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1 Speaker for 2 radio's

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KG5HHS

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Hello,
I have a Motorola Astro Spectra 110watt VHF radio installed currently and will be installing a GE Ericsson Orion 100watt UHF radio. I don't know the specific model of the speaker I have installed for the Motorola but it has a high and low switch. My question is, could I connect the two radio's to the one speaker or should I install two separate speakers.
 

Forts

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They won't play nicely together at all, likely resulting in serious damage to one or both radios. You would need to install a few caps to isolate the DC voltage from each radio so it doesn't backfeed.
 

KG5HHS

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Hmm, okay. I will install separate speakers. Also, I plan on using 3 different radios to host 3 different feeds. One VHF, UHF, and 800mhz. I planned on splicing a 3.5mm in to connect into my computers input ports, would that also have a bad effect?
 

Weaksignal

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You may want to check into the LDG ALK-2 for you needs. I have two radios and use one speaker and this unit works perfectly for the task. Besides its use as a speaker switch, it has other switching options as well.

Products LDG Electronics
 

Forts

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Yeah you wouldn't want to go speaker level audio into your PC. Ideally you want something around line level that isn't amplified. You can usually pick this audio from the accessory port at the rear of the radios. Another benefit of doing it this way is that it isn't affected by the radios volume control, so you don't have to worry about the audio level of your feed if you crank the volume of the radio up or down.
 

RFI-EMI-GUY

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There used to be commercial audio isolation transformers that could sum two stereo outputs onto a single speaker. They are hard to find, but easy to make up if you know what to do.

Most modern radios have speakers that are driven directly by a complementary pair of transistors so the installation manual will likely recommend you never short either speaker terminal to ground, they must float.

This means that driving an external amp or a PC line input may require a transformer to isolate the speaker output from ground. Using capacitors to do this is not the way to go as you will have distortion and possible damage if the capacitors fail.

If you can find line level at the accessory jack go with it.
 

RFI-EMI-GUY

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You may want to check into the LDG ALK-2 for you needs. I have two radios and use one speaker and this unit works perfectly for the task. Besides its use as a speaker switch, it has other switching options as well.

Products LDG Electronics
The specs dont say that it isolates the speakers from ground. It may be OK for unbalanced line level though. LDG should provide a schematic.
 

RFI-EMI-GUY

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As I posted their link in my first post, it's for speaker use as well.
Many commercial radios and new ham radios have balanced speaker circuits. If either lead touches ground the audio PA is toast. There is usually a warning in the installation manual, sometimes not. My new Uniden scanner has such a circuit, with a warning. Some products they assume you will use the supplied accessories and if not - warranty is void.
 

Weaksignal

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I appreciate your opinion RFI. I must say, that it has been working well for me and my modest VHF setup here. That is, two transceivers, one speaker and no issues.
 

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cmdrwill

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As I posted their link in my first post, it's for speaker use as well.
But NOT for two way radio speakers. Why? One speaker 'tied' into two radios will probably blow out the audio amps, or ground a speaker lead and that will blow out the amp.

The audio amp in the later two way radios, even some scanners, and handheld radios use a bridge stage that swings each side of the speaker from ground to battery voltage, so one side of the speaker swings to ground, and the other side swings up to supply voltage producing lots of current to drive the speaker without using a transformer, and it's losses, to match the speaker. Neither speaker lead is grounded or common. Auto stereo radios use the same bridge type audio output amplifiers.

A second speaker for the second radio is probably much easier, and the audio will be easier to hear when both radios are blaring out... or a separate audio amp with two ISOLATED inputs is what is needed.
 

RFI-EMI-GUY

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But NOT for two way radio speakers. Why? One speaker 'tied' into two radios will probably blow out the audio amps, or ground a speaker lead and that will blow out the amp.

The audio amp in the later two way radios, even some scanners, and handheld radios use a bridge stage that swings each side of the speaker from ground to battery voltage, so one side of the speaker swings to ground, and the other side swings up to supply voltage producing lots of current to drive the speaker without using a transformer, and it's losses, to match the speaker. Neither speaker lead is grounded or common. Auto stereo radios use the same bridge type audio output amplifiers.

A second speaker for the second radio is probably much easier, and the audio will be easier to hear when both radios are blaring out... or a separate audio amp with two ISOLATED inputs is what is needed.
Right, The OP has an Astro Spectra and those are most definitely of the sensitive bridge type. Earlier radios like the Syntor and Micor radios had a hefty audio transformer inside and could connect to just about any configuration and load. I have some 90's vintage ICOM ham gear and those have unbalanced speaker audio so the LDG would work with those.
 

RFI-EMI-GUY

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It can be done passively with three 70V audio transformers. Connect each radio and the one speaker to the Low Z 4 Ohm windings of each of the three transformers. Connect the 70V common wires from each transformer together. Select the 10 Watt or 5 Watt taps from each transformer and connect them together - Use 10W on the speaker and 5W on each radios transformer. - Adjust the 70V wattage taps as necessary to minimize distortion and maximize volume.

You can add radios and transformers to the mix and even use the method to remote a speaker in another room fed by a 70V transformer without losing volume.

http://www3.telus.net/Whalco/Audio70v/70v Transformer1.gif

70/25 Volt Audio
 

SCPD

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An audio mixer,an audio amp and the one speaker is a better way.
Weaksignal,I love your meters!
 

KG5HHS

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I think I will just install two separate speakers in the vehicle. However, For the home I'm going to have a scanner, a VHF, UHF, and 800mhz two way radio, and maybe even a dual band amateur radio. It sounds like there isnt going to be an easy solution to be able to have them connected to individual speakers and to the input ports on separate sound cards.
 
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