Flex-6000, new generation of SDR transcievers

Flex Radio Systems introduced yesterday at the Dayton 2012 Hamvention the all new Flex-6000 series of transcievers, called “Signature Series”. These are the first comercially available SDR products intended for HF amateur use that employ Direct Digital Conversion, sampling RF directly thanks to the high-performance Analog Devices AD9467 ADC without the need for mixers such as the Tayloe detector that was the heart of the previous generations of SDR equipments.

But this is not the only thing the FLEX-6000 series brings: it’s purpose seems to change a bit towards beter integration into the modern digital world as a shared resource. If until now a transciever was a piece of equipment one operator would use at a time, the FLEX-6000 series is a computer network equipment anyone can use (either on LAN or via Internet), allowing up to 8 virtual 384KHz bandwidth recievers in the 0.03-77 MHz range to be created and operated simultaneously. Ideal for club stations or conditions that require remote operation (Radio Arcala comes to mind), even though the transmission is limited to one user at a time.

Other hardware key points are the pair of Mitsubishi RD100HHF1 finals conservatively pushing out 100W at 13.8V, a rather unusual choice considering the other top manufacturers start moving towards 100V operated final stages wich offer better IMD figures and are easier to work with. Also, the main CPU is a Texas instruments ARM Cortex A8 1.2-1.4 GHz CPU with NEON coprocessor and 1.0-1.2GHz DSP processor. There will be 3 models available, the top dog FLEX6700 transciever, the FLEX-6700R reciever and the FLEX-6500 transciever, with rumored prices os US$7000, US$6000 and US$4000.

More details in the FLEX-6000 series presentation sheet.

Over-the-horizon radar operating in 27MHz

OTH radars are strategic military equipments that basically allow the operator to “see” beyond the horizon trough the means of ionospheric reflexion that allows HF signals to propagate all over the globe. Regular radars use signals in the GHz regions (better for detection of smaller objects) and are only good for direct visibility, that is why sometimes OTH radars were replaced by more expensive “flying radars” more commonly known as AWACS, but as the Cold War has ended armies are folding back to the cheaper technology and the OTH radard operating in HF are spotted more and more oftenly by amateurs. More details on the OTH Wikipedia page, if you are courious.

Such a signal could be recieved today in Bucharest between 27.480500 MHz and 27.499500 MHz at a S9 level, with a type of pattern I haven’t seen before.  Feel free to check out the video and to see how it looks on my SDR transciever.

233RC103/8SM – RC 8th Spanish Meeting contest

I’ll try to enter the 8th Spanish Meeting RC Contest that takes place in the first two weekends of May 2012 with the special callsign 233RC103/8SM; i will be my first contest and the purpose is just to gain some experience in these types of traffic conditions.. See you on the air !

Antennas side by side: Ground Plane versus Delta Loop

At the moment I am using two antennas for 27MHz operation: a 1/4 wave Ground Plane and a Delta Loop, and I had the chance to do a little comparison between them. For who’s not familiar with how these two antennas look, with my inexistent Windows paint skills I have quickly illustrated how mine look and how they’re placed:

The one on the left is the Ground Plane and has 5 elements of 268cm each: the vertical one is connected to the central wire of the 50 ohm coaxial feeder cable, the rest (“radials”) are connected to the outer shield of the cable. Typical impedance of a 1/4 wave Ground Plane antenna depends very much on on the angle between the vertical element and the radials, it’s around 25 ohm for 90 degrees and at 180 degrees should be around 70 ohm; i have used around 130-140 degrees wich should bring the impedance to aproximately 50 ohm, but it didn’t as we’ll see later. It is a omnidirectional antenna, has vertical radiation polarisation and it’s takeoff angle is around 20 degrees.

The Delta Loop on the right is basically a full wave loop in a triangle shape, and fed on the right corner as I did makes it’s polarisation inbetween vertical and horizontal, wich shouldn’t matter too much for DX but it will either be better or worse for line of sight contacts depending on what type  of polarisation your partner is using. To obtain vertical polarisation the feedpoint should be at a level where a line parallel to the ground trough that point would split the antenna in two equal perimeters; for horizontal polarisation, a vertical imaginary line trough the feedpoint should split the antenna in 2 equal perimeters as well. The impedance is around 100 ohm for a triangle with equal sides so it shouldn’t adapt perfectly to 50 ohm feedline, but closing one of the angles like I have done should bring it close to 50 ohm; if instead of a triangle we would make a square from the same perimeter, it would have 50 ohm feed impedance. Because it’s balanced it will need a 1:1 BalUn to work correctly with coaxial (unbalanced) cable, and it can be done either by winding a bifilar wire on a properly chosen toroid (i have used Amidon T80-6, enough for about 100W RF power), or by winding 15-20 laps of 50 ohm RG-58U coaxial cable on a PVC 10cm diameter pipe (enough for much more power). Length of the loop should be a full wave loop, but experiments proved that it properly tunes with a loop slightly longer than full wave: in my case, almost 10% more, 11.7 meters. This really depends on the type of wire used to build it, the height above ground level and what other objects are nearby. The takeoff angle is around 25 degrees but it has about 2dB gain over the Ground Plane so in some situations it might perform better; also the closed loop should offer protection against static noise and improve reception in some cases. It is also slightly directional, favoring the direction perpendicular on the triangle’s plane by 3dB.

Enough theory, now to the real life testing on the next page.

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