Skip to content

Transmitter

Asset reference

Concept

A transmitter is the RF source in a space–ground or cross-link budget.

  • Simple — frequency, EIRP, polarization, and modulation. Implicit isotropic antenna; no Antenna asset.
  • Complex — TX power plus a Linked antenna on the same parent (spacecraft, facility, or vehicle). Pattern gain and pointing come from that Antenna. Add the antenna under the parent first or the dropdown is empty. On ASTROLAB Web, Complex is available on every plan, including Trial, so the transmitter can be linked to an antenna. Plans and entitlements.

Link Analysis can run pure geometry between platforms, or enable link budget when the primary is a Transmitter and the secondary is a Receiver.

Common parameters

Parameter Type Options
Name text —
Active checkbox —
Type select Simple / Complex
Linked antenna select Complex only. Antennas on the same parent. Hidden in Simple.

Simple — RF Source & Modulation

Parameter Units / options Default
Frequency Hz / kHz / MHz / GHz 2.2 GHz
EIRP dBW / dBm / W 40 dBW
Polarization Linear / RHCP / LHCP RHCP
Modulator BPSK, BPSK-BCH, QPSK, 8PSK, 16PSK, DPSK, 2-FSK, 4-FSK QPSK
Data rate bps…Gbps 1 Mbps
Signal bandwidth mode Auto / Symmetric / Manual Auto
Symmetric bandwidth Hz/kHz/MHz 1 MHz (if Symmetric)
Lower / Upper band offset 0.5 MHz each (if Manual)

Complex — adds

Requires Type = Complex. The editor then shows Linked antenna.

Parameter Default
Linked antenna — (pick an Antenna on the same parent)
Power (W / dBW / dBm) 10 W
Additional gain [dB] 0
Additional loss [dB] 0

(Frequency, polarization, modulation block same as Simple.)

These fields are read when a Link analysis has Compute link budget on. Angles are the direction from this transmitter toward the receiver.

Setting What it changes
Frequency Carrier for free-space loss and Doppler. Free-space loss uses λ = c / f with c = 299792458 m/s. It does not reshape a linked antenna pattern. If it differs from the antenna design frequency by more than 10 %, the run prints a warning and still uses this frequency.
EIRP (Simple) The radiated level, already including an implicit isotropic antenna. No Antenna asset is added on top.
Power (Complex) EIRP = P_dBW + G_tx(θ, φ) + additional gain − additional loss. G_tx is the linked antenna toward the receiver.
Additional gain / loss Decibels added to or removed from that EIRP (cables, filters, a known margin). Counted once, inside EIRP.
Polarization Mismatch loss against the receiver. See the table below.
Modulator Required Eb/N₀, implementation loss, and — in Auto bandwidth — the occupied bandwidth.
Data rate Eb/N₀ = C/N₀ − 10 log10(R_b) − L_impl. A higher rate lowers Eb/N₀ by 10 log10 of the ratio.
Bandwidth mode Auto: B = (R_b / bits per symbol) · (1 + roll-off), roll-off 0.35 except FSK. Symmetric / Manual: the bandwidth you type. The receiver uses this as its noise bandwidth while Auto track transmitter bandwidth is on.

Polarization

RHCP is right-hand circular, LHCP left-hand circular, Linear is linear (horizontal and vertical are not separate). The loss is constant for the whole pass. It is applied only if the Link analysis has Include polarization loss on.

Transmitter Receiver Loss
Same as the receiver Same 0 dB
RHCP LHCP, or the reverse 30 dB
Linear RHCP or LHCP 3 dB

Modulator

A preset, not a waveform simulation. With Link Required Eb/N₀ left at 0, the threshold is this table. The receiver copies it while Auto track transmitter demodulator is on.

Preset Bits / symbol Required Eb/N₀ Implementation loss
BPSK 1 9.6 dB 0
BPSK-BCH 1 5.5 dB 0.5 dB
QPSK 2 6.5 dB 0
8PSK 3 11 dB 0
16PSK 4 14 dB 0
DPSK 1 10.3 dB 0
2-FSK 1 9.5 dB 0
4-FSK 2 11 dB 0

FSK bandwidth is 2 · deviation + symbol rate (50 kHz deviation for 2-FSK, 100 kHz for 4-FSK) instead of the roll-off formula. Implementation loss is subtracted from Eb/N₀, not from EIRP.

For RF budget mode, set Link primary = Transmitter and exactly one secondary = Receiver.

Transmitter editor

Transmitter Properties — Simple vs Complex RF source.