[Lowfer] W3EEE (was Re: Re: Level settings)

[k2ors at verizon.net]

Steve,

  Any chance of restarting the 'grabulators' in your new /4 location?

73 Warren K2ORS
          WD2XGJ
          WD2XSH/23
          WE2XEB/2
          WE2XGR/1


Jul 8, 2010 12:37:37 PM, lowfer at mailman.qth.net wrote:

Hi Andy, et al,

The optimum is to go for maximum gain *without* the AGC 
acting;  what the AGC wiggling does is to modulate the 
signals, creating little - and not-so little - modulation 
products close in to the desired signals on the 'Argo' display 
and cluttering things up.

The 'maximum gain' aspect is to eke the maximum 
signal-to-noise from the receiver so its self-generated noise 
is least significant.  Obviously, once band-noise is nicely 
above self-noise then no more gain is really needed, but I 
found that was sometimes a struggle daytime on a quiet day!

I used to run the Grabulators with no AGC at all, and use the 
natural clipping-point of the now unprotected receiver as an 
impulse noise / lightning clipper; the RF gain control 
effectively set that clip point.  The AGC within 'Argo' did a 
reasonable job of taking care of night/day level differences 
and such.

An easy way to find a good starting point is to see where the 
receiver 'S' meter is hovering with the AGC on, then back off 
the RF gain control so that the meter is JUST no longer 
dithering;  that way there are no intermod products being 
generated, and the gain is about right.  The headroom before 
the receiver clips varies RX to RX, so with the AGC off gently 
raise the RF gain unil you find a good point where only 
impulses are being smashed;  excessively deep clipping is a 
bad idea.

         73

                Steve        W3EEE / 4


Andy - KU4XR wrote:
> Hi J.B. :::
> 
> I have tried both ways you mention. From my own exeprience ( others may differ ), I leave the RF Gain at maximum gain ( minimum reduction ), and that seems to work best with my setup here. Reducing the RF Gain, or in other words, trying to control the audio level with the RF Gain control has adverse effects on received signals, and if the RF Gain is reduced too much; a weak signal that is actually there, may not get through. I do all my audio control by using a combination of the AF Gain on the radio, and the settings of my DSP filter software.
> One thing I have noticed, and I'm sure you have too, is that " more, is NOT necessarily better " from an audio standpoint anyway. Some of the software packages do not like high audio levels. I have gotten the best results by using audio input levels from 5% up to around 25% depending on the program I am using.
> On AGC; I usually leave mine set to fast. This has the least effect on weak signals by letting the gain return to maximum as quickly as the rig will allow after a heavy static burst, or gain reduction from a nearby strong signal that " Pumps " the AGC voltage. As with many modern HF rigs, I can't turn the AGC off, that's why I use the fast setting.
> I do use the Noise Blanker. On my Kenwood TS450S, it is very effective at greatly reducing the effects of static crashes, and powerline buzz, and yet not affect the received signal. I have no trouble in decoding any digital mode while using the Noise Blanker in this particular radio, and sometimes I can't get decodes without using it due to rapid impulse noise. I mention " This particular radio " because I also have a YAESU FT757 GX-II, it has great receive at LF, but its Noise Blanker will obliterate signals when you turn it on, and does not do a good job at reducing the noise either. So using a Noise Blanker will depend on whether or not it works for your particular setup. Basically; try it and see....
> 
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