Short loaded vertical antenna for restricted summits

[HB9EAJ]

Hi Ignacio,

Thank you for showing us your solution, very interesting!

I experimented as well with such kind of antennas, also mainly for space restricted summits.

I wanted an antenna that is usable between 40m and 6m, without the need of a tuner. It should be easily and fast deployable, either by a composed earth stake, some stones or supported by the backpack.

Like Ed @DD5LP, I experimented with the well known Kommunica/Gabil/Sharman branded antenna, or in my case, with a clone from WIMO.

The whole antenna system, including a ground spike, 3m of RG-174, 8 radials and wire winder weights in total 740g and needs little space in the backpack.

I created a short video that may give you some inspiration for your own solution:

Vertical Antenna for Tight Spaces

The video description contains further information about all used parts.

73 Stephan

[DD5LP]

Hi Stephan,
Yes, that is one of the copies of the Komunica Power HF-PRO2-PLUS-T design (I talked with the Komunica CEO and she said they had the antenna built to their design in Taiwan to avoid IP theft which often happens using manufacturers in mainland China). That was the case for the last 4 1/2 years but 6 months ago, these copies started appearing on the market.
I believe the “Gabil” branded version was available at Friedrichshafen for €99 instead of the €150 price from Komunica Power.
The new MFJ 1898 appears also to be a copy, except it has a 3/8"-24 (aka CB) mount instead of a PL-259 - perhaps they think that makes it OK to rip-off someone else’s design if you change it a little?

What's This Antenna?

As I do not seem to have a lot of luck with stakes and hard stony ground, I use a modified photo tripod rather than a stake with my antenna and 8 x 3 metre-long radial wires and this antenna performs better than it should! Three weeks ago while on Cyprus I worked into Australia three times with 20w of SSB on 20 metres (and those VK stations called me).
When in a good (quiet) portable location North American contacts are also easy to get - in both cases, you, of course, have to be on the air at the right time for the propagation and the chaser needs a good antenna system.

73 Ed.

[DL3TU]

Hello Ignacio,

thanks for this nice and interesting report! And congrats on the good results you achieved using it in the field.
It is interesting that you went for the solution with a short vertical wire instead of a telescopic whip. My thoughts went into the same direction when I was searching for a similar antenna, not too long ago. The biggest difference is maybe that I wanted to use it with the MTR-3B and thus only needed 40, 30 and 20m. The protoype is still somewhat provisional but it worked (and survived!) on two activations in harsh alpine environment.

Keep up the great work and cu soon!
73, Roman

Portable 3-band vertical for 40/30/20 metres

[HB9EAJ]

Thanks for the info Ed, I didn’t know the whole story!

And like you, when I first saw this MFJ 1898 in a video, I had the same thought.

Now with the improved conditions on the higher bands, such slightly shortened antennas are fun for DX, especially on bands that your other antennas can’t cope well with (12m in my case).

73 Stephan

[EA2BD]

@K6HPX

At 8 MHZ and higher frequencies, trees, especially those with a lot of vertical structure, interact greatly with vertical antennas, creating deep nulls in the radiation pattern.

Thanks Ken, I found the referenced article; interesting paper. I’ll take into account and avoid dense trees areas whenever possible.

@VK3SQ

a popular portable vertical antenna in VK is known as the squid pole

Thanks Geoff for your input: interesting antenna despite it is designed for 80m and up, and I don’t intend to operate that low. The squid pole requires a large pole for such a low band. Anyway, I rode it with interest.

@DD5LP

As you say all of these options need a good set of radials

Thanks Ed for your comments on whip antennas: sure that a proper extensive ground system make the work best.

@DL6GCA

to keep your luggage smaller and lighter on more strenuous tours…

Thanks Armin, yes, that’s the idea, to carry this one for some long tours, for tiny summits or for rocky summits not safe to deploy a proper large wire.

@MW0KXN

maybe a ground tunner for 7MHz

Thanks Kevin. Indeed a GTU would help dealing with fine tuning and to get rid of coil adjustments.

