Tuesday, April 30, 2019

Something yellow. Something runny. Something different.

Can you tune up a bowl of custard with an antenna coupler?

Michael Cullen has found that you can!


PS: For something a bit easier to tune up (and radiates better) consider the ideas in here.

Monday, April 29, 2019

Build your own knife switch

Most amateurs have used coax switches for switching one transceiver between multiple antennas or having the one antenna going to multiple transceivers. 

That's fine for coaxial feedline but what about open wire line? Sometimes you need to switch in an extra length of feedline to assist impedance matching. You may have two dipoles fed with open wire feedline, perhaps oriented differently. Or, you could be experimenting with switchable direction open wire-fed beams where again you may be switching balanced line. 

A knife switch can help. Immortalised by Frankenstein, they've been around since the early days of human harnessed electricity. I've seen cheap ones on eBay but their quality may not be good. You could be lucky and find an old one at a hamfest. Making your own is another option. If the latter appeals, here are some ideas:

* Instructables knife switch

PS: Returning to amateur radio? This book can help fill in what you've missed. Available for $US5 as an ebook with a paperback version also available, this will bring you up to speed in no time.  Available via Amazon, you can find out more here

Sunday, April 28, 2019

7 MHz WSPR tests with 100 microwatts

Back in February I mentioned WSPR as a means of testing an antenna's effectiveness. 

Continuously for the last week or so I've been running 100 microwatts (not milliwatts) WSPR on 7 MHz. 

About 20 stations, up to 2500km away, detected my signal. I didn't count them but there seemed to be hundreds of detections, some at quite good signal to noise ratios. This means one could easily go lower in power and still be detected. 

Anyway here's the video that goes into it in a bit more detail. 

Note: I reported 0.001w (1mW) due to software limitations. Actual power was, as mentioned, 100uW. 

PS: Want to read more about antennas? Consider this selection of antenna books. They are affiliate links meaning that I receive a small commission (at no extra cost to you) if you decide to purchase.


Saturday, April 27, 2019

Loaded dipoles

If you don't have the room for a full sized dipole (even after you bend its ends down or in) one solution is a loaded dipole. You lose a bit of performance and a lot of bandwidth (or a lot of performance and a bit of bandwidth) but one is still a good way to get onto a particular band. And the way conditions are at the bottom of the cycle, even a limited capability on 80 metres can be very valuable. 

A loaded dipole has some sort of loading. Either capacitive loading at the end of its element or inductive loading along it. You can make the latter by winding wire on a plastic pipe. Depending on how the coils are positioned you can even make a loaded dipole work on two bands (with the higher frequency band being served by both sides of the antenna wire between the loading coils and feedline).

Here's some ideas for and examples of loaded dipoles:

* Coil shortened dipole calculator
* M0MCX shortened 40m dipole for attics
* VK1HW 80 and 40m loaded dipole
* Adding 80m to a 40m dipole (video)

Have you had success with loaded dipoles? If so please leave your comments below.

PS: I have written five books on various facets of amateur radio. They are available in electronic or paperback form. Find out more here.

Friday, April 26, 2019

Antenna ideas for the 60m (5 MHz) band

Amateurs in many countries now have access to the 60 m or 5 MHz band. Often it's just a few spot frequencies. And there might be output power limits. Unlike on other bands these may be expressed as EIRP (effective isotropic radiated power) so you can't get around that limit by using a high gain antenna.

Before thinking about what antenna to use on 60m it's worth thinking about the band's characteristics. Right now, in the low part of the solar cycle, 7 MHz is somewhat unpredictable during the day for intermediate distances up to a few hundred kilometres. But 5 MHz may still be okay. And it may have less absorption than 3.5 MHz. An antenna with a fairly high angle of radiation, like a dipole around 10 metres above ground, would be excellent for this application.

Then there are DX possibilities. Given the low power limits that often apply this may be a challenge. A full sized quarter wavelength is 15 metres which you may just be able to hang from a tower if you have one. Or if your support is smaller then an inverted L (with as much vertical as possible for DX) would be a good pick.

