communication system

Nov 28, 2012, Required power for communication on Lunar distances.Igor - Assume MW7IC2425 25WT with narrow band PAE 40% will transmit 10WT (40dBm).Assume nRF24L01 sensitivity -85dBm (at 1Mbps). Assume cascade 3 LNA amplifiers (SKY67014-396LF) with noise 4dB, gain 36Db total. On distance 400000km path Loss 212 dB on 2450 MHz, all this will require on both side antennas with 28dBi gain to get -80dBm RX power. Enough to work with nRF24L01’s sensitivity -85dBm and margin for a noise 85-80 = 5dB. Using different LNA amplifiers (MC13850EPR2) will give 6dB noise and 39 gain, outcome in this case -77dBm with margin for noise 85-77 = 8dB. Pretty tight.

To test on Cubesat transmitter == 0.5WT transmit (27dBm), distance 400km path loss 152 dB, symmetrical antennas with 8dBi gain will give in that case -70dBm RX power. That is a goal for test flight.

For first test on ground, transmitter has to be stripped from power amplifier with LNA cascade 26-29dB and direct 1mWt (0dBm) output to same antennas (8dBi) as for Cubesat to get same -71dBm power on RX. Distance has to be 20 km (path loss 126dB). Direct distance = Cyprus – SFU hill ==25, Grouse Mt. – SFU hill == 15km, and Mt. Seymour – SFU == 9 km

For second test on ground, transmitter with 0.1WT (20dBm) and same antennas require 2km (path loss 106dB) distance for same -70dBm RX. In this case LNA amplifiers hast to be removed, or put into by-pass mode.

To calibrate 8dBi ‘s antennas, power amplifier and LNA has to be both removed and -70dBm RX achieved on distance 200m. Adjusting antennas from original can be done by reducing amount of turn on helix. Perfect spot for this - is my window on 14th floor and a BC place near steam's plant

Reduced size helical shows 10cm length with 15 dBi, and on 40cm around 28dBi (today it is only speculations). To confirm that needs to test on distance 200m antennas with 1/3 of turns. And after that conformation has to be done on regular helix 8cm (3 turns).

For testing 0.5-1WT PA pretty good is glass windows in my building – glass reduces signal – measuring distance with calibrated 8bDi antenna helix allows to calculate path loss over glass (LNA has to be bypassed) estimation for today is 15-25dB. Distance around 0.5km – 0.7km on spot of Olympic village can be used to test full system. To get -69dBm RX power needs to path loss 112 dB (4km) on 0.5WT or 115dB (5.6km) loss for 1WT.

Nov 21, 2012. PAE and efficiency. Boris – Q: – if PAE of transmitter amplifier == 40% then around 60% (definitely less, rest is noise) goes to the heat – assuming that a thermal radiation is only available method to heat transfer, then some of the heat will be possible to recycle by reverse Peltier thermoelectric heat pump. That is easy to check on our next tests with 1WT transmitter. Even more - with 25WT eating by amplifier and PAE=40%, 15WT goes to heat, each watt recycled will improve Ecclesiastes' ratio – “time to harvest power” / “time to transmit”, that will give for each one watt recycled = 2% savings in total time transmission == 0.5 low resolution frame per 10 minutes transmission session , or on 16hours (for required 15min HD video) will be 25 minutes savings. Efficiency of Pertier’s elements is kainda a question (especially reverse one) – in some sources it is stated == 5-10% in some up to 50% - needs to make experiments, but even with 5% it will be 1% savings in session time.

Nov 21, 2012. Calculations, calculation, and nothing more than calculations. Thanks Gregory! – FR-4 PCB’s dielectric constant ranges Er= 4.2 – 5.0 (assumed Er=4.8). Height of dielectric =62mils. Thickness of the board = 1.25 oz/ft^2 (1.7mils). Useful link to calculate Z0 =http://www.ekswai.com/en_microstrip.htm . Smith’s calculator resources http://sss-mag.com/smith.html (very good Smith.exe by Prof. Fritz Dellsperger from Switzerland). As a result for MW7IC2425NR1 on reverse calculation impedance on input pin = (58.535 –j9.834) on output pad (5.180+j59.876) – error 20% based on Er error. Looks like will be require for MOSFET to narrow amount of channels from 128 to 32. That can give PAE around 40% - for clamed in spec consuming 25WT it will be 10WT of transmitted power (with harvesting on 3-rd week max = 4- 5WT it will require 6 minutes to harvest for transmitter, 4 minutes for control and 1 minute for transmit totaling == 60sx10K = 600K/min, or 10 minutes == 1 HR picture ,or 24 low resolutions frames, or 15min HR video will be transmitted during 16 hours). On http://hamwaves.com/antennas/inductance.html for new design of antenna it is Zc=128om. For switches good HMC784MS8GE(10WT, isolation -32dB). Needs to re-trace PCB, order and test. That is best for today.

