Hairpn modified antenna for 40 m band – improvments and updates (h=5.5 m above the ground)

For ease of adjustment I found that it is necessary to mount a gear for variable air capacitors.

SWR graph - 7050 +/_ 50khz 

Resonant frequency = 7071 khz
Bw (swr<1.5 = 268 khz) Bw (swr<2 = 484 khz )

Hairpin modified antenna – estimated performance based on WSPR data analyse

So, we have an short antenna, easy to build and install. It was working in WSPR mode more than 3 days. It’s time to find the performances… and to see if our expectations are to big, or what can we improve.

First analyse is a simple one. Just go to VK7JJ site ( and follow the instructions. You can see when you see a lot of useful informations about your antenna, the antenna location and propagation.

It looks fine… it’s only an example of useful info. But is not enough. The chart say you can work from YO stations from VK, JA, North and South America. Yes, using WSPR mode.

What about other modes ?

Let’s go to KP4MD site ( and download the mode-comparison excel file.

Using your WSPR data you can find if you can work a specific station in another mode (CW, RTTY, SSB, etc.).

Let start with the bad news…

After you shall download and process the data, you shall find that the probability to work VK7JJ in RTTY or SSB mode is very low to very, very low. Red colour is not good….

Let’s check other DX stations

Sorry, no K1ABK, no JA5NVN.

OK, dont panique, let see what can we work.

TF4X                        3927 km

MM7BWK              2544 km

OH3FR                     1867 km

So, if you want more, try to find if you can use a higher position or re-locate the position, or improve soil parameters, etc.

For example, my location is very unfriendly regarding the obstructions around me. As you can see in the graphs (from 1st part, VK7JJ site), the existing freeway to 310 degrees azimuth is confirmed by number of spots and the obstruction from 230 degrees (a new big house, etc.) is also confirmed by no data/spots on that direction.

Hairpin elevated antenna 40 m band – tips & tricks


Before starting the construction of this type of antenna, consider the following advantages and disadvantages.


  • It’s a monoband antenna
  • For any mods or relocating position you need and antenna analyzer
  • Depending the parameters, the Bw can be very narrow for your purposes
  • The variable capacitors need to be with 2.5-2 mm spacing between plates for 100 watts.
  • The tuning point is very sharp, so a multiplier system for variable capacitors is welcomed


  • It’s a small antenna, maximum 3 meters lenght for 40 m band
  • No radials required
  • You can use on ground radials around the mast for improving the soil parameters
  • Can be made in portable pack version for mobile operations
  • You need only free obstructions position, not necessary high mast (2-4 m)
  • The bandwith is enough for rtty activity (more than 100 khz for SWR<1.5)
  • The preliminary results shows you can work easy all Europe countries (YO4DFT – I am located in KN44HD

So, let’s find some materiales for the Hairpin antenna made with aluminium tubes. What I found:

  • 2 old elements from a vertical Eco antena (diameter from 45 to 35 mm total lenght 2 m, with posibility to insert one to another to vary the total lenght)
  • 4 aluminium elements for old military stock with connectors ( 1 m lenght, 30 mm diameter)
  • Aluminium strip 20×1.5 mm for top connector

I decide to use the folowing parameter: 25 cm spacing and maximum 2.85 m lenght.

Building the top connector. Use metal screws (the black one) to obtain a good electrical connexions between tube and connector.

If you are using separate elements like me (not full tube, 2.85 m one piece) you have to cut a longitudinal space and use againg metal screws to obtain a good electrical connexion between elements.

I am using 2 old double sections variables with mechanical multiplier, modified (less plates) to obtain 2 mm spacing. Minimum capacity 10 pF, maximum 52 pF (each section).

Find a good enclosure and a piece of isolating material, with enough thick (15 mm in my example, I found an old textolit bar painted in blue !) to sustain the tubes. Use some Cu wires with big diametres (2.5 – 4 mm) for electrical connexions. Depending the parameters, it can be possibil to need both sections of variables to be connected (if the capacitance need to be more than 50 pF) or only one.

Find the proper mounting metal flanges. Use a common mode shocke (in my case, 20 turns of RG213 U equivalent on 12 cm diameter (on a piece of water drain pipe). Use an insulated tube for tuning the variable capacitors (the white tube in the photo). Connect the equivalent lenght of coaxial cable (as you are using for the trcvr) and start the tuning. Take care, the proximity of human body can influence the measurement. During the tuning procedure don’t touch antenna or mast. Use an insulated tube for variable capacitor (20-30 cm) to avoid your body influence.

