Posts by David G0MRF

    At last, a weekend and free time.
    I decided to have a look at the Spectrian amplifier I bought a couple of years ago from 'Pyro Joe' on e-bay, while QO-100 was still being assembled. The board comes mounted on a 1/4 inch (6.25mm) thick Aluminium heat spreader, so my first job was to mount it onto a decent sized heat sink. Being of US design, M4 screws were just a little too large to fit, but 4BA were perfect. A little drilling and tapping later and the the amplifier was ready for a DC test. The amplifier has a 14 pin connector with 4 pins for V+ (12V) 5 connections for ground or 0V , one ground to transmit pin, another which needs 24V input at 25mA and a pin which has a DC output voltage from a PA temperature sensor.
    With 12.2V and 24V @25mA applied, I connected a 30dB attenuator to the output and 50 ohms to the input. When the enable pin was grounded the supply current increased from a few milliamaps to 6.6A. - If this device is Class A, that should be fine. Now it was time for some for some RF input


    t  


    RF testing used a signal on 2400.50MHz at levels from -6dBm to +11dBm.
    With 12.2V and 6.6A standing current, I hoped that a class A amplifier would not need much more current across the range of input powers. Unfortunately testing shows the amplifier draws higher DC currents as you increase power. Clearly the PA stage is not class A after all. I wonder if efficiency can be improved. Overdriving this amp could be very expensive as it does not appear to go into compression...It just consumes more DC power and it can't do that forever. :(


    RF Input dBm
    RF Output Watts
    Apx. DC Current
    -6 0.625 6.6A
    -3 1.2
    0 2.25
    +3 4.2
    +4 5.2 6.8
    +5 6.6 7
    +6 8.2
    +7 10.9 8
    +8 13.5 9
    +9 17.5 10
    +10 21.5 11
    +11 26 12


    73 David G0MRF

    St2nh Hi Nader.

    Firstly, thank you for all your reports and data over the years for the FUNcube series of satellites.

    The AB003 amplifier should show an increase in supply current when you apply drive.

    If you have shorted pins 4+5 the transmit / receive LED should be permanently in transmit mode.

    For full output you should need about 170mW input RF input. What is the DC supply current with no drive?


    73 David

    Yes. DesignSpark integrates the schematic and layout pages so you know if there are connections missing.
    One feature I really appreciated was the parts library. If a part was missing, as most RF parts are, you can download a file from RS Components or Mouser with the PCB pad layout, the schematic symbol and a 3D model. If the file does not exist, then you can request one be produced within 24hrs. I requested one for the low pass filter and it arrived back in 3 hours on a bank holiday weekend.
    Chris also suggested KiCad.

    Alas, I am an analogue man in a digital world ;(


    With a circuit diagram completed, I set out to design a PCB for the upconverter. The size was determined by a handy looking BGA heatsink - 43 x 41mm
    After several days of spare time, I sent the design to China. Unfortunately 'Betty' from PCBway.com said they were unable to process my Gerber files as my rather ancient copy of Proteus used an old format of Gerber output. A few e-mails later and I realised the whole design had to be thrown away and I really needed some upto date CAD software. At the suggestion of Dr Chris Bridges at Surrey Space Centre, I downloaded a copy of 'DesignSpark'. After the usual frustration of learning how to use new software, several more late nights were spent doing the same work I thought I had already completed. There probably are mistakes... but at least 'Betty' was happy and my RS-274-X formatted gerber files were accepted.

    Now, while I am waiting for DHL, It's time to start work on the Spectrian amplifier and find out if it is functional.


    73


    David


    On with the story.... After reading many datasheets, considering options and getting valuable advice from this forum, I settled on the block diagram below.

    The upconverter uses an external local oscillator source at 1967.50 MHz, generated from an ADF4351 evaluation board. These are available on e-bay. It is the same board found in the RSGB project "Easy 100" by Giles Read, published in the June 2019 edition of Rad Com.
    Programming data for the PLL is held in an 8 pin PIC12F629 and is transferred when power is applied.
    The LO signal is amplified by a Mini-Circuits ERA1-SM which drives the LO port of the mixer with 7 to 10mW.
    RF input on 70cms passes through an attenuator and then to the input side of the mixer.
    The 2.4GHz output from the RMS30 is applied to an attenuator (not shown) to terminate it at the LO and image frequencies.
    A SF2124E bandpass filter removes unwanted products, then the signal is amplified by another ERA1.

