Ramsey Electronics FM10A - Manual (Page 17)

Although many sources exist for audio mixers, the Radio Shack No. 32-
1105 is the least expensive commercial device currently available. Bear in
mind that specifications and model numbers for such accessory equipment
can change from year to year. Also, some home-entertainment audio
equipment includes simple mixing capabilities which will permit you to fade
and "cue" music and microphone inputs. Ramsey now sells the MX-5 and
MX-10 mixer kits (and wired and tested units!) and the Stereo Transmitter
Companion (STC-1) for a “radio station” quality home broadcasting set-up.
ANTENNA IDEAS
The simplest, yet very effective, antenna for the FM10A 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 is not a great difference in antenna length from 88 to
107 MHz. Some antenna designers have the view that an "approximate"
dipole 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 dipole 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 suitable gain antenna. See Appendix A concerning FCC field
strength limitations. An FM- VHF TV receiving antenna could be modified for
such a purpose. Ramsey now has the TM-100 Tru-match FM broadcast
antenna, ideally suited for your FM10A