Nov 15, 2012. Class D and class E,F amplifiers.Alex- correction for previous post about class D: “. . .PAE (Power Added Efficiency) can be around 100%. Some matching for impedance should be done, but that is a minor question.. . .”

Tubes/wave. To make experiments needs to have ability to get high vacuum inexpensive way – glass can be printed, everything can be printed and packed into glass. It is funny – to get the vacuum (free on the orbit) needs to have a vacuum (expensive on earth) – Isn’t it?

Antenna will arrive tomorrow. It will be possible to make measurements with 0dBm to compare helical and modified helical designs. I discussed today with Boris crazy idea about make modified antenna with active antenna’s sections. He looked at me like professor of physics looks at perpetuum mobile’s inventor. Active antenna skipped.

And you have no idea what I bought looking for wave tubes! PDP-11 processor! – Old! golden pins shining brightly! (at least on picture). It will be embedded into Cube-sat – may be we can connect a power pin to a ground!

Nov 14, 2012. Class D amplifier. (translation). Alex- Finally got what is class D amplifier (thanks for Sasha ‘s tip) – two MOSFET with similar characteristics (one is N another is P type) working as switches. Gates and drains connected, one source (P)on a power another source (N) on a ground. In simulation shows when on gates voltage low then 1.1V, then on drains is ground, and when on gates >1.1v, on drains VDD. Even gain around 8-10Db can be achieved, but it does not matter. If to skip the gain then switches will be in open or closed state, as a result PAE (Power Added Efficiency) can be around 100%. Some matching for impedance should be done, but that is a minor question. Switching voltage depend on MOSFETs, the same can be said about impedance matching design. On exits needs to put filter to make sin-cos-things.

Some researchers (in scientific patents) stated that it can be important solution for low cost tooth-blue’s power amplifier because GFSK (Gaussian Frequency Shifting Keying == shift 180 degree) less picky then π/4DQPSK (45 degree shifting) and 8DPSK(8 phases). On Wi-Fi that idea does not work.

But like in that funny story about the hunter lost direction in a forest, does not matter what you find, matter how can use it.

a) Variety MOSFETs for 2.4Ghz available only in one polarity. Maximum what can be constructed from such devices is class A, A-B (theoretical PAE 60%)

b) Check for available switches bring “Ops”. Switches working on huge frequencies with power 1-5 watts can switch from channel to channel with maximum frequency up to 1GHz (1 nanosec), and for 2.4GHz needs to have 0.41(6) nano – Oops in full scale.

Well, what is about “space” – yep – looks like it working but topology for such chip needs to be ordered as customer’s order. Prices in that case will be around big green numbers.

With switches looks like more complicated case – restrictions on good toys is in place – you know –

What was left – (a) tubes, but needs to account power for heating, all those passive and active induct-capas-res-tors on the way into the tube and a signal's path out. (b) Traveling Wave tubes. (c) go to school to learn how transistors are working.

That’s it. Nicht gut. Today best is PAE 50% maximum, may be for Cubesat it is Ok but definitely not for the moon, solar panels on shoelaces required.

Nov 13, 2012. Class D Amplifier. (translation will be later). Шура! Наконец-то понял, че такое класс Д усилитель (туп был - сознаюсь! спасибо Саше за подсказку) - два полевых транзистора (один N другой P полярности) одинаковых характристик работают как ключи - входы (затворы) соеденены вместе, истоки запаяны тем же кренделем - сток одного на питании, сток другого на земле. Когда на входе одно значение (0) то на истоках земля == 0 вольтов - а при значении 1 на входе == на истоках получается питание.

За счет того что схема сидит либо в открытом, либо закрытом состоянии КПД достигает 100%

После выхода ставят фильтр для обрезания в синусоиду - некоторые утверждают (в высокоученых публикакциях), что зело быть решение для усилка мощьности голубозубого == т.к. максимум надо чтоб пролез сдвиг по фазе на 180 градусов. (для Вай-Фай не подходит = там что-то замучено со сдвижкой).

Но, как в том анекдоте, с заблудшим в лесу мужиком, от отчаяния кричащим - А-УУ! - Услышь-те ! Памаги-те! Кто-нибу-ть! - кричал -кричал - вдруг, кто-то ему лапу на плечо - оборачивается - медведь - Ну хорошо мужик - вот я тебя и услышал - а поможет ли тебе это?

