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.