Which HF Antenna?

Which HF Antenna?

When establishing your amateur radio station, it can be easy to focus your attention inside the shack. Radios with all the bells and whistles, computers with big screens, a fancy chair and expansive desk; and by all means, a comfortable and workable shack is important.

But… far too many operators ignore the most important component in the system; the feedline and antenna. You can have a $5,000 radio, but if your antenna system is sub-optimal, you’ll be missing out on lots of QSOs.

If you’re struggling to get QSOs in the log it might be time to look at your antenna.

General Principles

Aim to erect the best antenna possible given your goals, limitations and budget. What are your goals?

• DX on 20 and 15 metres?
• Rag chewing with locals on 80 and 40 metres?
• Working DXCC on the higher bands in one year?
• Working locals and DX on 40 metres?

Next, be clear with your limitations and budget.

• What is your budget and how much space do you have?
• Does your house block and location mean you can’t erect a tower?
• If you are tight on space and money, a tower and beam may be out of the question. But perhaps a Hexbeam antenna on an 8-metre mast is possible?

Consider which coaxial cable you’ll use. The cheaper RG58 may be fine for short runs (up to 20 metres). Longer runs (say 30 metres plus) would benefit greatly from a higher quality coaxial feedline, especially on 21 MHz and above; such as RG8 or RG213.  Ultimately it comes down to your needs and budget. But don’t skimp on quality feedline.

You can check coax cable losses with online calculators like this one: https://comset.com.au/coaxial-cable-gain-loss-calculator/

And remember, for every 3 dB loss in your feedline you’re effectively halving your radiated power.

Below are three basic options you can consider for an effective and efficient HF antenna system. These descriptions are basic and the pros and cons are generalisations. Do your own research, read the ARRL Antenna Handbook, and consider using modelling software to better understand how your antenna will perform.

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The Dipole Antenna

The dipole antenna and derivatives have been the mainstay of radio communications, both amateur and commercial.

Pros:

• Cheap and easy to construct.
• Can be easy to install if you have some decent trees or a mast.
• Easy to tune.
• Can configure as a flat-top, or inverted vee, or a variation.
• If low to the ground relative to wavelength, expect QSOs up to 1,000 – 2,000kms – this applies to most dipoles if up about 8 – 10 metres high for 80, 40 and 20 metre bands. On the higher bands (21 MHz and up) you may start to see better DX results from a dipole this high.

Cons:

• On balance, not really many.  This is a good beginner’s antenna.
• If low to the ground (relative to wavelength) most of the energy will be radiated at higher angles, so working DX will be a little more challenging. Ideally, a dipole should be at least ½ wavelength off the ground.
• Depending on the frequency desired, antenna length may be an issue, but there are approaches you can take to work around physical limitations.
• Usually works only on the frequency it was tuned for, however there are types of dipoles which are multi-band.

 Things to think about:

• Get your dipole as high as possible and in the clear; minimum of 8 – 10 metres.
• Be aware of potential dangers.  Keep all antenna wires and guys well clear of power lines, phones lines and other services.
• The dipole does not have to be straight.  You can have bends in it, for example to fit into your block. Another alternative would be to make some loading coils.  Coils add inductance, making the antenna physically shorter, whilst keeping the antenna resonant. Whilst not an easy project for beginners, it would be a great way to experiment, learn and prepare to upgrade your licence (if that is what you want to do).
• A 40-metre dipole is 20 metres long and it should fit onto most residential housing blocks. It should also work well on the 3^rd harmonic, being the 15 metre band.
• Consider building a fan-dipole for use on more than one band.
• It is good practice to add a common mode choke at the antenna feed point. Wind about six turns in the coax (say 20cm diameter) at the feed point to make a choke. This will attenuate common mode current. You could also wind the coax through a ferrite core 5 or 6 times for greater effect. To learn more about common mode chokes refer to your ARRL handbook or search on the web.

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The Vertical Antenna

The vertical antenna is another mainstay of radio communications, both amateur and commercial.

Pros:

• Cheap and easy to construct.
• This is a good beginner’s antenna.
• Easy to tune.
• Requires very little real estate.
• Great for working DX (low angle of radiation).
• From 10 to 40 metres, it is practical to construct and erect a Vertical Antenna in your back yard.
• Buried radials do not need to be resonant. More short radials will be better than a few long radials. A good target to aim for would be 16 radials each 3 – 5 metres long.
• Elevated radials – you’ll only need 2 to 4 radials, but they will need to be resonant.

Cons:

• Verticals are more susceptible to receiving local noise. It’s not that verticals receive more noise because they are intrinsically noisy, it’s just that they ‘see’ closer to the horizon.
• They may not be as good as a dipole for local QSOs
• You will require a good radial or earth mesh field.
• Elevated radials will require clear space and need to be cut to resonance.
• Usually works only on the design frequency, however you could make a multi-band vertical; there are designs similar to a fan dipole, or using tuned coils for multi-band resonance.

 Things to think about:

• Ideally, your vertical should be in the clear.
• Consider your best options for radials (elevated, buried, or a wire mesh).
• As a minimum you should aim for 16 buried radials at least 3 metres long, or four elevated radials (which will need to be cut to resonance). The diminishing return point for most amateur applications is 32 ground radials at least 3 metres long. (for bands down to 40 metres).
• Be aware of potential dangers.  Keep all antenna wires and guys well clear of power lines, phones lines and other services.
• The DX-Commander is a great option. You can make your own or purchase from Callum at DX-Commander.

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The Hexbeam – 2-element beam

This antenna is a great performer if you don’t have the ability to put up a tower and three or four element Yagi. It’s only two elements, but it packs a pretty good punch with approximately 5.4 dBi gain and 10 dB front to back ratio.

You can build your own: https://www.hex-beam.com/

Or there are various commercial products available from the UK and USA.

KIO Hexbeam

https://www.dxengineering.com

If you have the space and are willing to take on a slightly more complex project, a Hexbeam provides great performance over a vertical or dipole from 20 – 6 metres.

Pros:

• Multi-band; from 20m up to 6m.
• Directivity! You can point the antenna towards in the direction you want for improved reception and transmission.
• Homebrew or buy a kit.
• Lightweight and minimal wind loading; less demanding engineering requirements for a mast and rotator.
• Good front to back ratio and gain.

Cons:

• Will cost more money and require more infrastructure than a dipole or vertical.
• Will have a larger visual presence than a dipole or vertical.
• You’ll need some form of rotator to turn the antenna.
• Requires more effort to build, erect and maintain.