Any Hints on Improving CW Reception?

Frank Kirschner

Andreas Junge

George KF2T

Mike-VA3MW

Hi Frank

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

Mike



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.

Terry K8EET

You can try playing with the RX equalizer. Lower everything but the 500 or 1000 Hhz settings depending on your preference. 

Jeff_W4DD

I found the same to be true on my 6300 on 10, 15, and 20m vs my Orion II. I had to turn the 6300 preamp on to make them equal. The Sherwood performance web page seems to indicate a preamp may be needed for weak signals and I found a previous thread where it was suggested.

Sherman Banks

Duane_AC5AA

I set the first button on my FlexControl for AGC-T which makes it really easy to adjust and then jump back to tuning function.

Ernest

Geo,
You took the words out of my mouth. 
That is exactly what I have to do sometimes. I try adjusting the controls you mentions; if I am interested in the conversation or if I am trying to work something exotic that I have not worked or rarely hear.
73

dan flynn

Clay N9IO

Great idea Duane.

AC9S

Jamie WW3S

Depends on the band, and antenna....someone mentioned you don’t need a preamp on the hf bands....I use it on 160 with my rx loop and have worked a bunch of dx I couldn’t hear on my icon or k3....crank the agct down to next to nothing, turn the af gain all the way up.....ymmv....

Kevin

Hi Mike... The Flex SDR does have RF Gain. Is this actually doing something different than the RF Gain in a non-SDR radio?



Kev

bahillen

Frank 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. 73 Bill W9JJB

Frank Kirschner

What does the RF Gain control do if not control the RF gain?

Al_NN4ZZ

Frank Kirschner

John WA7UAR

That link didn’t work for me Al — was this what you were wanting to refer to? https://helpdesk.flexradio.com/hc/en-us/articles/204923669?mobile_site=true

Al_NN4ZZ

Stan VA7NF