Heinz, HB9BCB, our prolific antennas guru, proposed to prepare a set of base fixed coil per band and use a tuner at the feed point exactly for such purpose. So far I will try using the design as is, because I’m missing a small tuner and I prefer to try tuning on the coil if I can.

@MM0FMF

Repositioning where I placed my 90kg “fatty-salty-water” body could often effect a big improvement.

Hi Andy, here I’m missing some kilo as I’m a bit fit, so my body structure won’t improve the impedance/SWR that much, I’m afraid. I’m glad to share the thoughts and experiences; I’m learning a lot by reading other’s experiments here in the Reflector.

@HB9EAJ

I created a short video that may give you some inspiration for your own solution

Hi Stefan, thanks for your interesting video; your Wimo telescopic looks good with that large whip. It’s good to have such simple antennas available. As Ed suggested, I find difficulties using the stakes on rocky soil. We have to manage for putting antennas up on a variety of grounds.

@DL3TU

It is interesting that you went for the solution with a short vertical wire instead of a telescopic whip. My thoughts went into the same direction

Hallo Roman, thanks for your interesting version. I wanted also to do mine center loaded but you see I finally refused for ease of tuning control. Your input is much appreciated.

I have started preparing some modification and I’ll share them soom here.
73 Ignacio

[HB9EAJ]

Hi Ignacio,

@EA2BD

I find difficulties using the stakes on rocky soil.

I’m a big fan of ground spikes, because they work 90% of the times as intended for me, making the setup quick and don’t need much space in the backpack (with a wine cork as protection). Not exactly the same, but in a similar category goes the Decathlon mast holder.

For the remaining 10%, e.g. with rocky or sandy soil, I always found a solution, for example as shown in the video with the support of the backpack, or simply wedging the spike in a pile of stones.

73 Stephan

[DD5LP]

Hi Ignacio,
I’d want to do more than just click the like button on your latest post (which I have done) but also go on to say that your post is a perfect example of how people’s suggestions are clearly being considered (applied if helpful) and then added into the updated design. Your final design will be a “community effort” and I think that is wonderful and an example of how well amateurs from different technical backgrounds from different countries can work together to contribute to the final solution.

Well done Ignacio
Ed.

[EA2BD]

Part 2: short vertical antenna improvements

I had some free time this week to prepare the two modifications listed at the end of my first post, as I describe now. I’m excited to say the antenna is doing better with these two addition.

1) Common Mode choke

I found an old thread were HB9BCB described how to prepare a useful low power choke with a pair of stacked FT82-43. The coil is made with 8 turns of twisted pair of magnet wires.

The VNA plots of Heinz were good. This is the approximate Zcm (frequency dependent) of such choke:

Heinz also suggested that 11 turns would even provide higher blocking attenuation, but I decided to try the easy 8 turns version.

I built that CMC and inserted it into my connector box.

We will check later if this improves my antenna.

2) Capacity hat

The first activation with this antenna (see top of this thread) showed that the lowest resonant frequency achieved with the maximum loading of the coil (28 turns, 26 uHenry) was around 8 MHz. I couldn’t tune down to 40 meter band.

I reasoned I could add another extra coil in series for this band, but instead, I decided to build and test a capacity hat. This one should be a lightweight and easily dismantable version for portable.

I checked my junkbox and found some useful parts I could use:

• 2 mm diameter brass tube. I cut 4 spreaders of 20 cm long.

• Yellow thin wire. I soldered the ends of the spreaders to form an outer square.

• Plywood and a dowel for the center support.

• Copper adhesive foil, to warrantee the electrical contact between all parts in the center.

• Elastic cord, 2 mm diameter and cord lock stoppers. That holds the plywood as a clamp for the brass tubes.

• Alligator clip to connect it to the antenna radiator.

Images are self explanatory.

As you can see, the cardboard serves as a guide for the brass spreaders to keep them straight.

I use plywood on top and bottom held by the elastic cord and the locker.

The brass tubes can be removed. This is a foldable capacity hat that is assembled in a minute by hand!

