I have tried many different multiband ‘quick deploy’ portable/temporary antennas over the years. I have an idea of which ones seemed to work better than others, and I was interested to see if EZNEC agrees. I used the version 5 demo program of Roy Lewallen W7EL’s excellent antenna modeling software EZNEC to model these antennas.
The exercise: I created EZNEC models of several different multiband ‘quick deploy’ portable/temporary antennas which I have used in the field and then compared a vertical slice of the far-field radiation pattern along the azimuth bearing of the highest gain of all the antennas. For this exercise I chose antennas which cover 80m, 40m, 30m and 20m, are easy to set up and can be supported on a single Jackite 31′ pole.
The antennas were modeled with #26 AWG teflon coated copper wire at 1 foot over a high accuracy very poor quality ground using a split current source of 2W power. The transmission line was not modeled.
I chose to model two vertical antennas. One 28′ long vertical and one 50′ vertical. 28′ has a low enough impedance for most tuners to be able to tune it on 20m and it can be tunes on 30m and 40m also. It’s a bit short for 80m. 50′ is about the longest practical vertical I would consider in the field, it’s tough to find tree branches higher than that. It’s long enough to be easily matched on 80m as well.
For doublets, I chose four designs. The 88′ doublet is a favorite of antenna guru L. B. Cebik W4RNL. On 20m, an 88′ doublet forms an extended double zepp (EDZ), an antenna with at least 3dB gain over a dipole, so it performs particularly well on that band, and can be casually tuned on 30m and 40m as well. With a good tuner, it can also be tuned on 80m where is performs surprisingly well for it’s limited length. I also modeled a 132′ off center fed dipole fed at the 44′ point. This is a popular antenna is sold commercially as the buckmaster OCF dipole. I modeled both the horizontal and inverted-vee variants of those with the center at 31′ (e.g. supported by a Jackite 31′ pole), and in the inverted vee I took the ends down to 6′ above ground (supported by 6ft driveway markers).
I also added an inverted-L, a 31′ vertical run and then a 90′ horizontal run, fed against the same pair of 16′ and 32′ counterpoises as the verticals. I call this one ‘The Bear’. Dunno why
So how do they compare?
20m Far Field
The horizontal 88′ doublet (as an extended double-zepp EDZ) was the clear winner on 20m with a maximum gain of 9.3dBi at 30° elevation broadside to the antenna, which is a good 2dB higher than the 132′ off center fed doublet and the 121′ inverted-L. Bringing the ends of both doublets down to 6ft above the ground makes a big difference also, the there is 4dB less gain from the 88′ inverted-vee than if it is horizontal. Interestingly, the horizontal 88′ doublet at 31′ has higher gain at lower elevations (3°-15°) than either of the verticals (with only 2 counterpoise wires).
So it looks like the horizontal 88′ doublet is a good choice for maximizing my 1.5W input signal as long as I do not need an omni-directional pattern.
How does the W3EDP compare to the horizontal 88′ doublet on 80m?
So, the 88′ EDZ is still coming out ahead of the W3EDP by a wide margin, but the W3EDP has a little more gain than an inverted-vee 88′ EDZ. Compared to the 132′ horizontal doublet and the 121′ inverted-L the W3EDP is in the same ballpark but it does have a little more gain that either of them at lower elevation angles.
40m Far Field
The 88′ horizontal doublet has marginally more overall gain than the 132′ horizontal doublet but the pattern of the 132′ horizontal doublet could mean less noise (since there’s less gain at 90°), and its more omnidirectional. So while the 132′ horizontal doublet may be a better antenna on 40m, the 88′ horizontal doublet is still a very strong contender, and since it’s much better on 20m I think I will still favor the 88′ horizontal doublet on 40m. All the other antenna designs are down at least 3dB from those two.
How about the 88′ horizontal doublet versus the W3EDP on 40m?
The twinlead counterpoise version of the W3EDP is almost equivalent (<1dB) to the 88′ horizontal doublet and is certainly easier to erect, but since the 20m pattern is more favourable I would still prefer to erect an 88′ horizontal doublet is I was planning on operating on both bands.
80m Far Field
On 80m, the 132′ horizontal off-center fed doublet is marginally better for overall gain than the 88′ doublet, but it’s very close (<1dB). The 121′ inverted-L is quite a bit down (2.5dB) from the 132′ horizontal off-center fed doublet. The antenna choice for this band is less clear-cut. With an antenna tuning unit with a good matching range, the 88′ doublet is probably the best all-around choice, since it works so well on 20m and is also near the top of the pack on 40m. But my KX1 has a limited matching range on 80m and will not tune an 88ft doublet there. So for me, taking down one end and adding 44′ on 80m is probably the best solution.
What about the W3EDP?
EZNEC predicts a 2.5dB difference between the 88′ doublet and the twinlead version of the W3EDP, with the 88′ doublet being the better of the two. The W3EDP had better low angle radiation so should be a little better for DX.
As un-scientific as this is … The conclusion that I draw is that as long as I use an external tuner on my KX1, the 88′ doublet is the best overall choice for an easy to deploy multiband portable antenna as long as I intend to operate on 2 or 3 bands. It’s also a great antenna for 20m single-band operations. For operation on 40m/80m there are better options, but the 88′ is nearly as good.