After subscribing, check your e-mail (also the SPAM folder) and click the activation link.
Hallo Field Day project-Portable hf antennas
Hi, my name is Artur and my ham radio sign is SQ5NWA. (qrz.com card)
Light, field, effective, multi-band antenna solutions is a project that I called Hallo Field Day. These are my experiences from many years of amateur radio in the field.
A field HF antenna should meet several conditions at least, based on my experience, which are:
- Efficiency for both 5W and 100W power outputs
- Lightweight and compact for easy transport
- Easy assembly in the field
- Support for multiple amateur frequencies.
The HF antenna emits electromagnetic waves most efficiently when its length is equal to or close to 1/2 or 1/4 of the wavelength.
There are many solutions for HF field antennas, ranging from pocket “miracle” antennas for all bands to simple wire antennas for many or one band. There are horizontal, vertical, open, and closed antennas, among others. Antennas can be discussed at length, and everyone likely has their favorite and most effective option. I won’t argue with that. I’ve tested many of them and … returned to the basics of the half-wave antenna.
Creating the Hallo Field Day Project: Building a Better Multi-Band Antenna Solution
- At first, I wanted a small, multi-band antenna that could be installed anywhere (park, campground, etc.). I tested many short, multi-band antennas, but I quickly realized that I was only satisfied when propagation conditions were very good. As soon as conditions worsened even slightly, the short antennas stopped working effectively. I began looking for a better solution.
- Since I prefer low SSB power (though I also like 100W at times) and a few amateur frequencies are useful in the field, I was searching for a more effective, multi-band solution. I tried longer, unbalanced horizontal and vertical wire antennas, which worked better on some bands but worse on others. Then I decided that the antenna working on harmonic frequencies also needed improvement.
I built a half-wave dipole for three frequencies, which I manually switched by connecting or disconnecting the connectors on the arms.
Finally, I automated the frequency switching of the antenna. That’s how the Hallo Field Day project was born.
The HFD SWITCH is the primary component of a multi-band HF antenna. It is a high impedance LC resonant circuit that operates at the resonant frequency. This allows it to function as an automatic multi-band switch for the antenna’s operating frequency.
- I utilize mica capacitors in the resonance traps. Why? During testing, the less expensive ceramic capacitors did not perform well. When attempting to transmit at 100W power, the antenna resonance would change due to capacitance instability as a result of temperature and frequency changes. The use of mica capacitors has resolved this issue.m.
100W resonance traps
Small size, low weight, effective, 100W
Antenna signal loss
Two PCB solutions for stable and standardized ferrite core winding
- PCBs are available for constructing a 1:1 BalUn and a 49:1 UnUn. The PCBs can be installed in waterproof enclosures, which are also available for purchase in our store.
- Alternatively, a PCB is available for field use without an enclosure. An additional benefit of this PCB is the natural air cooling of the ferrite core.
Both PCBs are designed for a 35.55 mm core (FT 140-3) and have been used for 100W SSB and CW operations for several years.
The use of these PCBs ensures consistent and stable winding of the ferrite core, providing a tidy and standardized solution.
The End Fed antenna is an unbalanced structure that operates on harmonic frequencies, and its main advantage is the ease of installation in the field. To optimize the antenna’s effectiveness, there are several key factors to consider:
- Radial pattern (this is important to know) – at higher frequencies, the radiation beam tends to shift its direction of radiation parallel to the antenna wire. At lower frequencies, the antenna radiates like a half-wave dipole, i.e., perpendicular to the antenna wire. Therefore, the antenna may be more effective in one direction on some frequencies and in the other direction on others. The antenna has a better radiation pattern when it is hung as a straight line than as an inverted V, for example. If you decide to hang the End Fed in the shape of an inverted V, try to have a refraction angle of 120 ° -130 °
- Impedance transformer (this is worth considering) – there are many different opinions on the end fed antenna transformer winding and its effectiveness for various ferrite core variants. The proportions and the method of winding play a major role here. It is difficult to indicate clearly which solution is the best. There are many studies and experiments. Everyone can judge it individually.
- Asymmetry (it’s worth addressing) Despite the fact that the antenna is made up of one arm, it should be remembered that there are no single-arm antenna systems. An antenna always has two arms, although they can take different form
In the End Fed antenna, the second arm often becomes the outer part of the coaxial cable. Therefore, there are problems of asymmetry – sometimes visible as a pinch when you touch the radio housing, and sometimes they are invisible. However, they always cause antenna losses. The phenomenon of asymmetry of this antenna can be eliminated in two ways:
How to Eliminate Asymmetry Problems in End Fed Antennas
- Use a counterweight or ground the antenna The most effective counterweight length for the End Fed 80-10m antenna is 0.05 λ for the lowest bandwidth of the antenna.
- Use a common current inductor. In the latter case, it should be remembered that the choke has the best attenuation at 50 Ohm impedance. Therefore, it should not be installed close to the power point because the impedance is much higher there. The filter should be located approximately 1/4 wavelength from the feed point. Take the average for multi-band antennas.
YOU CAN CHOOSE THE VERSION OF THE IMPEDANCE TRANSFORMER
Two versions are available: a light, varnished version or a version with a very good quality waterproof housing.
You can build an antenna from practically any wire. In multi-band antennas, however, one of its properties is important – it should not stretch, because there will be problems with tuning the antenna
Hallo Field Day multiband dipoles are made of wire reinforced with Kevlar.
- The antenna wire must be light
- The antenna wire must be UV resistant
- The antenna wire must not stretch
Other accessories I use
I tested various antenna accessories and selected for you those that I found practical and very well made. Thanks to these accessories, your antenna will be comfortable to use.
HFD antenna isolator
I designed a convenient antenna isolator. It is different from those you often see in stores.
This insulator has clamps that make it easy to tune your antenna. Too short an antenna is no longer a problem
Out of the many ways to hang portable antennas, I chose the ones that I like best.
A mast or an arborist dart. These two solutions are different but can complement each other. I discovered the dart recently. I don’t know how I have been able to live without it so far