Bill, May I suggest a loop. Put a 10 foot support at each corner of that roof and put wire between each of those supports. You will have a longer than 80 meter full wave loop that will work locals nicely on 80 meters as well as giving you a great low angle (read good DX) radiator on 40 meters and above. In fact, for some bands, the gain may exceed that you get from the 20 meter Moxon, but in different directions.
I would think you bigger problem would be pickup of noise by the antenna, which will limit the number of weak signals that you can receive. It may be that your transmit signal is "getting through" but your receive capability is antenna limited. If your operation involves digging for weak signals then that could be a limiting factor for you. If the latter is your problem. then a better receiver (K2 or K3) is not likely to solve your problem. If the problem is adjacent channel interference, then yes, the K3 DSP filtering can easily take care of it. 73, Don W3FPR On 3/2/2012 9:56 PM, Bill Smith wrote: > > > I’m trying to improve my signal. > > > > I have limited understanding of radio and electronics, but > have picked up a few buzzwords and some of their meanings along the way. > > > > The bad: I live in a ground floor apartment of a very old (100+ > year) building (mish-mash of electrical and digital coax in the attic, none of > it in conduit). I am apartment manager > now (don’t own the building) so have essentially no options for antenna over > the yard. I have power lines at 20-25 ft in height about 60 ft north and 40 ft > west. I have telephone lines at the same height 40 ft east. The city I live in > limits my antenna height to 10 ft higher than the highest point on my > building. > > > > The good: I have access to the flat (6 degree grade) roof of > the building, 60 ft NS and 100 ft EW; 2 stories, so roof height is 22+ feet. I > have a 40M dipole at 10 ft over the roof, with one wire at 120 degrees (0 for > due north) and 240 degrees (essentially pointing south). It is fed with 110 ft > of a RJ-58A/U. I also have a 20M Moxon (also at 10 feet) pointing 45 degrees > (from Denver CO to Europe) fed with 140 ft of RG-8x. > > > > System specs are (I’m not good with electronics, so not sure > of the meaning of the R and X measurements supplied by my MFJ-259B antenna > analyzer): > > 40M dipole: > 1.6 SWR at 7.2 mhz with R = 76 and X = 15 (no balun) > > 20M Moxon: > 1.3 SWR at 14.0 mhz with R = 50 and X = > 15 (1:1 balun) > > K-2 with > SSB and ATU for QRP (recently put into to top shape by Don W) > > KPA100 > w/ATU for QRO (have used little with digital) > > Signalink > USB > > > > I am limited to digital (never could learn the code in 300+ > hours of practice), but that’s OK. > > > > I have made a number of contacts with the 20M Moxon. (I > limit my power to 5 watts digital, as it can be nearly 100% duty cycle for > over > 1 minute). It is incredibly quiet (a 30 db front to back ratio as I recall?). > But my DX contacts are usually South America (at 180 degrees) and sometimes > Southern CA (must be at about 240 degrees! – how does my signal get there??). > No European contacts yet, but now that I am retired, maybe I’ll have better > luck at noon (MST is –8hrs UCT). > > > > Possible improvement: I have limited (very) funds, but could > extract about 100 ft of 300 ohm ladder line from a G5RV, that I got for > $10.00, > and replace 90 feet of RG-58 with the ladder line and a 4:1 balun that I > purchased when I was “rich” (i.e. employed). I would hope that this would > reduce my loss by maybe 2 db, and allow me to work any band between 80M and > 10M > (I heard that a doublet is quieter than a dipole – is that true?). > > > > The smaller question is: I understand the impedance of the > 300 ohm ladder line could result in an SWR of up to 15:1 on some bands, so > will > my K2ATU handle that? > > > > The bigger question: can a 40M antenna be effective in my > situation? Or is the interference from the electrical wiring 10 feet below my > antenna, the low power (5 watts), the nearby power lines, and the radiation > pattern of a 40M signal off of a 10 ft ground (all my signal going straight > up?) too much to overcome. I have made > 0 contacts on 40M using PSK31 and JT-65. But maybe I need to try longer, as I > have only worked that band a total of 8 hours after 20M has closed – I SEE a > lot of JT-65, but have yet to be heard. > > > > Final question: What options do I have to improve my chance > of being heard outside of 20M (since my roof perimeter is 320 ft, I could fit > in an 80M loop. However, construction could be a challenge with limitations on > changes that I could make on a roof that I don’t own)? > > > > Whew! If you got through this post, you deserve a gold star! > > > > Thanks for any input. > > > > 73, > > Bill Smith, KC0TBO > > > > > ______________________________________________________________ > 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 > ______________________________________________________________ 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
