Scenario 8 - Callsign

Session: Saturday, 15:30 UTC

Stations: BKYD-YAGI (now with a transmitter) and BKYD-QFH

Operator: You

Riley: Here all evening, examining you

Riley’s Note

Exam night.

I know you’ve been flying this rig for weeks. The microphone is different. A receive mistake costs you a picture. A transmit mistake goes out to everyone with an antenna, at the speed of light, with your callsign attached to it.

So: two questions first. Get them right and the tape comes off the microphone. Get them wrong and we do more reading.

After that we listen to the afternoon pass, because I want you to hear something, and then — evening pass — you are going to talk to a satellite.

— Riley

Tonight’s Passes

Time	Satellite	Max Elevation	What Happens
15:55 – 16:07	CUBEHOP-1	28.9°	Listening pass. You have company.
17:31 – 17:43	CUBEHOP-1	25.7°	Your first transmission.
after 17:45	—	—	Riley’s last lesson.

The weather rig is powered up alongside the yagi tonight. Leave it running.

CUBEHOP-1 Transponder Plan

CUBEHOP-1 carries a linear transponder: it listens on one frequency, amplifies whatever it hears, and retransmits it on another. Everything in the passband goes up and comes back down. That is the entire design.

Path	Frequency	Bandwidth	Polarization
Uplink (you transmit)	435.900 MHz	30 kHz	RHCP
Downlink (you receive)	435.290 MHz	30 kHz	RHCP
FM beacon (unrelated)	435.250 MHz	15 kHz	RHCP

The Doppler Asymmetry

Your uplink leaves a transmitter bolted to Vermont, so it does not Doppler. The downlink does, because it comes from a satellite doing 7.5 km/s. You will hear your own signal walk across the waterfall while the thing producing it sits perfectly still on your desk.

AFC handles it. Let it.

The Transmit Rig

Component	Rating	Notes
Amplifier	~5 W brick (37 dBm max)	Boots powered — no separate amp panel on a ham rig
Uplink antenna	Crossed yagi, 12 dBi, RHCP	Same antenna you receive on
TX control	SDR Console → TRANSMIT section	Frequency, PA output, and the key

Five watts. That is a nightlight. It is also, tonight, enough to reach orbit and come back, because the receiving end is a satellite with a good antenna and nothing between you and it but sky.

Band Plan Notes (exam material)

70cm is shared. It is allocated by agreement and coordinated by people who have never met you, and essentially nothing in your radio enforces any of it.

What makes a transmission legal is the overlap of three separate things:

The frequency is in a sub-band your license covers.
You hold that license, and you are the control operator responsible for everything that leaves this yard.
The satellite in question is open for amateur use on that frequency.

And one rule that surprises everybody: no encryption. Not because it’s technically hard — because amateur radio polices itself. Every operator has to be able to identify every transmission and who sent it. Openness is the enforcement mechanism.

Hold that thought for the 15:55 pass.

Operating Checklist

Listening pass (15:55)

Track CUBEHOP-1 with the rotator
Watch the downlink side of the transponder passband, not just the beacon
Note anything on the air that isn’t the satellite’s own signal

Transmitting pass (17:31)

TX frequency set to the uplink center — 435.900
Rotator tracking before you key
Key the transmitter (the TRANSMIT section reads ON AIR)
Receiver tuned to your own downlink at 435.290
AFC on, and ride it
Unkey before LOS — the transponder is shared

End of Briefing

Seven sessions of listening. Tonight you answer back.

Somewhere between the exam and the evening pass you are going to learn the thing this whole campaign has been circling: the radio spectrum does not authenticate anybody. Not the pirate, not the impostor, and not you. A license is a promise, not a password. The only things that can’t lie are Doppler, geometry, and the clock.

Everything else is just a signal claiming to be something.

Seventy-three, operator.