I began to read about space and satellite operations a few months ago. Really interesting stuff, but I didn‘t have the right equipment for it. Until last week and so I started contacting the ISS repeater without success. One week later I found my stupid mistake. An overview of how to start and what errors to avoid.
Uplinks, Downlinks, Doppler, Duplex… It’s complicated
To make successful contacts with the ISS-repeater you don’t need much ouput power. 5 W is fine, unlike when doing other space stuff like Earth-moon-earth. Line of sight is not obstructed and attenuation along the way is quite low.
I bought myself a new Yaesu FT-5D HT for portable VHF/UHF-Operation and a handheld yagi made in the USA by Arrow.
Uplink to ISS is on 2m 145.990 MHz, while you can hear the repeater downlink on 70cm 437.800 MHz (more details to that later).
This is what you call a crossband-repeater. Such a kind of repeater allows you to actually hear your own input in realtime (with short delay) on the other frequency while you transmit – at least as long as you are using a full duplex capable radio with a duplexer at your antenna – that still receives while transmitting – , or simply a second radio to connect to the other bands antenna.
When working with fast moving space stations or satellites, you have to compensate the doppler effect on the 70cm band. This means, you use frequencies 10KHz +/- around the center or mid frequency during a pass. For example when I have just aquired the signal from the station above the horizon I use 437.810 MHz, changing to 437.805 MHz, at a quarter of the pass, changing to the center frequency 437.800 MHz when its above my head, changing to 437.795 MHz when the pass is 3/4 over, and changing to 437.790 MHz short before loss of signal when the station is nearly disappearing on the horizon.
When having this doppler effect in mind and being aware of how difficult it is to aim the antenna in the exact right direction, it gets clear, why it is a big advantage to hear our own transmission back from the repeater while transmitting: Only when you hear yourself, you can be shure others also hear you. Everything else is trying to find the needle in a haystack, you are flying through the fog.
I decided to go for the two radio-setup as full duplex radios are quite rare and expensive, mostly only available from Kenwood and while their radios are brilliant, I simply don’t find them easy to use.
Setting up the radio with all the frequencies needed
As I only had one FT-5D, I programmed all known ISS and ham radio satellite frequencies into that radio. I found this site by KE0PBR extremely helpful: https://ke0pbr.wordpress.com/2018/12/31/my-frequency-cheat-sheet/
It gives us an overview of all up- and downlinks with all the tones to open the repeaters. For example the uplink to ISS needs an 67Hz opening tone on every of our transmissions towards the station.
I used the FT-5D to listen to the 70cm frequencies and to record the downlink with the inbuild recorder. The FT-5Ds channel dial allows fast changing between the doppler-shift-frequencies and I used my old Wouxun UV-KG6, set it to transmit on 145.990 MHz to establish the uplink.
I was able to hear the repeater perfectly clear. Every time I tried to call CQ or to answer an ongoing call, I never hit the onboard ISS repeater. I never heard myself. I tested multiple times throughout the week and failed every time. Frustration started to grow.
Do you already know where I fucked up at this point?
And so I fucked up…
I couldn’t explain why I didn’t make it through the repeater, and at some point I could only imagine my Wouxun UV-KG6 used for 2m uplink had to be broken. So I had closer look at it and checked if it transceived at all. It did. WTF?
I was close to giving up when I had a closer look at the display of the Wouxon. No additional information was displayed beside the high TX power. That made me suspicious, shouldn’t the HT show that 67Hz tone is active? Yes It should. Wait, does that mean I didn’t activate 67Hz tone?
I felt so stupid.