Building a Portable FT-8 Vertical Antenna

Taking much inspiration from recent posts on the US Islands group.io reflector and his previous articles I’m endovoring to emulate John KL7JR’s efforts to use Wilson FTG-2 CB antenna tuned to useful ham band frequencies.

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FTG-2 with the 20m whip

A quick ordering spree at Amazon and a dash to the local Ace Hardware got things going.

What I bought were:

From Amazon:

From the Hardware Store:

  • A 10×32 knurled cap screw to replace the set screw in the FGT-2 antenna ($0.55 plus tax)
  • Several lengths (nominal 72 inch long) 12-gauge “ceiling tile” wire, the galvanized wire used by suspended ceiling installers to hang ceiling grids ($0.99 each plus tax)

For testing I used my SARK-110 analyzer and I used a common fence-pliers to cut & form the wire.

I unscrewed the FGT-2’s setscrew and removed its very short whip.  The 12-gauge wire is slightly undersized compared to the original 1/8 inch diameter whip.  It is also galvanized compared to the original’s stainless steel, but the ceiling tile wire is serviceable except perhaps in a salt water environment.  Being a bit smaller makes repeated removals for trimming easy as well.

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Clamp-on Antenna mount

Then I installed the Knurled Cap Screw so I could make my tests.  I’m going to figure a way to make the screw captive later.

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Thumbscrew replacement for the setscrew

Starting with KL7JR’s notes from his articles I first made an “eye” on the end of each replacement whip.  Safety first!  There is no point (pun intended) to have an unprotected end, so either round it by making an eye or put a cap on it.

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Safety “Eye” tip

I found my FGT-2 needed very different (shorter) whip lengths to achieve optimal SWR compared to John KL7JR’s notes.  Whether this is a difference in my individual FGT-2 antenna compared to the ones he used, a difference in test gear, or an effect of my testing the antenna inside where perhaps other metal influenced results, I am uncertain.  Or perhaps it is from the eye-tip acting different than a plain end?

Starting longer than KL7JR’s suggestions of 40.75 inches for 20m and 28.5 inches for 17m I found I have a lot of cutting to bring the SWR nadir to the frequencies I was aiming for.  Whether you start from his measurements or from mine, start longer and plan on cutting the wire down until you achieve the lowest SWR.

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Drops from trimming to resonance

At 14.074 MHz for 20m FT-8 and 18.100 MHz for 17m FT-8 I ended up with:

  • 20m whip – 32.25 inches
  • 17m whip – 10.875 inches

Achieved SWR without radials was:

  • 20m – 1:2.05
  • 17m – 1:5.24
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20m achieved a 1:2.05 SWR

I’m not at all happy with the 17m results, but that was the best match I could see.  It actually threw a second nadir almost at the 12m frequency of 24.915 MHz.

The 20m match was as good I could see and will be very workable.  I’m hoping to improve it with radials, though the short radials KL7JR suggested as a “universal radial” actually increased the SWR.  I saw where in some of his operations he actually used a 24 inch pizza pan strapped to several larger than 24 inch diameter metal band on a barrel he set up on.  That is a lot more metal in several planes than my tests with two radials at 180-degrees from each other.

I’m thinking of trying several 20 foot wire radials on 20m to see if I can drop the SWR.

i did confirm John KL7JR’s observations that SWR is better if you do not connect the loading coil built into the antenna.  I taped it for now but will zip tie it up after field testing.

My purpose with the antenna is as I build the Midnight Design Solution 20m Phaser FT-8 transceiver I wanted an antenna to match that also could go portable.  I’m thinking if this all works well I would have a small portable FT-8 setup that was a very modest investment.  Perhaps I would assemble all the parts as gifts to hams that wanted to get started.

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Antenna with mounts and 20/17m whips

With the Phaser kit, enclosure kit, and all the parts above except the superfluous 90-degree 3/8 x 24 to UHF-connector mount out of pocket is quite low to get on the air.  I’ve $54.30 in the antenna and the Phaser with enclosure ran $94.00 delivered.  I do need an audio cable and a power cable, but I’m thinking I can keep the costs under $160, though that excludes a power supply or computer.

Some links to John KL7JR’s work are:

http://www.hamuniverse.com/kl7jrcbverticals.html

http://www.hamuniverse.com/kl7jr10meterstealth.html

73

Steve
K9ZW

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