Re: Topband: FT-8 performance
Jerry, The difference in the FT8 reported SNR and how most hams think of SNR seems explained well by Jim, KC5RUO. http://www.arrl.org/forum/topics/view/1957 https://tapr.org/pdf/DCC2018-KC5RUO-TheReal-FT8-JT65-JT9=SNR.pdf He says for FT8, the noise bandwidth that impacts FT8 software´s ability to decode data is 6.250 Hz. WSJT calculates the total power (all signals and noise) in the 2500 Hz bandwith, and uses it as the denominator in SNR calculations. Jim says "it would make more sense to measure the SNR in the bandwidth that's really used by the receiver; but it may be hard to determine or define that "true" receive bandwidth. So in short, your eyes and ears are not deceiving you. Those JT65/JT9/FT8 signals are very much so well above the noise." The following shows if you focus on a single FT8 signal in a 6.250 Hz bandwidth, the WSJT reported SNR needs to have 26 dB added: SNRFSKFT8 = SNRreportedFT8 + (10 x LOG (2500 Hz/6.250 Hz)) SNRFSKFT8 = SNRreportedFT8 + (10 x LOG (400)) SNRFSKFT8 = SNRreportedFT8 + 26 dB 73, Paul K5ESW Raleigh, NC > I'm not sure how FT-8 calculates the reported S/N number. I found very > little information on the subject and what I did find was not easily > understandable. What I did was an experiment in which I was able to > get > close to the same number being reported. According to what I have > read > about FT-8, it does not implement the same method as I was using in my > testing. > > It was very obvious to me that the number being reported was useless. > Example: How would you be able to report a S/N of -1 dB when the > station is S9+40 db on the S meter and the receiver reads S1 when > tuned > to a spot with no stations. (Actual measurement) > > I made a guess that the number being reported was actually a signal to > noise plus signal ratio S1(S1 + N), where N is the sum of everything > else in the passband. The S9+40 db station in the example would be > the > main contributor to the overall level of the total stuff in the > passband > and that total is just a little more than his signal alone, so -1 dB > now > makes sense. This seems to work and it works on other FT-8 signals as > well. > > Jerry, K4SAV > _ > Searchable Archives: http://www.contesting.com/_topband - Topband > Reflector _ Searchable Archives: http://www.contesting.com/_topband - Topband Reflector
Re: Topband: FW: Hi-Z Around Trees
Lee, Thanks for the guidance. I plan to use 20-foot fiberglass tube with a wire down the center for Hi-Z array elements. Would you expect sensitivity to nearby trees to be about the same for these wire elements versus aluminum tube elements. 73, Paul K5ESW > > > Greetings Top-Banders, I have been away for a couple days, sorry for > the late comments. > The fact is, for me there is no definitive answer to the effect of > trees on the Hi-Z arrays. I have made tests measuring phase shifts > and amplitude changes with a variety of objects around these > elements. My original thoughts after the tests were that any tree or _ Topband Reflector Archives - http://www.contesting.com/_topband
Topband: Modeling Transmit Antenna Affect on Rx Antenna Performance?
For transmit I use a 160M T antenna with on ground radials. I am considering installing a Circle-8 receiving array such as one made by Hi-Z. The receive array would be very close to the T, maybe within 100 feet. I am using EZNEC to see how the transmit antenna proximity affects the pattern of the Rx array. I have a simple EZNEC model of a 4 square Rx array. The model uses a source on each 20-foot Rx vertical, with the pattern determined by the phase of each source. I put models of the T and the Rx array in the same EZNEC model. With the source removed from the T, the radials are connected to the T portion of the antenna. This configuration shows a big degradation in Rx front to back ratio. If I open the T at the feed-point by either putting in a source with zero current or simply breaking the connection between the T and its radials, running the model shows little to no affect on the Rx pattern. I could use a relay at the antenna to disconnect the feed line near the feed-point when not transmitting, but I would rather avoid the relay because of running QSK and wanting to avoid the wiring run. My modeling runs, using either an effectively open or shorted feed line at the T, do not represent my real system because it is not open or shorted. The feed is about 350 feet of coax to a K9YC-designed common-mode choke and a 1:1.56 unun. I am wondering if there might be value in disconnecting the feed line from the antenna and measuring the impedance looking back into the unun/choke/coax string. Take this impedance and add it as an RLC network connected across the feed-point of the T antenna. My thought is this would be close to what the Rx array is really seeing when I look for the affect of the nearby T in the EZNEC run. Am I on a decent path or lost in the woods? 73, Paul, K5ESW _ Topband Reflector Archives - http://www.contesting.com/_topband
Re: Topband: Steady Carrier on 80 CW
It peaks at 172 degrees from Raleigh, NC on a Hi-Z 3-element array (6 directions). We need some directions from Florida stations. 73, Paul K5ESW _ Topband Reflector
Re: Topband: Spurious Signal on 1810.8
I did a quick plot of 8 stations giving directional info on the spurious signal. The report from WT3Q SE of here S8 to 9 fn20ac helps narrow it down. The data suggest eastern PA (around Philadelphia), northern Delaware (Wilmington), or the lower part of NJ (toward Atlantic City). More reports from hams near Baltimore, Philadelphia, and NYC would be useful. 73, Paul K5ESW ___ Remember the PreStew coming on October 20th. http://www.kkn.net/stew for more info.
Re: Topband: Spurious Signal on 1810.8
From Raleigh, NC the 1810.8 buzzy signal comes from the Northeast direction. 73, Paul K5ESW ___ UR RST IS ... ... ..9 QSB QSB - hw? BK
