Rein Couperus wrote: > My comments were meant to be a bit provocative....
He! Well, you knew what you were doing.... > The ONLY point I wanted to make is that if you use a proper filter, > matched to the mode, you will have a lot more fun and hear/work many > more stations. The tradeoff is that you have to use a round knob > instead of a computer mouse to tune the signal. And as this is the > digital RADIO group I thought that a warning was appropriate :) That is a tradeoff...selectivity for "convenience"...sadly, not everybody is aware of that FACT. > Maybe I should advice to reread the articles about proper RX design > by Ulrich Rhode in QST, maybe around 1970... that also tells you how > large signals in your rx produce mixing products and desensing, and > also why a properly designed AGC system will actually work. And Ham Radio in the 80's (there is a VERY GOOD article on digital military communications receivers in april 1985). Also I would recommend his book "Communications Receivers". I am lucky I have been able to get a Ham Radio collection, a top notch magazine, indeed. > I am camping in EA at the moment, and 2 times during the day the > pskmail servers I use are slowly QSB'ing from S0 - 20 dB to S9. The > AGC easily fixes that (300 HZ filter on a FT897D, using PSK250). The > APRS backbone on 10.149 kHz which would be fully inside the 2.5 kHz > passband would make all operation impossible without a filter... > (These guys relay 300 Bd APRS packets from 2meters to HF by the way, > and I could read a book in the light of lamp connected to my > antenna... :) > > The 'noise and crap' I was referring to is the stuff your RX adds to > the signal by using non-linear circuits, before giving it to your > SOUNDCARD DSP. So even if your rig doesn't have one, your computer > does... > > And yes, I have visited several hams who could hear MORE than twice > the stations after switching from a 2.5 kHz (panoramic) to 250 Hz > filter. > > To answer some questions from Jose... > > Yes, I have worked in M/M and M/2 HP environments. Check CT9L, TS7N > (2003), 5A7A(2005), ED8A(last November), all top 3 WW operations. For > such activities we use K2's most of the time. And bandfilters on > every TRX. And yes, at home I am using a TenTec ORION (100Hz for > PSK31). OK, those seem to be better radios than the older ones I mentioned, which is not surprising at all. Nevertheless, it is funny to experience what at times a toggle switch and two resistors do with not so top notch stuff. If you are living part time in Spain, I assume you understand spanish. So, Calderon said: "En este mundo traidor, nada es verdad ni es mentira, todo será del color del cristal con que se mira". So, our experiences are certainly tainted (among other things) by the radios we use. I have used quite a few and not owned all of them...so far, I have not tried a K2 or an Orion... 73, Jose, CO2JA Linux User 91155
