FT 991A DSP and DNR performance

FT-991A DSP and DNR performance

The FT-991A sports a modern (as of this article writing) DSP, a Texas Instruments TMS320C6746 - Matter of fact, it is the same DSP that powers the flagship FT-DX101MP/FT-DX101D. If you are curious, check this video where Bob Naggy compares side by side the FT-DX101D and IC-7610 DNRs.

First of all, the DNR should not be mistaken with a magic signal maker. It is a filter, which will remove some parts; enhance others of the received signal. It means, it depends on having some signal present. No hay milagro, amigo.

Effective use of the DSP

• The FT-991A provides 15 different DNR programs, not levels. Each DNR program processes differently the incoming signal - Try the one that suits the to-be treated signal.
• If you have some nearby interfering signal, you will help your DNR a lot by narrowing your bandwidth settings to 2400 Hz or even less.
• When narrowing the bandwidth, you will notice that the audio will tend to mid levels, cutting the bass almost entirely. You can Shift the audio to something between -200 to -600 in SSB
• Some complaint about the DNR sounding "bubbly" or "waterish". Well, as stated before, the DNR is not a signal maker - this scenario will happen on weak signals. However you can reduce that significantly.
  1. Ensure that you have set your AGC in either AUTO or SLOW mode;
  2. Turn the RF Gain knob counter-clockwise slowly, until the S-Meter stops swinging on the receiving signal that you are working. Ensure to move back the RF Gain to the full clockwise position after you worked the station. With these two simple steps you will ensure a way more comfortable DNR operation.
• Ever been in a good QSO when suddenly some lid tunes over the receiving signal? The FT-991A can also filter out that signal automatically. That's named Autonotch; and it is named DNF in FT-991A. Just hit DNF and it will eat away the interfering signal. Turn off the DNF after the interfering signal is gone.
• Use the amplifiers sparingly. If you already have a high noise floor (above S1) in IPO position, why amplify even more the signal? With more amplification, comes more distortion and more noise too. Use amplifiers only when your noise floor is below S0. Do yourself this favour.
• A trick that I learned in the manual is that the Attenuator is of help when you have static crashes that makes your S-meter jump more than 3 S-Units.
• Do you know how to use the RF Gain knob? Increase the RF Gain counter-clockwise until the point that the S-Meter stops swinging on the SSB signal. You will have a heck of a more comfortable reception than the fully-open (full clockwise) position.

Video

In the below video, there's a demonstration of my FT-991A filters. After 7:55 minutes, I turn on a LED lamp that jumps my noise floor from S0-S1 to S6-S7. Notice in the waterfall that it washes away a lot of signals - But it is still of some help though.

Yaesu Transceivers and DSP Matrix

DSP	MFLOPS	Shipped in
TMS320C6711B	1200	FTDX-9000
TMS320C6713B	1350	FT-950, FT-2000
ADSP-BF531SBST	N/D	FT-450, FT-450D, FT-450AT
TMS320C6727B	2100	FTDX-1200, FTDX-3000, FTDX-5000
TMS320C6746	2250	FT-891, FT-991, FT-991A, FTDX-101D, FTDX-101MP, FTDX-10