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E2A

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Amateur radio in space: amateur satellites; orbital mechanics; frequencies and modes; satellite hardware; satellite operations

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E2A011 of 12

What is the direction of an ascending pass for an amateur satellite?

Why Satellite passes are named for the direction of motion relative to the equator, not the ground track's east-west drift. An ascending pass is when the satellite is climbing in latitude, crossing the equator heading northward, so it moves from south to north over your location. A descending pass is the opposite, north to south. The ascending node is literally the point where the orbit crosses the equatorial plane going north.
Watch out West to east describes the general eastward drift of many low-orbit satellites (or the apparent motion in geostationary work), but that is not what ascending and descending mean.
Ascending = going up the globe = South to North. Descending = North to South.
HamSandwich explanation, first draft. The question and answers are the NCVEC text.
E2A022 of 12

Which of the following is characteristic of an inverting linear transponder?

Why An inverting linear transponder works by mixing the whole uplink passband with a local oscillator so that the output spectrum comes out backwards. That means a signal near the low edge of the uplink passband appears near the high edge of the downlink passband, and the sideband sense flips, so a USB uplink is heard as LSB on the downlink (which is why operators use LSB uplink on Mode B linear birds to get USB down). Because the spectrum is reversed, a Doppler shift upward on the uplink translates into a shift downward on the downlink, so the two partially cancel and the net drift you must chase is smaller. All three statements describe the same inversion process, so the combined choice is correct.
Watch out Each individual statement is true on its own, so picking just the sideband reversal or just the band reversal misses that inversion causes all of these effects at once; this is a classic pool question where the separate facts are all consequences of one mechanism.
Inverting transponder flips everything: band position, sideband, and Doppler direction.
HamSandwich explanation, first draft. The question and answers are the NCVEC text.
E2A033 of 12

How is an upload signal processed by an inverting linear transponder?

Why A linear transponder doesn't demodulate anything; it takes an entire slice of uplink spectrum, mixes it with a local oscillator, and retransmits the resulting difference product on the downlink band. Because the downlink is LO minus uplink, the passband comes out reversed: a signal near the low end of the uplink window appears near the high end of the downlink window, and upper sideband becomes lower sideband. That spectrum reversal is exactly what the word 'inverting' describes, and it also makes uplink and downlink Doppler shifts partly cancel.
Watch out Detecting and remodulating on the reverse sideband describes a regenerative or demodulating repeater, not a linear transponder, which must stay linear so it can relay many SSB and CW signals at once without touching their modulation.
Linear transponder = mix, don't demodulate. Difference product means the band flips: transmit USB up, listen LSB down.
HamSandwich explanation, first draft. The question and answers are the NCVEC text.
E2A044 of 12

What is meant by the "mode" of an amateur radio satellite?

Why For satellites, "mode" is shorthand for which band you transmit on (uplink) and which band you listen on (downlink), not anything about the orbit. The modern notation uses a letter for each band in uplink/downlink order: H (21 MHz), A (29 MHz), V (145 MHz), U (435 MHz), L (1.2 GHz), S (2.4 GHz). So a Mode U/V satellite hears you on 70 cm and sends the transponder output down on 2 meters. Older single-letter designations like Mode B and Mode J meant the same kind of band pairing.
Watch out The orbit-related choices describe the satellite's orbital parameters, which matter for pass prediction and Doppler but are described by terms like LEO, geostationary, polar or equatorial, not by "mode"; satellite orientation is called attitude or spin stabilization.
Mode = two bands, uplink first: U/V means up on 70 cm, down on 2 m. V=145, U=435, L=1.2G, S=2.4G.
HamSandwich explanation, first draft. The question and answers are the NCVEC text.
E2A055 of 12

What do the letters in a satellite's mode designator specify?

Why Modern satellite mode designators are written as two letters separated by a slash, uplink first and downlink second, with each letter naming a band: H for HF (21 MHz), A for 29 MHz, V for 2 m (145 MHz), U for 70 cm (435 MHz), L for 23 cm, S for 13 cm, and so on. So a U/V satellite takes your transmission on 435 MHz and returns it on 145 MHz. Knowing the mode tells you instantly which radios, antennas and frequency ranges you need to work that bird.
Watch out Polarization is a real satellite concern (many use circular polarization to fight spin fading), but it is never encoded in the mode letters; power levels and control station location are not part of the designation either.
Mode = Up letter / Down letter. U/V means Up on UHF, down on VHF.
HamSandwich explanation, first draft. The question and answers are the NCVEC text.
E2A066 of 12

What are Keplerian elements?

Why Keplerian elements (a "Kep set" or TLE, two-line element set) are the six-plus orbital parameters that mathematically describe where a satellite is and where it is going: inclination, right ascension of the ascending node, eccentricity, argument of perigee, mean anomaly, and mean motion, plus an epoch time stamp. Tracking software takes these numbers and propagates the orbit forward to predict pass times, elevation, and Doppler shift. They are named for Johannes Kepler, who worked out the laws of orbital motion, and updated sets are published regularly because orbits decay and drift.
Watch out The Yagi answer plays on the word "elements" meaning antenna rods, but antenna elements have nothing to do with orbits; the magnetron and spread spectrum choices are unrelated filler.
Kepler = planets and orbits. If the question says Keplerian, the answer is about an orbit, not an antenna.
HamSandwich explanation, first draft. The question and answers are the NCVEC text.
E2A077 of 12

Which of the following types of signals can be relayed through a linear transponder?

