---
title: RF Specifications
description: RF input parameters, LNB voltage and current limits, and symbol rate range for the SkyWalker-1.
---

import { Aside } from '@astrojs/starlight/components';

## RF Input Parameters

| Parameter | Value |
|-----------|-------|
| IF frequency range | 950 -- 2150 MHz |
| Symbol rate | 256 Ksps -- 30 Msps |
| Input connector | IEC F-type female |

The IF frequency is the intermediate frequency after LNB downconversion. The host computes it as `(RF_freq - LO_freq) * multiplier` and sends it in the [TUNE_8PSK](/bcm4500/tuning-protocol/) command payload.

## LNB Power Supply

| Parameter | Value |
|-----------|-------|
| LNB voltage (standard) | 13V / 18V |
| LNB voltage (boosted) | 14V / 19V (with USE_EXTRA_VOLT) |
| Maximum continuous current | 450 mA |
| Maximum burst current | 750 mA |

<Aside type="caution" title="Current Limits">
750 mA is the maximum **non-continuous** (several minutes) allowable load. To avoid overheating the on-board voltage regulator, do not exceed **450 mA** for permanent load. Exceeding these limits may damage the SkyWalker-1 hardware.
</Aside>

LNB voltage is controlled via GPIO P0.4 on all firmware versions. The voltage selection determines the polarization:

| wValue | Voltage | GPIO P0.4 | Polarization |
|--------|---------|-----------|-------------|
| 0 | 13V | LOW | Vertical / Circular-Right |
| 1 | 18V | HIGH | Horizontal / Circular-Left |

The USE_EXTRA_VOLT command (0x94) enables a +1V boost for long cable runs by toggling bit 3 of the LNB control register at XRAM 0xE0B6 (0x62 = normal, 0x6A = boosted). See [Vendor Commands](/usb/vendor-commands/) for the command interface.

## Switch Control

The SkyWalker-1 supports multiple satellite switching protocols:

| Protocol | Implementation | Command |
|----------|---------------|---------|
| 22 kHz tone | GPIO P0.3 gates external oscillator | SET_22KHZ_TONE (0x8C) |
| Tone Burst (mini DiSEqC) | Timer2-based carrier gating | SEND_DISEQC_COMMAND (0x8D) |
| DiSEqC 1.0 | Timer2 Manchester encoding | SEND_DISEQC_COMMAND (0x8D) |
| DiSEqC 1.2 | Timer2 Manchester encoding | SEND_DISEQC_COMMAND (0x8D) |
| Legacy Dish Network | 7-bit serial bit-bang on P0.4 | SET_DN_SWITCH (0x8F) |

## 22 kHz Tone

The 22 kHz tone signal is generated by an external oscillator on the PCB, gated by GPIO P0.3. The firmware does not generate the 22 kHz carrier directly -- it only enables or disables the oscillator output.

| wValue | State | GPIO P0.3 | Band Selection |
|--------|-------|-----------|------|
| 0 | OFF | LOW | Low band (9.75 GHz LO on universal LNB) |
| 1 | ON | HIGH | High band (10.6 GHz LO on universal LNB) |

## Signal Path

```
Satellite
   |
   v
[ LNB on Dish ]  <-- 13V/18V + 22kHz from SkyWalker-1
   |
   | Coax (950-2150 MHz IF)
   v
[ SkyWalker-1 F-connector ]
   |
   v
[ BCM4500 Demodulator ] -- demod + FEC decode
   |
   | 8-bit parallel MPEG-2 TS
   v
[ FX2 GPIF Engine ] -- zero-copy DMA to EP2
   |
   | USB 2.0 High-Speed Bulk
   v
[ Host PC ]
```

The USB/GPIF data path has substantial headroom over the satellite link throughput:

| Metric | Value |
|--------|-------|
| USB 2.0 HS bulk (practical) | ~280 Mbps (~35 MB/s) |
| GPIF engine (theoretical) | 48 MHz x 8 bits = 384 Mbps |
| Typical DVB-S TS rate | 1--5 MB/s |
| Maximum symbol rate (30 Msps) | ~58 Mbps |

The bottleneck for all supported modulation modes is the satellite link, not the USB data path.