MFJ MFJ-207, Инструкция по эксплуатации

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MFJ-207 Instruction Manual HF 10-160M SWR Analyzer
EASY START INSTRUCTIONS
FACTS ABOUT TRANSMISSION LINES AND LINE LOSS
The MFJ-207 should be connected to the input to the transmission line looking toward the load. You do NOT
have to know the length in wavelength of your transmission line, but you do need to know the length in feet (or
meters) and the loss (in db) for the length of line that you are using at the frequency you are testing. Using the
SWR/Line loss chart in Appendix C you can readily determine the SWR at the antenna. The most important
consideration for any antenna system is probably the loss in the transmission line. The less loss, the better.
Two important points about transmission lines need to be understood:
1. On a LOSSLESS transmission line, the SWR read at the transmitter is the same as the
SWR at the antenna. For any line with loss the SWR is greatest at the antenna and
minimum at the transmitter.
2. Regardless of the losses in the transmission line, if the SWR at the transmitter is 1:1,
then the SWR at the antenna is 1:1, but if there is any SWR at the input to the
transmission line there is a higher SWR at the antenna (assuming anything but a
lossless line). Let’s go through a practical example.
Let’s say you are using RG-58/U which has a loss of 2.3 db at 30 MHz per 100 feet. You are only using 50 feet
of cable, so your loss when matched at the transmitter is 1.15 db at 30 MHz.
Go to Appendix C and find the 1 db loss line which curves up and to the right.
Now assume you are using your MFJ-207 and find the lowest SWR you can get on your antenna is 2.0:1.
Follow the 1.15 db line (between the 1 db line and the 2 db line) down to th point it reads 2.0:1 on the horizontal
axis (SWR at transmitter).
Look at the vertical axis we can see that the point corresponds to an SWR of about 2.5:1 on the vertical axis.
Reading this chart correctly tells us that with 50 feet of RG-58/U that has a loss of 2.3 db per 100 feet at 30
MHz and a line input SWR of 2.0:1, the SWR at the antenna is 2.5:1.
By the way, the 2.0:1 SWR at the load only adds about .225 db of loss to the already matched 1.4 db of loss foe
a total loss of 1.625 db. (See ARRL Antenna book)