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

Sat Apr 2 22:52:47 EDT 2016

You may be right Barry ... it may be mislabeled ... there can't be much
chance of a real 20M whip resonating on 17 ... .... FWIW I've had a full set
of the MFJ whips for several years and did SWR testing on each one when I
first got them .... but I did not connect them directly to my Rig Expert
analyzer ... I had built a stand alone aluminum base with a BNC connector
for the whips and wingnuts for attaching counterpoise wires so I did my
testing in that configuration

My 20 meter whip is resonant at 14.400 .... and runs from 1.2:1 at the top
of the band to 2.2:1 at 14.025

My 17 meter whip is even better ... resonant at 17.900 ... but tests at
1.2:1 all through the band

All of my high band whips are usable (10, 12, 15, 17, and 20) .... but my
30, 40 and 80 whips have never worked well ... the 80 resonates at 3.350
... and SWR is at infinity throughout the band .... my 40 resonates at 6.800
... and my 30 resonates at 9.700  ..... all my testing was done with the
whips fully extended .... I figure if I shorten them I will essentially be
turning them into non-radiating dummy loads..

I personally do not like to attach the whips directly to my KX3  ... it
feels to me that they're putting too much torque on the BNC connector and
the antenna seems like it weighs almost as much as the radio .... which is
why I made the aluminum base ... 

But I later bought a CrankIR vertical which has become my "Go To" portable
antenna ... so the MFJ whips have been retired to a box in the shack...

Don, N5LZ

-----Original Message-----
From: Elecraft [mailto:elecraft-bounces at mailman.qth.net] On Behalf Of Barry
N1EU
Sent: Saturday, April 02, 2016 6:15 PM
To: Elecraft Reflector; KX3 at yahoogroups.com
Subject: Re: [Elecraft] Strong recommendation: MFJ 18xx-series single-band
whips for KX3, etc.

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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