Re: No Power Out on UBITX
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Here is an interesting little mike that uses the same Electret microphone as the BITX ,uBitx.? This is the construction manual and may have a? schematic or block diagram.? ? The electret element has a little single fet amplifier in it, as can be seen in this article? A dynamic microphone is very similar to a dynamic cartridge used in a turntable, and is essentially a little coil and magnet., with the coil attached to a diaphragm.??The output voltage on a may be very low, typically in the 1 to 100 microvolt range. A microphone preamplifier increases that level by up to 70 , to anywhere up to 10 volts The electret microphone doesn't have quite the? level of a Dynamic microphone with preamp, but doesn't need it. It is substantially higher than a dynamic microphone without a preamp.?
On Feb 23, 2018 8:24 PM, "Raj vu2zap" < rajendrakumargg@...> wrote: Walter,
Try the original mic element as is. Dynamic mic out is low and I could hardly get any power with mine.
It will need another gain stage.
You need to yell a bit for full power..
reduce value of R63 to increase the mic amp gain.
Raj
At 24/02/2018, you wrote:
>I turned it on for the first time.? Checked the current draw, which was easy with my Lab power supply with meters.? All looked good.
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>Hit the ptt on the mic, Display shows TX and I get 200ma increase on PA bus with not modulation.? Looks good.
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>Talk into the mic no Power out on watt meter.? I'm using a watt meter and dummy load on antenna.? Not Good.? Maybe Mic is not wired correctly.? I am using a Kenwood MC-42S Dynamic Mic.? I put a Cap in the mic line (violet) to protect form the power supplied to an electoret Mic.? Does anyone know if the mic element in a Kenwood MC-42S requires power?? The 8 Pin connector has 8vdc on the Kenwood pin out but I don't think that is for the Mic element, as I thought a dynamic mic did not need power.? I did mount an 8 pin mic connector on the front panel of my UBITX and wired it according to the Kenwood Pin Out.? Which I have verified multiple time.? I may be that isolation cap.? What do you think?
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>Hit the Keyer I get about 1/2 watt out on watt meter.? I think that should be much more than 1/2 watt.? Same on 80m, 70m and 20m.
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>Advice and help would be greatly appreciated.
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>Thanks
>--
>73, W9KJO
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Michael Shreeve