really really high frequencies

[ab3a]

So you're probably wondering what these frequencies are good for. Allow me to remind you that Ham Radio is about the art of the possible, not the engineering of the reliable.

There are several modes of propagation that bear some investigation: First, you have troposcatter. This is a method the US military used during the cold war to build reliable connections over distances of as much as 900 km. Basically, you're scattering signals using the Tropospheric boundary with the Stratosphere. With enough power and directional antenna systems you can do impressive things.

If you live near places that have regular thunderstorms, you can scatter signals off of the upper layers of that thunderstorm and talk across distances of hundreds of miles.

All this works on bands as high as 10 GHz. Past that point you start seeing significant effects of signal attenuation from water vapor. There are compensating factors, however. As wavelengths get shorter, antenna performance becomes easier to come by.

I read recently of a new record distance for 76 GHz: New UK 76GHz distance record | Southgate Amateur Radio News

This is fascinating stuff. Also note that as bands go higher, bandwidths are significantly greater. The opportunity to send faster and faster data rates is certainly there.

Good Luck!

 

[zz0468]

All this works on bands as high as 10 GHz. Past that point you start seeing significant effects of signal attenuation from water vapor. There are compensating factors, however. As wavelengths get shorter, antenna performance becomes easier to come by.

There are various parts of the microwave spectrum that are affected by water vapor and oxygen. The 24 GHz band is in what's referred to as the "water hole" where water vapor absorption is particularly high. At the next higher band, 47 GHz, water vapor attenuation is actually less, but molecular oxygen absorption is at an even higher peak.

I believe all the higher frequency amateur bands are centered around areas of maximum atmospheric absorption, and the spectrum that suffers minimal absorption is allocated to other services.

 

[walruspwaterhead]

wow all this information is great and i appreciate all this info

 

[acyddrop]

I was only familiar with the "water hole" term in relationship to SETI until now, which is the radiation frequency of Hydrogen which is 1420.40575 MHz. Though I was aware (due to my line of work) that 24Ghz signal is in the middle of a group of frequencies heavily effected by percentage of moisture in the air and to some degree temperature + moisture.

There are various parts of the microwave spectrum that are affected by water vapor and oxygen. The 24 GHz band is in what's referred to as the "water hole" where water vapor absorption is particularly high. At the next higher band, 47 GHz, water vapor attenuation is actually less, but molecular oxygen absorption is at an even higher peak.

I believe all the higher frequency amateur bands are centered around areas of maximum atmospheric absorption, and the spectrum that suffers minimal absorption is allocated to other services.

 

[KB7MIB]

Wirelessly posted (Opera/9.80 (BREW; Opera Mini/6.0.3/27.2338; U; en) Presto/2.8.119 320X240 LG VN530)

I've heard of folks modulating visible laser beams (lightwave communications) and conveying information that way since at least the 90's, if not the 80's.
That would be an interesting way to make a secure point-to-point communications path.

 

[902]

Wirelessly posted (Opera/9.80 (BREW; Opera Mini/6.0.3/27.2338; U; en) Presto/2.8.119 320X240 LG VN530)

I've heard of folks modulating visible laser beams (lightwave communications) and conveying information that way since at least the 90's, if not the 80's.
That would be an interesting way to make a secure point-to-point communications path.

Lasers have been used to send video for a number of years and are now transporting data in free-space. Free-space optical communication - Wikipedia, the free encyclopedia Actually, fiber optic circuits are very similar, except the medium the signal is transmitted through is the fiber, not free-space. At a former employer, we had a camera looking at the employee parking lot beaming back to the shop across the street using FSO. It looked something like a bulky camera housing.

Fascinating discussion, BTW! I used to do the June VHF contest with a bunch of mountaintoppers. One year we guested a rover from another group who brought his portable microwave gear - and he made contact with his home team quite a distance away. I've always wanted to play in this league, but have not. I've got some very active microwave folks on an email reflector I lurk on, but the conversations and equipment are usually well over my head. My extent of "microwave" has been using 4.9 GHz with IDU/ODU configurations.