так и у меня - от того что что-то нашел - не значит что решение найдено - Пунктик номер один - на нужную частоту полевые транзисторы только одной плярности. Максимум что можно собрать из таких транзисторов, это класса А-Б усилитель (тетеретическийКПД максимум 60% )

Пункт номер два - прикинул что можно использовать обычные свитчи - ан -нет! - свитчи пашущие на сумашедших частотах, с мощностями 1-5 ватт, (!) переключаются с канала на канал (!) с максимальной частотой только до одного гигагерца (1 наносекунда) - а надо 2.4гига (или 0.41 и шесть в периоде наносукунды).

Начал рыть, а как же для космоса работают - да работают - только топологию для такого устройства разрабатывают индивидуально - после разработки профессора пишут статью - а цена такой цацки минимум 100 штук зеленых.

А для свичев пронблема еще веселей - судя по всему лапу наложили ребята с шевронами - и хотя есть надежда как в случае с гироскопом - в спецфикации одно, а на деле переключаются быстрее - но это вряд ли! - должны бдить!

Остаются радио лампы - но у них дикие габариты - нужно учитывать все емкости и индуктивности по пути в лампу и из оной. Или лампы бегущей волны. Или изучать принцыпы работы транзисторов.

Вот такая карусель получается - максммум КПДна сегодня 50% - для кубсата может быть ОК - а для луны явно не хватит батарей - на шнурок придется дополнительную привязывать - что не есть зер-гут!

Nov 5, 2012. Sania, Thanks for info. That is exactly what I need now. I download exact software last week. It allows matching impedance of PA and antenna, LNA and BT. Demo version of it take in account of a strip of cupper trace and impedance can be easily matched. With that software finally I matched PA and helical antenna it is simple as ABC – impedance of antenna 180 and exit of PA 50 just need to place tiny 403 resistor = 180-50 = 130om. Thanks again for info. Gregory also give me nice website (in Russian) with detailed explanation what to do - http://www.avr123.nm.ru/soglasie.htm. Gregory also shake head about my approach – he asked what oscilloscope I am using to check signals – My answer- “build in 1976” - and he replied - “Саня ! на коленке ничего не сделаешь!” == "Alex! Good oscilloscope for 3GHz is mandatory."

Status is on critical part today (communication amplifiers) and options available–

- I finally ordered antenna, will be printed on 14 November, only after tests I think will be possible to draw patent – nobody knows may be I am wrong with my “reduced size design”. As far as it is impedance will be 70-80om, for cubesat it will be smaller size (more space in cube will be available) – for ground station also smaller – for example amount of material to print is 1/3 of original helical. But until tests done it is premature to talk that it will be working.

- Victor suggest to use LAMPA BEGISCHEI VOLNI (traveling wave amplifier) – looks promising. 70Db. Spread spectrum. Prices 25-2000. Up to 1kwt. Questions: how to heat electrons emission’s element, how to place in Cubesat (it is long – also available shorter version – but nobody knows parameters – kainda Russian military leftover), what to do with series of magnets (from another prospective magnets is not bad it will stabilize Cubesat by itself). How to cool down internal element inside helix. Used previously successfully in space. Not sure about – just investigation and experiments will take time. May be require experiments in vacuum chamber.

- Also found modem for cubesat on 2.4Ghz frequency (price=1000-2000CND) in Calgary http://www.microhardcorp.com/MHX2420-HV.php http://www.microhardcorp.com/n2420.php . But not sure about error correction and compatibility with my hooping frequency protocol. I can give-up protocol in favor to use that modem, but I am not sure – for cudesat it will work ok but what will be on main path – the design of scalable 10wt TX and protocol still will be required. That modem uses 1wt transmit with 5V – 500ma = 2.5wt power needs to be accumulated before TX. For a modem recommended just a regular antenna. Our approach sound better – if antenna (again if- after tests – today it is a speculation) will be polarized then 10 cubesats flying together will be not created disturbance to each other in communication; in favor to hooping protocol the same - interference avoidance can be done by protocol also.

- On tip from Alex - still working on it – need class C amplifier – found yesterday one – PAE=45% but input require 40mwt – needs to have “middle” amplifier from 0Dbi to 15-18Dbi. MOSFET is a probably choice for class C – MOSFET is heavy for me – but proper design can give PAE=90%.

- No information from Serg – he promised to check with his friends - they did in Donetsk region modems on 2.4GHz – modem supported IP connection btw mines on distances 10-20 km.

