Is there anything I can do to bring the signal out of the noise better?
AGC-T is something to look at closely. There's usually a sweet spot that reduces noise while letting the signal through beautifully.
I usually use Fast AGC, but some folks prefer medium. Depends on the code speed.
On HF, you probably don't need preamps on, so make sure they're off and not contributing to more noise.
Hope that helps!
SDR's do not have an RF Gain control. :) I suspect that you are using the AGC-T control like an RF gain control and that is the wrong way to use it.
This should help you out.
We discuss AGC-T in the manual on Section 13.1
13.1 AGC THRESHOLD
Automatic Gain Control (AGC) is a feature which automatically adjusts the Slice Receiver’s audio gain (volume) based on the strength of signals in the receiver’s passband filter. The goal of AGC is to amplify weak signals and attenuate strong signals so that they all lie within a comfortable listening range.
The receiver Automatic Gain Control Threshold (AGC-T) can be adjusted for optimum performance in noisy or quiet environments. The AGC-T sets the maximum gain applied under any circumstances. Since the noise floor is relatively constant on a given band at a given time, the AGC can be adjusted using the threshold control so that the AGC never applies gain to noise, but it will apply gain to signals just out of the noise. In doing so, the AGC can reduce the level of noise you hear, and help signals pop out of the noise.
The AGC system in SmartSDR is a dual track system, meaning that it can track both slow and fast increases in signal strength, making appropriate gain correction decisions in the presence of each. The speed of the AGC (FAST, MED, SLOW) determines how quickly or slowly the AGC recovers after attenuating a strong signal. You can easily hear this by tuning to a CW signal and going through the three settings. On FAST with a strong signal you can hear the gain pump up and down while on SLOW it recovers after a longer pause once the signal stops. When the signal stops, you will hear the noise floor increase as the gain returns.
How to Set AGC for Different Operating Conditions
If you are listening to a loud voice signal, AGC SLOW will resist increasing the gain between syllables and therefore reject most of the noise which is at a level far below the signal. FAST and MED provide faster levels of recovery for situations when you want the system to more closely follow the dominant signal in the passband. Any time you have a very strong signal that causes the gain in the AGC to be reduced, you could experience a loss of gain to a weak signal you are listening to. The filter passband edges, which are continuously adjustable, and TNFs can be used to eliminate signals that might interfere with AGC operation.
The operator might prefer to use SLOW settings when rag chewing in a high signal to noise environment where there isn't much QRN and the noise floor is stable. This keeps the gain at more of a constant level that is less distracting. If the operator is trying to pull a weak CW signal out of the noise, they may prefer to use FAST mode to quickly ensure that the long-term average of the noise floor doesn't overcome the signal and prevent it from being heard. MEDium is a reasonable compromise.
To adjust the AGC Threshold, tune to a quiet spot between stations. Starting with the AGC-T at a high value adjust the AGC-T slider to the left (lower gain values) until the background noise just begins to decrease. This is the AGC-T "sweet spot" or the "knee" of the AGC algorithm. Depending on band conditions, if the AGC-T is set below 50, you may have to compensate for the loss in audio gain (volume) by increasing the Slice or master AF volume to a higher value. When you get the knee and AF volume adjustment correct for the band conditions, it will keep the volume of strong signals constant which will allow weaker signals to be heard even with AGC in FAST mode. Thus AGC-T is one of the most important adjustments, and often overlooked, to achieve the maximum weak signal receive performance out of the FLEX- 6000 series SDRs.
There is a request to automate the AGC-T setting since it is critical. Thank goodness the Maestro has a knob for it to make it easy to change on the fly. See the link below.
Don't forget mechanical resonate speakers. Here's a link to building one. (there are plenty other designs if you google around..)
Also, here's a starting point on the science.
My standard approach to 160 now is to set the filter latency to minimum and use a 50hs filter width. In addition, of course, I use the APF and fiddle with the AGC-T.
In the last 160 meter CW contest there were lots of very weak whisper traces that were totally unreadable with my standard 250hz automatic latency. 50hz and minimum latency allowed me to work a dozen or so previously unreadable Europeans. 50hz and APC pop the signals out of the noise and minimum latency stops the ringing. You will hear stuff off the sides with the wide filter slope.
Keith - AC9S
You have to spend some time with weak signals under different situations. For me NR has been significant. As suggested the EQ can make a big improvement in attenuating high and low frequency noise.
What works for 80m May be different than 15 m. Your type of noise make different things work more or less. The mode you are operating make a difference also.
Since the he noise blanket subject was raise here recently, I have been trying different options, settings and gain. This lead me to realize that flex has many tool to abate noise. Learning how to use them takes an invest of your time and skill. I have pulled stations out of the noise that were well below the noise. That said there is always room for improving software and inventions. New software releases can change the fundamental behaviors with the same hardware. If your radio works with S9+10db noise I would keep it. If your Flex doesn’t deal with your noise like your last radio, document it and submit a help desk ticket, maybe it will help all of us on the long run.
We often want more in the radios we acquire. The downside of that is the options that the Flex has requires that we learn how to choose and operate what we want. Engineers in the past decided for you what settings to make and thus restricted the capability to suit tha majority. My FT1000MP had limited capability to pull someone out of the noise, you could hear him or not.
This is not only a radio but a communications system and does some unbelievable things. But there is a comfort level with what he have used and is maybe not for everyone. My National NCX-5 from 1961 still works, very simple to operate and can be fun to operate.
I would like to hear back from you Frank what you find as you implement the suggestions provided above and how the FTdx5000 compares. What kind of noise is in your environment. If you add what you find, six months from now someone will read this thread and learn from your experience. I personally am interested as others would be too. When you write down on a pad what you find, you will be surprised additional things you learn or a couple other aspects you want to look at.
I also found that reversing the connections on one of the speakers helps. With identical signals going to both left and right channels, the desired signal was cancelling right at the center, where I sit. Reversing one causes the signal to add in the center.
- Don't add anything with resonance, speakers, peaking filter etc - It just muddies the CW. Especially if it is cross polar as that stuff has so much aurora distortion already.
- Narrow the filter to below 200. 50-90 is my preference - That reduces the noise significantly BUT the AGC will bring up the background and because of the narrow bandwidth, any noise will sound like signal and muddy the signal again.
- Everybody talks about the AGC-T, that is the remaining best tool EXCEPT bring it down slightly more than normal, that will reduce/eliminate the AGC action on the background noise so the CW pops out that little bit more.