magnetic loop bandwidth

[p.larner]

well i have ordered 10m of 22mm dia copper tube,would that be ok in an octogon shape for an 80m magloop for ssb?.

[Wallace Gasiewicz]

Don't make an octagon, you will have silver solder or weld. Just bend it into a circle. fill it with sand and bend so you do not get any kinks.With the right capacitor you should get 80 M.

[radiolistener]

If you're planning to use it for transmission, you're needs to know that this is not safe for your health to be near magnetic loop antenna during transmission, because it has extreme high fields strength which exceeds safety limits even if you push just 10 Watt, for 100 Watt it will even worse. This is because such kind of antennas are too small relative to it's working wavelength and needs to accumulate a lot of RF energy in their near field region in order to compensate it's low radiation efficiency due to small size.

And this is why it has very narrow bandwidth, because it spending many cycles to accumulate energy, so it works like bandpass filter.

If you want TX antenna there is serious reason to use large size antenna to avoid damage to your family health.

[iMo]

My first 6m band antenna was a magloop, aprox 35cm ring in diameter made of an 8mm copper tube
The mag loop is a difficult antenna, I would not recommend to mess with it unless you can tune it with a special High Voltage capacitor coupled with a fine remotely operated mechanical stepper.
The bandwidth is quite narrow and you have to tune it always precisely.
Otherwise it works, but its effectiveness is rather low (depends on its diameter vs the wavelength ratio).
Also mind the voltages and currents around the tuning capacitor are Huge (it is a high Quality LC circuit with a LOT of kiloVolts RF around the tuning capacitor even with 100W into it).

[radiolistener]

yes, when you push 100 Watt into magnetic loop antenna, there is high voltage up to 200000 Volt and high magnetic field strength more than 70 A/m near antenna.

[Andy Chee]

For reference, here's a simulation of E and H fields for a transmitting loop operating 1W @ 7MHz

https://owenduffy.net/blog/?p=1842

And dipole for comparison

https://owenduffy.net/blog/?p=2064

The simulated 1W loop above required 1.45 meteres safe operating distance (according to Australian radiation standards), operating at 100W would require even more distance.

In summary, definitely keep your distance from transmitting loops!