What do you like about ham radio

On the Elecraft List Server there were a number of messages about the AGC settings of the K3 and "rough" NF on the K3. Both are dependent on the interference radiation occurring at the location and the antenna on a certain band.

If your S-meter shows the ambient noise with S0 or S1, then the default (standard) settings of the AGC are sufficient for your situation. You can congratulate yourself on this almost trouble-free situation and indulge in radio operations without further changes.

But if the background noise level increases annoyingly during the speaking pauses of a QSO (whether in CW or SSB) then you can improve a lot for the AGC by changing the various parameters of the K3.

Some information about the AGC settings of the K3:

The most important parameters for changing the AGC characteristics are the values ​​for AGC THR and AGC SLP in the CONFIG menu.


The setting of the AGC THR (= AGC Threshold = Automatic Gain Control Threshold) determines how strong a signal must be before it activates the AGC at all. If the value is set correspondingly low, the background noise of an inanimate frequency already causes the AGC to start. Look at the S-meter while you tuned in to a frequency that is not in any activity. If the S-Meter now shows anything, the AGC is already activated by the background noise. If S1 is displayed and the bar for S2 only flickers from time to time, then this can be tolerated. But if you have a display around S5 at your location with the antenna used on this band, then you should change the value for AGC THR.

A higher value for the AGC THR setting increases the response threshold of the gain control. So you should try higher values ​​to see what effect will be achieved in your situation.


When trying out the influence of AHC THR, the following must be observed: Make sure you only use the background noises that occur during the pauses in a QSO that is running. If you only listen to the background noise without any useful signal, then you will have the impression that lowering the response threshold reduces the background noise. However, this is a wrong assumption. What really happens: with lower values, the background noises activate the AGZ earlier. This reduces the gain of the receiver, which gives the impression that the background noise has become weaker. If you listen to this setting in the presence of useful signals, you will find that exactly the opposite is the case.


The slope value of the AGC characteristic determines how strong the difference in the LF volume is displayed between a weak and a strong HF signal. At higher AGC SLP values, all signals are amplified to a similar AF level. This is great for rag chew (long chat) rounds. Please note, however, that the AGC detector cannot differentiate between a real useful signal and a broadband interference signal. If the value for AGC SLP is set high, background noises are also played back at a higher volume.

If you reduce the value for AGC SLP, then weaker HF signals on the LF level sound quieter than strong signals. As long as the signals of interest are above the level of the background noise, they sound louder than the background noise. Conversely, if you use a high value for the slope and the background noise is as strong as the useful signal, then you will hear the background noise in your headphones as loud as the useful signal.

So what does that mean for my K3?

The K3 has a very sensitive receiver and a very large dynamic range. This means that e hears very weak signals (sensitivity), but at the same time can reproduce very strong signals without overloading or distortion. A typical K3 still hears signals at a field strength of -140dBm (specification is -136dBm), but still manages to process signals in the order of magnitude of 0dBm without restriction.

If the interference level is now -110 dBm, then 26-30dB of the dynamics of the K3 are wasted. In order to regain at least part of this dynamic, switch off the preamplifier and, if necessary, even switch on the attenuator (ATT) as soon as the tape being used is so clogged with interfering signals. You don't need the extra amplification because you can't hear signals that are weaker than the interference level anyway and because the interference level otherwise unnecessarily steals dynamics. OK, some radio amateurs can still pick up signals well below the interference level, but this is an exception and these OPs already know how to improve their reception conditions J

If the band is relatively free of interfering radiation, the factory values ​​for the AGC are usually good enough and the receiver works fine with it. But every band and every location are different. Determine the best values ​​for your K3 by using the tape and antenna that have the worst radiation in your location.

For the first try you can start with the values ​​that I use here. For me, the threshold is 008 and the slope is 002, if you want to start with other values, then do that. Ultimately, it all depends on you and the conditions in your shack

Listen to existing useful signals when trying out the changes. If you only listen to the background noise, then - as already explained - you will get a wrong impression. (The noise level gets weaker if you set the threshold to a lower value because the overall gain is reduced.) Don't let you fool you! This supposed improvement then increases the volume of the interference radiation in the presence of useful signals.

Observe the interference level in relation to the useful signal during pauses in speech at SSB or the pauses between words at CW. The point is to find a value at which the distance between the useful signal and the interfering signal is greater. Threshold and slope have a certain interdependency. If the slope is set to higher values, then the distance between different field strengths in volume becomes smaller and smaller. If the threshold value is set too low at the same time, the AGC is triggered by both tape background noise and real signals. The combination of a low threshold and a high slope means that everything that is received is brought to the same NF volume and this also includes any background noise because this is ultimately nothing more than a broadband signal for the AGC.

If the threshold is too low, the K3 AGC considers every interfering signal or tape noise to be a real signal that it dutifully amplifies --- and that is actually NOT what we want.

Increase the threshold on the noisiest band to the value at which the AGC just doesn't respond or only responds minimally. THEN adjust the slope value as you like it. If you are the Rag Chew (permanent QSO / long chat QSO) type who transmits in large rounds, then set a higher value so that weaker stations sound as loud as strong ones. If you are more interested in keeping the noise level low during the breaks, then choose a lower slope value. Contesters, for whom it is important to recognize the actual strength of the opposing stations with their ears rather than with the S-meter, will set a significantly lower value than the average.

My personal settings are 008 for the threshold and 002 for the slope. This gives the AGC an effect similar to that of the K2, which I am used to because I used a K2 for 10 years before the K3.

Bottom line:

If a K3 seems too noisy or nervous, the first step is to reduce the input gain. This means: switch off the preamplifier and, if the tape noise is very high, switch on the attenuator. This increases the dynamic range of the K3 like any other receiver. The interference level is reduced by these simple measures. The K3 remembers the settings for PRE / ATT that were selected for a certain band and automatically restores them when you switch back to this band.

The AGC settings are universal, i.e. they cannot be set separately for each band. Therefore, a reasonable compromise has to be found for the tapes you normally work on. If you are more at home on the upper HF or the VHF / UHF bands, then the settings will be different than if you prefer 160m and. There is no one universal setting that is optimal for every situation. As difficult as it is to find a setting that works best for your way of radio and one of your favorite bands…. I think we should be grateful that the K3 offers the possibility of influencing the AGC in such a way that a wide range of band and environment-typical disturbances and personal preferences are covered.

Yes, it takes some time and effort to find out which settings are optimal for your personal preferences and band situations, but as a result you get a K3 that is precisely tailored to your situation.