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The End Fed Halfwave antenna will give you the best performance for your 2m handheld, it doesnt need a large counterpoise and the current maxima will be in the clear above your head. The down side is its 1m long and needs an efficient matching network to transform down to 50 ohms. There are a few halfwave antennas sold commercially such as the MFJ-1714, Smiley Antennas, Nagoya NA-144H and the dual band Diamond RH-770. The RH-770 type has been widely copied and is available cheaply on ebay etc.
I picked up a Nagoya NA-144H with BNC from ebay cheaply, it worked but when I checked the match with my AA230 antenna analyser it didnt show anything like a 50 ohm match on 2m. I wondered if it was in fact faulty as showed no sharp reasonace and a DC short between the BNC centre pin and the whip. Not impressed so I decided to break it open and have a look!
Here it is, an L network with a series Inductor and what appears to be a shunt capacitor formed by the brass collar inside the BNC body. The inductor is thin wire so the Q will be poor and mechannically unstable, probably why I was seeing no real VSWR dip. But the components are of good quality, as is the telescopic whip so it has potential.
Remembering there was a QEX article on Halfwave antennas for handhelds, I searched my archive CD and turned up March/April 2005 High-Efficiency Antennas for Hand-Held Radios by Richard K0DK. In this excellent article Richard built handheld simulators to replicate the handheld chassis and measured the feed impedance of the mounted halfwave end fed with a network analyser. On 2m he measured 177–j468 Ohm
Here are the two solutions. It appears that Nagoya were probably trying to use the series L of roughly 286nH and the 2pF shunt.
Richard K0DK used the series C solution, with the 4.2pF capacitor made from wire in a PTFE sleeve. Then he used a high Q shunt inductor round a Delrin former.
I decided to use a series C with a 4.3pF low esr RF chip capacitor (ATC100B series) , then form a shunt L of about 197nH with reasonable Q. I found a cheap offcut of PTFE tube on ebay 10mm OD and 6mm ID which was perfect for the purpose. I filed down one end to fit inside the BNC body then assembled the whole thing with Superglue.
Finally I wound the shunt inductor, this is 6 turns of 1.2mm enameled copper round the 10mm PTFE former.
I then used my AA230 antenna analyser while tweaking the inductor, outdoors away from nearby objects. I easily got a nice resonace at 145.5Mhz with a pure 55 ohms. VSWR less than 1.2 at resonance, really excellent match compared to many handheld antennas. Both the chip capacitor and the inductor with have a reasonable Q giving us a low loss matching network.
I then sealed in thick wall adhesive lined heatshrink to protect it and hold it together, this dropped the resonace down to 145.0Mhz which is OK.
Attached to my Icom V-86. There is a second collar of heatshrink to keep water from settling round the BNC socket. It lives on the outside of my rucksack when doing SOTA so often gets wet!
I have a feeling that the OEM manufacturer of the MFJ-1714 is in fact Nagoya. The whip looks identical with 3 destinctive bands at the bottom of the whip. The base is different, it would be interesting to see the feed arrangement inside the MFJ-1714 as a comparison.
It has proved to be a good performer and should give good service, until the day I snap the telescopic whip!
Gavin Taylor, GM0GAV
08/11/2021
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