Yes 50dB is about 30dB too high... Simple modelling says it all...
Dr. William J. Schmidt - K9HZ J68HZ 8P6HK ZF2HZ PJ4/K9HZ VP5/K9HZ PJ2/K9HZ Owner - Operator Big Signal Ranch - K9ZC Staunton, Illinois Owner - Operator Villa Grand Piton - J68HZ Soufriere, St. Lucia W.I. Rent it: www.VillaGrandPiton.com email: b...@wjschmidt.com -----Original Message----- From: Elecraft [mailto:elecraft-boun...@mailman.qth.net] On Behalf Of Joe Subich, W4TV Sent: Friday, July 03, 2015 9:21 AM To: elecraft@mailman.qth.net Subject: Re: [Elecraft] K3 FD report in high RF (K3 vs Flex 6xxx) > What would people expect for power loss between the G5RV and the > beam? Based on other comments, distance, and the beam heading the > wrong way, I'd guess about 50 dB. 50 dB is probably optimistic. The equation for free space path loss (coupling between antennas) is -40 dB + antenna gain - a wavelength dependent factor. However, that only holds in the far field (30m is near field for anything below 144 MHz). My hunch is that the isolation between two resonant antennas in the near field will be something less than 30 dB unless they are [reasonably] collinear. 73, ... Joe, W4TV On 2015-07-03 10:03 AM, Greg Troxel wrote: > Jim Brown <j...@audiosystemsgroup.com> writes: > >> Your expectations are unreasonable -- 20 ft is WAY too close, even for >> two great rigs on the same band at 500W. We run K3s to KPA500s on the >> same band for CQP (Cal QSO Party) county expeditions and use 250 ft >> spacing with antennas carefully located to be essentially >> colinear. 150 ft is not enough. > > I was at a FD site where we had significant interstation interference, > and I think it was a combination of just too close and a dirty > transmitter (IC7200), with the other station being a K3 with new synths. > We didn't measure the antenna coupling, and I made a mental note to do > that next time. What we had was > > 40m 2-el wire beam > 20/15/10 wire beam > > G5RV > > The two beams had ends separated by only a few meters, but were almost > collinear. The G5RV was parallel (in a bad way) about 30m away, but on > the back side of the beams. > Our troubles seemed worst on 20m. I know the spacing is not > reasonable; past FDs at the same site/club had used KX3s or K2s QRP, and > things were mostly ok then. > > So, I wonder: > > When you used the 250 ft spacing (and in the nulls), what kind of > measured coupling did you see? > > What would people expect for power loss between the G5RV and the beam? > Based on other comments, distance, and the beam heading the wrong way, > I'd guess about 50 dB. > > > I guess another question is, given a pair of K3-newsynth transceivers, > what level of antenna isolation is necessary to bring the wideband noise > from reciprocal mixing and transmit noise down to say the S1 level? > > Assume S1 is -121 dBm (from -73 and 8 units). Or really lets say that's > the level we care about. TX at 100W is +50 dBm. If one uses -128 dBC > for transmit noise, and assumes some improvement from the 108 dB of RMDR > (taking the average of ARRL/sherweng) at perhaps 118 dB, then we need 53 > dB of isolation. > > The IC-7200 has transmit noise at -94 dBC, so I'd expect 24 dB worse, > which is S5 noise instead of S1 imposed on a perfect other receiver. > > I am curious if my math is confused, and how real measurements and > experiences compare. It seems that reviews should set up 2 of the radio > under test with controlled isolation and see how in-band artifacts are. > And also test against a K3s both ways. > > 73 de n1dam > ______________________________________________________________ > Elecraft mailing list > Home: http://mailman.qth.net/mailman/listinfo/elecraft > Help: http://mailman.qth.net/mmfaq.htm > Post: mailto:Elecraft@mailman.qth.net > > This list hosted by: http://www.qsl.net > Please help support this email list: http://www.qsl.net/donate.html > Message delivered to li...@subich.com > ______________________________________________________________ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:Elecraft@mailman.qth.net This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html Message delivered to b...@wjschmidt.com ______________________________________________________________ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:Elecraft@mailman.qth.net This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html Message delivered to arch...@mail-archive.com
