We’re searching for a better solution for connecting an SDR to the GAS Ground Station, currently used to communicate with the GASPACS CubeSat. Essentially, we have a UHF radio from Endurosat (1W output) connected to an amplifier (10W output), which is able to communicate with GASPACS (both TX and RX). The ground station has a rotator and yagi antenna. We would like to connect an SDR to observed the signals we receive from satellites, so that we can monitor both GASPACS transmissions and add the ground station to the satnogs network.
Here is a diagram of our current setup (left) and desired setup with SDR added (right):
We tried using this SDR switch from MFJ, which does have the correct features for what we need, but is very poor quality and adds a lot of loss and noise (as I’m sure many of you could guess). We either need a way to disconnect the SDR from the RF path when transmitting (to not fry the SDR), a setup with circulators that @Kevin has suggested, a RF power limiter between the Endurosat TRX and SDR, or something else. GASPACS transmits down “pings” after a command approximately 75ms after tx, so if we use a system that disconnects the SDR from the circuit, it needs to be rapidly switchable. We are using a Raspberry Pi Zero W to send the transmission commands to the Endurosat TRX, so we can control a relay/switch from the GPIO pins if needed.
Our budget is preferably under $500 USD, with a maximum of $1000 (we could potentially exceed that with a very good reason).
We have a pretty good setup with an SSB SP-70, and we’re upgrading our rotator to a SPID RAS, but we don’t have a way to let this station be a part of SATNOGS.
Hi, we are putting together a Cubesat (Owlsat) and are stuck using the Endurosat satellite module. We are thinking of having our data come down in Beacon mode so that all Satnogs locations can access our data, but we still need to use the proprietary Endurosat compression technique to communicate with our bird. Who has (successful) experience with this? I heard you could put a SDR on a Windows machine but then the power out is too low. Endurosat’s solution is for us to purchase the matching hardware for the ground but I’m a bit nervous that we will invest even more money and not end up with functionality. We are newbies at this and would LOVE some help from those who have successfully managed using the Endurosat to get their data down!
I am a bit confused, if I understand correctly you have a proprietary Endurosat transceiver and you are now looking at a way to send and receive data with the help of a SDR that can receive and send this data.
If you are able to create the proprietary frames you can use a Ettus research SDR and connect it to the power amplifier to boost the signal and command the satellite.
Then it all comes down if you are able to create those frames and have the ability to interact with the SDR to send those frames.
And let me be honest, there are quite some challenges.
I think I can help you out here. Are you using the Endurosat UHF transceiver? If so, we flew the same transceiver on GASPACS and were able to communicate successfully. I would highly recommend taking Endurosat’s advice (in this specific case ) and purchase a matching Endurosat transceiver for your ground station. Trying to build a transceiver with an SDR to talk with the Endurosat radio is theoretically possible, but I have yet to see it done successfully.
A few things to note with that radio:
You should use a power amplifier to boost the 1W signal to improve your link budget. We used the B-TECH AMP U25D which does work with one caveat: the amp has a bit of a “charge up” time, where you have to transmit a couple packets in a row through it before it starts amplifying to its maximum power. If you just send one packet through it, it won’t be very amplified. We solved this by transmitting the “enable pipe mode” command several times through the radio before sending any data or other command packets through.
I would highly recommend doing a long-range test of your ground station ↔ satellite link. That’s how we discovered the above issue with the amplifier (it worked perfectly at close range, but not at all at long range)
The Endurosat UHF radio (at least the version we used) claims to have built-in doppler correction, but that’s not entirely accurate. It does have some level of automatic doppler correction (around +/- 5 kHz) but it’s not enough to talk with your sat at the beginning and end of passes (you need about +/- 10 kHz). There are solutions to get around this (none of them entirely elegant) but perhaps Endurosat has improved their system in the last couple years since we bought ours. Our plan was to continually update the ground station radio’s frequency throughout the pass, but our radio didn’t allow setting the frequency while in pipe mode. We ended up just talking with GASPACS during the middle couple minutes of each pass, which was acceptable since we had power issues due to the Endurosat components failing on day 1 of the mission . Hoping for your sake they’ve updated the hardware/software to have a better solution for this.
Make sure to test everything, don’t trust anything in a datasheet unless you’ve verified it yourself.
You can relatively easily receive signals from your sat using an SDR, but sending signals to the sat with an SDR is a whole different story.
I would highly recommend setting up a satnogs station to test all of your ground station hardware and RF path. This will let you diagnose issues with your antenna, rotator, LNA, cabling, etc. If you’re doing UHF, the LNA to get is the SSB SP-70. Using a linear antenna and taking the 3dB loss is way easier than dealing with two CP antennas and you’ll still close the link without a problem assuming the rest of your system is good.
If you have any more questions, feel free to jump into the Satnogs matrix chat
Wow, that is very helpful. I would love to talk with you more about the GASPACS procedures. I know the Kansas group is also struggling. Could you please email us at owlsat73@gmail.com and we can set up a zoom maybe?
) and purchase a matching Endurosat transceiver for your ground station. Trying to build a transceiver with an SDR to talk with the Endurosat radio is theoretically possible, but I have yet to see it done successfully.
. Hoping for your sake they’ve updated the hardware/software to have a better solution for this.