Another possibility, to save the clutter of wires, is to see if an existing antenna can be made to work on 60m. Your chances are best with a tuned feeder dipole. The old 102 foot (31 metre) long G5RV is pretty much exactly a half wavelength dipole on 60 metres. So you can expect excellent performance from one on the band. If you lack the room them a tuned feeder dipole that's 20 metres end-to-end (ie a half wavelength on 40 metres or 7 MHz) will also still be efficient down on 5 MHz.

Since 5 MHz is so narrow, bandwidth shouldn't be much of an issue. So if you're really pressed for space you could use a short dipole with loading coils. You may be able to get it so the antenna is full sized on (say) 7 or 10 MHz with the loading coils allowing 5 MHz as well. A trapped dipole is another possibility.

Want something quick for portable use? An L-match and 30 metres of wire should be fine as an end-fed half wavelength. That length of wire is getting a bit long for a single 8 or 9 metre pole (it will sag) so find somewhere where there's a tree to hold it up at the other end. Or take a second pole.

What about magnetic loops? Many homebrew designs go down to 7 MHz. You could add extra capacitance to get 5 MHz. There will be a substantial drop in efficiency but you should still get contacts. And, bear in mind that where the 5 MHz power limit is expressed in EIRP terms you can increase power going into the loop to compensate for its losses. Just be mindful of not sparking across the loop's capacitor if you designed the loop for QRP operating.

So there are many possibilities for 60 metre antennas. M0MCX has some more ideas here.

PS: Want to learn about portable antennas? You'll find many ideas and projects in the top-selling Hand-carried QRP antennas.

Thursday, April 25, 2019

Some rhombic ideas

You can go through your whole amateur life without ever hearing a station using one. At least on HF, they require you to own a farm to fit them in. They need four masts to the yagi's one. And their radiation pattern is not easily steerable.

I'm talking about the rhombic antenna. Commonly found in older antenna books, they have utility if you have a lot of land and are mainly interested in one direction. Plus they are broadbanded and low noise on receive. If you've inherited some large rolls of wire and have room to string it up, then the rhombic might be your friend.

As the name suggests, the rhombic is rhombus shaped. Like a square but pushed over. It's fed at one end with balanced line. At the other end is a terminating resistor. This enables it to be directional, like a beam. The sides are several wavelengths long. For this reason they are made of wire.  Beam-like gain is possible if your rhombic is big enough and the angles are right.

If you're intrigued by all this it's cheapest to experiment with rhombics on the higher VHF or UHF bands. At least on UHF you may be able to mount it on a timber frame and turn it like a beam.

Some rhombic ideas are here:

* W8JI's rhombic write-up
* KB1SB's rhombic pages
* Joby's rhombic ranch
* Royal Aircraft Establishment rhombic design guide
* Dave Casler's Mighty Rhombic video
* Rhombic designs for UHF and microwaves

PS: Want some practical antenna ideas? Consider this selection of antenna books. They are affiliate links meaning that I receive a small commission (at no extra cost to you) if you decide to purchase.


Wednesday, April 24, 2019

The horizontal loop

Do you have a squarish backyard? Maybe it's not long enough to fit in a dipole for your desired lowest frequency? If so then the horizontal quad loop might be worth considering. Especially if you want something effective to work locals on 80 and 40 metres.

A wavelength of wire perimeter on the lowest frequency of operation, it goes by several names including the 'German Quad'. Its enclosed loop is said to make it a good receiving antenna. And operation on multiple bands is possible, especially if fed with open wire line to an antenna coupler.

The shape is normally square. Though it doesn't matter if not all sides are equal if that is convenient for the four trees or masts you will need to find to mount it. It could even be triangle. But it is desirable to enclose as much ground area as you can.

Here are some horizontal loop links that will get you started:

* 4X4LH horizontal quad antenna
* AB2RA on why you should use a horizontal loop
* DJ0IP 8 band horizontal loop
* K5RCD horizontal loop
* N4KC horizontal skywire

I've never built one. But I've heard excellent signals from them. So if you're looking at trying one it's something you might be happy with.

PS: I have written five books on amateur radio topics. They are available in electronic and paperback form (most countries). Ebooks are under $US 5 each. Find our more here or follow VK3YE Radio Books on Facebook.

Tuesday, April 23, 2019

Homebrew antennas for 23cm

It's the 23rd of the month so what better than to discuss practical antennas for the 23cm (or 1296 MHz) band?

