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Transmitting on 160 metres

Picture of microphone Picture of antenna Picture of tx

160 metres can be a challenging band to operate on, especially if you have limited space. Nevertheless results can still be good provided attention is paid to sound antenna practice. Compared to other amateur bands it features more AM activity and a slower pace of operating.

Activity

160 metre activity can involve local contacts on AM during the day and longer distances on SSB at night. International DX contacts at night are also possible. The videos below provides a sample of 160 metre AM and SSB activity.

Equipment

160 metre AM operators use a mixture of home-constructed, broadcast, military and commercial equipment.

Some commercial gear is designed for SSB with AM thrown in as an afterthought. This may result in poor quality transmit audio and modifications may be required. Even where AM performance is satisfactory, a nominally 100 watt SSB transceiver may only put out 30 or 40 watts AM, but this is normally sufficient.

Ex-broadcast transmitters can be hard to find unless you're in the industry. However it offers superior audio quality at the legal limit, is built well and capable of 100% duty cycle. However these should only be considered if you're conversant with working on high voltage equipment and have a large space to house them.

Homebrew AM equipment is practical on 160m and a 1 watt transmitter can be very simple. If you're centrally located and using an efficient antenna good results are possible. Crystal control is not a serious disadvantage and 1843 kHz crystals are cheaply available off the shelf. Transmitter complexity increases with power though Drew Diamond VK3XU has developed several 160 metre AM transmitters that work well.

160m SSB operators mostly use commercial equipment similar to that used on other bands. When shopping for secondhand equipment note that some 1970s and 1980s transceivers did not include coverage of 160 metres or AM transmit capability.

Power, propagation and modulation

Ten watts AM to a well-built vertical and counterpoise will provide daytime coverage of most of metropolitan Melbourne. However some will struggle if their noise level is high or they're more than about 20km distant. One watt AM will provide readable signals just above the urban noise threshold up to about 15-20 km. Stations in quieter locations will do better and copy a one watt signal from 40 or 50 kilometres away. Conversely, outer suburban and fringe stations may require 100 watts to be heard by those with noise or on the other side of the city.

At night low power is routinely suitable for paths of up to several hundred kilometres, with contacts of a few thousand kilometres (or even half a world away) sometimes achieveable. Signals are stronger over the water and bayside stations will find pronounced improvements in some directions.

On AM good modulation is important any time, but especially when signals are barely above the noise level. A punchy 10 watt transmission will cut through in cases where a poorly modulated 50 watt signal fails. Also even where modulation is good, if it is too muffly or bassy then readability will suffer. A 'broadcast quality' transmission is appreciated but only if other aspects of the station (eg antenna efficiency) have been optimised first to assure a strong signal. Otherwise, especially if running low power or portable equipment, it is better for listener comfort to aim for maximum readability without obvious distortion.

Transmitting antennas

The type of antenna you will put up depends on your location, type of contacts you wish to make and space available.

Popular 160m antennas include:

a. Full-sized dipole for 1.8 MHz: Requires more room than most have. Poor performance for local ground-wave work. Poor performance for DX unless mounted very high above the ground. Good performance for medium distances at night.

b. 3.5 MHz dipole with coax feeders: Requires an antenna coupler. Even so feedline loss will be high and 160m performance will be poor.

c. 3.5 MHz dipole with tuned feeders: Requires an antenna coupler. Lower feedline loss than above but generally mediocre performance especially for local daytime ground-wave work (up to 80km) and DX working. May be acceptable for medium distances at night.

d. 3.5 MHz dipole with feeders tied together and fed against ground with an antenna coupler: An effective first antenna for 160m for local and more distant work.

e. Inverted-L fed against ground with an antenna coupler: A good basic general purpose antenna for 160m. Radiation contains both vertical and horizontally polarised components. Suitable for both local and long distance contacts, but aim to make the vertical section as long as possible.

f. Vertical T fed against ground: An effective vertical radiator with excellent local ground wave coverage and DX performance. The flat-top capacitance hat plus a top loading coil can shrink the size of the antenna (even to as small as 10 metres) but keep efficiency high, as proved by the many successful builders of the VK3XU version. As a portable antenna it can be made very light yet outperform many home-station installations but a good ground system or counterpoise is essential.

g. Magnetic loop: Able to be used indoors and the ultimate in space-saving antennas. The results on 160m are suprisingly good for local and interstate work, and a larger version mounted outside could likely outperform a low dipole for some work. Build one if you have no alternative or need it to experiment with receiving antennas.

Recommended antennas

If it's already up, d. is a good way to sample the band. If you want a dedicated antenna for 160m, either e. or f. are the best picks. Take a tip from the broadcast stations and aircraft beacons and build f. if optimum ground-wave coverage for the AM net is most important. Or pick e. for a good all-round antenna.

The Index Page contains examples of e, f and g that have been used successfully on 160m.

160m antenna demonstrations

Antenna and propagation software

There's a lot of free computer software of interest to the 160 metre operator. One of the best sources is G4FGQ's site.

Some of his most useful programs are:

* RJELOOP1 - calculates the efficiency and performance of small magnetic loop antennas
* GRNDWAV3 - a ground wave propagation modelling program that calculates signal strength at a specified distance based on transmitting frequency, antenna efficiency and ground conditions. You will be amazed how well 160m does, even with 1% efficient antennas.
* TOPHAT2 - useful when building short verticals for 160m.

Further information

These favourably reviewed books may be useful for those seeking more information on 160 metre equipment, antennas and operating.

 

Disclosure: I receive a small commission from items purchased through links on this site.
Items were chosen for likely usefulness and a satisfaction rating of 4/5 or better.

 

Books by VK3YE

 

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(c) Peter Parker VK3YE 1997 - 2017.

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