I just purchased a Cushcraft MA8040V for my place. My understanding is these antennas work well. Got this one for $200 from AES. Bandwidth on 80/75 is supposed to be 100Khz 2:1 SWR and they recommend only 8-10 radials. I will let you know how this all plays out if you are interested.
Stan AH6JR On Wednesday 09 November 2005 05:06 pm, Larry Loen wrote: > Jim Lux wrote: > > At 12:58 PM 11/9/2005, [EMAIL PROTECTED] wrote: > >> Thoughts on my vertical > >> > >> 2. Got the HF2V vertical in place with 60 radials. Got it "mostly" > >> tuned > >> up. Missing: Serious plan for more than 25 KHz of band coverage at a > >> time, esp. for upcoming CQ WW SSB and also covering both the DX > >> Window on > >> SSB plus CW and maybe RTTY. > > > > -- 25 kHz is about right for SWR bandwidth on a single vertical on > > 75/80, unless there's some huge loss source to kill the Q. > > The antenna analyzer seems to agree with you. I _think_ I'm OK. The > ohms part of the reading is about where the manual said it should be. > Given Frank's comment about the gain I should be expecting, everything > is making more sense, in fact. > > > -- You might seriously consider putting some sort of variable > > reactance at the base of the antenna. The radiation efficiency of the > > antenna is reasonably constant over the band you're interested in, but > > the reactive component varies quite quickly. You really, really don't > > want to be tuning out that reactance at the other end of a length of > > coax. You might be able to get away with a few switched inductors or > > capacitors, and just tune out the last bit (say, to get from 3:1 down > > to 1.x:1) at the shack end. > > I'd appreciate a link or two or more explanation of this. OK, if doing > it on the shack end is bad, I need something that I can do easily, > quickly, and reliably at the antenna end. > > > -- The folks at Force 12 have an interesting loading coil for the > > middle of their vertical low band dipole that basically stretches and > > shrinks a big spacewound coil to tune it. Think in terms of building > > yourself a coil out of something like 1/4" copper pipe that's a foot > > in diameter and a foot high that can be stretched to 2 feet high. A > > motor driven lead screw does the stretching (like in a screwdriver > > antenna). > > Well, I already have a nice coil on the antenna already that expands and > contracts. The problem is, at least the way it sits, it's kind of hard > to do quickly and easily. > > How would I get something like this working by the end of the month and > where would it go? > > > The capacitance hat probably won't broaden the bandwidth much, but > > might raise the radiation efficiency (in that it increases the average > > current in the radiator). > > That might be worth it all by itself. > > >> This is mostly about the vertical. My main problem of the moment is > >> better frequency coverage. > >> > >> My roughed in plan is some combination of the following: > >> > >> OTOH, the antenna is clearly "out-hearing" the G5RV, by upwards of 40 dB > >> in at least one case. I am now hearing zone 15 (Croatia), if > >> faintly, on > >> SSB and I expect I could probably work a lot of Europe, even as I > >> have it, > >> with 100 watts on CW. But, is there something else I have overlooked to > >> improve the DX radiation angle? I laid out the 60 verticals assuming a > >> velocity factor of 50 per cent as per ON4UN's book. Did I misread that? > >> Should it have been longer wire or something? > > > > Wires laying on the ground (or buried in it) aren't really something > > you can "tune" for resonance (at least not without knowing a whole lot > > more about the EM properties of your soil than you're likely to > > know). They basically provide a low impedance return for the "image" > > of your vertical, and the length is totally non-critical. (to a very > > rough first order, the propagation speed in the buried wire is > > 1/sqrt(epsilon), but I doubt you know epsilon with an accuracy of > > better than 50%, and that would really only apply to a wire that is > > immersed many skin depths (in the soil), which yours are probably not) > > I get mixed reports on this. ON4UN's book (as I recall) said the > velocity factor was between 40 and 60 per cent "depending on the soil" > and basically said (in practice) no one would know what it was like at > any given QTH. So, that's square with what you say, just about to the > word. > > It's just I had a few folks claim the velocity factor was more like 100 > per cent. But, as you and others are making clear to me, my results are > more like the 50 per cent plus or minus velocity factor is about right. > Or, at least, it is doing me no harm to play it as if it were so. > > > The basic guideline is that more is better, and that having wires > > closer together than 1/100th of a wavelength (or 1/50th, or other > > numbers in that vicinity) isn't worth it. > > > > The recommendation of 120 radials 1/2 wavelength long, etc., are > > really holdovers from the broadcast industry, as well as measurements > > and analysis by George Brown back in the 30s. The goal there is to > > produce a particular measured field strength with a certain licensed > > radiated power, so as to conform to the terms of your broadcast > > license grant. > > > > > > Jim, W6RMK > > ON4UN says much the same. He gives some small difference between 60 and > 120 radials (.5 DB or something like that) and in another nearby > section, has an example suggestive that 43 radials is a good number, too. > > My reading suggested that "around 60" was about as good as I could > expect. My only question now is whether I need a handful of longer ones. > > From the sound of all this expert help I'm getting, that's really not > my problem now. The problem is rigging up something to make frequency > shiting practical. > > It is helpful to know it is mostly about reactance, though. > > > Larry WO0Z > > > > > _______________________________________________ > FlexRadio mailing list > FlexRadio@flex-radio.biz > http://mail.flex-radio.biz/mailman/listinfo/flexradio_flex-radio.biz -- He is your friend, your partner, your defender, your dog. You are his life, his love, his leader. He will be yours, Faithful and true, to the last beat of his heart. You owe it To him to be worthy of such devotion.