Even more so than 70cm, you can achieve very high gain with a small antenna. Although you do need to be very accurate with your measuring and cutting. Another side-effect is that higher antenna gains mean narrower lobes. So you need to be more accurate with your pointing. Or, particularly if your activity involves working though local repeaters over a fairly unobstructed path, you may be able to get away with omnidirectional low gain vertical antennas.

Here's some practical ideas to get you thinking on 23cm antennas:

* DJ9YW 23cm yagi for DX
* PA4DAN 23cm yagi
* VK1AD's 12 element yagi for portable work
* VK1AD's compact bi-quad antenna
* WA6SVT omnidirectional vertical collinear

PS: After portable antennas for lower frequencies? There's ideas in the top-selling Hand-carried QRP antennas. Available in ebook or paperback it's been favourably reviewed by hams all around the world.

Monday, April 22, 2019

One error after another: The Manual Days QRP antenna coupler kit

Most kit reviews are pretty routine. You read the instructions, put it together, make one or two minor errors, fix them and the thing works pretty much as described.

This one is an exception. The instructions were terrible, construction was a nightmare and things didn't fit together well. Still, it did actually work. The video was made a while ago, with the giveaway having long found a new home.

The video is presented here because you can still find these antenna tuners on eBay.  And you might find, what was easily my worst review of any piece of equipment I've had, entertaining!

PS: For some better antenna couplers that you can build yourself, check out Hand-carried QRP antennas. It's available in either ebook or paperback form. Couplers are just the start - there's also ideas and designs for numerous portable and pedestrian mobile QRP antennas.

Sunday, April 21, 2019

HF wire antennas - a quick comparison table

The number of wire antennas is just baffling. They all work but their suitability for what you want varies. Here's a table that presents, in summary form, the main types of wire antennas and their pros and cons.  It may appear small - if it is click to enlarge. 

Do you agree or disagree with any of the points made? Are there antennas that should be listed but aren't? Please let me know in the comments below.

PS: Want to read more about antennas and other amateur radio topics? These books could be of interest. Available in both electronic and paperback.

Saturday, April 20, 2019

Measure radio frequency with wood and wire - experiments with a lecher line

OK it's not quite antennas but it is a transmission line. And transmission lines have many applications in antenna systems. Not only do they form the connection between the transceiver and the antenna but they have other applications like impedance matching at the driven elements of antennas. And, in a crude way, you can determine wavelength and measure frequency.

Below is a video showing experiments I did with possibly the original form of transmission line called a Lecher line.  All I needed as a source of RF (a UHF transceiver) and an RF indicator in the form of an LED.

PS: Want to read more about antennas and other amateur radio topics? These books could be of interest. Available in both electronic and paperback.

Friday, April 19, 2019

Homebrew antenna analysers

You don't hear about dip oscillators or noise bridges much any more. In the last 10 or 20 years the antenna analyser has emerged as the all-in-one must-have instrument for the serious antenna experimenter. 

They are certainly handy. You connect an antenna, dial up a frequency on the analyser and you will get an indication of how it presents as a load, including its resistance and reactance. Better analysers have a display to show everything in graphical form.  You can buy or build them.

The cheaper analysers have had somewhat mixed reviews so it seems to be a matter of getting what you pay for. The more practically inclined may be able to save by building one. DDS VFO modules and cheap microcontrollers, specifically the Arduino, have revolutionised their construction. Here's some ideas that could be handy: 

* AB1ZO homebrew antenna analyser

* Cheap antenna analyser by Electronics Lab

* No frills antenna analyser (video)

* YD1CHS poor man's antenna analyser

* Tenna Dipper another poor man's antenna analyser

PS: Want some practical antenna ideas? Consider this selection of antenna books. They are affiliate links meaning that I receive a small commission (at no extra cost to you) if you decide to purchase.


Thursday, April 18, 2019

Triband end-fed antenna for portable use

40 & 20 metres is a good two band combination. You can cover a wide range of distances on them over much of the day.

If you want a portable antenna that you can use without adjusting an antenna coupler when changing bands then this convenient end-fed antenna may be the answer. It operates as a full sized half wavelength vertical on 14 MHz and a loaded vertical on 7 MHz. Plus it works on 10 metres as well.

