[Elecraft] Strong recommendation: MFJ 18xx-series single-band whips for KX3, etc.

[Wayne Burdick]

Hi all,

I've been using an MFJ-1820T telescoping 20-meter whip for a few months. Considering its length (48"), results have been excellent. I typically use it with the KX3 on a picnic table at 15 W (with an external battery), or hand-held at 3 to 5 W (internal battery). 

During the ARRL DX contest I worked many countries in CW and RTTY modes, and have also had a number of longer QSOs on 20-meter SSB. Of course at these power levels, with an electrically short whip, good band conditions can't hurt. 

I prefer a 25' or so wire-in-a-tree antenna when there's time. But when I need a quick deployment antenna that weighs very little, I pull out the 1820T. Note that you *must* use at least one counterpose wire. More than one helps, but all of the QSOs I described were made with a single 13'-long wire laid out on the ground. With no ground wire, you'll be down some 15 to 20 dB in transmit mode.

Since the 20-meter results were so good, I also bought the whips for 40, 17, 15, and 10 meters. 40 meters is a rough ride at 48", but I was still able to check into daytime SSB nets all over the west coast running 10 W. On the higher bands, results improve as you go higher in frequency. I worked a few JAs on 15 meter SSB running just 1 watt. 

A traditional problem with such antennas is that the the SWR can sometimes be unexpectedly high, requiring that you micro-adjust the telescoping length and/or adjust the length of the counterpoise wire. This is completely unnecessary if you have an auto-tuner available. In particular, the KX3's ATU can quickly match any of these whips over their full target band. In a pinch the ATU can also match a given whip on adjacent bands. In the DX contest mentioned I tuned up the 20-meter whip on 17 and 15 meters as well, and made a few Q's there, despite the losses due to off-resonance operation.

These whips can handle a surprising amount of power. They're rated to 25 W, but I ran 50 W through the 20-meter version for several minutes without damaging it. Some other compact whips I've tried overheated quickly even at 10 W, including some of the Maldol models. When this happens, the SWR goes up and stays up until the coil cools down. 

Caveat: Always use a full-size antenna when possible. But if you've just crested a new hill and only have a couple of minutes to see if the RF really is greener on the other side, this is an excellent choice.

73,
Wayne
N6KR