    A second bandpass filter is included to make sure the signal is clean, - This is important if the board is used from 144MHz to 2400MHz

    The final amplifier is a 10pin surface mount IC from Qorvo. The RFPA5208 has high gain (40dB) and an output power of at least 500mW. This device was selected because it can be used with the popular 8W (really 3W) output Wifi amplifiers, which need about 170mW for full power. Or, it could be used with the SG Labs 20W amplifier module which requires 500mW of drive.
    The PA has a DC Voltage output from an RF detector indicating the amount of RF being produced. The final block is a low pass filter to remove harmonics. The TDK product selected has a maximum power rating of 3W so is comfortably within its limits.
    The board requires 12V for the ERA1 MMICs and 5V at about 500mA for the PA. A 3V regulator is included on the PCB for the 12F629 and for the device enable pin on the PA.


    Hi Mike. For a demo I thought it's important to not 'scare people away' by using a lot of high tech solutions, e.g. GPS locking, which athough very good, may be a little intimidating for the HF contesters etc who will be attending the RSGB event that runs alongside the AMSAT-UK colloquium. I have fitted the Octagon LNB with a (new) TCXO and thought it could run into an SDR for display on a 32in monitor while also having the 9700 receiving an output on 145MHz via my 739MHz to VHF converter. So 2 methods of RX.
    I didn't know you had a board for locking. I look forward to reading about it here when you have one built and operational.

    In the meantime....see next post....my upconverter PCBs are finally on their way from China. However, that turned out to be a time consuming process due to me using outdated software. Thanks for the PCBway.com recommendation. They got the job.


    David

    A couple of months ago I volunteered to provide a narrowband transponder demo station for use at the AMSAT-UK colloquium in October. Now I have to convert this collection of parts into something suitable.

    I have chosen to use a single 0.8m dish with POTY dual band feed for the antenna. I had previously purchased a 20 / 25 Watt Spectrian amplifier from 'Pyro Joe' via e-bay. The final major component is an upconverting mixer to take 432MHz in from an IC9700 and to output a signal on S Band. This will be designed around some available parts and built on a PCB to be ordered from China. - What can go wrong !!

    Hopefully this short series of posts may help people trying to assemble a station of their own.


    73 David

    CT2IRJ


    Oh, yes I see. I hear the Pluto has a fairly low output, so you may need 30dB or so of gain depending on what PA you need to drive.
    I am waiting for some upconverter boards to arrive from China. I hope the amplifier chain I've used in that may be useful for a Lime or Pluto SDR.
    Have a look at the RFPA5208 from Qorvo. That chip with a bandpass filter in front of it may work for you.

    73 David

    Hi Salomão.


    These amplifiers look to be receive preamps rather than anything that useful for QO-100. With a max linear output of 20mW ( 1dB compression) they are similar to the Minicircuits ERA products at about 2 Euro. Of course they do come in a nice box with connectors.

    G8UGD
    Hi Adrian. If it helps...The internal heating of the BU500 is fairly low, so for SSB or CW the internal oscillator is very good. - Way better than the TCXO issues at 10GHz on the downlink. There is some supplied software for changing the LO frequency used, but as I recall the options for a reference are either 'internal' or '10MHz'.
    However, it may be worth looking at the manual just in case 5MHz is possible.

    Nice example Mike.
    I thought I saw some evidence of a large signal activating an AGC a few days ago, The PSK beacon appeared to drop in level. but I'm not aware if there is an AGC on the NB transponder or if it was an effect within my RX. ??

    73

    David

    I have finally joined the 21st Century and have a 9700 awaiting collection in a few days time.

    How are IC9700 owners driving upconverters?

    My upconverter needs 12mW drive and I don't want to damge it. At the moment I have a FT736R running about 5-10W with a 10W attenuator. But the 9700 output power is an order of magnitude higher.

    spikes in the first few milliseconds of TX and power output changing accidentally with an unintentional mode or memory change are worring possibiliies.....

    Re CW Beacon. Please check that going to FSK will not affect the ability of SDR Consol to lock the a receiver's frequency to that beacon. I can't recall if the software uses the CW or PSK signal as a reference. ??

    73 David

    oe9dgv Hi Guntram
    The 0.35fd may be OK for the 2.4GHz section as the POTY over illuminates a 0.6fd dish.
    However, the gain of the dielectric lens on 10GHz is too high for a 0.35fd. It will only illuminate a small section of the dish. You may have better results with an open waveguide feed. Try setting the focal point....take an RX measurement, then remove the lens and measure absolute beacon signal strength again.

    73


    David

    Hello Heiner.

    Can you tell me what length of 22mm tube, or LNB feed is needed to fit into the compression fitting?

    I have a Octagon OTLSO and wonder if I cut off the horn section, if there will be enough left to use the same fitting as you?


    Thanks David