The antenna is 12 metres of wire with a loading coil 10 metres from the feedpoint. At the feedpoint is a small transformer unit to step the 50 ohm transceiver impedance up to the few thousand the antenna needs. The short counterpoise can be a few metres of wire.

You can buy them commercially but it's also fairly easy to build your own. The only other item you need is an 8 or 9 metre telescopic pole to act as a mast. Watch this video to learn how to build one and the results achieved.

PS: Want to learn about other portable antennas? You'll find many ideas and projects in the top-selling Hand-carried QRP antennas.

Wednesday, April 17, 2019

Antennas for the 630m (472 kHz) band

The amateur 630m band has some great propagation characteristics. You can get a sample of that by checking the daytime range of broadcast stations below about 700 or 800 kHz. The more powerful ones can be heard for several hundred kilometres, even during the day.

Yes, they may be running 10 - 50 kilowatts to no-compromise antennas that amateurs have no hope of duplicating. But consider they're using AM. And they must be heard on pocket radios with tiny ferrite rods. Take away those constraints and use more efficient modes like SSB, CW and narrowband digital techniques, and amateurs can compensate for their lower power and budgets.

As for antennas for 630m, a horizontal dipole, being about 300m long is out of the question. And it wouldn't be any good for groundwave or DX anyway. So you're likely to be using some sort of vertical, even though it may be 1% or less efficient.  Hear from amateurs who have had this problem and succeeded on 630m through these links below:

* VK2DX simple 630m antenna

* VK5FQ suburban 630m antenna

* NO3M 630m vertical

* N6LF 630m antenna notes

* 472 kHz.org antenna links

* Kevin Loughlin's 630m magnetic loop (video)

PS: I have written five books on various facets of amateur radio. They are available in electronic or paperback form. Find out more here.

Tuesday, April 16, 2019

Apartment HF antennas that work

Amateur radio and apartment living do not mix. Or do they? It's true that your antenna choices are much more limited than if you had a separate house on land. But in many cases you can still get on air.

Having your own open balcony helps. I discussed balcony antennas last month.  Another possibility, if you don't want anything permanent and you're on a high floor, is to drop a temporary wire out and feed it at the top as an end-fed. A fishing pole that keeps it away from the building is desirable.  You may need a weight but be careful that it doesn't blow into someone else's window or attracts undue attention.

Indoor antennas are always compromises, with higher noise pick-up on receive and weaker signals on transmit. But you could try a magnetic loop. A diameter between about 90 and 150 cm will allow operation on many popular HF bands.  They may look out of place but you may be able to disguise it by wrapping its copper or aluminium element with white tape.

Another option, particularly if your place is open-plan, is to string a dipole or similar across. Let's say that you have two rooms about 4 metres wide. That gives 8 metres of antenna space. In other words enough room for a full sized dipole for 15 metres.  Now 21 MHz isn't that active at this phase of the solar cycle so you would probably want other bands. You could add about a metre either side (dropping down) to provide a full sized dipole for 14 MHz.  Or consider adding a trap on each side for a dual band 14/21 MHz antenna.  Alternatively, feeding a 21 MHz dipole with open wire feed line would allow efficient operation on 14, 21, 24 and 28 MHz. That is providing your building's walls don't shield too much of the signal.

There are other possibilities as well. Some are mentioned in my 'Antennas for confined spaces' posts a few days ago. I also suggest the links below:

* ARRL's tips on limited space antennas
* VE7AOV's trouble free apartment antennas Read much more here
* AG4DG's apartment antenna options
* G4ILO's stealth antenna options
* VK2TPM apartment ham radio operation

Have you tried operating HF from an apartment? What are your experiences? Please leave your comments below.

PS: Want to support The Daily Antenna
You won't be charged extra and I'll get a small cut from any purchases you make (affiliate link). You can buy lots of stuff there, including electronic parts and my books.

Monday, April 15, 2019

Historical 1930s - 1970s antenna articles

Today we'll go back in time. Presented below are links to articles in old issues of Amateur Radio magazine, published by the Wireless Institute of Australia.  Issues dating from the magazine's inception well in to the 2000s are here. I'll look through pre-1970 April issues only, starting with the earliest ones that have substantial articles on antennas and related topics.

