Over a hill question.

[WRFP457]

There is a high ridge between my home and my son's home. On top of that ridge is a big water tower that hosts cell antennas etc and is at 45 deg between our homes. Now the possibly dumb question. Since UHF is a fairly short wave, would it be possible to bounce our signals off of the water tower using directional antennas? There are no GMRS repeaters in our area.

[marcspaz]

No. UHF is a line of sight service. The tower will either have zero impact or (using a beam, etc.) absorb the waves.

 

Ground absorbs UHV signals. The rest goes into outer space. You just get to talk to anyone from in front of you, to the visual horizon while the wave is on the way.

 

We bounce UHF and VHF signals off of satellites (such as Earth-Moon-Earth) successfully because they are not grounded.

[JohnE]

some more info would be helpful

how far away is sons location, same for the ridge/hill in question as well as direction.

[berkinet]

While marcspaz's response if mostly accurate, signal reflection, while difficult to achieve, is possible. In the days when microwave was in common use for long haul links, mountain top reflectors were fairly common (see photo below).  The same principal will work on UHF,  IF the antenna is properly positioned at the right angle between the two transmitter locations. It is possible, though not likely, the water tower could act as a reflector. But, the transmitters would have to be well positioned and the antennas would have to be very high gain, probably a dish, and well aimed.  So, I'd say if you can borrow two nice dish antennas, give it a try. But, don't expect too much.

 

 

http://www.rfcafe.com/references/electronics-world/images2/radio-mirrors-communications-electronics-world-may-1969-2.jpg

[axorlov]

In the rocky canyons of California, I had a reliable communications many times with over-the-hill and around-the-hill propagation path. 65cm waves (GMRS) reflect quite good from granite surfaces. Locally at home, I keep failing with using TV antenna on Mt Allison and power transmission lines over Sunol grade as passive reflectors. But I haven't tried yagi yet. Experiment!

[WRFP457]

Thanks, it won't hurt to try, but I'll not get my hopes up. He is 4.8 k (crow flys) away with the water tower 2.8 k from me and 2.5 k from him. I sure would like to have space on that water tower for a repeater but it already looks crowded and I bet it is expensive. I have a friend that does microwave networking here, and I once installed a T1 for a TV station to run over their microwave running between Pensacola Fl and Ft Walton Beach FL, but that was as simple as plugging in a box on each end and they had deep pockets which I don't have. I may check with him to see if I can ride on one of his towers and set up a GMRS repeater. 

 

PS, just getting started with radio and was ready to test for ham, but no ham tests being given so I decided on GMRS in case the government (or China) turns off cell and internet which wouldn't be hard to do.

[Solly]

It may be possible, but very unlikely. Uhf is very line of sight and dose not bend as remotely well as HF. May have better luck with CB, it is HF. AT the distances (short) requires sharp angles of reflection, extreme concentration of energy, think parabolic array antenna. GOOD LUCK and have fun it will be a great learning experience. keep us posted.

[JohnE]

forgot about doing this too

use Google earth find your location and the 2nd location

tools, ruler . make and save the profile close the ruler

right click the saved profile and look at the elevation profile

that should give you a better idea "if"it will work.

now to add to that I can talk to a machine that is ~40mi away from me. my elevation is ~1215 the machine is ~1350 on a 60' water tank. w/3 "hills in my way

at 1 mile out is 40'

10 miles out 230'

25 miles out 315'

[Lscott]

 would it be possible to bounce our signals off of the water tower using directional antennas?

Maybe. It would be like reflecting a light beam off a mirror. It all depends on where the two antennas are located relative to the water tower. I know this could work because years ago I was talking to my brother on the Ham 70cm band which is just below the frequencies used by GMRS. He lived several miles from the airport. When a plane was at just the right point and orientation his signal jumped from an S0/S1 to over S9 for several seconds. He was using a base antenna and all I had was a simple magnet mount about 10 miles away.

 

As a matter of fact back in WWII some of the early radars ran around 150 MHz, some used up to 300 MHz, and used a flat reflector with a number of dipole antennas mounted in front in such a way to get a directional beam to bounce off aircraft.

 

https://en.wikipedia.org/wiki/Mammut_radar

 

That was before Britain invented the cavity magnetron.

 

https://spectrum.ieee.org/tech-history/dawn-of-electronics/from-world-war-ii-radar-to-microwave-popcorn-the-cavity-magnetron-was-there

 

Other Hams bounce signals off the ionized trails left by meteors as they enter the Earth's atmosphere. It's called meter scatter.   

[Lscott]

I was doing some searching for anybody that may have tried the idea and stumbled across this gem. Got me a bit interested in the idea.

 

https://az276019.vo.msecnd.net/valmontstaging/vsna-resources/microflect-passive-repeater-catalog.pdf?sfvrsn=6

 

While not exactly a water tower the idea is along the same direction, a passive reflector repeater.

[taco6513]

How about a repeater on the water tower or inside the compound? Who own the water tower? Doesn't hurt to ask?

WRCW870

[WRFP457]

The city water system. I may have found access to a 20 story building free of charge. One of my computer network friends has a microwave tower there and they own me a BIG favor.