Thanks Jose and Scott. So, my original question was related to my observations were that lowering RF gain on my receiver did range of the waterfall. Apparently this is related to AGC circuitry being activated . On my radio the disappearance of weaker signals from the waterfall when a very strong stations is received., does not get improved by turning down the RF gain. I am making an assumption that the improvement reported as a result of turning down the RF gain, would lead to the lost weaker signals reappearing on the waterfall. My tests this weekend were not able to replicate this.
On 9/18/06, Scott Hill <[EMAIL PROTECTED]> wrote: > > Andy and the group, > > A thousand and one apologies. I can't even claim a senior moment. In > my rush to a knee jerk reaction I misread AGC as ALC and RF gain as RF > power.. Duuuuuuuh! > > So, this EHam article is talking about receiving, not transmitting. > Now the statement makes sense. The same is true of voice SSB. The > only voice I work is a local net on 80 meters. If I don't turn down > the RF gain I can't copy the conversation at all. Since I normally > use only Digital or CW I keep the AGC turned off. > > This writer (in EHam) has a good point, and one to consider when you > get a bad IMD report from someone. If your signal is very strong into > his receiver you might want to ask him to turn down his RF gain and > take another reading. > > > Scott/K6IX > > Andrew O'Brien wrote: > > On 9/17/06, Scott Hill <[EMAIL PROTECTED] <scott%40k6ix.net>> wrote: > >> > >> > >> > >> > >> > >> > >> Where did you see that statement Andy? The thing to turn down until > >> you have no AGC is the audio drive from the soundcard, NOT the RF > >> gain. Nothing wrong with turning down the RF gain if you want to run > >> lower power, but that will not get rid of splatter caused by the AGC. > >> > >> Scott/K6IX > >> > >> > > > > > > In an article on PSK at Eham... > > > > > > RE: The Good Bad and Ugly on PSK31 > > by AA4PB on December 12, 2005 > > It's the AGC in the receiver that can cause distortion of strong > > signals just like ALC in the transmitter can. A fast AGC action will > > "follow" the amplitude of the PSK31 signal and attempt to level it out > > - that is distortion. A slow AGC action cannot react fast enough to > > "follow" the signal and so will just maintain an average without > > distorting the signal. Turning down the RF gain will reduce the signal > > below the level that causes any (or much) AGC action. Always use your > > slowest AGC setting. > > > > PSK31 has amplitude changes. Any non-linearity anywhere in the system > > from the transmitter input to the receiver output will cause > > distortion which results in poor IMD readings and wide signals. This > > can be the result of ALC or AGC action or overdriving an amplifier > > anywhere in the system. > > > > I've done a considerable amount of testing to look at this issue. On > > an IC761 with the AGC set to fast I could have as much as 10dB of IMD > > caused by the AGC with an S-9 signal strength. I measured the output > > of my test transmitter an knew that I was transmitting a clean test > > signal. Switching the AGC to slow, reducing the RF gain to weaken the > > signal, or reducing the signal strength to S2 or S3 would clean up the > > signal. > > > > For transmit ALC testing I used a K2 because I could easily change > > component values inside the transmitter. I found that with some ALC > > action I could actually see a copy of the PSK31 signal on the ALC line > > and of course the IMD reading at the receiver was poor. By changing > > the ALC decay time (adding a capacitor) the waveform on the ALC line > > went away and the IMD improved considerably. I found that with the > > proper selection of decay time the ALC could be used to level the > > average transmitter output without distorting the PSK31 signal. > > > > The time constants for most of our receiver AGC and transmitter ALC > > were designed for typical voice signal rather than PSK31. > > > > > > Need a Digital mode QSO? Connect to Telnet://cluster.dynalias.org > > > > Other areas of interest: > > > > The MixW Reflector : http://groups.yahoo.com/group/themixwgroup/ > > DigiPol: http://groups.yahoo.com/group/Digipol (band plan policy > discussion) > > > > > > Yahoo! Groups Links > > > > > > > > > > > > > > > > > > > > > > > > > > > > > -- Andy K3UK Skype Me : callto://andyobrien73 www.obriensweb.com www.myspace.com/k3uk [Non-text portions of this message have been removed] Need a Digital mode QSO? Connect to Telnet://cluster.dynalias.org Other areas of interest: The MixW Reflector : http://groups.yahoo.com/group/themixwgroup/ DigiPol: http://groups.yahoo.com/group/Digipol (band plan policy discussion) Yahoo! Groups Links <*> To visit your group on the web, go to: http://groups.yahoo.com/group/digitalradio/ <*> Your email settings: Individual Email | Traditional <*> To change settings online go to: http://groups.yahoo.com/group/digitalradio/join (Yahoo! ID required) <*> To change settings via email: mailto:[EMAIL PROTECTED] mailto:[EMAIL PROTECTED] <*> To unsubscribe from this group, send an email to: [EMAIL PROTECTED] <*> Your use of Yahoo! Groups is subject to: http://docs.yahoo.com/info/terms/
