with the BF-U3, UHF model. The speaker microphone has very good transmit and receive audio with the UV-3R as reported by amateur operators on various repeaters locally. No push to talk issues were observed during operation. The speaker microphone audio response is a little on the high side (bright) for my taste,but overall quality is acceptable. I prefer the UV-3R internal speaker response and quality, but the brighter pitch of the speaker microphone is an advantage when operating in noisy environments.
The Baoefeng UV- 3R's speaker microphone configuration. When viewed in this position and from left to right, tip is speaker out, ring two is microphone input, ring one is PTT input and the sleeve is common/ ground. On this microphone, the impedance of the speaker is around 8 ohms and the microphone element is 1,500 ohms. This was calculated by the dc resistance readings obtained with my DMM (digital multimeter).
The same tests were performed with the BF-U3 UHF radio. According to suppliers in Hong Kong and China, speaker microphone operation is not possible with the BF-U3. I discovered that it works with the speaker microphone, but the audio is weak. When tested with the supplied earphone / mic, the audio is loud and clear. I measured the dc resistance of the earphone/mic and found that it is above 30 ohms. The BF-U3 speaker microphone jack impedance is designed for higher impedance and does not work with the 8 ohm impedance of the speaker microphone. Adjusting the volume had little effect on the received audio when using the speaker microphone. Transmit audio was not a problem with the speaker microphone, on air reports were as good as with the UV-3R.
The BF-U3 is shown transmitting on high power with the speaker microphone. No PTT issues were observed, even with the microphone cable in close proximity to the antenna. The transmitted audio quality is the same as with the UV-3R , as reported by tests performed on the air,with other amateurs via repeaters. The speaker microphone provided better audio quality than the supplied earphone / microphone.
The BF-U3 receiving with the speaker microphone. The received audio quality is acceptable but very weak. In conclusion, the reason for this difference in volume is, the impedance of the speaker microphone ( 8 ohms) when compared to the higher impedance (30 ohms) of the supplied earphone microphone. Some vendors are selling speaker microphones and they claim compatibility with the BF-U3. I have tested different microphones from different suppliers and the results have been similar. This speaker microphone was purchased on E-bay from Solid Radio in Hong Kong. They cost less than $15.00 including shipping. There are other more expensive ones, including waterproof versions, but they cost more than the radio alone. The other UHF mini hand held from Baofeng, the BF-U8 also suffers from the same speaker microphone compatibility. I will keep the speaker microphone for use with my UV-3R's and will use the BF-U3 with its internal speaker or with the supplied earphone microphone. This information was added to my blog as a complement to the Baofeng UV-3R and BF-U3 reviews and observations published earlier. You may find a very nice compilation of information and FAQ's for the UV-3R . Any questions or comments are welcomed via e-mail, as well as your tests and observations with Baofeng radios.