I've been fascinated by satellites from the very beginning of my amateur radio live. So I started as soon as I got my own station equipment with working over AO-7 and AO-13 (as long as it was operational). In the last years I was less QRV due to other amateur radio activities.
This had changed with the launch of QO-100. I quickly soldered some modules together for an experimental TX setup while RXing was done via web SDR @ Goonhilly.
Now, about one year later, I finished my transverter project to become QRV on a regular basis. I decided to realize a conventional (but very flexible) concept, which can be used as a standalone transverter inside and outside the shack, with or without a computer.
Well, it doesn't look so pretty inside. This is because the device was developed "in-situ". Changing concepts and modules during the development process resulted in a lot of orphaned drillings in the mounting plate and in a sub-optimal arrangement of particular modules. But it works, anyway.
The idea was:
- not to use a complete SDR solution for the transverter (like AdalmPluto or similar)
- rather use a convetional setup which can be operated with classical transceivers
- not to use a commercial solution
- rather use own ideas with cheap Chinese boards and learn how tey work and how to use them
This was requiring:
- a conventional mixer for TX uplink
- a modified LNB for downlink and output the IF inside a amateur radio band
- PLLs to generate all frequencies needed
- microprocessor or a computer to control the PLLs (Raspberry Pi seems to be ideal)
And these requirements resulted in a lot of additional functionality:
- fully integrated RX solution with a RTL-SDR stick and gqrx
- spectrum display on the front panel
- headphone jack and loudspeaker
- remote operation of RX via Bluetooth or WIFI
A clear statement first
This transverter is my personal trade-off between best possible technical parameters and best possible flexibility. It is more or less an experimental platform for different setups.
If you are looking for "the ultimate concept" with outstanding technical data you can stop reading here.
1. Operation @portable with one single 144 or 432MHz transceiver
Designed to work outside with a minimum of external components. Running with a single 144 or 432MHz transceiver for uplink. The internal RTL-SDR is used for receiving the downlink. All frequencies are controlled by the internal OCXO. A tablet or smartphone (connected via WIFI) can be used to remote the sdr console.
2. Operatin @home, simple configuration with one single 144 or 432MHz transceiver
work from the shack with a very simple configuration. Running with a
single 144 or 432MHz transceiver for uplink. TX-signal is amplified to compensate cable losses. Receiving is done with a web sdr, no need for a dual feed with LNB. Dish can be a simple WIFI dish. TX frequency is controlled by the
3. Operatin @home, full setup with 144/432MHz SAT-transceiver
work from the shack with full setup. Running with full duplex SAT-transceiver for uplink and downlink. TX-signal is amplified to compensate cable losses. A second RX with spectrum display is possible with the internal RTL-SDR stick. All frequencies ere controlled by an external GPSDO. The station computer can be used to remote the sdr console.
Main Modules / Components / Ideas used
TX-PLL with ADF4351
This module is used unmodified with external 10MHz input. Controlled from Raspberry Pi via SPI interface. Delivers 2252MHz LO frequency for the TX mixer.
TX mixer This TX mixer is sold by Hartwich RF. Not the cheapest solution on the market but with clean output due to intregrated filters. Can work with IF 100..900MHz. LNA4All as small signal amplifier I've got some of these modules from 9A4QV some time ago and found them in my shack. This broadband amplifier is equipped with PSA4-5043+ chip with very good data. Used to reach the required signal level for TX mixer and PA. Other (cheaper) solutions with Chinese modules are also possible here. Multi-PLL with Si5351 for LNB, RTL-SDR
This module was modified by removing the crystal and adding an external SMA-connector for 10MHz input. This modification was described in CQ/DL magazine (please contact me for details). Controlled from Raspberry Pi via I2C interface. Delivers 25,7884615384615MHz for the LNB and 28.8MHz for the RTL-SDR. One output is unused so far.
It turned out that using a Si5351 as LNB reference is not the best possible solution. The jitter & spurious of the output signal (multiplied by 390 in the LNB's PLL) are limiting the receiving capabilities. With some fine tuning on the IC's registers I was able to keep the spurious -30dB on the whole satellite RX passband. With my setup (60cm offset dish) the beacon is abt. 25dB above the noise level, means: all spurious are vanishing. There are still problems with the Leila alarm signal when active. Things may become different on a bigger dish...
I should consider a better solution here.
RTL-SDR stick V3 as internal RX This stick sold here was modified to an external reference input jack which the stick is already prepared for. See user guide here. Raspberry Pi 3 as contoller and RX with Linux & gqrx
The Raspberry Pi is the heart of this transverter. Used to control all the PLLs and the RTL-SDR stick. Outputs the spectrum on a small display at the front panel. Connected to local network for remote operation.
3,5" display as a spectrum display
This is a cheap Raspberry PI standard display (MPI3508). Native resolution is 480 x 320, but running here on HDMI with 1280 x 720. The touch interface is not used.
This cheap dual splitter module is modified with a DC-block to inject the 13.8V LNB supply. One output is used to feed the RTL-SDR stick. The other goes to an external BNC-connector for the conventional use with transceiver.
PAM8610 10W AF amplifier
This cheap module is used for headphone and speaker output. AF can be muted on TX. Biggest challenge was to get it working with one output grounded at the front panel (beacuse of the headphone jack with integrated switch). I have to use a small transformer to de-couple this.
Diavolo Dual LNB
This LNB is modified for the use of external reference. I removed the crystal and soldered the PLL input to one of the F connectors. The best way was to crack the ceramic housing of the crystal, after that the small SMD connectors can be removed from the soldering pads. Not easy but can be done on a workbench. The LNB is located at the end of the cylindric waveguide of the POTY.
POTY patch feed for 2.4GHz TX
This patch feed seems to be a good compromise for working with one dish for RX/TX. Equipped with a 22mm adapter it fits into a commercial satellite dish.
Automatic reference input switching This great idea by KK6DF was taken from here and was slightly modified to my needs. It allows an automatic switch over between the internal OCXO and an external 10MHz source like a Leo Bodnar GPSDO.
SG-Labs 20W - PA with telemetry
My latest project finished in December 2020. As the distance from my shack to the roof is more than 15m I need to amplify the 13cm uplink near the antenna. A SG-Labs PA in a separate housing is placed right underneath the roof to provide the necessary RF power. The homemade telemetry pcb with an ATMEGA 8 perfectly fits on the top of the PA. It is getting voltage, current, temperature and output power and is sending it via RS-485 to the transverter in a simple ASCII format.
The software package is essential to get all the PLLs and components working. It is written by myself in CSharp and runs on Linux /Mono on the Raspberry Pi. It currently consists of:
- ADF4351 PLL control via SPI
- Si5351 PLL control via I2C
- CAT synchronisation of TX frequency to RX frequency (for ICOM transveivers only)
- Watch the PLL status and set LED on front panel
- Monitor of the remote PA and show values on the screen
Other software running on the Raspberry PI:
- gqrx as an SDR console (Linux equivalent to SDR console by Simon Brown)
- Actiona to run all the startup scripts (Linus equivalent to AutoIt for Windows)
Current Configuration @ home
Screenshot from Raspberry Console
Thats all, folks! Feel free to ask me if you have any questions.
73 es hpe cuagn via QO-100