DIY Cheapskate AX1 antenna

I’ve been looking with awe K4SWL’s videos how he uses AX1 with such a good results - and with an ease of just handheld or instant deployment of the radio station on table. That just looks so cool. Sometimes I would like to go for activation, pull out the whip and make few QSOs without need to set up a lot of wires.

Some time ago I purchased this kind of small manual tuner. It was broken when I received it and dunno if it is still correctly built. It transmits and I can get some SWR readings with VNA and I can hear the transmission on some local KiwiSDRs so all is not lost. However none on RBNs catch the CQ on any bands so I believe the performance is horrible. I didn’t expect that much from 1.5m whip, chinese tuner and max 5W of power but still - I believe something isn’t right on the tuner.

As you can see from the photo, I attached all together to make a really ugly KH1 clone from external parts. It even has CW key (the capacitive one).

I dissasembled the beautiful creation as a result of no luck and put things aside. Until I got an idea, what if I try make similar kind of antenna that AX1 is - all I need is a coil, right? I calculated the needed amount of windings for 20m on some web calculators (Coil-Shortened Vertical Antenna Calculator and Solenoid Inductance Calculator) and wound up coil and attached the 1.5m whip to it.

Probably you guessed right, I couldn’t get the antenna to be resonant on 20m band at all, not even close.

So next thought was: could this coil help my ATU10 to tune the antenna? I mean AX1 usually needs tuner too. So I attached the coil to ATU10 and to my IC-705 and tried to tune it. No luck. Closest I got was 1:7 on 80m band. Also I had some erratical issues on the tuning: sometimes I got good SWR but if the ATU10 started re-tuning, I lost the tune completely. I couldn’t get it back. Something was WAY off in the calculations. I decided that last resort I would just roughly double the coil amount and see what happens.

After some unlucky tuning, I got the antenna to tune on 40m at 1:1.5 by holding on the coax connector shield. The counterpoise was not enough, it seems or was it that I was the antenna? The crazy thing is that I made QSO from inside my house on 40m SSB / 10W to 150km station that was activating WWFF ref . I was blown away. And funny thing is that from that same setup I couldn’t make the QSO on CW, the IC-705 was really struggling with receiving - it was really bitcrushed kind of sound. I quickly grabbed all stuff and went outside, I made QSO with clear 599 - no problems.

So the antenna is kinda working but we are pretty pretty far away from that AX1 or even KH1 experience.

Any ideas what to try next?

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I would debug methodically with the vna. Attach antenna somewhere outside and start playing with the different parameters one by one and check the vna every time.

I would try to find the main source of problem and start with non destructive tests such as:

  • add 4 wires to make a counterpoise
  • add a piece of rigid wire on the whip to change it’s length
  • check your smith chart, make sure you have no short or something
  • remove coil and measure if the whip resonates well at its fundamental frequency

I always find antennas like this exciting…

In general, they can work in three different ways:

As an endfed with a coil to extend the radiator - a 0.05 lambda counterpoise helps (which can also be the shield of the coaxial cable). Then you have a base impedance that is usually brought up to 50 ohms via a 1:49 to 1:64 Unun.

As a random wire - i.e. a radiator of a specific length that is not in resonance anywhere… then you use a 1:9 Unun… and still need a tuner… a counterpoise often helps here too

Or as a ground plane (or other tuned vertical radiator), which then has radials that are also in resonance.

For all these antennas, the placement of the coil is an issue… I would definitely try using an Unun for your antenna…
I don’t have a separate wire for the counterweight on any of my antennas. I always have 0.05 lambda from the “longest” band (normally 3m because of the 60m band) of the coaxial cable and use the shield. The coaxial cable is then wound directly onto a 140-43 Amidon toroidal core… and then has about 30cm to the BNC connector.

I have a 5.8m wire with 1:9 Unun on a 6m Decathlon mast. It can be tuned with the ATU of the KX2 with an SWR of better than 1.3 on all bands 10 - 30m.

BTW… it was my standard antenna at my trip to Cyprus in December…

Good luck - 73 Armin

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It’s not a good idea to just use your hand as a counterweight. The wire as a radial works well if you

  • If possible, stretch the wire at least half a meter above the ground or preferably higher

  • brings the length of the radial to about a quarter of the wavelength and then changes it by a few centimeters to get a low SWR.

Good luck 73 Chris

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Hello,

There have been many homebrew telescopic antennas succesfully built in the past.

They have been put to resonance with the appropiate inductance in the base. An antenna analyzer is very useful to check the project and modify the coil if necessary.

Read the info of these good ideas:

Good luck, 73 Ignacio
A quick

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Yes, and as we have seen the AX1 really works. Also my sketchy SSB QSO from inside house on 40m with 10W over 100km was telling the same thing. I’m not trying to make EFHW or tuned 1/4 wave replacement at all, I know the limitiations for such tiny whip. For me this is pure radio fun / play…

I dunno why the search didn’t return the “AX-1 Clone” thread but that is pure gold. So many good examples of working antennas built similarly like I have done. However it confuses me a bit since I’m in the same ballpark as some of the antennas - how did they get their antennas in tune. Also the variance of turns is quite large. One coil had 80-90 turns and some have 24 on the antenna build on that thread. Go figure…

I need to pursue this and find out how to make the antenna tunable with ATU10 for one or two bands.

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The ax1 as a compromise antenna works very well
John ve3ips

Makes a nice back up antenna as well up on the hilltop

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