Home |
Search |
Today's Posts |
#13
![]() |
|||
|
|||
![]()
On Mar 4, 5:48 pm, Mike Coslo wrote:
Solid state transmitters are notoriously finicky about matching to the antenna. Tube equipment is not, so I am told, and early experience seems to bear that out. I don't know if "finicky" is a good term, Mike. "Different" might be the best word to use. Transmitters with vacuum tube finals can match a wider range as a rule, but there is a limit to what they can handle. Some of the older Johnson and Globe/WRL rigs matched a wider range than some of the other brands. Certainly I can see one of my newer rigs start to fold back at 2:1. Most Japanese gear is designed to do just what you're experiencing. That's a form of protection for the final transistors. Ten-Tec does it differently. Ten-Tec rigs do not start to reduce power. They depend upon the supply to fault and trip if too much current is drawn. That's why it is important to use a Ten-Tec supply with them or to use a fast breaker rated to trip near the maximum current draw expected of the transmitter. What are the practical limitations of the Tube finals apparent flexibility? That depends entirely upon the design specifications set by the manufacturer. If the manufacturer's manual says "45-90 ohms", that's the practical limitation. Some of those old Globe transmitters used to have ranges of up to 1000 or 2000 ohms as I recall. At the other end of the spectrum, Hallicrafters produced some transmitters without even a loading control. These were designed to be used with an antenna presenting something very close to 50 or 75 ohms. Is it safe to compare the load, plate, and drive controls to some of the functions of a tuner? (possible real dumb question) Not the "drive" control, but certainly the other controls of a tuner could be considered comparable to the "tune" and "load" controls. If the only antennas we have are trapped verticals, tribanders or dipoles/inverted vees cut for the band to be used, we might get away with not having to use a tuner at all. Still there are likely to be frequencies significantly removed from the antenna's resonant frequency where one might need a tuner to enable the transmitter to make full power. We aren't likely to need a wide range tuner for those times. A simple T-match will likely enable us to find a combination of settings which will present a low VSWR to the transmitter. The main alternative is to have a variety of antennas which present a VSWR of under 2:1 to a transmitter. Dave K8MN |
Thread Tools | Search this Thread |
Display Modes | |
|
|