Wednesday, August 15, 2012

The $3.79 antenna

The $3.79 antenna
Among users of the Baofeng dual band UV-5R HT a popular topic of discussion is what antenna to buy for improved performance. The general consensus sees to be that the stock Baofeng antenna is not much good. But no-one wants to spend $30 on a $40 radio to buy an antenna made by Diamond or Comet. The trouble is that half the antennas sold on eBay seem to be fakes that are about as much use as a piece of wet string.

A popular choice recently is known as the "$3.79 antenna." This antenna - which also goes by the name "$3.42 antenna" after a recent price cut by one eBay vendor, has an SMA-F connector and a very flexible 6.5" whip. It's very similar to the Nagoya NA-666 but with a different base. You can find sellers by searching eBay for "female universal antenna for Kenwood".

Both the Baofeng stock antenna and the $3.79 jobbie appear to be made by the same manufacturer. Printed round the SMA connector of the Baofeng antenna is the words "FM/136-174/400-480MHz". The $3.79 antenna has the wording "FM/136-174/400-470MHz" in identical print but on a red not a black background.
UV-5R stock antenna

Despite the aspersions cast on the effectiveness of the UV-5R stock antenna, I found that it isn't half bad. In fact, it is one of the most accurately tuned rubber duck antennas I have come across and performs remarkably well for a 12cm (4.5in.) long antenna. As the SWR plot shows, the VHF resonant point is exactly at 145MHz. I am unable to plot SWR at UHF but I can measure it at a fixed frequency and it was 2:1 at both 145MHz and 433MHz.

$3.79 antenna
The $3.79 antenna appeared to be tuned to 154MHz. The tuning is not as sharp as the Baofeng antenna and the SWR at 145MHz was just over 3:1. I measured a similar SWR at 433MHz. The actual SWR of handheld antennas will vary depending on whether the radio is standing on a desk, being held in the hand or worn on your belt so an SWR of 3:1 is nothing to be alarmed about. Even the best HT antenna will exhibit a poor match in some situations.

Measuring SWR can tell you whether an antenna is working as well as it should but it is no guide to on-air performance. After all, a dummy load will have a perfect 1:1 SWR and yet radiate nothing.

I measured the field strength of the signal radiated by the UV-5R at a distance of 1m using both antennas. I also tried a known genuine Nagoya NA-701 which is about the same length as the $3.79 antenna. There was nothing to choose between any of the three antennas at UHF. On 2m the $3.79 antenna was possibly marginally worse than the Baofeng UV-5R standard antenna. The Nagoya NA-701 was 3dB better, equivalent to doubling the transmitter power.

My conclusion after performing these tests is that buyers of the UV-5R (and the UV-3R which comes with an identical stock antenna) should save their money and use the antenna that came with the radio. To try to improve on this involves dabbling in the shark-infested waters of eBay and risking ending up with a worthless fake antenna that will need to be larger to give any improvement in performance. The $3.79 antenna is easily worth its price but it is 3 inches longer than the stock antenna and offers no significant improvement.


Rick said...

Is the quality of the match alone enough to fully describe the performance of the antenna? After all,
a dummy load is a pretty good match, but usually
not a good radiator.

Unknown said...

I thought I said that. A better way to put it perhaps is that a high swr shows power that is wasted and cannot be radiated by the antenna.

Rod Mollise said...

I was skeptical myself, but the vaunted $3.79 antenna has undeniably improved the performance of my UV5R. Formerly I had to stand a certain way on my front porch and hold my mouth just right to hit one of the repeaters here. Not any more. The thing works. That said, there is probably considerable seller to seller and unit to unit quality variation. But the one I have does, yes, work much better than the stock antenna. de AC4WY