Total weight is 38 gram. Capacity hat geometry is square 30 x 30 centimeter; small.

Activation test.

I agree with Jorge, EA2LU to do a joint activation on October 12th 2023 on EA2/NV-053.

This is not a restricted summit but I just wanted to check if the two changes improved the antenna.

I installed the antenna with ease and extended the radial, keeping it quite straight and parallel to the soil. There was a light breeze and this kept the radiator separated a few centimeters from the pole.

I was afraid the wind would cause some troubles now that I had the Hat on top, but my 4 meter pole was straight and stable. Seems the reduced diameters and light wire gauge wasn’t obstructing the air flow that much.

I checked first with the antenna analizer to see the resonant frequency: (round values)

I was very happy to see that the capacitive hat had reduced resonant frequency about 2,6 MHz. Now I could use the antenna for 7 MHz!

In the other hand, when the antenna wasn’t connected with the hat I could just go up to 20 MHz. Therefore I should add a link on the radiator to shorten it and be able to operate on 15m – 10m.

With the capacity hat on, I annotated the turns required in the coil for some bands:

• 7 MHz: 16 turns for CW / 15 turns for SSB (12,1 / 11,1 uHenry)
• 10 MHz: 7 turns (3,7 uHenry)
• 14 MHz: 2 turns (0,5 uHenry)

What about the Choke? The measurements in the antenna analyzer were stable compared to the previous test without the CMC. Impedance was around Z=50 + j0 in all tuned bands and the readout values were not fluctuating anymore.

Adding the choke was essential for a stable operation with this design, preventing from RF back in the coax.

The activation

After the measurements it was the time for the SOTA activation. I decided to start in the worst scenario, that is 7 MHz SSB. I set power to 7 watts, selfspotted and started CQing.

I was very happy to log 50 QSO, all EA / EA8, in 22 minutes. Reports were okay and I felt like the antenna was performing well, no spaces nor repeats after my reports and over. Seems the capacity hat did the deal, very good for a 3 meter radiator in this band!

I ran a bit on 7 MHz CW and there I logged a few more, now including HB9.

After, I tried 10 MHz and got 11 EU QSO, including 4 S2S summits with @EB2GKK, @EA4DOS & @EA4DON, @IW2OGY and @EA3M.

Jorge had already ran on 14 MHz, it was a bit late and I just added a quick QSO in 14 MHz to work @HB9BHU S2S before calling it a day.

All in all 69 QSO this time. I felt very enthusiastic with the positive results.

Future development

The antenna is quite okay now, but I must add a link in the radiator, at about 2 meters off the start so that I can cut and run the 15m – 10m bands.

I have the antenna ready for any true restricted summit activation.

73 Ignacio

P.s: whenever possble I’ll try recording a video for the setup and tune process. We’ll see…

[EA3BV]

Your brain doesn’t stop, Ignacio!

I enjoyed watching your post, great proyect and well done. Congrats!

[EA2BD]

@EA3BV

Your brain doesn’t stop, Ignacio!

Hi dear Jon,
you know, there are never enough antennas in the backpack!

Glad you find it interesting. Un abrazo

73 Ignacio

[KI6BTY]

Nice setup and great video. Have you experimented with aluminum window screens as counterpoises? I’ve seen this on the POTA side of things lately. It’s probably too big for hiking in, but maybe cut down?

[EA3M]

Very interesting, it was a pleasure to help you testing. Congratulations on your new antena and thanks for this (another one, actually) great post!

[OE5EEP]

Hi Ignacio,

I checked first with the antenna analizer to see the resonant frequency: (round values)

I was very happy to see that the capacitive hat had reduced resonant frequency about 2,6 MHz. Now I could use the antenna for 7 MHz!

I suggest to increase the capacitance hat just a little more and get also active on 60m! You are just 300 kHz off. Maybe you can fit another turn on your coil former. That would also do.

Could you please report what the usuable bandwith (e.g. SWR <1:2.0) of your vertical is.

