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Ham Microwave FAQ's
If you have questions, e-mail to firstname.lastname@example.org
(1) How far can you transmit with microwave?
Generally, a microwave path works as far as you have a line-of-sight path to the other station. This means that distances of 10 Km to 50 Km are pretty normal. I have worked 10 ghz mobile at 60 mph (90 Km/h) holding the radio out of the window for a distance of 6 miles (9 Km) with rock-solid signals. The voice-quality on microwave was even better than the 2-meter mobile radio in the same car.
(2) What kind of signals can microwave carry? Microwave is very broad-banded, and generally, a good microwave station can carry signals up to 15 mhz wide. This means you can carry at least 2 tv signals, or from 1 to 500 voice channels, or telemetry data to 300 baud to over 10 Mb (Ethernet). For anyone interested in using Gunn Sources or Dielectric-resonant Oscillators for Spread-Spectrum, here is Randy Robert's very fine SS link to explore, click here!
(3)Can I do Ethernet or other data with microwave? Several Hams have built microwave stations to carry data. A good place to see what is possible, click here to go to n6gn's web page. The speed of these experiments has been increasing for the last 4 years, and now it seems possible to use microwave equipment to send Ethernet at 10MB. Here is a link to John Miles' web pages, describing what he has been doing.click here to go to ke5fx's web page, and here to go to Luis Yanes' web page. The "secret" appears to be the use of a Gunn source with a Varactor diode modulator, or to use a Dielectric-Resonant Oscillator that has a Varactor diode modulator. Varactor diode modulators have important characteristics, such as higher impedance, wider frequency deviation of the transmitter, and less capacitance to distort data bits. KE5FX has solved all of the interface problems concerned between Ethernet and microwave data equipment, building on N6GN's first efforts of 10 years ago. PC board design has been finished, and you can now build your own Ethernet microwave link!
(4) How does a gunn source work? A Gunn source is both a transmitter and a receiver at the same time. It transmits by generating microwave energy in its metal cavity by the action of the gunn diode, and this power comes out of the waveguide exit into the horn antenna. It receives at the same time by using this same gunn signal as a local oscillator and mixing with the incoming receive signal from the other station to produce an I.F. frequency determined by how far each gunn frequency is separated from the other gunn frequency. Example: If one station operates on 10.300 ghz, and the other station operates on 10.370 ghz, then the I.F. frequency on each end is the difference, or 70 mhz! This I.F. frequency comes out of the schottkey mixer diode, which is also contained in almost all gunn sources. From this I.F. output, the receive signal is sent to an I.F. amplifier and detector for use. (A simple (tunable) I.F./detector/audio amplifier is a common FM pocket radio)
(5) Is frequency-stability important? This question is the reason there are two different groups on each microwave band. Gunn sources drift quite a bit, and are not useable for narrow-band (less than 100 Khz) receiver bandwidths. The microwave faction that uses Wide-band FM takes advantage of very wide receiver bandwidths for their experiments, and some drift is less noticable. WBFM'ers like to make data links for short distances, and some like to go hill-topping for other WBFM'ers. There are a few tricks to stabilizing gunn sources so they stay for weeks or months on end without tuning, and new Dielectric-resonant Oscillators are much more stable for FM use. The narrow-band faction of microwavers cannot make use of drifting gunn sources, so they use more exotic phase-locked loop oscillators and much better receivers to achieve their goals, which is mainly DX'ing. If you don't want to drift around the band like I do, but with rather freeze ur patootie on a mountaintop, then here is a fine URL to see! just click here!
(6) What is the cheapest WBFM microwave station I can make? If you just want to experiment, and would be happy with voice communication for 8 Km or less, you can be working for about $US50.00. Of course, you will need two stations (one on each end), but if each station has a Gunn source with a schottky detector and a 6 db horn antenna, a simple modulator/power-supply (sold above), a good 88-108 mhz FM radio to be used as a tunable I.F. strip, a cheap set of computer-style headphones/mike, and 12 vdc at 500 ma, you can be having fun! Adding the heater kit (sold above) will allow for much less re-tuning to stay in-touch with the other station for hours on end.
For more information on on cheap microwave experiments, please click here
(7)Can I put a repeater on microwave frequencies? click here to see how to build an OCARS In the last couple of years, some Hams out in California have built and are using a new kind of microwave ham repeater, called an "OCAR". (On Channel Amateur Repeater). These guys have really "discovered" something that can make microwave communication more fun for all of us in Ham Radio! This sort of "on-channel repeater" could also be made for other microwave bands, and in general they are very economical to build!