You will see things, like coaxial cable and ferrite baluns, considered as novelties then that are accepted practice now. And you'll discover how people tested antennas before accurate test equipment or computer modelling. And you might find some of the other articles in these issues so enjoyable that you could be reading for hours.

28 MC transmitting antennae by VK3BD (April 1936, p4)

Concentric line feeders by W9FM (April 1937, p11)

The skeleton slot antenna for 144 MHz by VK5XU and VK2NO (April 1955, p2)

Some considerations in the selection of an antenna tower by W4QDZ (April 1960, p 8)

The HB9CV Swiss Quad by VK6DR (April 1965, p6)

* The corner antenna for 7 MHz by VK2SA (April 1967, p7)

* The ferrite balun by ZS1SC (April 1969, p9)

PS: Want to read newer items on antennas? Consider this selection of antenna books. They are affiliate links meaning that I receive a small commission (at no extra cost to you) if you decide to purchase.


Sunday, April 14, 2019

The 50 ohm rectangular loop

Many of us have seen diagrams of the square quad loop. It's an effective antenna. You can feed it at the bottom centre for horizontal polarisation or in the middle of either side for vertical polarisation.

Something that makes its construction slightly harder is its 100-120 ohm feedpoint impedance. Unlike a half wavelength dipole (especially the inverted-vee variety) it can't be fed directly with 50 ohm coaxial cable.  A 4:1 balun is not quite right either. Instead you need to make a transmission line transformer (using 1/4 electrical wavelength of 75ohm coax) to reduce ~100 ohm to ~50 ohm.  Or you could feed it with open wire line and use a balanced antenna coupler. 

Another issue with a square loop is height. You don't want the bottom wire to be on the ground. Raising it a little helps but you still want it to be above head height to avoid crashing into it. So, assuming you make the square loop from wire slung between two poles, the masts need to be at least 1/3 wavelength tall.  

That's a little beyond the 7 or 8 metre fishing poles many portable operators use. Especially if you don't use the top metre or so due to its fragility.  However, especially if you're portable you can spare some extra ground space.

One solution is the rectangular loop. It's still a wavelength around but its no longer square. That reduces its feedpoint impedance to 50 ohm with certain dimensions. And if you make it 1/3 wavelength wide and 1/6 wavelength high then you can erect it with shorter masts.  The shorter side also make it easier to feed in the middle, which is desirable if you want vertical polarisation.  

Here are a couple of videos I've done. The first was with a loop 20m in perimeter. The second was a loop with a 30m perimeter. The latter, if fed with open wire line and a balanced antenna coupler, can work efficiently on popular bands including 7, 10, 14 and 18 MHz. 

Some rectangular loop ideas from others:

Rectangular loops are so simple to build. Try one - I think you'll like it. 

PS: I have written five books on amateur radio topics. They are available in electronic and paperback form (most countries). Ebooks are under $US 5 each. Find our more here or follow VK3YE Radio Books on Facebook.

Saturday, April 13, 2019

Portable antennas for your VHF handheld transceiver

The antennas that come with VHF/UHF handheld transceivers are often not very efficient. That's not surprising. They have to be compact. They have to also work on 70cm. And they have to be built very cheaply (given the low prices many transceivers now go for). Their inefficiency means that you often need to run your transceiver on the high power setting. And not even that is always enough to guarantee a good signal into a repeater.

If you can tolerate some extra length, you can get better results if you build your own. The cost is low. Your handheld will hear better and transmit further. And the simple designs around make it a great evening or weekend project.

Here's a few practical ideas to get you building:

Add a counterpoise antenna wire
F3WM pocket antenna
M0PZT Slim Jim
VK1NAM 2m flexible Slim Jim and a coaxial dipole
ON6MU rubber duck portable antenna
PI4ASV 2m or 6m coax vertical
PA0FBK 2m & 70cm coax roll up antenna and a half wavelength vertical for 2m

If you try any please let others know how you go in the comments below.

PS: Want to read more about antennas and other amateur radio topics? These books could be of interest. Available in both electronic and paperback.

