Disabling the AGC in the K3 certainly does "do the trick" in terms of preventing strong signals in the passband from reducing receiver gain and thus affecting the weaker signal I'm decoding - that's exactly why I do it.
As for ADC overload -that's a risk I'm well aware of but most of the time it's a non-issue, for me at least. If it happened I would react to it, but I rarely encounter signals in the passband at anywhere near the level to cause trouble of that sort. Bob NW8L On Wed, Jan 7, 2009 at 6:23 PM, Don Wilhelm <w3...@embarqmail.com> wrote: > Bob, > > That will do the trick in an analog only receiver, but a receiver like the > K3 has an analog front end followed by an ADC and DSP processor. The trick > is to keep from overloading the ADC - should that happen, the copy will be > garbage. > > That situation is not limited to the K3 - overload of the soundcard ADC is > also a possibility with equally bad results. > > I have to admit that in many cases, one can operate with a wide bandwidth > with no problem, but when that strong signal enters the passband, the wide > bandwidth possibilities are "all over". I chose to take preventive measures > before that happens. > > 73, > Don W3FPR > > Bob Cunnings wrote: >> >> I simply disable AGC when I wish to run a wide receive bandwith with >> PSK31 for "point and click" tuning - precisely to avoid such a >> problem. >> >> Bob NW8L >> >> On Wed, Jan 7, 2009 at 5:44 PM, Don Wilhelm <w3...@embarqmail.com> wrote: >> >>> >>> Thomas, >>> >>> I will not answer your questions directly, >>> BUT >>> From an operational standpoint, using a wide bandwidth for data modes >>> is *not* the best way to do it. >>> The reason is AGC in the radio. Any signal in the receiver passband can >>> activate the AGC - and that is fine *if and only if* the strongest >>> station in the receiver passband is the one you are working - usually >>> that is not the case. The strong signal will reduce the receiver gain >>> due to its AGC action and the station you are trying to QSO with will be >>> reduced along with it. Overload of the DAC by the strong signals is >>> another similar consideration - fortunately, the K3 employs a hardware >>> AGC ahead of the DAC to avoid just that possibility. The DSP ADC can >>> handle an S9+20 signal without overload, but there are signals stronger >>> than that even in the sub-bands commonly used for digital. >>> >>> Using a narrow passband for data modes allows one to avoid that >>> situation. Yes, one must tune with the VFO to place the desired station >>> inside the receiver passband, but the possibility of a QRM free QSO is >>> much greater with the narrow passband. >>> >>> Just because the software application can display a 4 kHz slice of the >>> spectrum is not sufficient reason to use a wide receiver passband IMHO. >>> >>> Elecraft may well consider it just because some folks want to operate >>> that way, but it certainly does not make much sense to me. >>> >> > _______________________________________________ Elecraft mailing list Post to: Elecraft@mailman.qth.net You must be a subscriber to post to the list. Subscriber Info (Addr. Change, sub, unsub etc.): http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/subscribers.htm Elecraft web page: http://www.elecraft.com
