Posts by iz2eeq

    Hello David, thank you!

    I’ve always loved GNU radio and have been using it for many years, starting with a USRP1 and two basic tx and rx boards... the software has improved a lot since then and the opportunity to embed it in a small device like a Raspberry makes it really interesting for experimentation.

    I am using HackRF because I had an old unit in my box... I would say it works well but the required minimum sample rate (2M) is unnecessary high (and computationally expensive) for narrow bw applications, so I would recommend anything that can work with a lower bandwidth... I read somewhere that the Pluto supports as low as 312.5KHz, so that alone would make it a better device, hardware wise.

    Pluto is also better when it comes to DAC/ADC, it uses 12 bits, while HackRF uses just 8.

    On the other hand the support of HackRF on GNUradio, specifically with Osmocom and Soapy plug-ins is quite good and working well, especially the TX/RX switching that works out of the box.

    I have not tested the Pluto on GNURadio so I wouldn’t know about it.


    matteo iz2eeq

    Hi everyone, I've been finally able to (successfully) test an all digital, Gnuradio based implementation of a TX path on QO-100.

    The idea was to build some Gnuradio Flows that could be run on a Raspberry PI and that implemented different transmission modes, using an UDP source as signal source so that the whole thing could be used remotely via wifi from another computer.

    The HW used is a Raspberry PI 3 rev. B, connected to an HackRF One board cascaded with a 2.4GHz preamplifier and finally the ubiquitous Chinese 4W Wifi amplifier.

    A build of Gnuradio 3.8 has been built on the Raspberry in order to achieve the max performance possibile on that architecture.

    Everything worked nicely and I could work the TX remotely by sending characters via UDP and have them transmitted as CW, PSK31 and QPSK31. HackRF One is equipped with TCXO so frequency was very stable, which is fundamental and assured perfect reception.

    Code for the tested flows is here :

    More modes are coming - now testing voice single sideband modulation using gsm vocoders, looks promising!!!

    This is the picture of the hardware assembly:

    73 de Matteo iz2eeq

    Has anyone tested one of these Green on the satellite? I’ve just got one from Amazon, the single model, and it’s quite chirpy if compared to the good old Octagon one. Now going for modification to inject frequency ref, but I’m a bit sceptic... if it’s already chirpy with quartz, could it get any better with an external ref, no matter how clean it is? Unless the problem is with a bad quartz obviously...

    73 de iz2eeq

    Hello Markro, do you think there would be any chance for this to run on a last generation raspberry from a computational power point of view? Obviously there would be mods needed because of moving to Arm, but do you think there would be enough power in an Arm processor to work?


    Hello Harry, thanks for your comments. I had read the NEO7 was much less jittery when divided by powers of two but, as it turns out from your experience, it is not jittery free enough to be used on its own. Yet I wanted to go for a GPS disciplined solution, so I will end up using NEO as a reference together with a controlled oscillator and see where it gets!

    73 iz2eeq

    I'm finally on the air with QO-100! The receiving part was already active, I was just waiting for the 2.4GHz transceiver and PA to arrive from SG Labs, and they finally did.

    The RX part is composed by the LNB voltage generator, a raspberry pi 3 and a RTL based SDR; the LNB voltage generator is controlled by the raspberry, as well as the power to the TX part and to the rotator of the TX dish (controlled by a k3ng rotator controller on an Arduino Nano). Antenna is 80cm offset dish and the feed an Octagon PLL LNB, no clock injection.

    The TX part is made of SG Labs transverter and a buck step down converter from 24V (from the RX box) to 13.8V. Dish is prime focus 1m and feed is an old AO40 self made patch antenna. In the end PA has not been used as the bare output of the transverter (about 1w at the patch antenna after 2 meters of RG58) is enough to bring me on the bird. A 20w PE1RKI isolator has been used at the output of the transverter to make sure nothing gets fried in case of bad matching with the antenna.

    Here there are a few pics of the TX and RX chain; now that the work is done I can relax on an armchair and have a little fun on this beautiful satellite. See you on QO100!

    73 de iz2eeq

    I made other patches from FR4 PCB but the small spacing between the plates makes it difficult to solder the inner surfaces to the copper pipe.

    But there is hope! M0EYT makes his patches from 36mm OD copper pipe. He anneals it, cools it red hot in water, sledges it with a hammer and CNC's it. He already send out about 50 (or may be even mode) plate pairs.

    Oh my, that's where blacksmith meets ham :D

    Hello everyone, i have a question about the material that can be used to assemble patches and helices reflectors... since I'm having a hard time finding a copper or brass foil supplier, would it be possible to use pcb to build those parts? What would be the effect of a double sided pcb FR4 at these frequencies (supposing that the patch and the reflector are made of pcb for example with the two sides connected together). Maybe it's a newbie question but that's what I am after all 😊. Thank you!

    Hello Charlie, which software are you using to make measurements? Does it work with RTL based SDRs? I am looking for such a software to get repeatable measurements...

    thank you

    73 de iz2eeq matteo

    Would it change alot if the reflector had a diameter of 95mm?

    I have a number of old hard disk platters, but they are smaller. Yet my karma would benefit from the reuse some stuff from my junk box.

    Hello everyone, after setting up rx with 95cm prime focus dish and octagon lnb to SDR, I am now in the process to setup the tx section - I still have the old patch antenna I used for AO-40 RX, design from PE0SAT -, and I was considering to reuse it with another offset 90cm dish.

    Nevertheless, I have noticed many are choosing the helix approach and I was wondering what are the advantages of helix with respect to patch, as the latter is in my opinion easier to build... not to mention I have it already ready :)

    Thank you all and hope to talk to you soon on Es'hail 2!!!

    73 de iz2eeq