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-

59or 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

Page 16 Page 18
Page 17
Image 17
Ramsey Electronics FM10A manual Antenna Ideas
Page 16 Page 18

FM10A specifications

The Ramsey Electronics FM10A is a compact and efficient FM transmitter tailored for hobbyists, educators, and anyone with a passion for creating their own radio broadcast. This device stands out in the world of electronics due to its user-friendly design and array of features that make it an ideal starting point for both beginners and experienced users.

One of the main characteristics of the FM10A is its simplicity in setup and operation. Users can quickly assemble the kit without the need for advanced soldering skills, making it accessible to a broader audience. The transmitter operates in the FM band, allowing for high-quality broadcasts with minimal distortion. Its frequency stability is maintained through a PLL (Phase-Locked Loop) technology, ensuring that the transmitted frequency remains consistent throughout its operation.

The FM10A features adjustable transmission power, allowing users to customize their broadcast range. With a maximum range of approximately one mile under optimal conditions, this device is versatile enough for personal use, small events, or classroom demonstrations. Additionally, the transmitter is equipped with an audio input for connecting various media sources such as smartphones, computers, or other audio devices. This flexibility makes it suitable for a range of applications, from playing music to broadcasting educational content.

Another notable feature is its compact design, which makes the FM10A easy to transport and set up in different locations. The device is powered by a standard 12V supply, which is widely available, making it convenient for users at home or on the go. The lightweight nature of the unit further enhances its portability, enabling users to take their radio broadcasts anywhere.

The FM10A also includes an LED power indicator and a built-in antenna for straightforward operation. Users can enhance their transmitting range by adding an external antenna, providing further customization based on specific needs. The kit comes with comprehensive instructions to guide even those new to radio transmission through each step of assembly and operation.

In addition to its engaging technical features, the FM10A serves as an educational tool. Users can learn about radio frequency technology, electromagnetic theories, and audio broadcasting principles, making it an excellent addition to any STEM program. Overall, the Ramsey Electronics FM10A is a stand-out choice for anyone looking to delve into the world of FM transmission with a robust, user-friendly device that doesn't compromise on quality and functionality.
Top Page Image Contents