Interorbital did tests – needs to force development. Communication is a critical one – that is a main – Power plant also was not started yet – but I hope that solar panels can be simpler – I planning to control it by a PIC and empty space from antenna can be used to deploy some extra panels.

Jun 6, 2012. Well, communication protocol done. Now core BT module (cubesat/lunar modem) is capable to work in modes:

(a) 3 frequencies listening; 3 frequencies for transmit; 2 from 3 majority bits correction, bits shifting correction fix for preamble lost; synchronization of a frequency switch; lost switch frequency correction; adjust frequency on temperature drift.

(b) 1 frequency listening; 1 transmitting; the same functionality as on (a) but switching is disabled.

(c) 1 frequency listening; 3 transmitting; again same functionality; that will be main mode for a cubesat and lunar probe.

(d) 3 frequency listening; 1 transmitting; difference from (a) that it will be 3 receivers monitoring 3 frequency but transmitting goes over 1 frequency. That mode will be on ground station – to maximize probability for cubesat/lunar probe to get less noisy data;

In mode (d) instead of processing and fixing packets inside micro processor data will be tunneled to a PC and fix of data can be done locally on a more powerful desktop, or distributed to network of a computers for simultaneously error correction (for such process can be used screen savers with instant win notification for a Team Plan B supporters).

Mode (c) allow to have transfer data from cubesat/lunar probe without delay for frequency switch synchronization. That can increase data transfer from 50 kbit/sec to 70-80. Transfer date for upload is not critical. Another reserve is tweaking core module from 250kbs to 1mbs – that can give increase of a speed up to 160kbs for download data from cubesat/lunar probe, for sure such increase will require more computer power after ground station processing, and will make a sense only with good network of a “fixing” packets screen savers.

Why to invent a communication protocol? Usually 99% of a time of software development spend (lost) on following standards. Needs to do something fast == ignore standards and write from scratch (see code at http://www.adobri.com/misc/STM_BT/STM_BTCM.c).

Range test, two helical antennas, one for Cubesat prototype 3 turns http://www.shapeways.com/model/322768/small_2_4ghz_antena__for_cubesat_.html?gid=sg85851, another for a ground station with 1/3 of a turns on 3D printed antenna http://www.shapeways.com/model/322767/2-4ghz-antena.html/?material=6, transmitting power 1mWt, LNA 12dB. Normally that is a Bluetooth with a range of 10m. Testing on 25m == OK, testing on 100m == OK, but it shows that best reception will be with antennas pointing 10-15 degrees up instead of direct pointing (do not judge seriously = truly speaking designers was zero experience in antenna’s design), test over water at False Creek at Vancouver did not show good reception – looks like ground or water disturb signal, lifting tripod with transmitter and receiver manually just 1m up improve communication. Problem was corrected on a 5 block near Queen Elisabeth Park – road is strait, not much cars, hills from both side == manual holding and pointing allows to confirm communication over 450m.

That actually brings limits of a test for a ground station, the best place will be a Squamish Chief == face of cliff is around 700m and ground station has to be pointed with 45-60 degree to horizon.

Next step – amplifiers to increase power transmitting to 1Wt (in Canada allowed 4Wt), and mobile ground station assembly/functionality.

Communication system requare to communicate with probe on a distances ranged low earth orbit (200-300km), high orbit (>500km), earth-moon flight (< 400,000km).

Communication with a probe will be on 2.4GHz frequency. Core of a transmitter and receiver will be done with a regular Bluetooth chips. Instead of an antenna transmitter there will be a connect to power amplifier capable to 100Wt pick transmit power. Receiver pin on chip will be connected to exit from low noise cascade amplifier capable of 92dB gain. Both amplifiers and Bluetooth chip will be controlled by additional microprocessor.

Protocol will support: low speed, medium speed 5bit/3bit with majority error correction, compatibility, and hash protection. Mode transfer: half-duplex with hardware flow-control and each packet with sequence number.

Portable ground stations will include 4 helical double size antennas, receiver’s and transmitter’s amplifiers, same chip as a probe and microprocessor unit. On portable ground station microprocessor unit will be connected to a personal computer using a serial port. On PC special software will collect packets and send its over IP to a central ground control station. Because of restrictions to communication on 2.4GHz band in different regions of the Earth some stations will be working in “receiver-only” mode. 6 stations will be located around the globe to cover 24 hours communication with probe, these stations will require a permit to operate in transmit mode. All stations will be equipped with horizon – azimuth orientation system controlling from the same communication software. Backup (manual) orientation assumed.