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The FXTenna Portable HF Antenna

from Dave Land, KD5FX on August 24, 2017
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"Editor's Note: Due to the popularity of some of eHam's older articles, many of which you may not have read, the team has decided to rerun some of the best articles that we have received since eHam's inception. These articles will be reprinted to add to the quality of eHam's content and in a show of appreciation to the authors of these articles." This article was originally published on: 05/26/2011

The FXTenna (TM) Portable Antenna
by Dave Land KD5FX

20 through 6 meters, QRP to full legal power, lightweight, easy to carry

I've been looking for an inexpensive portable HF antenna for my new (to me) ICOM IC-706 radio. I looked at several models but most were rather expensive. I found several designs on the web to build your own but most involved coils and covered the lower bands. I was more interested in 20 meters and above since the HF bands are coming back now that the solar cycle has finally rolled back around (this is my 3rd solar cycle!).

I did find one design that used the 10 ft MFJ-1954 telescoping antenna so when I went to look that up on the MFJ website I noticed they also have a 12 ft model for just a little more! Hmmm, what bands could I cover with a 12 ft antenna? So, I did the math and discovered that it would cover 15 through 10 meters! Well, it could certainly cover 6 and 2 meters too! Just shorten it up! But I'd like to cover 20 through 10, what can I do? After some more math I realized that a couple of 3 ft 3/8" aluminum rods would make it cover down to 20 meters. I could use one 3 ft rod to cover 17 meters and two for 20 meters.

I was able to find the aluminum rods for a little more than $5 each at Lowe's and already had a 3/8" 24 thread die so I could thread the rods to work with my 3/8-24 mobile antenna mount. I got that mount at a local truck stop, in their CB radio supply area. Lots of various 3/8-24 mounts there, I chose one that will work in the yard or with longer bolts I can mount it on top of my SUV and go mobile HF with it too but not with this antenna! MFJ says not to use this telescopic antenna while moving, it will break! I plan to use a 'hamstick' type HF antenna on the truck.

I also needed some 3/8-24 couplers to hold the two 3 ft rods together and mount the 12 ft whip on top. I was able to find those at the CB shop and later I discovered that you can use 1/8" NPT pipe couplers, the thread is a little different but will work according to what I've read online. I used the Stainless Steel (SS) ones I found at the CB shop, they were cheap.

This antenna covers the whole band with a low SWR and best of all it is very efficient since there are no coils involved! The optimum length for your ground radials are shown in the table below, it will work OK with something shorter, I'm using eight 114" radials.

Here's an equipment list:

EXTRA-LONG TELESCOPIC ANTENNA, 12 FT (758-1196) MFJ-1956 Price: $34.953/8-24 mirror mount for CB antennas from the local truck stop (about $10)
3/8-24 SS couplers from the local truck stop (about $4 each, you need 2)
3 ft 3/8" aluminum rod from Lowe's (about $5 each, you need 2)
3 ft 1/4" or 3/8" steel rod from Lowe's for a ground stake (about $5) Cut it down to 24", 3 ft is just too long!
3/8"-24 thread die to cut the threads on each end of the aluminum rods
4 to 8 ground radial wires, I used some 114" wires left over from another antenna, longer is better if you have the wire, see the table below
3 - 8 to 10 ft long 1/8" nylon ropes or heavy duty fishing line to use for guys, I attached them with a small tie wrap
1 large nail to use for the end of each guy rope and for each radial wire, I use 16d size, they are about 4" long

Here's a table of the dimensions you need for each band.
Note that for 15 to 6 meters you use only the 12 ft telescoping antenna from MFJ and you shorted it the 'amount to shorten'
For 17 meters you use one 3 ft 3/8" rod plus the MFJ antenna shortened by 1.53 ft
For 20 meters you use two 3 ft 3/8" rods plus the MFJ antenna shortened by 0.85 ft

Band Freq Length (Ft) Extension to 12 ft Amount to shorten (ft) Radial length req'd
6 Mtrs 50.1 4.87 - 7.13 4.79
10 Mtrs 28.3 8.62 - 3.38 8.48
12 Mtrs 24.93 9.79 - 2.21 9.63
15 Mtrs 21.2 11.51 - 0.49 11.32
17 Mtrs 18.11 13.47 3 ft 1.53 13.25
20 Mtrs 14.225 17.15 6 ft 0.85 16.87

For 17 and 20 meters you'll need to guy the antenna with some small nylon rope or fishing wire. I use large nails to stake the end of the guy ropes and ground radials in the grass/dirt. Might need to do this even for 15 meters and above if it's windy.

Here's some pictures:

First off, here's the MFJ 12 ft telescoping antenna collapsed all the way at the top of this picture and one of the 3 ft 3/8" rods below it
Next is the 3/8-24 mirror mount bolted to a 1/4" steel rod (still with some dirt on it)
The grey wire is the 114" radial wires, I use 8, longer is better, see the table below
The white small nylon rope is used to guy the antenna when it's windy, tie it on with a wire tie
Last is the 16d nails I use to secure the ends of the radial wires and the guy ropes.

Now here's the antenna setup for 15 meters, it was rather windy, you can see it leaning a bit.

And here's a close up of the CB antenna mirror mount. It's clamped to a 24" long 1/4" rod pushed down in the dirt.
Note how the radial wires are connected to the mount.

Below is the antenna setup for 17 meters, one 3 ft rod installed and the 3 nylon guy ropes

Member Comments:
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The FXTenna Portable HF Antenna  
by W4FJT on August 24, 2017 Mail this to a friend!
The only thing I would add is MFJ sells the 17 foot whip that will do all this without the extra 3/8 rods. Perhaps this was not an option in 2011. I have one and use it all the time on 20 meters.
The FXTenna Portable HF Antenna  
by ONAIR on August 26, 2017 Mail this to a friend!
I use a few 5 foot PVC poles, joiners, and wire! On top I have an old telescoping antenna from a discarded transistor radio. Total cost was under $10 bucks! ;)
The FXTenna Portable HF Antenna  
by K1YPB on August 31, 2017 Mail this to a friend!
I use a MFJ-1979 17 footer mounted with an Alpha jaw mount on a telescopic Wooster Sherlock painters pole (from Home Depot) temporarily affixed to my rear deck (we are HOA restricted) with one elevated quarter wave radial. Low SWR across whole band and very efficient. Works great!! Massachusetts to France with 5 watts JT65. Whole antenna system around $100 with new stuff. Quickly change band by lengthening or shortening antenna and radial to quarter wave of frequency desired. Touch up tune with MFJ-259B and tweaking length of radial wire by a few inches. QSY and set up relatively quick. Works great, cost effective, efficient, and stealth. Can't get any better for an HOA environment. Anyone looking for a solution this is a truly viable option. The MFJ-1979 is well made, durable and one of the best products the MFJ produces.
The FXTenna Portable HF Antenna  
by KF9F on September 18, 2017 Mail this to a friend!
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