I use a Motorola amplified speaker and an audio combiner circuit. Since some of the newer radios don't like to have either of their speaker leads grounded I had to design a circuit that not only combined the audio but also isolated the speaker leads from ground. What I came up with was to use audio isolation transformers for each radio. A shielded audio cable goes from the speaker jack on the radio to each isolation transformer. Each transformer has an 8 ohm 1 watt resistor in parallel with the primary. This provides an 8 ohm load for each radio. These transformers are also available at Radio Shack. The secondary of each transformer has one lead grounded and the other lead goes to a resistor. Each transformers secondary lead with the resistor is tied together and feed the input of the Motorola amplified speaker. This is a simple resistive mixing network that isolates each radio not only from each other but from ground as well. Since this is a passive circuit there is some loss but the amplified Motorola speaker more than makes up for it. In actual use the volume level on each radio is just a little less than if you were using the internal speaker. And turning up the audio about 3/4 of the way produces enough audio to drive you out of the car. The disadvantage is as noted that all the audio comes from the same place and it is necessary from time to time to look at the radios to see which one is receiving. However if each radios volume is set at slightly different levels it is easy to determine which one is active. This has also been tried with the amplified Radio Shack speaker with almost the same results. It is pretty hard to beat the amplified Motorola speakers for loudness and clarity. Bill - WA0CBW In a message dated 4/10/2010 8:32:04 P.M. Central Daylight Time, [email protected] writes:
Hello Folks, I am wondering what people are doing these days with multiple two-way radios and scanners in their vehicle and then outputting it to one speaker in the vehicle? How are they isolating each radio? Thanks, Mike
