USA

MOTOROLA HT-200 (H23DEN).

The workhorse of the walkie-talkies. There are probabiy more of these units in use than any other. Good specifications, many accessory options, and two-frequency kits (and a four-frequency kit for amateur use) still make this transceiver desirable. As newer units are put into service, more used HT-200s become available. (Motorola sells reconditioned units to commercial customers; Spectronics, Inc., near Chicago, sells used Motorola units to amateurs.)

We hope our research and this short summary will help you choose the right walkie-talkie for your VHF amateur system. More details and data sheets can be obtained by writing the manufacturers listed in the preceding summary.

Preamp - Compressor Clipper

H.P.Fisher VE3GSP 1379 Forest Glade Road Oakville, Ontario, Canada

After a thorough literature survey on speech compressors, I built several of the more promising circuits and compared their performance. After this effort, all preferable features were combined in a single unit. The "unit" can take Sow- or high-impedance microphones with outputs from 0.1 mV up and delivers a husky 40 mV rms output with a total compression of 30 dB for a 4 dB output change. Output noise is —35 dB without signal and better than -35 dB with an audio signal, thus there is no noise "rush" when your voice ceases.

Experimental

1 built five preamp-compressor units over the last few months; one is the "Carin-gella" compressor, one by DJ6BV (DL-QTC), one by W2EEY (73), one from "Electronik," and one of my own design. Four of them are somewhat complex and use four or more transistors; they use a variable-gain amplifier which produces its own age for gain regulation. The other one is a clipper-type preamp-compressor which has a smaller compression range and more distortion, but has low noise characteristics. I used a scope and signal generator to measure compression, sensitivity, noise, and distortion. Attack and release times were calculated from R and C values in the line. On the Caringella compressor, I

noted insufficient gain for low-Z dynamic mikes, which could be obtained by changing the FET input stage into an amplifier rather than an emitter follower. The unit distorted on iow tones due to its fast attack time. Noise output was low, but frequency response was much too wide, particularly below 300 Hz, where an SSB crystal filter can't do anything for you. The compression is 30 dB all right, but there was a 6 dB output change versus 30 dB input change, which could have been an anomaly of the particular unit I had.

The compressors by DJ6BV and W2EEY are similar in design and yield roughly 25-30 dB compression for 6 dB output change. Both units lack sensitivity and are noisy in speech pauses. Attack and release times were adequate and no noticeable distortion occurred. The unit from Electronik was specified at-40 dB compression, but I judged it to be a rather odd circuitry since gain control is achieved by resistive shunting in various amplifier stages; therefore, too many transistors were required. Also, the sensitivity was not adequate and, in order to change the frequency response, some component changcs were necessary. The last unit, one of my early designs, is a two-transistor preamp with a clipper at the output. Though the output noise is very low, the compression range is 20 dB at the most for reasonably low distortion. This unit is very professional quality, solid state, two-way radio, designed and sold exclusively for amateur use in the United States and Canada.

Standard Communications Corp., the world's largest manufacturer of marine V.H.F. equipment, has just developed a new industrial quality, high performance 2-meter unit. This rugged, compact transceiver is available only in the U.S. and Canada thru an authorized Standard dealer. The "826" is so compact that it makes mobile installation practical in almost any vehicle or aircraft, it becomes fully portable with the addition of Standard's battery pack.

Was this article helpful?

0 0
Disaster Preparedness Kit

Disaster Preparedness Kit

Don't get caught out in a disaster, be prepared for the unlikely. You just never know when disaster will strike, but if it does you will be more then prepared for it with the information this ebook gives you.

Get My Free Ebook


Post a comment