The Red Pitaya SDR board is based on the Xilinx Zync SOC and has 14 bit external A/D converters. However, for SDR usage on the HF bands from 0.1-30 MHz (and for that matter up to 50 MHz) the Red Pitaya is a bit “deaf” in the stock configuration. I have made a broadband amplifier that has a fairly high gain and very good IIP3 properties. Below I have posed some pictures of the prototype amplifier.
This is the prototype amplifier. I inserted a ferrite ring on the input lead to roll off the VHF / UHF sensitivity to reduce problems with nearby broadcasters etc. There is a also a PI network attenuator on the ouput and I have inserted a couple of beads in that as well to roll of the outpu response when frequency increases. The other components in the lower part is a input pi attenuator I used when I did some VNA frequency response measurements. This as well as the RCA plus is not used (RCA plugs are surprisingly good for low level RF signal routing in the HF bands and nice to use in the lab). I used a more professional attenuator with a large attenuation range and flat response to determine the proper attenuation level after the preamp into the Red Pitaya. Reducing gain after the first amplifier has very little effect on the noise figure. Reducing it before the first amplifier directly adds to the noise figure. I added some protection diodes over the input to reduce the risk of strong RF signals or static voltage build up damaging the input. Below I am measuring the response of the attenuator with the DG8SAQ VNA. It was flat from 0-1,3 GHz.
I have been working on a trackball based controller for my HDSDR SDR project lately. This is a small R&D project that is run on my spare time where the goal is to determine if it is possible to use a trackball as a VFO for software defined radio (SDR) in contests. The project started out based on a demand for a more ergonomic way to operate a mult receiver in a contest environment that is less fatiguing during 48hours duration of a major contest like CQWW or CQWPX. The goal is that it should be possible to operate all radio functions you need from one hand only: VFO, speed of vfo, band, mode, filter width, volume, gain. I have modified a Marconi trackball and the controller is a Trinket Pro controller (Arduino)
I blasted my LDG antennatuner some time ago. Or …. I thought I blasted it….. It appeared that it was only the resistor in the SWR detector circuit that got burned out. I replaced that resistor and now its ok again.It was easy to repair. However these small LDG tuners dont take more than 100W max. The designers have used ferrite cores, whereas it would have been a much better idea to use carbonyl cores or air core inductors. The latter doesnt get so easily saturated.
However I must say that the design of the LDG equipment I have seen so far is not very impressive. Why use that BIG chasis when you dont need it? Why use DB9 style connectors on a chassis that is supposed to be watertight? Look at that coax termination there. Both on the board and on the PL259 chassis connector. Why use RG174 teflon coax when you have such crappy terminaions? Perhaps it would be better with no coax at all 🙂 However when the tuner works it works fairly OK. Just dont trust this kind of equipment in a contest or on a dx expedition.
Sketchup is a nice 3D drawing program. It is also free. (Lets hope it will stay that way after Trimble bought Sketchup from Google).
One very annoying “feature” of Sketchup that makes many new users abandon the tool is that there seems to be no way to control the plane you draw a rectangle onto (when using the rectangle tool). The arrow buttons don’t work (why?) and it seems arbitrary what plane the rectangle ends up on. Thanks to the nice people over at Sketchuation, I learned a secret: the rectangle locks on to the PLANE THAT IS MOST PARALELL to the PLANE OF YOUR SCREEN! TRY IT!
By the way, the shift lock doesn’t seem to work properly even if the Sketchup documentation seems to indicate that it should
Many sources on the internet seems to indicate that lead based solder is no longer possible to purchase and is in fact banned for use in electronics. However, this is not the case. It is correct that the EU has passed a regulative that prohibits the use of lead based solder in new consumer electronic products. However, the use of lead based solder for repair of older equipment is still perfectly OK as far as I know. Also, new military electronics is ok to manufacture with lead based solder. I was starting to worry about soldering problems that may affect many amateur radio projects like soldering PL259 coax connectors, after my supply of solder went out. With leadfree solder, a much higher temperature is often necessary to use. The center of the non teflon PL259 connectors then melts and several other problems occur. The leadfree solder doesn’t flow as well as lead based. I us the 60 Sn / 40Pb variant that has been the standard for decades. Farnell sells it and has it in stock. I have replenished the stock to last for several years in different thicknesses so i have for SMD, hole mounted, plugs and larger devices.
