Andy, Will you be cutting the 2m/70cm portions for FM or the SSB portion? Those two might get tricky as 70cm is a harmonic of 2m. It of course can potentially be advantageous if using one antenna (or radiator) for both so long as you can live with the way it radiates. Radiation lobes for 2m will not generally be pointing the same direction as 70cm. People quite often build vertical J-poles as a dual band antenna, and while the vast majority load just fine on both it is absolutely not true that they radiate efficiently on both. On 70cm they radiate both up 45 deg & down 45 deg- leaving the horizon virtually uncovered. Which is not to say one can't use it for a given repeater on 70cm but it won't be efficient no matter how you slice it. (Fong J-pole is an exception to this rule since it has a phasing section which corrects this- if you want a truly omnidirectional this is an easy & inexpensive way to get those two bands in a vertical) A fan dipole built as a sloper this may or may not work for you and is likely to be somewhat if only slightly directional, but 70cm might be iffy. Horizontal likely should be no problem at all (though more directional again), so long as it worked out resonant for both bands. It is all in making the radiation go somewhere useful. I have not calculated nor experimented with this on the SSB portions yet; though a rough guesstimate suggests they should line up close enough.
Simply leaving separate wires for each 2m & 70cm will likely leave the 70cm section doing little unless you install traps on the 2m wires- assuming the 2m portion remains close to being resonant on both 2m & 70cm. At least this is my recollection from an experiment some years ago- I recall I could never get the 70cm element to do much no matter how I oriented it. Wire is cheap, so have fun playing with it! By the way, you'll find the interactivity (the multiple wires trying to detune each other) reduced quite a bit if you can manage to keep the wires far enough apart. Spreading them out in different directions to some degree can help a lot- if that is an option at your QTH. These are all quite short which should help. Stu AF6IT --- In digitalradio@yahoogroups.com, "obrienaj" <k3uka...@...> wrote: > > I am planning another HF installation soon and may have a 33ft mast begging > for some extra creative thing to hang off it . I do not do 70cm -2M-6M much > and think I should , just to be able to get out when there are bands > openings. Nothing with DX in mind, just something omni-directional would do > (or ANY direction) I was thinking about a fan-type dipole , one feed line > going to dipoles for 70cm - 2M - 6M and maybe 10M. Most likely not fully > horizontal , more of a sloper. Any thoughts on something like this? Quite a > wide range of frequencies. > > Andy K3UK >
