HF radio mics. - Page 1
Forum section: electronics / beginners

author: davelectronic
author_rank: Frequent Contributor
timestamp: May 02, 2016, 09:26:21 am
content: Quick question here. On a cb radio can I use a dynamic mic on a radio that came with an electret mic. Thanks any help appreciated.

author: danadak
author_rank: Super Contributor
timestamp: May 02, 2016, 11:22:50 am
content: The radio should have mike specs required to operate it. In generala coil based mike preamp circuits quite different then an electret,so not high confidence it will work well.Regards, Dana.

author: electrongeek
author_rank: Contributor
timestamp: May 02, 2016, 01:17:44 pm
content: Might work. If the radio came with an electret mic, it will have a bias voltage applied to it. This won't be helpful to a dynamic mic, so if you can find a way to turn off the bias, it might be OK.

author: Zero999
author_rank: Super Contributor
timestamp: May 02, 2016, 03:26:37 pm
content: Quote from: electrongeek on May 02, 2016, 01:17:44 pmYou could try adding a DC blocking capacitor: two 22uF electrolytics wired back-to-back should do.

author: Richard Crowley
author_rank: Super Contributor
timestamp: May 02, 2016, 04:20:34 pm
content: As has already been noted, the original electret microphone requires operating power (mistakenly called "bias" at times). This power should NOT be applied to a dynamic microphone. So you should either disconnect the (likely) resistor which feeds the power, or block the DC from the microphone with a capacitor. The voltage is typically quite low (~5V) A 0.5 or 1uF capacitor would be more than adequate for voice frequencies. And the polarity is fixed, so back-to-back capacitors are not required in this case.HOWEVER. Unless you have an unusual dynamic microphone (not identified), it almost certainly has a LOWER signal output than a typical electret microphone capsule. So you face the real risk of not being to completely modulate the radio signal because your audio signal is too low. Since you did not identify your radio we don't know whether it possibly has a gain adjustment that might be able to compensate for the lower microphone signal. But it would not be surprising to find that an additional gain stage was required to boost the dynamic microphone signal level.

author: davelectronic
author_rank: Frequent Contributor
timestamp: May 02, 2016, 08:49:50 pm
content: Thank you for your replys, you've answered my question. Its more than one radio, so tricky to specify just one. In general I will try and find an electret mic, using a dynamic looks unlikley to carry the audio signal in a circuit designed for electret use. Thanks again for the help.

author: Zero999
author_rank: Super Contributor
timestamp: May 02, 2016, 10:38:59 pm
content: Quote from: Richard Crowley on May 02, 2016, 04:20:34 pmThat's a point: a dynamic microphone will have a lower signal level than an electrect. You could amplify it with a transistor powered from the input's power supply.

author: vk6zgo
author_rank: Super Contributor
timestamp: May 03, 2016, 03:34:10 am
content: Quote from: Hero999 on May 02, 2016, 10:38:59 pmI did something similar years ago to replace a carbon mic ( any of youyoungstersremember them?),with a dynamic mic.It wasn't my original idea,it was in a 1977 "73" magazine.It worked a treat!