IC-R8600 Preamp, Attenuator, IP+ & AGC

Summary: How to use the IC-R8600’s preamplifier, attenuator, IP Plus function and AGC to get the best reception from weak and very strong signals.

Each band remembers its preamp, attenuator and IP+ settings.

Preamplifier

For weak signals: touch P.AMP on the FUNCTION screen. The gain is about 20 dB on HF and 14 dB on VHF/UHF. With a strong signal it can cause distortion; turn it off then.

Attenuator

Touch ATT repeatedly to cycle ATT10, ATT20, ATT30 and OFF. It prevents distortion when a very strong signal or field is near. If OVF (overflow) appears, reduce the RF gain, turn the preamp off, or turn the attenuator on until OVF disappears.

IP Plus (IP+)

The IP Plus function improves third-order intercept (IP3) and intermodulation by optimising the direct-sampling ADC against strong input signals, with minimal loss of sensitivity. Touch IP+ on the FUNCTION screen. ON prioritises IP quality; OFF prioritises sensitivity.

AGC

The AGC keeps the audio level constant as signal strength varies. There are three presets (FAST, MID, SLOW) for all modes except FM, WFM and DIGITAL (fixed at fast). Touch AGC on the FUNCTION screen to cycle them. To change a preset’s time constant, touch AGC for 1 second, choose FAST, MID or SLOW, and rotate the MAIN DIAL. Default time constants (seconds):

• SSB: 0.3 fast, 2.0 mid, 6.0 slow (choices OFF, 0.1 to 6.0)
• CW/FSK: 0.1 fast, 0.5 mid, 1.2 slow (OFF, 0.1 to 6.0)
• AM: 3.0 fast, 5.0 mid, 7.0 slow (OFF, 0.3 to 8.0)
• FM/WFM/DIGITAL: 0.1 (fixed)

When receiving weak signals a strong burst can make the AGC pull the gain down so the weak signal is lost for a while; use FAST or turn the AGC off.

Choosing Between Them

For strong-signal problems try, in order: lower RF gain, preamp off, attenuator on, IP+ on. For weak signals: preamp on, IP+ off, attenuator off. See IC-R8600 Troubleshooting.