Scenario 1 - First Light

Session: Friday evening, 16:00 UTC (12:00 local)

Station: Riley’s backyard, Burlington VT — the QFH on the back fence

Operator: You

Riley: In the kitchen, making a sandwich, yelling instructions through the window

Note Taped to the Laptop Lid

Okay! You’re here, the laptop’s on, and there’s a weather satellite coming over in three minutes, so read fast.

Everything you need is below. Two things I want to say out loud before you touch anything:

One: the antenna on the fence doesn’t move. It never moves. That is not laziness, that is the design.

Two: the radio is exactly how I left it after FM night on Tuesday, which means it is wrong for what you’re about to do. Both settings. Figure out which two and you’ve basically learned the whole console.

Sandwich first. Back in five.

— Riley

Tonight’s Pass

Satellite	AOS	Max Elevation	LOS	What It Sends
WXSAT-19	16:03 (T+3 min)	55° at 16:10	16:18	APT weather imagery, continuous

Fifty-five degrees is a good pass — better than most. WXSAT-19 is a polar orbiter: it comes up in the northwest, crosses high overhead, and sets in the southeast about fifteen minutes later. While it’s up it draws a picture of the weather below it, one scan line at a time, and anyone with an antenna can listen.

The Observations tab has the live countdown. Check it before you go hunting on the waterfall.

The Rig

Component	What It Is	Notes
Antenna	Hand-wound quadrifilar helix, 137 MHz	Zip-tied to the fence, pointed straight up, 3 dBi
Receiver	RTL-SDR v3, direct sampling	RF goes straight into the ADC — no downconversion
Software	SkyWatcher SDR Console	Waterfall, VFO, decoder

The QFH’s beam is roughly 140° wide. That is the entire trick: a big dish has to be aimed and followed, but three decibels of gain buys a beam so fat that the satellite spends the whole pass inside it. Big antennas point. Little antennas wait.

Link Reference

Direct sampling means there’s no LO and no IF math. What you tune is what’s on the air.

Signal	Frequency	Bandwidth	Mode
WXSAT-19 APT downlink	137.100 MHz	34 kHz	BPSK 1/2

Doppler

At 137 MHz, a low-earth pass shifts the carrier by roughly ±3 kHz across the pass. That’s real, and you can watch the stripe lean on the waterfall — but it fits inside a properly-set channel, so once you’re locked you do not need to chase it.

Remember that number. It will not be true on 70cm, and Scenario 2 is going to make you feel it.

Rig State at Handover

Riley was working FM voice on Tuesday and left everything set for that.

Setting	Current Value	Correct for APT?
VFO frequency	137.170 MHz	—
Channel bandwidth	15 kHz	—
Mode / FEC	BPSK, 1/2	Yes
RF gain	79 dB	Yes
Antenna	Fixed, pointed up	Yes

Getting a Picture

Three things have to be true at once, and the console will tell you which one you’re missing:

On frequency — VFO within a few kHz of the APT downlink. Click the stripe on the waterfall, use the bookmark, or walk it over with the tune buttons.
Channel open — wide enough to bracket 34 kHz of signal. Too narrow and it’s invisible; far too wide and you’re just collecting noise.
Left alone — once the decoder is running, hands off. The picture builds one line at a time and every fiddle costs you scan lines.

The lock indicator diagnoses itself. NO LOCK means nothing’s there. BW TOO NARROW means the passband is lifted but the channel can’t fit what’s in it. LOCKED means stop touching things.

End of Briefing

This is the whole hobby in fifteen minutes: a wire antenna, a cheap dongle, and a satellite that has no idea you exist, drawing you a picture of the clouds over Vermont because physics says it must.

Riley has been doing this for eleven years and still goes outside to watch the sky during a good pass.

Get the picture.