Main Controls

This page describes the common controls that appear across most receiver and transmitter apps.

Frequency

When the frequency field is selected, the frequency can be changed in three ways:

• Encoder dial: Adjusts the frequency by the currently set step size.
• Short press of Select: Opens the direct frequency entry screen, where a frequency can be typed in.
• Long press of Select: Toggles digit mode. In digit mode, the cursor highlights a single digit of the frequency. Left/Right move the cursor between digit positions; Up/Down (or the encoder) adjust the value of the selected digit. Long press again to exit digit mode.

The nine digit positions represent: 1 GHz, 100 MHz, 10 MHz, 1 MHz, · (decimal), 100 kHz, 10 kHz, 1 kHz, 100 Hz.

Step size

The step size used when turning the encoder dial can be changed as a secondary option when the frequency field is focused. The available steps are:

10Hz · 50Hz · 0.1kHz · 1kHz · 5kHz (SA AM) · 6.25kHz (NFM) · 8.33kHz (AIR) · 9kHz (EU AM) · 10kHz (US AM) · 12.5kHz (NFM) · 15kHz (HFM) · 25kHz (N1) · 30kHz (OIRT) · 50kHz (FM1) · 100kHz (FM2) · 250kHz (N2) · 500kHz (WFM) · 1MHz

Bandwidth

The IF filter bandwidth selects which FIR filter is applied to the received signal. Available options depend on the modulation mode:

AM: DSB 9k · DSB 6k · USB+3k · LSB-3k · CW

• DSB 9k and DSB 6k are standard double-sideband AM (9K00A3E and 6K00A3E).
• USB+3k and LSB-3k are single-sideband (2K80J3E), upper and lower respectively.
• CW uses a 200 Hz filter centred at 700 Hz.

NFM: 8k5 · 11k · 12k5 · 16k

• 16k (16KF3E) is for 25 kHz channel spacing.
• 12k5 is standard for 12.5 kHz channels; overmodulated systems may benefit from 11k.
• 8k5 (8K5F3E) is for narrow 12.5 kHz spacing where tighter filtering is needed.

WFM: 80k · 180k · 200k

• 200k covers a full stereo FM broadcast signal.
• 80k is a narrower option useful for weaker stations or reduced bandwidth.

Gain controls

The HackRF has three independent RX gain stages and two TX gain stages. The image below shows their position in the Audio receiver app — the layout is the same across all receiver apps.

RX gain

Label in UI	Stage	Range	Step
AMP	RF amplifier (at antenna port)	0 dB or +14 dB	on/off
LNA	IF / low-noise amplifier	0 – 40 dB	8 dB
VGA	Baseband variable gain amplifier	0 – 62 dB	2 dB

The RF amp is shown as 0/1 in most RX apps. In the Audio app, it appears as Amp on the line below LNA/VGA when one of those fields is selected.

A good starting point for most signals is: AMP off, LNA 16, VGA 16. Increase LNA and VGA roughly equally until the signal is clear. Enable AMP only for very weak signals — it can degrade SNR if the noise floor is already high, or if a strong signal is present.

[!NOTE] Setting gain too high causes ADC saturation, which appears as broadband noise or spurious signals across the waterfall. The Satu% field in the DFU-overlay shows the current saturation percentage in real time and helps dial in the optimal setting.

TX gain

Label in UI	Stage	Range	Step
AMP	RF amplifier (at antenna port)	0 dB or +14 dB	on/off
Gain	TX VGA	0 – 47 dB	1 dB

The TX amp is shown as 0 or 14 in TX apps.