The DSP Noise Reduction (NR) and Noise Blanker (NB) are the primary tools for reducing band noise and electrical impulse noise, respectively. The Auto-Notch (AN) will remove multiple tones or carriers. It is post-AGC, so strong in-band carriers can still swamp (desense) the receiver. The NR level and NB threshold* are both adjustable.
The Manual Notch (MN) is inside the AGC loop, and is 70 dB deep. It will remove a single tone without any swamping, and is tuneable. You can select AN or MN by pressing the NOTCH button. (AN is disabled in CW mode.)
You can also use the Twin PBT controls to cut out QRM above and below the IF passband, or to modify the spectral content of the received signal. The Manual Notch can be used in conjunction with Twin PBT to steepen the upper or lower passband skirt. You can also select sharp or soft shape factors for the CW and SSB filters for best SSB articulation or CW copy; press EXIT/SET -> DSP*
It is possible to adjust the bandwidth of the FIL 1, FIL 2 and FIL 3 filters continuously, using the FILTER menu. The minimum CW filter bandwidth is 50 Hz. In CW, USB-D* and LSB-D* modes, the shape factor automatically narrows (BPF Indicator on) for bandwidths of 500 Hz or less. You can "mix and match" BPF and Sharp/Soft settings for IF bandwidths of 500 Hz or less, as described in my IC-756Pro/Pro2 User Review.
You should set the IF filter bandwidth as close as possible to the occupied bandwidth of the received signal, to maximise S/N ratio. You can then use a combination of Twin PBT, Manual Notch and NR to pull up the signal. If necessary, switch in Preamp 1 below 21 MHz or Preamp 2 above 21 MHz.
If the distant station is transmitting excessive "lows" on SSB, you can slice these away by setting the lower flank of Twin PBT to +50 or +75 Hz. This will improve articulation.
Depending on band conditions, you can switch AGC between Slow and Mid (SSB) or Fast and Mid (CW). This may help pull up that "weak one". There is a procedure for exploiting the band noise/noise floor margin for quieter reception on the lower HF bands. I have termed this "dBm from Heaven".
Using a combination of all these controls, you can tailor the IF bandwidth for optimum reception of pretty well any signal. The NR and adjustable* Noise Blanker will help in reducing impulse noise. (To open the Noise Blanker adjustment menu, press and hold the NB button.) It takes a little bit of practice to get used to the signal-management tools offered by the Pro2 or Pro3.
The Noise Blanker can cause distortion in the presence of strong adjacent signals. If you hear such distortion, try turning the NB off.
The real-time† Spectrum Scope, with its -125 dBm (Pro2) or -131 dB (Pro3) sensitivity and 1 kHz resolution bandwidth, is a very useful tool for detecting the presence of weak signals - especially on a quiet band.
The Pro3 has a Mini-Scope‡ feature. This mini-scope screen can be displayed simultaneously with another screen indication, such as bar-graph meter scales, set mode menu, decoder screen, memory list screen, etc. Push and hold MAIN/SUB•M.SCOPE for 1 sec. to toggle the mini-scope indication ON and OFF. Now, if you wish to display the bar-graph meter scales (for example) below the mini-scope, press and hold METER for 1 sec.
Dual Watch† combined with Split allows you to monitor the distant station's transmit and listening frequencies simultaneously.
To suppress the SUB frequency display, select a blank memory via the [^ v] up/down arrow keys, press CHANGE to bring it up on the Sub display, and then press VFO/MEMO to blank the Sub display. Press MAIN/SUB to highlight the MAIN frequency display. (The SUB VFO frequency setting will still appear in a small font below the blank field.)
The built-in autotuner is in the RF signal path on receive and transmit. You can use the tuner as a simple RF preselector, to provide additional front-end overload protection in the presence of many extremely strong signals. (Note: Do not activate the internal autotuner when feeding an external tuner!)
I encourage you, the new IC-756Pro III, IC-756Pro II or IC-756Pro owner, to study the Instruction Manual thoroughly, then try out the controls on your radio and get accustomed to their operation and effect. Don't be afraid!
Manuals and other documents for these radios are downloadable here.
The above suggestions are also applicable to the IC-746Pro, IC-7400, IC-7800 and IC-7000.
Further reading: Check out the Icom IC-756PRO Advanced Operating Guide, much of which also applies to the IC-756Pro II and IC-756Pro III. Read my IC-756Pro/Pro II and IC-756Pro III User Reviews.
IC-756Pro2/3 LCD Display Replacement
* Not IC-756Pro. † Not IC-7000, IC-746Pro or IC-7400. ‡ IC-756Pro3 only.
Copyright © 2003-2008, A. Farson VA7OJ/AB4OJ.
Last updated: 06/16/2018