With patience, start the tuning. After you shall obtain the resonance and R=50 ohms at desired frequency (most probably you are climbed on a ladder near the mast), step down and re-check the values at 3-4 meters away from antenna. Check the Bw for your specific needs. Re-tune if you are not satisfied.

Go into the shack and re-check the values obtained. Most probably you shall see some differences. The most important is the resonance frequency to be the same (or with minor differences).


Congratulations, you have an antenna ! But, don’t forget, is a small one, is not a miracle. You can make QSO’s 3000 km around you, more or less, depending the obstructions, depending the soil, etc.

Good luck and 73’s !

24 hours WSPR tests,  1 watt power

(14.03.2021 09:00 UTC – 15.03.2021 09:00 UTC)


40 m band – Hairpin antenna – Theme with variations (part 2 of previous article)

200mW WSPR test

After 2 weeks of testing the Hairpin antenna for 40 m band (the light model with Cu wires), it’s time to build the regular prototype with Al tubes. But, first off all, let’s play with MMANA- GAL to see what are the limits.

The main differences between classic Hairpin antenna and this model are:

  • The antenna is mounted on a metalic grounded mast.
  • The spacing between arms is larger to obtain a wider antenna


Now, let’s play with parameters.

  1. Spacing

Aluminium tube diameter = 24 mm
Hairpin length = 3 meters
Height from the ground = 4 meters
Ground setup = 14 / 5
Q capacitors = 500
R =50 ohms (+/- 1)
jX = -1 /+1 ohms

Higher spacer, better gain and Bw

2. Aluminium tube diameter

Spacing = 24 cm
Height from the ground = 4 meters
Hairpin length = 3 meters
Ground setup = 14 / 5
Q capacitors = 500
R =50 ohms (+/- 1)
jX = -1 /+1 ohms

Higher tubes diameter, better gain and Bw

3. Q capacitor

Spacing = 24 cm
Height from the ground = 4 meters
Hairpin length = 3 meters
Ground setup = 14 / 5
Aluminium tube diameter = 24 mm
R =50 ohms (+/- 1)
jX = -1 /+1 ohms

Vacuum capacitor (High Q), high gain but narrow Bw

Regular air capacitors, lower gain but wider Bw

4. Height from the ground (grounded mast length)

Spacing = 24 cm
Q cap = 200
Hairpin length = 3 meters
Ground setup = 14 / 5
Aluminium tube diameter = 24 mm
R =50 ohms (+/- 1)
jX = -1 /+1 ohms

More height, more gain and Bw

5. Hairpin length

Spacing = 24 cm
Q cap = 200
Ground setup = 14 / 5
Aluminium tube diameter = 24 mm
R =50 ohms (+/- 1)
jX = -1 /+1 ohms
Height = 4 meters

Too short, less gain. Too long, you can not tune the antenna (value of Cv1 will drop to parasitic capacity, or to zero)



New type of shortened antenna for 40 meters band – part 1 – Light version

Why this antenna has no name ? I dont know… I dont know exactly what kind of antenna is this (….hmm, I know, is a variant of magnetic antenna, is using the parallel line inductance, etc, etc, etc. is the same setup when you need to find Qf for a capacitor).

So, let’s see how was borned. Few weeks ago, a heavy storm distroyed my telescopic mast and the 40 m band delta loop, so I need something for a small yard, with a lot of higher obstructions around me, with a limited telescopic mast (max. 6 m), etc. The hamradio nightmare !

I tried to design a magnetic loop… to narrow for rtty contest… too large if you need a good efficiency (2.4 meters diameter…). But, I found something in Mmana library, named HAIRPIN magnetic antenna. It looks nice, but still to narrow.

it looks friendly, like this

but the swr chart, wasnt friendly…

So, I’ve started to play with dimensions, diametres, etc. After one week of simulations the result was something like this:

  • a parallel line of 2.6 metres lenght with 24 cm spacing, shorted at upper side
  • 2mm diametre Cu wire
  • 4 meters up from the ground
  • Two air variable capacitors (max. 100 pF each)

This is the theoretical model

The real world shows something different

As you can see, the practical prototype has a larger Bw, aprox. 75 kHz for SWR < 1,5. Why this difference, from 22,5 khz to 75 khz ? Because in simulation I didnt complete the Qf for capacitors.

If we are playing with Qf, we can find a value when the two charts are matching


7000-7100 khz / Practical model

7000-7100 khz / Theoretical model

7000-7200 khz / Practical model

7000-7200 / Theoretical model

So, starting this point, we can assume the simulation match the practical model.


Preliminar traffic results -WSPR (200 mW)

and some pictures from prototype

And schematics

Next part will be with Heavy version, more commercial aspect (I hope), with proper capacitors and better gain.

Any questions, dont hesitate to send mail: