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None of the major amateur radio manufacturers make a rig for the 3cm band (or most of the microwave bands for that matter). The common practice is for hams to buy or build a transverter which downconverts the received signal from 10GHz to (often) 146MHz and upconverts the transmitted signal from 146MHz to 10GHz. In essence, 146MHz becomes an Intermediate ...

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5 GHz and 25 km range is hard. Let's do a quick free space loss calculation: \begin{align} a &= \left(\frac{4\pi d}{\lambda}\right)^2\\ &= \left(\frac{4\pi dc}{f}\right)^2\\ &= \left(\frac{4\pi \cdot 2.5\cdot 10^4 \text{ m} \cdot 5\cdot 10^9\text{ Hz}}{3\cdot 10^8\frac{\text m}{\text s}}\right)^2\\ &= \left(\frac{5\pi}{3}10^6\right)^2\\ ... 5 Disclaimer: I am not a lawyer and this is not legal advice. The interpretation of the regulations I am giving is based entirely on the reasoning I have seen other hams make in discussing how to operate properly. There is no one set of rules for the particular band. Rather, there are two entirely separate general regimes: Title 47 Part 15, for unlicensed ... 4 According to this site, the maximum allowed for non-licensed ("Part 15") equipment is 1W to the antenna, and the maximum EIRP is 4W. For point-to-point links, the limit is higher, and the site mentions that on 5.8GHz the maximum allowed would be 53dBm EIRP (30dBm transmitted plus 23dBi gain of the antenna), which is 200W EIRP. For licensed radio amateurs, ... 4 At least in Finland you are allowed to use the entire band from 10.0 GHz to 10.5 GHz with "secondary rights". Maximum TX powers are 30 W (basic class) and 150 W. The 3 cm band is also available at least in the USA: http://www.arrl.org/frequency-allocations 4 It's theoretically possible to have a narrow beam width at any frequency, but it's the ratio of size of the antenna to wavelength that determines the narrowest possible beam width. So you need either very large antennas, or very small wavelengths. Or both. There are many relationships like this in physics and engineering. Lasers Lasers have very narrow ... 2 One way to estimate line-of-sight before you even step outside is to calculate the radio horizon. For the horizon distance in miles and antenna height in feet, the formula is \text{horizon} = 1.23 \sqrt{\text{height}} $$For kilometers and meters, it is:$$ \text{horizon} = 3.57 \sqrt{\text{height}}  The horizons of each station add. If you need a ...

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25KM is a really long distance. You need to be up fairly high to beat the curve of the earth. If you are at sea level on a beach, and your eyes are 1.7m above the ground, the horizon would be at 4.7km. Source wikipedia:Horizon In actuality both ends would need to be elevated so that the beam path passes high enough over terrain between the 2 points. A ...

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If you want to calculate the height required for a 25 km radio link. Check out this link. http://www.everythingrf.com/rf-calculators/line-of-sight-calculator This link gives not visual line of sight but also the radio horizon which is slightly longer. At 5 Ghz with sufficient gain antenna to direct the signal as close to the horizon as possible and height ...

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To add to the already given answer. Most countries have a 100mW / 20dBm ERP maximum for license free usage of those bands. (You will have to check if this is your case, but chances are) As this is usually expressed in "ERP" which is "Effective Radiated Power" it will take antenna gains into account. Example by using an antenna with 3dBi gain, you will have ...

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