73 Heinz

[EC7ZT]

Qué buena pinta tiene Ignacio! muy buen trabajo!
72. Manu.

[EA2BD]

@OE5EEP

Could you please report what the usuable bandwith (e.g. SWR <1:2.0) of your vertical is.

Hi dear Heinz,
I will do these measurements whenever I can. Some rain forecasted on the next days, I wait for a right chance.

73 Ignacio

[EA2BD]

Part 3: Antenna bandwidth measurements

According to OE5EEP Heinz’s request for bandwith data of this antenna, I went to my test bench on a park in my town, installed the antenna and measured the SWR levels band per band using my Rigexpert AA-54 analyzer.

Here you have the results:

Bandwidth is very wide for 10 MHz and up, covering the whole band.
Only in 40 m, as expected due to the inductance required, the full band is not covered with an SWR < 1,5, but the achieved bandwidth is not that bad. Just a slight fine tuning of the radial length could be necessary to improve SWR when moving from the lower to the higher extreme frequency.

See pictures of the SWR sweep while testing:

I still need to add a link on the radiator to cut out some wire in order to make the antenna work in 15 m band.

I took the chance of the testing to record a video. In the next days I will edit the footage and put a link here.

73 Ignacio

[W4GO]

@EA2BD

I tried to tune the antenna on 21 MHz without success, SWR was 5,5 at best. Is perhaps the wire too long for the band? That is pending to check.

I have dealt with this problem for mobile HF operation. I use an antenna that is 2.16 m (= 7 foot 1 inch) tall on the roof of the vehicle. The loading coil I use is manually tuned with a jumper, much like yours. I’ve made over 12000 QSOs with this antenna on 80 m through 10 m.

The phenomenon at play is this: even with a jumper bypassing all turns of the coil, the coil is still contributing significant inductance.

If I’m reading your description correctly, your vertical is 3 m long, which is a quarter wavelength at 24.9 MHz and quite a bit shorter (by 16 %) than a quarter wavelength at 21.1 MHz. If you can further reduce the inductance of your coil, resonance on 15 m, and maybe 12 m, should be possible without reducing the wire length.

To lower the inductance further, you have to use multiple jumpers tapped to roughly-equally-distributed points along the coil, like this:

Or, construct a daisy-chain jumper with multiple taps, like this:

The more taps distributed along the coil, the lower the inductance for a given position of the upper-most tap.

The highest frequency at which I’ve been able to resonate this antenna is 30.1 MHz (not that I operate there, but I took measurements with the antenna analyzer for curiosity’s sake). This was achieved with the four-tap clip jumper in the second photo bypassing the entire coil combined with the three plug-in jumpers placed as in the first photo.

30.1 MHz corresponds to a quarter wavelength of 2.49 m in free-space. The antenna, at 2.16 m, is shorter than that by 13 percent, so the coil is still contributing some loading effect even with a total of seven bypass taps. Perhaps some of this loading effect is not only lingering inductance but a slight capacity-hat effect from the coil and jumpers.

All of the above is without an (intentional) capacity hat. At the other end of the dial, to resonate the antenna on 80 m, I put a capacity hat on the top of the antenna. On that band, I use a single jumper bypassing about 1/4 to 1/3 of the turns; my usable bandwidth per tap location (VSWR < 2.0) is only 13 kHz (at the CW end) to 17 kHz (at the SSB end)!

[EA2BD]

Hi Matt,
that’s an interesting contribution, glad to find another happy user of a short loaded vertical.
I’ll try testing your mod for the coil and see what happens.
73 Ignacio

[EA2BD]

@EA2BD

In the next days I will edit the footage and put a link

There we go, now on your video player:

Short multiband vertical HF antenna (Antena corta de HF)

You can get the idea on how it’s setup.

73 Ignacio

[HB9EAJ]

Hi Ryan,

Sorry for the late reply. No, I haven’t tried any kind of screens. I think it’s a good alternative, probably even better than radials, but not the best solution on a small summit. It would also take up more space in the backpack, which I try to avoid.

73 Stephan