Friday, April 12, 2019

Antenna ideas for the 160 metre (1.8 MHz) band

160 metres (1.8 MHz) can be a tricky band for antennas. In fact it's a band that many (most?) amateurs don't bother with due to the space many antennas require. Because basic 'building block' full-sized antennas are massive. For example a half wavelength dipole is 80 metres long. And a quarter wavelength vertical is 40 metres high.  For this reason, unless you've got plenty of space your antenna will need to be significantly smaller. While that compromises performance, you're probably in the same boat as most others on the band. And unless you are in a very remote location contacts should still be possible on the band.

Whereas on bands like 40 metres a half wavelength dipole is almost guaranteed to give good results, greater thought is required for 160 metres. This is not only due to space constraints but where you wish to work. This is because 160 metres supports both ground and sky wave propagation. That's different to other bands where 99% of contacts are skywave and an antenna's groundwave characteristics can be almost safely ignored.

Look at what the AM broadcast stations use. They aim to maximise groundwave coverage within their 50 - 200 km service area. For that they use vertically polarised antennas. So should you if that's your aim, for example if you enjoy local chatting around town or across a bay near you. While your first reaction might be to use VHF for that, 160 metres can also be suitable and is particularly enjoyed by those who use AM.  Good antenna choices include a vertical, or if you want a bit of everything, an inverted-L. You can even use antennas that look horizontal (like a flat top horizontal dipole for 80 metres) as a vertical if you tie the feeders together and load against all the radials you can roll out.

What if you live (say) 200 - 300 km out from a main population centre? They're still good distances for the 530 - 800 kHz end of the AM broadcast band and also our amateur 630 metre band. But they're long for groundwave coverage above 1 or 1.5 MHz.  You can still span those distances on 160m but it will need to be at night employing skywave. The antenna polarisation doesn't matter very much. But you do want the radiation angle to be fairly high. A horizontal dipole, inverted-vee or end-fed wire at any practical height should be fine for that.

What if you want DX? Yes, you can work 10 000km plus DX on 160 metres, though it requires more patience than on easier bands like 40 metres. But it is desirable to have a low radiation angle. A vertical with a good ground system (like we used for local communication) should be OK. But, unless it's very high, a horizontal dipole is unlikely to be.

The above paragraphs settle it. Unless you wish to work some immediate distances then your antenna will likely be some form of vertical (or inverted-L). With as good a ground system as you can manage. And if you're seriously into DXing and you find noise a problem then a separate antenna for receiving is desirable as well.

Below are some ideas on antennas for 160 metres.

* Inverted L by W1FB
M0MCX inverted L for 160 80 40m
* W8NX space-efficient dipole (pdf)
* VK3ZZC 160m vertical
* 22 different wire antennas for 160m
A 160m antenna for a small backyard
PA1M 80 & 160m antenna for the small garden

Have you had experience with these (or other) antennas for 160m? If so please let us know what worked and what didn't in the comments below.

PS: Want to get the most from low power amateur radio? You need Minimum QRP. It covers the equipment, antennas, operating and strategy you need to succeed with QRP. It's available as an ebook or paperback and has been favourably reviewed.

Thursday, April 11, 2019

A flick through some amateur radio antenna books

You can't have too many amateur radio antenna books.

Here's a few and what's in them.

PS: Want to read more about antennas? Consider this selection of antenna books. They are affiliate links meaning that I receive a small commission (at no extra cost to you) if you decide to purchase.


Wednesday, April 10, 2019

Antennas for confined spaces (Part 2)

Yesterday I gave some tips on accommodating amateur antennas in confined spaces. Today I'll give some ideas for compact antennas by band.

Picture of magnetic loop

80 metres

A challenging band for the amateur with little space. Though a compact antenna is unlikely to yield regular DX contacts, it should be possible in almost every case to enjoy fairly regular QSOs up to about 500km when band conditions are quiet. There is always a trade off between bandwidth and efficiency with small antennas. Always aim for efficiency; it is better to be heard on one frequency than to be heard on none.

First we'll talk about dipoles.

Of interest to those with limited space, is how well they operate below their resonant frequency. As a rough rule of thumb, you can cut about a quarter off a dipole's length without severely compromising performance. In other words an 80 metre dipole (40 metres of wire) will work with just 30 metres (5 metres cut off each end). If you droop each end down by 5 metres then you'll be able to fit it into a 20 metre span. Like with a full-sized dipole, it is acceptable for the mast supporting the feeder to be higher than the masts or trees supporting the ends; this is known as an inverted-vee.

