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— | mission:log:2012:08:02:active-wideband-receiver-antenna-for-sdr [2015/09/16 13:28] – [Ultra-Cheap LNA alternatives] chrono | ||
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+ | ====== Active Wideband Receiver Antenna for your SDR ====== | ||
+ | [{{ : | ||
+ | |||
+ | Software Defined Radio (SDR) has finally reached a much broader mass of people, who wanted to play with RF technology, but didn't find the time or resources to learn all necessary skills, to build a hardware based radio. Thanks to the work of the [[http:// | ||
+ | |||
+ | The last [[mission: | ||
+ | |||
+ | However, the antenna itself, is still hardware and will most likely never be replaceable by software. On [[irc:// | ||
+ | |||
+ | Other people often recommend Discone-Antennas for wideband reception, but there also are other, less known alternatives, | ||
+ | |||
+ | One of them was the Dressler ARA-2000, covering 50-2000MHz, designed and built in the 90's. The company died the usual death by capitalism (bought by another company and then stripped down and moved production to China). Today there are only a few of these left in the wild and are traded for unrealistic prices on $bay. This particular one was used for the [[lab: | ||
+ | |||
+ | ~~CL~~ | ||
+ | |||
+ | ===== ===== | ||
+ | |||
+ | ===== Disassembly ===== | ||
+ | |||
+ | In order to open the ARA-2000, the black top cap has to be removed first. This can be done with a screwdriver that is pushed under the side of the cover, prying it free. After the cap is removed, the bottom plate needs to come off next. This was a tougher job and required the use of a hot-air gun, to heat up the glue and then carefully applying pressure with a wooden rod through the center of the open tube. | ||
+ | ===== Original Assembly ===== | ||
+ | |||
+ | The following section shows the inner structure of the original ARA-2000 assembly, without the protective white PVC tube. Each image roughly represents | ||
+ | |||
+ | [{{: | ||
+ | [{{: | ||
+ | [{{: | ||
+ | |||
+ | ~~CL~~ | ||
+ | |||
+ | | Length | 405mm | | ||
+ | | Diameter | 80mm | | ||
+ | ==== Antenna Element ==== | ||
+ | |||
+ | The antenna element itself is a simple quadrilateral monopole, in the shape of a wedge, with a narrow start and a wider end. For lack of a common nomenclature and a relatively close optical proximity to a log-per design, this type is going to be ignorantly called // | ||
+ | |||
+ | [{{: | ||
+ | er Antenna Element}}] | ||
+ | [{{: | ||
+ | [{{: | ||
+ | |||
+ | ~~CL~~ | ||
+ | \\ | ||
+ | The small start of the original copper log-per-spiral begins at a 25mm offset from the bottom part of the white, rolled 80mm cylinder, the wider end extends 75mm over the upper edge. After 55mm from the edge of the white cylinder, the rest of the copper is bent around the outer tube and then covered by the cap. This has probably no effect on RF properties (can someone verify this?) but is probably a way to give the whole structure more mechanical support. | ||
+ | |||
+ | <WRAP round download> | ||
+ | **Downloads: | ||
+ | [[https:// | ||
+ | </ | ||
+ | === Properties === | ||
+ | |||
+ | | Material| Copper | | ||
+ | | Height | 0.2mm | | ||
+ | |||
+ | === Sources === | ||
+ | |||
+ | [[http:// | ||
+ | [[http:// | ||
+ | |||
+ | ==== Structure Tube ==== | ||
+ | |||
+ | Further analysis and research regarding material and availability lead to the speculative conclusion, that this foil probably is [[http:// | ||
+ | |||
+ | [{{: | ||
+ | [{{: | ||
+ | [{{: | ||
+ | |||
+ | ~~CL~~ | ||
+ | |||
+ | PVC seems like a logical choice for this support structure material. It shouldn' | ||
+ | |||
+ | The transparent outer foil with the printed grid pattern (non-adhesive), | ||
+ | |||
+ | |||
+ | === Properties === | ||
+ | |||
+ | | Material | [[http:// | ||
+ | | Length | 405mm | | ||
