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

[Barry N1EU]

If anyone else out there has an MFJ-1820T and also an antenna analyzer, I
wonder if you could please do me a favor.  Please just connect the whip
directly to the analyzer and tell me what the SWR looks like across the 20M
and the 17M bands.

I swept my MFJ-1820T with my Rig Expert AA-30 and my MFJ-1820T is resonant
on 17M, not 20M.  I'm wondering if I have a mislabeled MFJ-1817T.

Thanks & 73,
Barry N1EU

On Thu, Mar 24, 2016 at 2:12 AM, Wayne Burdick <n6kr at elecraft.com> wrote:

> 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
>
>
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