Why A linear transponder does not demodulate anything. It receives a whole slice of spectrum, amplifies it linearly, and translates it to a different output band, preserving the amplitude, frequency and phase relationships of everything inside that passband. Because the modulation is never touched, any mode that fits in the passband comes out the other side intact: CW, SSB, FM, SSTV, PSK and packet alike. Contrast this with an FM repeater-style transponder, which demodulates one FM signal and retransmits it, so only that mode works.
Watch out Each single-mode choice is tempting because operators mostly use CW and SSB on linear birds, and wide FM signals are discouraged since one hogs power from the shared transponder, but discouraged is not the same as impossible.
Linear = mode-transparent: it moves spectrum, not messages, so every mode rides through.
HamSandwich explanation, first draft. The question and answers are the NCVEC text.
E2A088 of 12

Why should effective radiated power (ERP) be limited to a satellite that uses a linear transponder?

Why A linear transponder amplifies its whole passband at once, and the satellite's downlink transmitter has a fixed total power budget shared among every signal in that passband. Automatic gain control in the transponder sets the overall gain based on the strongest signal present, so one station running excessive ERP grabs a large share of the power and forces the gain down for everyone else. The result is that all other users' downlink signals get weaker. Good practice is to use only enough uplink power that your downlink is about as strong as the satellite's beacon, never stronger.
Watch out Telemetry corruption and out-of-band emissions are not what happens; the transponder stays linear and in band, it just redistributes its limited output power. Terrestrial interference is not the issue since you are pointing a beam skyward at a frequency the satellite is listening on.
Shared power pie: don't be louder than the beacon, or you eat everyone else's slice of downlink.
HamSandwich explanation, first draft. The question and answers are the NCVEC text.
E2A099 of 12

What do the terms "L band" and "S band" specify?

Why Amateur satellite operators use single-letter band designators borrowed from radar/microwave nomenclature: H is 15 m, A is 10 m, V is 2 m, U is 70 cm, L is the 1.2 GHz band (23 cm), and S is the 2.4 GHz band (13 cm). So a satellite listed as mode L/S takes a 23 cm uplink and delivers a 13 cm downlink. These letters appear in satellite mode listings like U/V or L/S, describing the uplink and downlink bands.
Watch out The 2 m and 70 cm bands are designated V and U, not L and S; and the letters say nothing about sideband choice or the type of digital system carried.
L is Long wave of the microwaves (23 cm), S is Shorter (13 cm). V/U = 2 m/70 cm, L/S = 23/13 cm.
HamSandwich explanation, first draft. The question and answers are the NCVEC text.
E2A1010 of 12

What type of satellite appears to stay in one position in the sky?

Why A geostationary satellite sits in a circular orbit directly over the equator at about 35,786 km (22,236 miles) altitude, where the orbital period is exactly one sidereal day. Because it circles the Earth at the same rate the Earth turns, it stays over the same spot on the ground, so from your location it hangs at a fixed azimuth and elevation. That means a dish or beam can be aimed once and left there, with no tracking needed.
Watch out LEO satellites orbit only a few hundred kilometers up and race across the sky in minutes, requiring tracking, and HEO (high or highly elliptical orbit) birds move and change range over a long pass. Geomagnetic refers to the Earth's magnetic field, not an orbit at all.
Geo-stationary = stationary in the sky, 22,236 miles up over the equator, one orbit per day.
HamSandwich explanation, first draft. The question and answers are the NCVEC text.
E2A1111 of 12

What type of antenna can be used to minimize the effects of spin modulation and Faraday rotation?

Why A satellite tumbling or spinning changes the apparent orientation of its antenna, and the ionosphere rotates the polarization plane of a signal passing through it (Faraday rotation), so a fixed linear antenna on the ground sees deep fades as the polarizations drift in and out of alignment. A circularly polarized antenna, such as a crossed Yagi or helix, has a constant response to any linear orientation, so those fades largely disappear. You pay about 3 dB in mismatch loss to a purely linear signal, but you trade deep nulls for a steady, predictable signal.
Watch out A linearly polarized antenna is exactly what suffers the problem, since its response drops toward zero when the incoming polarization is rotated 90 degrees. A log periodic dipole array is a wideband linear antenna and an isotropic radiator is a theoretical reference, not something you can build.
Spinning satellite plus twisting ionosphere equals twist your own signal too: go circular.
HamSandwich explanation, first draft. The question and answers are the NCVEC text.
E2A1212 of 12

What is the purpose of digital store-and-forward functions on an amateur radio satellite?

Why A low Earth orbit satellite is only in view of any given ground station for about 10 to 15 minutes per pass, so two distant stations are rarely in view at the same time. A store-and-forward digital satellite acts like a flying mailbox: it accepts uploaded messages into onboard memory, carries them around the orbit, and lets stations download them on a later pass when the satellite comes over the horizon. This is packet-style messaging rather than a real-time transponder relay.
Watch out The choice about relaying messages between satellites describes crosslinking, which is a different technique; store-and-forward moves mail between ground stations using the satellite's memory, not between spacecraft.
Store-and-forward = orbiting mailbox: upload now, someone downloads on a later pass.
HamSandwich explanation, first draft. The question and answers are the NCVEC text.
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