+ | | Width | 405mm | | ||
+ | | Height | 0.3mm | | ||
+ | |||
+ | === Sources (DE) === | ||
+ | |||
+ | [[http:// | ||
+ | [[http:// | ||
+ | [[http:// | ||
+ | [[http:// | ||
+ | |||
+ | Judging by the original build quality, it seems that there is some room for tolerances. It should be possible to hack the assembly ghetto-style, | ||
+ | ==== Cover-Tube ==== | ||
+ | |||
+ | The outer cover tube is made of sturdy white PVC, to protect the inner assembly from rain, hail and UV-radiation and is also used to mount the antenna. Even after several years out in the weather, the tube still looks like new. Again, other materials could also be used here, as long as they won't interfere with RF and can withstand weather and UV-radiation. However, experience has shown, that a more professional looking antenna has a higher chance, that other people like neighbors or landlords won't raise objections to the installation. Depending on your local circumstances, | ||
+ | |||
+ | === Properties === | ||
+ | |||
+ | | Material | PVC | | ||
+ | | Length | 450mm | | ||
+ | | Diameter | 90mm | | ||
+ | | Inner | 84mm | | ||
+ | | Color | white | | ||
+ | |||
+ | === Sources (DE) === | ||
+ | |||
+ | [[http:// | ||
+ | [[http:// | ||
+ | [[http:// | ||
+ | [[http:// | ||
+ | |||
+ | ===== LNA ===== | ||
+ | |||
+ | [{{ : | ||
+ | |||
+ | The low-noise amplifier PCB is mounted directly on the bottom plate and consists of 2 cascaded MMIC Amplifiers. Although the types of the MMICs are not 100% known, DD1US speculated that they most likely are Avago (Avantek) MSA-1105 cascadable Silicon Bipolar MMICs. The specification, | ||
+ | |||
+ | ~~CL~~ | ||
+ | |||
+ | [{{: | ||
+ | [{{ : | ||
+ | |||
+ | ~~CL~~ | ||
+ | ==== Alternative LNA Proposals ==== | ||
+ | |||
+ | === BFP420 === | ||
+ | |||
+ | Due to the venerable age of the original LNA, it is very likely, that more recent semiconductors can deliver superior performance compared to the old design. The LNA is going to be replaced by a new LNA based on Infineons BFP420 which is cheap and available and should perform equally or better. The following two schematics show typical LNA configurations for the BFP420, the left one is the most simple approach (to be tested first), the right picture shows a more refined approach, with better base/ | ||
+ | |||
+ | [{{: | ||
+ | [{{ : | ||
+ | |||
+ | ~~CL~~ | ||
+ | |||
+ | Both designs should also be equipped with a 50MHz high-pass filter between the antenna and the LNA input, to increase their large-signal immunity by attenuating lower frequencies, | ||
+ | |||
+ | * Antenna element -> RTL/ | ||
+ | * Antenna element -> LNA -> coax cable -> RTL/ | ||
+ | * Antenna element -> LNA -> coax cable -> Bias-T -> RTL/ | ||
+ | * Each setup with and without a high-pass filter after the antenna element | ||
+ | |||
+ | === OK3ZB ARA-2000 LNA === | ||
+ | |||
+ | {{: | ||
+ | {{: | ||
+ | |||
+ | See also: http:// | ||
+ | |||
+ | === LNA4All === | ||
+ | |||
+ | http:// | ||
+ | ==== Ultra-Cheap LNA alternatives ==== | ||
+ | |||
+ | Another possible way which would keep the price low would be using inline amplifiers, such as these one: | ||
+ | [[http:// | ||
+ | |||
+ | The internal PCB is not that bad and it can be powered via a bias circuit. | ||
+ | After removing the back cover you can take a look on the insides: | ||
+ | |||
+ | [{{: | ||
+ | [{{: | ||
+ | |||
+ | Here you can see why these Amplifiers get all these bad reviews. I left and right mark show long wire endings, which could lead to bridges in the circuit. In the middle there is some solder on one via at the PCB. Again this dirt could cause a short circuit. | ||
+ | All in all the inner manufacturing was poor but nothing that couldn' | ||
+ | After some research the MMIC that is used was found as a [[http:// | ||
+ | Beside the loose solder in the case there were two little pieces of copper wire. | ||
+ | |||