Here are Farnell’s ordering codes for good old lead based solder:
Just go ahead and order so you have solder supplies for hobby use for 30 years. Not easy to know what the bureaucrats in EU will think up next!
For some time several vendors in Hong Kong has offered HD video cameras for below USD 50. There are several versions of these cameras. Some cameras are good and some are not so good. Over at RCgroups http://www.rcgroups.com/forums/showthread.php?t=1556994 they have done extensive testing of the type 808 #16 camera.
The inside details and the chassis can be seen in the above pictures. In the left picture, it can be seen that the designer has used a image sensor that has been designed for the cellphone industry. There is a detachable lens (with threads in some of the sensors used) and the lens is attached to the mainboard via a flexiprint and via a controlled impedance and controlled delay connector. The sensor has the type designation OV9712. It can deliver 1280×800 in 30 fps or 720p WXGA HD format. The sensor has gain control, color balance control, and can even correct distortions caused by optics on die. Here is the datasheet of the sensor: http://www.ovt.com/products/sensor.php?id=29 There is a memory chip and a System On Chip (SOC) on the printed circuit board. The SOC has the designation NT96632BG. This SOC appears to me manufactured by the Taiwanese company Novatek . Their website was slow when I visited it, but here is the link http://www.novatek.com.tw/products/SoCSolutions.asp The manufacturer says this about their chip: “Novatek provides DSC/DV SoC solution, which features high image quality, high performance, excellent digital still image capturing and video streaming capabilities at a cost effective base. It is targeted for the application of VGA to 32M pixel DSC/DV resolutions. It can be easily adapted to many CCD and CMOS sensors with on chip programmable interface timing approach. Novatek’s DSC/DV controller provides sophisticated video processing methods with built-in hardware acceleration pipeline. Hardware H.264 video CODEC is embedded with The HDMI 1.3 Tx.“ A significant feature would be analog low latency video out. Then this camera would be ideal for FPV RC flying.
There is a reliable Ebay source for this camera here: eletoponline365
Finally Elfa has increased their range of SMD lab kits. It is somewhat difficult to select the kits from their webpage (that detoriated after they started to use SAP). The manufacturer Nova has a website with better information. You can check out the resistor kit pictured above here http://www.nova-elektronik.de/en/compcards/chip0805.php
Nova also has capacitor kits. Their SMC-36 kit contains 6030 pcs. SMD ceramic capacitors in size 0603. (6 mil x 3 mil). The range is E6 to 4,7pF with CØG dielectricum. Then they have a 6,6 pF to cover the gap and after that the kits includes the E12 series up to 680 pF. This also CØG dielectricum. Wikipedia has some info about C0G diectricum here: http://en.wikipedia.org/wiki/Ceramic_capacitor You can probably use < pF values up to approx 1400 Mc/s (Megacycles per second = 1/p = Megahertz, p= period) before hitting the self resonant frequency.
By the way the information in Elfas catalog is inaccurate in a lot of areas so make sure to do research before you order from them. For example they stated that the above resistors can dissipate 1W. The manufacturers datasheet says 0,1W. Only a factor of 10 wrong. (Probably due to that incompetent spotty teenagers are making their catalogs these days, instead of engineers?)
The newest version of PileUP! magazine from Contest Club Finland has been uploaded to http://www.helsinki.fi/~korpela/PU/PU3_2011.pdf
Take a look. Very good contesting and technical info as well as very good jokes.