Quote:
Originally Posted by OberGeiss
Does anyone know of a source of plans for building one's own low/high VHF antenna.....I searched the forum and could not find anything. JUst toying with the idea of using a separate carbon fiber mast and some wiring and parts I have laying about........my idea is to have an integrated short mast and VHF ant. Any ideas as to where I might consult for some basic design parameters?
Thanks!
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A low/high VHF antenna is just a VHF-only antenna. There are several standard types of VHF-only antenna. The best such antenna is probably log-periodic. The log-periodic antenna design allows you to effectively "dial-in" the gain that you want. Be warned. Because it must cover the long-wavelength end of the TV frequencies (54-216 MHz), a full-spectrum VHF log-periodic TV antenna will be rather large.
You will need computer assistance to build the antenna. The
RF Toolbox application from Black Cat Systems will give you the dimensions for a number of different types of antennas of interest to HAMs including the log-periodic type. The application is not free, but it can be used without paying the fee.
Having said all that, I have to wonder if you have really thought this out. Building an antenna is not the issue. Building a VHF-only antenna is. It is not 1957 anymore. Even before the digital transition, the majority of TV broadcasts were in the UHF band, not the VHF band. Today, there are metropolitan areas were there are no VHF transmissions at all. In others, all of the VHF transmissions are low-power. A VHF-only antenna makes sense if you want signals received from the best possible VHF-only antenna to be combined with signals from the best possible UHF-only antenna via UVSJ.
Now to your mast. There is a recent thread about using fiberglass masts. Like fiberglass, the rigidity of carbon fiber is provided by the hardened resin that holds the fibers in place. The fiber reinforces the hardened resin. There are several reasons that I recommend against a mast made of carbon fiber. They are they same reasons that I recommend against fiberglass:
- Carbon fiber has no track record as a mast material. A galvanized or painted steel tube or tower will stand for decades with no appreciable loss of rigidity. Without maintenance, the resin holding the fibers together will deteriorate. Examine the body of an old Corvette. Examine a fiberglass boat that has not been maintained.
- The resin that binds carbon fiber is non-conducting. This makes it impossible to ground your mast.
It might be helpful if you would explain what you are trying to accomplish by building your own VHF-only antenna. As for the carbon fiber mast, forget about it.