+ | [{{: | ||
+ | |||
+ | This is a close-up of the inside PCB and the used MMIC. Confusingly the pin-numbering of the MMIC is obviously wrong and I'm not sure if that is a mistake / stupidity or a distraction to " | ||
+ | |||
+ | [{{: | ||
+ | |||
+ | The schematic revealed no surprise. It seems that a Zener-diode was used to stabilize the voltage of standard 12V BIAS supplys to the needed 5V. | ||
+ | On the input-path there is a attenuator installed, right after the first decoupling C. It seems that it has an attenuation of 3 dB. | ||
+ | |||
+ | In order to be used with a direct power supply you have to remove two inductors on the input and output Path of the power supply. In order to be used in different positions in the signal path I solderd two SMA plugs in the case, after removing the standard F-connectors. | ||
+ | I attached an USB connector to the power supply line and after a short test the amplifier was ready to be closed and used. | ||
+ | |||
+ | This one was equiped with cables to be installed better. | ||
+ | |||
+ | |||
+ | [{{ : | ||
+ | |||
+ | The first picture was taken with an Agilent network-analyzer. In advance to the measurement the device has been calibrated. The device number will be added in some days, I forgot to write it down :-) I think it is an [[http:// | ||
+ | |||
+ | For this test I put an attenuator with 10dB in the output-path of the measurement. Keep in mind that there is a attenuator circuit installed on the input path of the amplifier. I will make some measurements after removing it later. | ||
+ | |||
+ | [{{ : | ||
+ | |||
+ | The other pictures were made with an [[http:// | ||
+ | |||
+ | [{{: | ||
+ | |||
+ | |||
+ | [{{: | ||
+ | |||
+ | To put it in a nutshell: Thes amplifiers are just amazing after you clean them and I was surprised of the performance. A comparison to LNA4all and similar projects will be done as soon as the orders arrive. If someona has other amplifiers to be tested please let me know and we can comepare even more amplifiers out there. | ||
+ | |||
+ | ===== Bias-Tee ===== | ||
+ | |||
+ | Although it won't be used anymore, for sake of completeness, | ||
+ | |||
+ | [{{: | ||
+ | [{{ : | ||
+ | |||
+ | ~~CL~~ | ||
+ | ===== Replication ===== | ||
+ | |||
+ | Ideally, the // | ||
+ | |||
+ | < | ||
+ | |||
+ | Since the lab has no vector network analyzer yet (it's on the [[support: | ||
+ | |||
+ | The following assembly guide is a conclusive mini-howto, trying to best guess the original assembly instructions, | ||
+ | |||
+ | <WRAP round tip> | ||
+ | **Assembly Instructions: | ||
+ | - Cut out the antenna element according to specs above | ||
+ | - Solder the small LNA connector to the element | ||
+ | - Cut a 405x405mm sheet of Aslan S22 lamp shade film | ||
+ | - Place Aslan S22 with satin side down (release liner/ | ||
+ | - Remove Aslan S22 release liner (protective foil with the printed red grid) | ||
+ | - Place antenna element on self-adhesive side of Aslan S22 according to spec above | ||
+ | - Get a [[http:// | ||
+ | - Begin rolling the assembly around the cylinder (clockwise from top view) | ||
+ | - Roll the release liner around the assembly and fixate it with tape | ||
+ | - Remove the 80mm rolling cylinder from the assembly | ||
+ | </ | ||
+ | |||
+ | As soon as the new LNA prototype is tested and all other relevant parts are delivered, the new prototype is going to be built and a more extensive and practically proved assembly documentation will be released. | ||
+ | |||
+ | This would also be the perfect scope for some SDR-Wideband-Antenna-Building workshops, so if you're interested in having/ | ||
+ | |||
+ | <WRAP round tip> | ||
+ | **Related Mission-Logs: | ||
+ | [[mission: | ||
+ | [[mission: | ||
+ | [[mission: | ||
+ | [[mission: | ||
+ | </ | ||
+ | |||
+ | |||
+ | {{tag> | ||
+ | |||
+ | |||
+ | {{keywords> | ||
+ | |||
+ | ~~DISCUSSION~~ |