Verticals for 30, 40, 80m

[VK4ADC]

Wayne

Re "Doug, the existing mast is 10m high and is tilt-over. It would not be hard to put an insulator a the bottom and fed it against ground with an unun and putting out some ground radials would be easy.  A wire from the top of the mast to the corner of the block would give me an "inverted L" about 14m long when is the same as the popular 42ft vertical marketed by DX Engineering. This is obviously my preferred option unless there is evidence that the trapped vertical would be better."


Extract from my web page at http://www.vk4adc.com/web/hf-projects/45...na-options titled "Portable HF Antenna Options", 29 July 2017:

" A large resonant antenna (eg full size dipole) will always be more efficient than a reduced-size antenna (eg a trap dipole), which will always be better than an untuned whip (eg a squidpole with vertical wire radiator) and it, in turn, is more efficient than a helical whip (even though it too is resonant).  Size is important!


I set about comparing three antenna types during a recent trip with the caravan out to a bush campsite, plenty of space and low noise levels.  The reference antenna was the trap dipole, the frequency around 7110KHz on the 40 metre band, the signal source was a VK3.   The coaxial feeders from the antennas were terminated in BNC plugs which made it possible to change through the three antennas all within a minute thus virtually eliminating QSB effects.  

The outcome was: trap dipole = S9, 7 metre vertical squidpole with 4:1 UN-UN = S7 (& occasionally to S8), Mobile One M40 helical whip = S5. The relative signals test was repeated the following day at a different campsite, similar dipole direction, and that provided exactly the same results (S9, S7, S5). 

I have noted previously there has been a one-to-two S-point difference between a full size dipole versus the trap dipole with the full-size dipole providing the stronger signals.

The summary effect is that if you have enough space available then erect full size dipoles, if not then try to fit the trapped versions, even just for short-term portable operations."

Note the signal level comparisons between full size & trapped dipoles and untuned (/ nonresonant) vertical antennas.

The same comparisons should be mostly true for a trapped vertical = trapped dipole provided that the vertical's ground effect in place will mimic the second side of the dipole at all frequencies. Similarly, mast radiator = squid pole, provided the a suitable ground effect in place for either instance.

Based on the above comments and where you are dealing with several bands, a larger array of independent wires is required to provide a suitable multi-frequency ground effect, not just a single 42ft wire.

The XYL may have said to reduce the wires that she could see but maybe didn't realise that some of them could go just under the ground's surface. Still there, just not visible.

73 Doug