultaneous DttSP and SDR-Shell instances. 4 instances causes a lot of xruns. I've written a chunk of software that sits between JACK and a single instance of DttSP and SDR-Shell that sums the 4 I/Q signals and effectively performs the beam steering. JACK is a wonderful idea. My lump of software, which I've dubbed "Phasor" for lack of a clever name performs channel "equalization", steering, and summing. Summing adds channels with the appropriate binomial distribution according to the number of elements configured. Steering shifts the phase of each channel by the appropriate amount to form a beam. Equalization adjusts the amplitude and phase of each channel according to an external reference signal. The most difficult part of the process is equalization. Despite considerable care, each receiver contributes about a 10 degree variation in phase and up to 3 db variance in amplitude. Also, each end-fire element varies a few degrees in phase and has a db or two variance in amplitude. Best performance seems to occur when I use a stable over-the-air signal as a reference for the "calibration" process, which merely FFTs each channel, selects the strongest signals, and records the difference in amplitude and phase from channel 1. Then the equalization process merely applies the inverse of the calibration data to each channel. I wish to use this array on the 160 meter ham band. However, the nearby AM broadcast band provides a very convenient collection of well documented signals with which to test. Daytime testing lets me listen to 2 or 3 three AM radio stations on each frequency merely by banging on my "steer" key. So far, I've made one ham radio QSO using this array to work a station (SV3RF) that I could not hear (very well) with my collection of Beverage antennas. And that contact was prior to the most recent round of improvements. Hopefully, this array will shine when there are some African stations on the air. My long, narrow lot allows long Beverages that favor northern Europe, but not so much due east towards Africa. The other difficulty has been keeping the set of short verticals in tune. Since the entire array is an experiment, I did not construct the verticals with a mind to great longevity. That was perhaps a significant mistake. After some effort this summer, I've finished the array and retuned all of the verticals to be as similar as possible. It appears that lightning (or maybe my own transmitter) increases the inductance of a coil wound on type 61 material when said coil is part of an antenna. There are several improvements yet to be made: frequency compensated calibration / equalization and automatic I/Q balance are the two main areas. Alex, VE3NEA shared Rocky's I/Q balance scheme with me, but so far I have not been able to replicate his success with my software, although his method works very well in a contrived set-up. I'm also looking for some insight into making a digital filter that applies an arbitrary phase and amplitude correction given some frequency dependent function. I intend to write a QEX article or maybe a paper for TAPR when this project is complete, but I wanted to share my current excitement with some of the people that have made my efforts possible, especially Alex, Tony, Frank, Bob, and Edson. I hope I didn't leave anyone out. I have a few old pictures up on my Web site of the array as it existed last year. I'll try to get some more pictures of the other hardware up there soon. Also, a few diagrams would probably be useful. Visit http://k1lt.com. Please don't laugh at the crudeness :-) Thanks! Vic, K1LT PS: the comments about adding DDS6.0 control to SDR-Shell inspired this post. I would like to get that software.