开云体育

Hi,
I was testing output power and I noticed that there was some issues with my microphone.

I only could get output power (10watts un 40 meters) when I blow directly to the hole of the baofeng microphone. If I Talk or I screamed a little I didn't notice a little bit movement in my? power meter (1 watt or less)

I have read that un bitx20, bias voltage un electrect microphone should be 10 volts.

What is bias voltage for mic un ubitxv6?

I measured It and I only got 5 volts un baofeng microphone...

Is this ok?

Any ideas about what is happenning yo my microphone?

73
EB2ELU
Felipe

Disassemble the mic, lift the capsule out of its molding and ensure the path to the front is not blocked by a film of plastic ('flashing'), a frequent artifact of the injection-molding process. The Manufacturer (Baofeng) makes so many of these it's not economically worth post-process inspection and correction: that would likely double the cost-per-unit.

73 de ZL2DEX

5V is probably normal: half a 10Vsupply via a (typically 2k2) resistor.

I dissambled the mic and it didn't have any obstacles to the encapsulation. To be sure I even tried to talk using the mic capsule directly and it didn't work fine...

I will try to substitute mic capsule or buy a new microphone

--
73,

Rick WK4R

I have had good luck with the following amplified mic:



Of course a better choice would be to add a speech compressor module between the mic and the input to the ubitx. I bought the module, however have not yet installed in any of my ubitx radios.

FWIW and YMMV
73
Evan
AC9TU

Hi Felipe,

It would take some investigation to know what the proper bias voltage is.? Perhaps HFSignals could help the group with this?

Electret elements do have a maximum operation voltage depending on the specifications of the FET transistor inside.? In the ubitx the bias voltage supplied is just whatever is supplied to the rig, so it could be 12V, 13.8V, or more.? This could easily be over the limit for an electret element.

It seems like the supplied Baofeng microphones are made for their HT's.? If that is so, they are probably using a lower voltage electret element where the bias voltage should be something more like 3V.? Someone with a Baofeng HT may want to measure the bias voltage the HT supplies on the external mic port.

Electret elements can easily be tested with just a load resistor of 2.2k and an electrolytic blocking capacitor of about 1uF.? Supply the microphone with about 3V through the 2.2k resistor.? Measure the current in this circuit and is should be somewhere around 0.2-0.5 mA.? Audio output can be measured with a multimeter on the AC mV range.? Put one lead on the capsule negative? terminal, and the other lead on the negative capacitor lead and the positive capacitor lead on the positive capsule terminal.? Blowing on the mic should then easily generate 50mV or more.? This will obviously not check audio quality, but it is a good first check.

Given that these mics are having the two pin plugs cut off and a 1/8 phone jack installed, it could be that there are wiring mistakes.? Are the mics individually tested after the plug installation?

73,


Mark.

try an extra 4.7k in series with the existing one. That should bring the bias to within Baofeng spec. If really blown 10k resistor needed instead of 4k7. There were no problems with original capsules, 4k7 worked fine there.

I did a search on condenser mics and all I could find was a maximum of 10 volts, 2-10.? As my UBitXv6 is going to be my go-to radio when we loose power I am going to have to make some changes. I am going to use a buck converter to lower the voltage to the radio. so I can use it on my solar-charged batteries. When they go into equalization made the voltage can go to 15 volts.?

These are dynamic microphone, how did you keep the? DC bias voltage from hurting the mic.
?I have a? lot of there laying around.

Mark,
If 12 volts is too high, what is the design voltage for this radio? How low can it go? The schematic shows 12 volts.
I am going to use a buck converter to lower my 14.4 (15? when in equalization phase) volts to just 12 volts.? Other people are not having a problem with blowing their microphones, what are they running fo DC voltage?
thanks.
73
KE5NCR

If I add the resistor will that not decrease the audio level as well. How about bypassing the resistor with a cap to eliminate that signal loss through the resistor. The original capsule is shot, it did not like 14.4 volts.?

Hi,

I have no idea what the operating voltage of the mic should be -- it's not my design and I'm not selling them.? I was only stating some ideas I had on what could be going wrong.? In the past there were posts about blocked mic ports etc, but these recent posts show this not to be the case.? It could be that the voltage is too high for the capsule, it could be a bad batch, or something else.

Personally I suspect that these are HT mics that are meant to be operated at lower voltages.? The bias resistor is not made for lowering the operating voltage, this is easy to see because drawing 0.5mA across a few kohm resistor is not going to drop much voltage right?? If the operating voltage is to be lowered, you could use a resistor divider network, a zener diode regulator, or a simple three terminal voltage regulator.? The high voltage, might not have damaged the capsule, it could be that the signal out of the capsule is distorted if the FET is not operating in its proper range.? Some checking would have to be done.? Earlier I mentioned some tests that might be tried.? Also a computer mic port probably provides some bias voltage and obviously has an input there so that would be another way to test.

The bias resistor is a load resistor and does not reduce your mic signal.? In fact -- up to a point -- increasing the resistor increases the voltage output of the electret capsule.? Anyway, the signal is not being taken through the resistor, but through the DC blocking cap.

73,


Mark