Tuesday, 21 November 2017

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, Baofeng UV-B5 battery chargers.
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!

Baofeng UV-B5 battery charger auto On/Off mod / hack.
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.

DIY Baofeng UV-B5 battery charger Auto On/Off mod / hack circuit.
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.

DIY Baofeng UV-B5 battery charger mod / hack base unit.
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.

DIY Baofeng UV-B5 battery charger Auto power On/Off mod / hack.
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!

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!

Thursday, 6 July 2017

Nagoya NA-771 antenna review

Practically all handheld radios are sold with a small whip or "rubber duck" type antenna. Sometimes this antenna is so small than it is not even 1/4 wave length at UHF (440Mhz). As you probably know, these small antennas are not very performant, specially on the VHF band (136-174Mhz), where the whip is so short that performance is severely affected.

For better performance a bigger antenna is needed. The Nagoya NA-771 is a dual band VHF/UHF (144/430Mhz) antenna that delivers improved performance compared to the typical "stock" whip or "rubber duck" antennas. The Nagoya NA-771 is about 39cm in length, much bigger than the typical handheld radio "stock" antenna, but still a good match for small handheld radios. For a review of the Baofeng antennas that come with Baofeng handheld radios, please check my previous post.

Nagoya NA-771 antenna
Nagoya NA-771.

Disassembled Nagoya NA-771 matching circuit
Disassembled Nagoya NA-771 with matching circuit.

As always, the laws of physics rule and, as expected, compared to the antennas that come with most portable radios (Baofeng and others), performance is noticeably better, specially in the VHF 2 meter band and the commercial FM band. But UHF performance is also improved. Nagoya claims a gain of 2.15 dBi and a VSWR of less than 1.5:1. I don't trust this specs since this is a 5/8 wave antenna and a higher maximum gain is to be expected. A 5/8 wavelength pole has more gain at lower elevation angles (i.e. near the horizon) than a 1/4 wave pole, which it is what is normally desired. Also, Nagoya's claims the same gain for the NA-701, a much smaller antenna! Don't confuse the NA-771 with the NA701, which is only 22 cm in length. The NA-771 has more gain than the NA-701!

Nagoya NA-771 VSWR and return loss chart
Nagoya NA-771 VSWR and Return Loss chart.

Some people say that the NA-771 is no better than the "stock" antenna that comes with your radio. That is not my experience. Probably they have a negative opinion of the NA-771 because their antenna is defective. Unfortunately it seems that many NA-771's sold are not the original product, but imitations!

A "fake" NA-771 antenna could be as good as a genuine Nagoya NA-771, but you are more likely to get a defective product. In case of the NA-771, if your new NA-771 offers no improvement over the smaller stock "rubber duck" antenna, probably you where sold a defective antenna. If you were to disassemble the antenna you would probably find a bad solder joint in the matching circuit.

You can buy a NA-771 for about 4 USD delivered from Banggood here.

Tuesday, 4 July 2017

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.

Baofeng UV-5R, UV-5R+, UV-B5 antenna sizes
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.

Baofeng UV-5R antenna teardown inside.
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.

Baofeng UV-5R, UV-5R+, UV-B5 antenna matching.
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.

Thursday, 29 June 2017

Baofeng UV-5R, UV-5RA, UV-5RE, UV-5R+ Review

The Baofeng UV-5R is one of the most popular portable dual-band VHF-UHF two-way FM radios available. They are well suitable for use on the 2m and 70cm amateur radio bands. A decent set of features and specs and a very low price tag are the recipe for success. You can buy a Baofeng UV-5R for less than 30 USD delivered. Now that's value for money!

This is a quick review of the Baofeng UV-5R, based on my experience with a UV-5RA radio.

Baofeng UV-5R controls

At the heart of the UV-5R is the RDA1846, a highly integrated single-chip transceiver for Walkie Talkie applications. The chip integrates nearly all the functional blocks needed to build a Walkie Talkie. A powerful integrated DSP (digital signal processor) accomplishes both the demodulation and modulation of the FM signal. The RDA1846 specs guaranty operation from 400MHz to 500MHz and from 134MHz to 174MHz. The radio has excellent sensitivity and wide/narrow bandwidth selection, which is great for receiving weak signals. It's possible to receive several popular amateur radio satellites and the ISS with just the provided whip antenna. With a software hack it is even possible to receive part of the Air band.

The UV-5R can be programmed using the supplied Baofeng software or using the more advanced CHIRP program. A special USB to serial programming cable is needed. Fortunately these cables are very cheap. If you just want to program your frequencies or menu settings you can do so using the radio's keypad. But you can only program channel names via software. I strongly recommend using a Baofeng radio programming cable.

