Electronics > RF, Microwave, Ham Radio

The "fat max" antenna

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was seeking for ideas for a relatively restricted space antenna covering as much as possible of the HF bands (a friend in sweden has some HOA restrictions <sigh>)

anyhow, stumbled upon this design


do you think it may be worth or... is it another "miracle" do-it-all antenna ?


It's hardly a miracle antenna, but it should be a decent adjustable vertical having untuned radials.  You will still need a tuner somewhere, and low-loss coax between the antenna and the tuner.  That 1:1 balun is probably a good idea as an isolator, even though the antenna is unbalanced.  I suppose we could consider it at least partially unbalanced, given the (random?) radial design.  Having the adjustable-length feature will certainly help reduce the SWR seen by the coax and tuner. 

Steel isn't the best metal for a radiator, but it's not too bad.  My boat uses a stainless steel backstay as an untuned vertical (with a good seawater ground), and a wide-range tuner at the antenna base, and it performs well enough.

A run of QuickField with steel strip 20mm by 0.2 mm at 14 MHz:
A straight run of 1 metre length in free space, not considering radiation.
The current density concentrates at the corners and thin edges.

(Impedance /m)
Steel, rho = 0.16e-6 Ohm.m  Ur = 66, Steinmetz = 1.8
Z = 0.43 +j39 Ohm

Stainless steel, Ur = 1
Z = 0.06 +j39 Ohm

It's fairly straightforward to make a crank up tower out of telescoping tubing, such that it can be "cranked up" to attain a height of 10-12 meters or more.  This is so it can spend most of the time close to the ground and can be raised when you want it at its highest. This is likely to allow you to have a long-lived tuned adjustable length vertical antenna.

You could even screen scrape weather reports in order so that predictions of high winds or high winds recorded on your anerometer would trigger it to crank itself info its lowered position. This way you could be confident a sudden windstorm wouldn't take it out. To anchor it you could use a pipe perfectly vertical set in a mass of concrete. and three or more guy wires.

What about replacing the tape measure with a metal slinky? At least you get the added bonus of linear loading.


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