Re-radiation from antennas?

[VK2UL]

Having done that, I think the idea of "re-radiation" not only from passive antennas cannot be totally dismissed...
73
Wayne VK4WDM

Don't need to be an RF engineer; it cant reradiate more than is incident, that's just plain physics, so if it is at safe levels near the antenna then it cant be more nearby In the worst-case an ideal passive and perfectly resonant antenna in the near, or far, field could only reradiate the same power density that it sees, which has been established as safe. Now there are no lossless and perfect antennas so whatever is reradiated is going to be even less...

cheers,

[VK2HRX]

So. If I carry 2 smart phones in the same pocket will I get RF burns due to the infinite amount of radiation I will be subjected to?

[VK2XSO]

It's interesting because I do on rare occasions see examples of re-radiation which set off our RF worker's Radman detectors.
A good example is AM broadcast towers re-radiating on a mobile phone tower even though they are over a kilometre away.

I have also had a nearby FM broadcast transmitters doing the same off an empty mounting structure on a tower.
It was confirmed by an RF safety officer that the structure was radiating and the direct path RF was not responsible for the alarm on the device.
A wire with an alligator clip on each end made the problem go away and work resumed. No alarm was caused by the nearby FM transmitter directly and when the new antennas were mounted on the frame the jumper cable was removed and the area checked with no alarm.

So without actually seeing the setup and the proximity of various antennas the site would need to be assessed. I can think of all kinds of points and triggers for re-radiation of HF energy but it is harder to consider if they might even pose a problem with a relatively low exciter power of 100W. The only real way to know is to take a E&H field probes out and look for RF demons.

[VK4BZ]

A friend of mine years ago who had worked with high power MF broadcast stations told me the story about some blokes digging holes for a fence (if I remember correctly) near an antenna and transmitter similar to the Bald Hills instilation. They had a crowbar in the ground, poured water around the ground entry point and, voila, they were able to listen to the radio whilst they worked!