Distorted talkback on a Mirage 88

[wyatt knight]

I bought a Mirage 88 from a friend of mine and it works great, except the talkback in sideband. It has a switch on the back for turning talkback on and off. It's not a major issue and I can just turn it off when I'm in sideband mode but I do like it on sometimes. The issue is that when I'm in sideband mode, the talkback is distorted?garbled and was wondering if any one knows how to clean it up.

[dirtyjob]

does talkback even work on sideband?? since their is no carrier

[wyatt knight]

My talkback on my 959 works great on sideband just like it does on AM. I would like it to work the same on my Mirage 88 if possible. I was wondering if this would work, Talkback can become distorted if these radios have been "peaked," and there is no cure because the talkback just amplifies what goes to the RF section. Try adding a 470k ohm resistor from junction of C154/R207 to the junction of C187/R235 on the solder side of the board. This will also give you clean talkback on SSB and FM. Try different values of resistance to get the amount of volume you want. The less the resistance the louder the talkback will be.
I found this on cbtricks.com for the Galaxy 88.

[hilltop 439]

Seems to be a common thing with the Mirage radios my friends Mirage 66 does it and my Mirage 9900 does it also. Now you say your Mirage 88 does it. Must be something is the circuitry of these radios. I did'nt buy mine new so i don't know if the whole distorted talkback on sideband thing was a design flaw or just a cause of wear and tear. It would be nice to know.

[wyatt knight]

Looking at the echo board schematics on CB Tricks website, it looks like the talkback originates from the echo board. I wonder if the muffled talkback is in the echo board or the main board. It's not a big deal, but if there's a way to fix it, I'd like to.

[rbodenbender]

the only way the talkback would be on in the first place is if the echo board was powered on, and you do not want that when you are on sideband. my DX88 talkback turns off when the echo is turned off.

[wyatt knight]

I have a switch on the back of my radio that turns the talk-back on or off independantly of the echo. I can run my echo without the talk-back on or run the talkback without the echo having to be on. I will not mess with it unless there's a sure fix for it as it's not a major issue since my transmitted signal is clean with plenty of modulation.

[TheCBDoctor]

Most talk back modifications on the export radios come from the mic gain circuit and goes to the audio chip. If the audio signal is picked up at the balance modulator or another part of the SSB circuitry it will not work because you are listening to a side band signal.

If the talk back is like most export radios then the resistance needs to be increased that feeds the audio chip; the factory resistance is 1 mega-ohm. I will assume it is. If the radio sounds fine on AM, then there is no reason it should sound bad on SSB if it is set up like most export radios.

Does the Mirage 88 have a Mic gain control? I know a few of the oddball exports, like the Pluto, do not.

Respectfully,

[wyatt knight]

Yes it has a mic gain control. I was told it is was basicly a Galaxy 88 with a black bezel and knobs and buttons instead of the shiny stuff. I would like the talk-back to sound nice on sideband like my Galaxy 959 does. I haven't messed with it yet as the radio works great as is but if there's something simple that can be done to clean up my talk-back in sideband mode without compromising the integrety of the radio, I'd be interested. Maybe a better description of the talk-back in sideband mode would be muffled/distorted.

[TheCBDoctor]

Yes it has a mic gain control. I was told it is was basicly a Galaxy 88 with a black bezel and knobs and buttons instead of the shiny stuff. I would like the talk-back to sound nice on sideband like my Galaxy 959 does. I haven't messed with it yet as the radio works great as is but if there's something simple that can be done to clean up my talk-back in sideband mode without compromising the integrety of the radio, I'd be interested. Maybe a better description of the talk-back in sideband mode would be muffled/distorted.

The way they get talk-back on the Galaxy 88 is by disabling the circuit that is used for CW operation. The radio does not have that feature, but the same board is used in almost all of the exports. The talk-back muting circuit is disabled by cutting or opening a diode that clamps the circuit off. I believe it is D-88, but I may be wrong on the exact labeling.

The Galaxy 88 is not my favorite radio. If you compare the board on the 88 to a Connex you will find that it is paper thin, unlike the Connex. Out of all the radios that have bad solder connections the Galaxy 88 is the worst. Try and use the method that most AM exports use by running a jumper using a resistor and a cap from the op amp audio amplifier to the input of the audio chip.

The resistance is 1 Mega-Ohm; it has a capacitor of .1 ufd in series. The cap is not needed if you connect the resistor to a point before pin 4 of the audio chip that is the cap used to couple the signal to the audio chip. The lower the value the louder the audio talk-back.

If you shut the echo off the talk-back will be disabled. Wet your pointer and middle finger and touch the area of the audio output of the operational amplifier to input of the audio chip (Pin 4) on the solder side of the board and you will get talk back. It doesn't take much resistance to get talk-back. It is an interesting experiment and may help you get the clear talk-back you desire.

Respectfully,

[wyatt knight]

Thanks, I'll check out that circuit when I open it up next time. It isn't giving me any trouble, save that one issue, but that's just an annoyance. Thanks again CB Doctor.