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: cristian.moldovanu@gmail.com