Ramsey Electronics FM10A 用户手册

   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