DIY Baofeng Battery Charger base with Auto On/Off

I like my Baofeng Ham radios. But, one thing that annoys me is the battery charger. The radio's battery charger uses a charging base and a separate transformer. To turn off the charger you have to unplug the transformer from the mains power socket, which is not practical at all. If you leave the transformer plugged to the mains it will be wasting some electricity and generating RFI, as all switching power supplies do, not matter how good they are. 

Baofeng UV-5R, UV-B5 battery chargers.

So, I modded my Baofeng UV-B5 battery charger into a single unit device with automatic On/Off power switch. After this mod or hack, the Baofeng battery charger turns itself On automatically when the radio is put in the battery charger and turns itself Off when the radio is removed from the charging base. No more wasted energy, no more RFI, no more flashing leds!

Modified Baofeng battery charging base with AC power source.

The mod is really simple. All that is needed is an small AC switch, power cord and a soldering iron. You can find links to buy the parts at the end of this post.

Automatic On/Off charging circuit.

After the teardown of the Baofeng UV-B5 battery charger base unit, the transformer PCB can be placed inside the unit with minimum hassle. The DC input jack is de-soldered and the DC output from the transformer PCB is connected to the input of the smaller base unit PCB. One wire of the AC cord is soldered to the transformer PCB AC input and the other to one pin of the micro-switch. Another wire connects the micro-switch to the transformer PCB. The transformer has a 3mm LED that you may need to bend in order to fit both PCB's inside the base case. To prevent any accidental short circuit insulate any wire solder joint and use some insulation material between both PCB's.

Add isolation to prevent any short circuit!

The switch can be placed in place of the center charging contact spring, since is is not connected to the charging circuit. Some glue will hold the switch in place.

Battery charging base. Note the micro switch in the center of the contacts.

And that's all. Now you have an single unit radio battery charger with auto power On/Off! 

This project was done for the Baofeng UV-B5, but it can be done for other radios, like the Baofeng UV-5R and other brands and models as long you find a way to place the transformer PCB inside the base unit.

Please take a look at the following video describing the project and give it a thumbs up if you like it!

Parts
You can buy the micro switches here.
You can buy a power cord that matches your country's plug type here.

Interested in the Baofeng UV-B5?
Buy the Baofeng UV-B5 cheap from Banggood!
Buy a Baofeng UV-B5 battery charger from Banggood!
Buy a Baofeng UV-B5 replacement or spare battery from Banggood!

Baofeng UV-5R factory antennas teardown and review

Today I'm going to compare the Baofeng UV-5R, UV-5R+ and UV-B5 factory antennas. These two whip or "rubber duck" antennas are built for use on the VHF (136-174Mhz) and UHF (400-480Mhz) amateur radio bands and commercial FM band reception. They are sold with Baofeng two-way portable radios. When you buy a Baofeng portable radio, it comes with either one or the other. 

As you can see, one antenna is bigger than the other. The shorter antenna is just under 12 cm in length, while the bigger one is a little over 16 cm. That is a substantial difference in length. These antennas use a SMA female connector.

Two Baofeng radio antennas sold with the UV-5R and other models.

Almost all whip or "rubber duck" type antennas are small. They are designed to be used on small portable radios, so performance is sacrificed in favour of size. While this has little effect on the UHF band, usually performance on the lower frequency VHF band suffers. This is easy to understand, since small whip antennas are 1/4 wave length and 1/4 wave at 440Mhz is much shorter than 1/4 wave at 144Mhz. Wave length is calculated by dividing the speed of light by the operating frequency. For the UHF 70cm band, 1/4 wave length will be 300/440 then divided by 4, about 17 cm. For VHF, a 1/4 wave antenna would be 52 cm.

So, the length of these small antennas is optimal for UHF, but far from optimal in the VHF band. If you connected a simple wire 1/4 wave in length at 440Mhz to the antenna socket of your radio and press the transmit button on a VHF frequency, you would probably damage your radio's power amplifier. This has to do with impedance and VSWR. To be possible to use such short whips or "rubber duck" antennas on both bands without destroying your radio these antennas have matching circuits to improve the VSWR on the UHF and VHF bands. These matching circuits use inductors (coils) and capacitors. Bellow is a teardown of the the two Baofeng UV-5R antennas.

The insides of two Baofeng UV-5R antennas.

As you can see, they are quit different internally. The shorter antenna's radiator is constructed using a long helical wound wire, while the other uses a longer and thinner radiator. Although this is more easily seen on the longer (top) antenna, they both have a matching circuit at the base.

Matching circuit detail of the Baofeng UV-5R, UV-5R+, UV-B5 16cm antenna.

So, these antennas are different. Will this have an effect on performance?

After some tests, I came to the conclusion that performance is very similar between the two antennas on the VHF and UHF bands. On the commercial FM band however, the longer antenna is noticeably better! 

If you frequently use your radio to listen to commercial FM stations, the bigger antenna is the clear choice. You can, of course, use this antenna on any other VHF/UHF two-way radio, as long it uses the same SMA type connector, or with an adaptor. They can be bough for about 3 USD online. 

If you want better performance on both the UHF and VHF bands a bigger antenna is needed. More on that in a future post. 

Buy the Baofeng VHF+UHF+FM antenna (16cm) from Banggood.