Bill has linked to and quoted Eric's paper (http://wiki.contesting.com/index.php/Setting_receiver_gain_controls) which quite frankly seems way too complicated to me. IMHO, a modern DSP, microprocessor-controlled receiver should figure all of this stuff out automatically and do it for me.
Make no mistake, as someone licensed for over 50 years and who has designed and built some receivers "back in the day", I've been through all of this "turn off the AGC and back off the RF gain stuff", before. That made sense when the RF gain control was a rheostat in the cathode of the RF stage and actually adjusted RF gain and radios didn't even have product detectors, but I don't think it makes sense today, except possibly is some rare situation. If the receiver has a properly designed AGC system then there are only two variables that are potentially the operator's responsibility: 1) Preamp On/Off and 2) Attenuator On/Off. With the smarts built into modern radios, why can't the radio do, for example upon band switching, a little routine of turning each of these on and off and measuring the resulting SNR and then setting them accordingly? If an S9+50 dB neighbor suddenly pops up, the DSP should know sooner than the operator that the ADC is being overloaded and act accordingly. If an antenna is changed or a noise source pops up, a simple macro executed by a key tap could run the routine automatically and be done with it. We have DXpeditions operating on some chunk of coral that are running wireless networks between stations and uploading their logbooks in near real-time to the Internet via satellite yet their operators are still "riding the RF gain control". Something is wrong with this picture. Wes N7WS --- On Fri, 12/18/09, Bill W4ZV <btipp...@alum.mit.edu> wrote: > Bill W4ZV wrote: > > > > > > > > Ralph Parker wrote: > >> > >> I'm used to leaving the RF gain wide open on the > MkV, leaving the audio > >> gain pretty much alone, and maybe switching > between SLOW and FAST > >> occasionally. I don't seem to have any trouble > hearing the weak ones > >> under > >> the strong ones. > >> Now I have to fiddle with the RF gain (a small > knob hidden amongst the > >> others) while running a pileup. Not enough hands > (or enough brains). > >> > > > > If you set up your K3 as you described above, I > guarantee you will have a > > noisy RX. Furthermore, you are wasting the > dynamic range of the K3 (or > > your MkV for that matter). In a previous post I > described how to set up > > the K3. Once set up correctly, you should seldom > need to touch either RF > > or AF gain during an entire contest and can simply let > the K3's excellent > > AGC and dynamic range do the work for you. IMHO > good ergonomics doesn't > > mean having access to 24 knobs that need to be > continually adjusted, it > > means not having to adjust them in the first place. > > > > 73, Bill W4ZV > > > > Several have asked for more info about how to set up the K3 > gain. The > following is a simplified version of a comprehensive > article by K3NA below: > > http://wiki.contesting.com/index.php/Setting_receiver_gain_controls > > Note that Eric's setup is for AGC Off, which is probably > not a good idea for > most casual users. I would start with AGC-F using the > default AGC Menu > settings. You can check the defaults for each CONFIG: > AGC Menu by tapping > the DISP button while in the appropriate CONFIG Menu (all > AGC settings begin > with CONFIG: AGC xxx, and remember that some are only > accessible with > CONFIG: TECH MD On). > > 1. Have available your desired antenna and a dummy > load (both on a coax > switch is ideal) for each band you want to set up (you'll > at least need to > do this for major segments like 80/160, 40-18, 15-10 and 6 > separately (if > you have the external preamp). > > 2. Set AF GAIN back to about 9 o'clock and RF GAIN to > MAX (fully > clockwise). This assumes you have the proper AF GAIN > menu setting for your > specific headphones (I use AF GAIN - LO for my 32 ohm > headphones and still > have tons of audio). > > 3. In the following order (first ATT ON, then ATT > OFF, then PRE ON) > alternately switch between your antenna and the dummy > load. When you hear > noise increase when switching to the antenna, use the > lowest gain setting > (i.e. ATT will likely be the correct setting on the > noisy low bands and PRE > will likely be correct for 10m). Remember that the K3 > will remember these > settings for each band. Once you have the correct > setup on each band it > will automatically recall that PRE/ATT setting when you > return to that band. > > 4. Now adjust the RF GAIN knob counterclockwise until > the antenna noise on > the meter just stops flickering on the meter. This > will be familiar to OTs > since this is the way we set RF GAIN many years ago on > analog radios. > > 5. Now adjust your AF GAIN knob for a comfortable > listening level (mine is > normally 9-10 o'clock which may vary depending on what type > of headphones > you have). > > If you still don't like the amount of background noise > compared to signal > levels, adjust CONFIG: AGC THR to a lower setting than the > default 5. This > which will reduce the apparent noise level by moving the > AGC onset point > down and acting as sort of a noise squelch. > > Regarding settings for speakers, I never use them since I'm > normally > listening for extremely weak signals on 160m or in contests > and I don't want > ANY extraneous noise between my ears and the signals. > Perhaps someone who > uses speakers can add comments. > > I hope the above helps but please read K3NA's article for > more comprehensive > suggestions (remembering that his setup is for AGC Off). > > My general rule for all gain settings (PRE/OFF/ATT, RF Gain > knob, AF Gain > knob, CONFIG: AF GAIN) is LESS IS BETTER (as long as you > can hear signals). > This is contrary to the thinking of some but following it > will ensure that > you get the ultimate dynamic range performance available > from the K3. > > 73, Bill W4ZV ______________________________________________________________ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:Elecraft@mailman.qth.net This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html