One of the most interesting things about the UV-5R is that its frequency range (VHF and UHF) can be expanded via a software hack. For example, you could modify the VHF band limits to go as low as 127Mhz (receive only!), well into the Air band and well below the factory default 136Mhz VHF limit.

One of the UV-5R high points is its LCD display. It uses a backlit matrix LCD which has excellent visibility and readability even at extreme angles.

Signal meter
Unfortunately the Baofeng UV-5R doesn't have a  signal strength meter. The LCD indicator just shows a signal icon when the radio receives a signal at a level above the squelch level, but it does not show signal strength variation. This is a shame since the lower priced UV-3R has a signal strength indicator.

Another complaint regarding the UV-5R is the squelch function. Despite having 10 squelch levels (0 - 9), the levels are not correctly defined and, as a result of this, squelch does not work well. For example, there is little (if any) difference in setting the squelch level at 1 or 3. However the squelch levels can be altered via a software hack.

The UV-5R is sold with a small "rubber duck" or whip type antenna. Depending on the exact UV-5R model, the antenna is either 12cm or a slightly longer (and better) 16cm. The radio uses a reverse SMA connection, so an adaptor will be needed to use regular SMA or BNC antennas. I prefer BNC connectors since they faster to use than SMA. This way I can quickly switch from a small  whip antenna to my Yagi antennas which use BNC connectors.

FM radio
The Baofeng UV-5R is capable of broadcast FM radio reception (65-108MHz) with station scan functionality. Unfortunately stations can't be stored on the UV-5R, but the radio is very sensitive.

Models and accessories
The Baofeng UV-5R is available in several "variation" models. There is the UV-5R, UV-5RA, UV-5RE, UV-5R+ and other less popular variations. I bought the UV-5RA, but all models are functionally the same. Most differences are cosmetic variations of case and colours. Regarding the case, it's quite robust, easily resisting small drops without major damage. However, some models like the Baofeng UV-5R+ are sold with a slightly bigger (16cm vs. 12cm) and better antenna. The radio is sold with a rechargeable battery, battery charger, earphone/mic, belt clip, wrist strap and whip antenna. Before buying one I recommend checking with the seller the exact model and accessories that come with it. I also recommend getting a Baofeng UV-5R programming cable.

Baofeng UV-5R radio + accessories + manual

Firmware upgrades
Unfortunately the Baofeng UV-5R is NOT firmware upgradable. This is because the firmware chip is a write once-device, it can't be re-flashed. The only reliable way to know what firmware your UV-5R has is to use the CHIRP program.

Main specs:
Frequency range: 136-174MHz (VHF), 400-520MHz (UHF).
5 watt maximum output power.
Wideband (25kHz) and Narrowband (12.5kHz).
Dual Band, Dual Display and Dual Standby.
Dual watch on same or different band.
CTCSS/DCS/DTMF tone options.
128 programmable memory channels.
Customizable channel names.

Note: older versions of the Baofeng UV-5R may have different specs.

Download the Baofeng UV-5R user manual from Baofeng.



Very low price.
Good feature set.
Excellent sensitivity.
Display with excellent visibility and readability.
Programmable via software.
Programmable via keypad.
Direct frequency entry.
2.5Khz frequency step.
FM radio.
Many accessories available.



No signal strength indicator.
Badly implemented squelch (but can be fixed with software hack).
Somewhat noisy earphone audio.

The Baofeng UV-5R is probably the best "bang for the buck" two-way radio on sale. It is not perfect, but considering the features and specs and the fact that "big brand" radios of similar specs cost much, much more, it's a bargain.

Buy the Baofeng UV-5R
Buy the Baofeng UV-5R from Banggood
Buy the Baofeng UV-5R from Dealextreme

If you are new to amateur radio, please be aware that to transmit in the amateur radio bands you must be a licensed amateur radio operator. To operate a radio on receive (listening) mode you do not need a license.

Saturday, 24 June 2017

Welcome to My Radio Hobby blog!

Well, finally got some free time to put together a blog about my long time favourite hobbies.

I’ve started My Radio Hobby as a way to document my personal projects, experiments, thoughts and research in a  (hopefully) informative way. In the near future you can probably expect my experimentations with software defined radio (SDR), amateur radio gear reviews, satellite amateur radio reception and DIY projects.

I hope this space will be useful to those who (like me) are passionate about electronics, satellite communications, amateur radio and telecoms in general.

Your comments are welcome!