Joe said "The only problem is that my poor antennas don't given me enough strong signals to really evaluate strong signal pile-up with off air signals at the higher thresholds. "
Turning on the pre-amp will increase the noise level, increase the signal strength of those signals already there and perhaps bring in a few more signals to help with the testing. It's a simple thing to do. David G3UNA On 12/05/2012 22:19, Don Wilhelm wrote: > I fail to see any advantage to turning on the preamp when it is not > needed. If you can hear the atmospheric noise without the preamp, > leave it off (if the noise level increases when the antenna is > attached, you have enough gain). By extension, if you can still hear > the atmospheric noise with the attenuator in, leave it in - using more > front end gain than is necessary for the band and antenna conditions > will only reduce the dynamic range of the receiver. If you do not > know what that means in terms of operating, let me put it simply - you > may not hear that weak one that you would have heard if you had set > the preamp and attenuator properly. > > Technical discussion - the band noise is S-3 with the preamp off. The > K3 will start to overload on a signal that is S9+70, and will hear > signals that are greater than the S-3 band noise level. Turn the > preamp on, and the band noise raises to about S-5, but the K3 > overloads on that signal that is now S9+70, so you can now only hear > between S5 and S9+70 where before you could hear between S3 and > S9+70. You have reduced the dynamic range by turning on the preamp > when it was not needed. > BTW - The S9+70 overload point I used was just an example off the top > of my head - I do not have the overload point for the K3 at handy > reference, so use that as a "for instance" rather than as an absolute > data point. (also BTW - my "overload" term is technically referred to > as the "compression" point). > > 73, > Don W3FPR > > On 5/12/2012 6:56 PM, David Cutter wrote: >> Would it help the tests to engage the pre-amp? ie make things more >> challenging. >> >> David >> G3UNA >> >> On 12/05/2012 17:22, Joe Subich, W4TV wrote: >>> On 5/12/2012 12:17 PM, Ted Bryant wrote: >>> > Was v4.51 sent to the 4.50 testers? >>> >>> Apparently not all (I had to request it). >>> >>> I've been doing some crude testing ... with 4.51 AGC THR = 15 is >>> approximately -73 dBm/S9 (to the best of my ability to measure with >>> the XG3 and step attenuator). >>> >>> With high values for AGC THR it is important to use higher values of >>> AGC SLP otherwise a sudden very strong signal will drive the audio >>> amp and/or headphone amp into severe distortion - particularly if the >>> AF Gain is high. >>> >>> I'm finding AGC THR in the 12/13 range and SLP in the 8/10 range is >>> very comfortable and seems to "open up" the K3 receiver. The only >>> problem is that my poor antennas don't given me enough strong signals >>> to really evaluate strong signal pile-up with off air signals at the >>> higher thresholds. >>> >>> 73, >>> >>> ... Joe, W4TV >>> >>> > ______________________________________________________________ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:[email protected] This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html
