HF Multi-band Portable antenna

An ‘easy’ wire antenna that covers 160 – 6 metres.

By Des – VK3DMP.

a member of East Gippsland Radio Group.

Shown here at one of the operating positions of VK3EG Point Hicks (AUS-133) 2005

Purpose:

 This article is intended to describe a multi-band antenna option for portable (or home base) use which provides excellent performance while being easy and low-cost to make, easy to transport and easy to erect.

 This article is not intended to:

•  Neither promote the use of one particular antenna design in favour of another nor provide detailed theory of operation for the antenna described.  (The Internet is full of detailed information about this antenna).  The idea behind this story is to show others a way of putting together something that works.

   Promote one particular brand of radio equipment in favour of another.  Several manufacturers produce the equipment types shown & described here.

Description:

When it comes to portable operation, quite a respectable signal can be generated with a simple wire antenna.  The ideal would be; one which performs well on all HF bands, will present the transceiver with an optimum match, is easy to erect by one person, requires no bulky masts to support it and can be carried around in a back pack if necessary.  The antenna arrangement described in this article satisfies all of these criteria.

The basic design of the antenna will be instantly recognisable to those that have used it before in some other variation – it’s a G5RV fed at the base of the twin line by connecting it to a remote automatic tuning unit - where coaxial line is terminated in the original design. 

The G5RV has proven to be a high performance, multi-band antenna for many years by amateurs all over the world and is an ideal choice for portable work.

This antenna has been constructed from lightweight materials to enable it to be supported by a telescopic composite fibre fishing pole (AKA squid pole) and, although not apparent at first view, has proven to be strong enough to withstand 54 knot winds in the field!  During the 2005 International Lighthouse weekend, this antenna and mast were deployed at the Point Hicks Lighthouse (AUS133).  The early hours of the final morning saw the wind strength peak at 54 knots – well over 100 km/h.  Initially, I was preparing to outlay the necessary for another fishing pole but to my surprise when inspecting the antenna first thing that morning – it was still standing and the dipole was still intact.

For storage and transport, the antenna is rolled up onto 3 small diameter cable reels.  The antenna is fed at the base of the telescopic mast via an auto tuner that interfaces directly with the transceiver, which in this case, is the Icom IC-706Mk2G & AH-4 combination.  The advantages of feeding the antenna this way include providing the radio with a perfect load at all times, virtually no losses along coaxial lines from the tuner back to transceiver, fast tuning when changing bands and more efficient radiation from the antenna elements as the coaxial line is not trying to radiate as well.

Construction of the antenna.

There are no special materials needed.  I have used plastic coated wire about 2mm overall diameter and some slotted 300 ohm TV ribbon.  The slotted variety is probably preferable to the solid core version as the it could exhibit less loss if it gets wet, has less wind catching potential and is fractionally lighter.  The length of the ribbon is 30.6 ft or 9.3 metres.  This length will vary depending on what type of feeder is used here.  This section should be resonant at 14.1 Mhz to be true to the G5RV design – different velocity factors of feed lines will alter the final length. The radiator elements are 51 ft or 15.5 metres per side.  But as we are feeding the antenna differently to the original design of the G5RV, these dimensions are not critical but can be used as a starting point.  An insulator is used at the dipole centre – mine is just a piece of PVC conduit about 15mm diameter.  The end insulators for the antenna wires can be made from the same material if desired.  The antenna requires no tuning once made as the antenna tuner takes care of this.  I have also made the use of an RF choke at the ‘feed point’ of the antenna in place of the auto tuner.  This provides the option of using a manual type tuner back at the operating position if necessary although losses along the coaxial line back to the tuner will be more significant on some bands when compared to using the matching unit at the feed point.  As was stated earlier in this article, for more detailed information on how the G5RV antenna works on the various bands there are many books and internet resources available.

Finally, this antenna has been used successfully in several portable situations – including VK3EG’s activations of Point Hicks Lighthouse during the International Lighthouse weekend for 2004 & 2005.  It performs well on all bands from 80 to 10 metres and contacts have also been made on 160 metres between VK3 – VK5 & VK7 and 6 metres locally.  This antenna would not usually be considered usable on these bands but the matching network easily achieves a match and thus allows some RF to be transferred.  As stated earlier, the dipole can be transported easily, erected by one person in minutes and is very inexpensive to make.

Basic Construction Details

The complete portable kit (note the telescopic mast is approximately 1 metre long when collapsed). All this - except the mast - fits into a conveniently sized toolbox.

Here is the erected antenna at Point Hicks light station – 2005

Another view of the antenna at Point Hicks - 2005

Telescopic mast & auto tuner (on top of the rubbish bin).

This time with a blue sky and ocean

Here is the Point Hicks Light Station – 2005. Look closely at the building on the right hand side, you’ll see the antennas of the VK3EG station