AFEDRI SDR-Net description
- Category: EME
- Published on Tuesday, 19 April 2011 12:09
- Written by 4Z5LV
- Hits: 48126
There is short description of my 23cm EME setup:
- First one is "old" setup is containing 1.8m dish and Azimuth/Elevation mechanic
My first QSO with PI9CAM was done at 8:40 UTC 10-07-2010 using 1.8m dish and 10W output power.
Further I had built single MRF-286 W6PQL amplifier that gave me 50W output to feed.
Next step - I added to the dish above 1.8m dish "extra size", extended it by mesh up to 2.6m diameter, shape is not exactly parabolic, but gave me gain improvements close to expected
Currently I had built 2xMRF286 amplifier of W6PQL design, it give me now near 100W only, but I have not finished its tuning yet.
So my present EME Setup is:
Transverter: self maid 1296Mhz/28Mhz + Yaesu FT897D / AFEDRI SDR (on RX)
Antenna: 2.6m dish (1.8m SatTV dish extended by mesh)
LNA: G4DDK ~0.3dBNf
PA: 100W amplifier (2xMRF-286 W6PQL design)
There you can download and hear recorded I/Q file of DUBUS CW EME Contest that was done on my system using AFEDRI SDR receiver + 1296MHz/28MHz transverter.
next page has information about my dish's Azimuth/Elevation control.
Azimuth / Elevation mechanic and control
Azimuth movements is done by AlfaSpid BigRAK rotator, controlled by its own control box.
Elevation movements is done by 36'' linear actuator for Satellite TV, controlled by home maid control box with microprocessor MSP430F149 from Texas Instruments.
To calculate real elevation angle - the elevation controller uses simple algorithm, where number of pulses (from embedded in actuator pulse encoder), actuator and dish mounting geometric dimensions are used in elementary triangle equations see image below:
We can see triangle that is formed by dish support two sides "a" and "b" and linear actuator "c",
where sizes of two sides "a" and "b" is constant and one side "c" - has changing size that in reality defines elevation angle of the dish. Size is changing, but we can know it with relatively high resolution using actuator's encoder pulses. relation between sides "a", "b" and "c" is defined by next equation:
c2 = a2 + b2 - 2*a*b*cos(angle_between_sides_a_and_b);
So we can easy calculate angle_between_sides_a_and_b (in degrees) and from equation below find elevation angle:
elevation_angle = 180 - offset_angle - angle_between_sides_a_and_b;
where: offset_angle - is constant angle, that defined by dish support construction (can be easily measured or calculated).
There is the short 23cm transverter description:
I am using home built transverter of my own construction, the transverter is was designed as modular construction and divided on four main modules:
1. Receiver module
2. Transmitter module
3. Local Oscillator (PLL) module
4. OCXO 10MHz - reference clock module
From beginning RX module was designed as RF part of Sound Card based SDR, i.e. direct conversion of 1296Mhz signal to I/Q audio IF and further processing on Personal Computer SDR software. But in reality it was hard to struggle against Local Oscillator leakage and phase noise, so I decided to leave this idea and to use it as 1296Mhz/28Mhz converter. So now two I and Q channel are adding together, after simple 28Mhz RF phase shifting RC network, this gives additional attenuation of image channel (the main filtering is done in input 1296Mhz helical filter).
Second issue with this RX design it is - input LNA it is exact copy of input stage of DB6NT transverter. Because I was unlucky to get from this LNA noise figure better than 3dB, plus poor stability (existence of higher band microwave oscillations) , decided to change both amplifiers stages and now I am using there ATF51343 as input amplifier and GALI39 as second stage amplifier. It give me no oscillation and NF=1.5dB, that is good enough for system that using additional LNA on the antenna feed. Please, pay attention, the RX module schematic, that is located in Download area, contains only old LNA design. I need some time, to prepare electronic copy of my, hand written, changes to schematic :-)
Similar story like in RX part, but working in opposite direction:-) It had poor signal as zero IF (Audio) to 1296MHz conversion transmitter, but working nice as 28MHz/1296Mhz Up converter. Simple phase shifting RC network (it splits 28MHz signal going from transceiver to two 90 degrees shifted I/Q channels) has been added to suppress image channel.
The Transmitter board contains also embedded microcontroller that is controlling next parameters:
- Local Oscillator Frequency
- TX mixer DC balance (using serial DAC)
- RX-TX switching sequencer (to protect LNA from transmitted signal)
Transmitter PCB is stacked together with Local Oscillator (PLL) PCB.
Transmitter and Local Oscillator (PLL) + (Phase shift network) staked together
3. Local oscillator (PLL)
Now Local Oscillator produces 1268Mhz signal for the transverter. At beginning I planned to use as reference oscillator, the 10Mhz TCXO (24$ cost), that can be soldered directly on LO-PLL board without any external connection, but due to significal for microwave band thermal drift, I decided to use external OCXO.
4. OCXO 10 MHZ reference clock
OCXO was purchased from one of Chines Ebay sellers for ~30$, I mounted it together with power supply IC on simple wire-up PCB. This solution is perfect functioning and has nice stability, what else I need? There is only frequency drift after power-up till reference Oscillator's Oven heating up to needed temperature. This OCXO has frequency voltage control input that is not used by me present time that can be used used in the future for GPS base frequency looking/calibration.
I'm finishing on this point..
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