Ramsey Electronics FM30, Руководство пользователя

Страница: 29 / 40

FM30
•
29
You can greatly add to the versatility and professionalism of your transmitting
station by adding an audio mixer and/or processor. Mixers allow you to
smoothly ‘blend’ from one audio source to another just like the commercial
stations do. Our STC1, Stereo Transmitter Companion provides audio proc-
essing in one easy package. The STC1 allows you to ‘sweeten’ the audio for
more impact and punch. Plus, it has brick-wall low pass filtering on the stereo
inputs to prevent that bothersome ‘swishing’ and squealing sound that is often
found when using lower quality CD players as the audio source! Check out our
free catalog for all the details.
ANTENNA IDEAS
A simple, yet very effective, antenna for the FM30 consists of a "dipole", set
up either horizontally or vertically, and connected to the transmitter output jack
through a few feet of coaxial cable (either RG-58, RG-59 or miniature RG-174,
available at Radio Shack and other sources). Correct dipole lengths for major
sections of the 88-108 MHz band are:
88 MHz, each side: 2.7 feet; 5.4 feet total
98 MHz, each side: 2.4 feet; 4.8 feet total
108 MHz, each side: 2.2 feet; 4.4 feet total
You can see that there’s not a great difference in antenna length from 88 to
107 MHz. Some antenna designers have the view that an "approximate" di-
pole such as 2.5 ft. on a side will do fine, while others believe it is worth the
effort to calculate the length for your exact frequency, using the simple formula
of Length (of one side, in feet) = 234/Frequency in MHz.
If the dipole is installed vertically, the end connected to the center conductor of
the coax should be the upper (higher) end. If young children will be around the
set-up, a flexible wire antenna is preferable, rather than rigid tubing.
A "ground plane" antenna can be quite effective. A ground plane consists of
one vertical element, the same length as one side of a dipole, connected to
the center conductor of the coax. Four "radials" are connected to the shielded
side of the coax at a 90 to 135 degree angle to the vertical element. The di-
pole formula is also used to calculate the length of the radial; since radials
should be slightly longer than the main element, use 240 rather than 234 in
your calculations.
If you are equipped to make the field strength measurements required by Part
15 FCC rules, and if you think it would be best to aim or "focus" your signal in
a narrower direction, you can consult an antenna handbook and design a suit-
able gain antenna. See Appendix A concerning FCC field strength limitations.
An FM- VHF TV receiving antenna could be modified for such a purpose.