Of course such a shortened dipole will have a feedpoint impedance wildly off 50 - 70 ohms and present some reactance as well. So you won't be able to use coax cable with it. Instead you need 300 - 600 ohm open wire feedline and an antenna coupling unit. As well as allowing the abovementioned short antenna (often known as a G5RV) to operate on 80 metres, you'll get other bands as well. It really is a lot of antenna for the money, provided you have a yard long enough to accommodate a 20 metre wire span.

Use much shorter than 30 metres of wire and the antenna's efficiency drops enourmously and it might be time to think about other methods.

One possibility is a 40 metre dipole (20 metres of wire) and end loading coils for 80 metres. This will operate on both bands but the bandwidth on 80 metres will be narrow. Nevertheless I've had a good results on that band and can recommend it. The one I built used just the longest element of the VK5AH 4 Bander.

The dipole can be shrunk further and even made rotatable by mounting two mobile whips end to end. Such antennas have directivity and do not need extensive grounding systems. Bandwidth will be extremely narrow, but experimentation with remotely controlled relay switching schemes, to allow a choice of operating frequencies, may prove fruitful.

Some operators use end fed wires. That may suit your situation if your shack is nearer then end than the centre of where your wire will go. Disadvantages include 'RF in the shack' and increased interference pick-up. Hence this arrangement is most suited to low power or temporary operation. If the wire length is exactly 20 metres you may be able to get away without using an antenna coupler. Otherwise you will need one.

An effective counterpoise is also important, particularly if the wire is a quarter wavelength (20 metres) long or less. Some people use the gutters on their house for this. However, there is a risk that poor electrical contact between lengths of guttering could act as crude rectifiers and cause interference-producing harmonics to be radiated. Half wavelength-long end fed wires exhibit high feedpoint impedances and are less dependent on an effective earth for correct operation.

Vertical antennas are another possibility, especially for people with backyards too small for a dipole or G5RV. They're especially attractive if you have a large metal roof, eg a shed or carport, and the vertical can be raised to be mounted on or against it. A full sized quarter wave vertical on 80 metres is truly a monster (20 metres high) but traps can be used to greatly shorten it. Several 80 metre operators known to the author have had good results with the commercially-made verticals manufactured by Andy Coman.

Trapped verticals can disappoint as much as delight; they don't offer the sure-fire predictability of a dipole. Traps risk loss. The extensive radials needed for best efficiency are either hard work (if buried) or an eyesore (if raised). And, most importantly, the vertical's radiation pattern, though good for very short (groundwave) and very long distances (low angle, towards the horizon), is often deficient in the 50 - 500km range that is so critical to the bulk of contacts on 80 metres.

magnetic loop is perhaps the smallest practical antenna for 80 metres and the only option for some. It consists of a circle or square of metal tubing brought to resonance on the operating frequency by a variable capacitor. A single loop can cover several bands over a 2 or 3 : 1 frequency range. Their efficiency is somewhat lower than for larger antennas, but no ground system is needed and the antenna does not have to be very high off the ground. Loop sizes as small as 2 metres square are practical on eighty metres, though larger loops will be more efficient.

A good loop will be made of thick copper tubing and have solid connections. The bandwidth will be very narrow; maybe 10 kHz on 80 metres. Such narrow bandwidth, though it makes the antenna a pain to adjust when changing frequency, indicates the antenna is low loss, has high Q and is performing efficiently.

I'm a big fan of magnetic loops. They've always worked when built. Effort and expense in building them well pays off. Their directionality is especially good on receive, allowing local interference to be nulled out. Thousands of amateurs living in flats or units have access to HF, thanks to the magnetic loop.

40 metres

Comments and recommendations for 80 metres also apply for 40 metres. 40 metres offers propagation characteristics well suited to low power and small antennas.
However size requirements are relaxed and it is vastly easier to build an efficient, yet compact antenna for the band. For example, it will be easier to fit a 40 metre dipole in the roof space or build an efficient magnetic loop for the band (even 1 - 1.5 metre loops work suprisingly well on 7 MHz).
No matter how small your accommodation is, time and money spent in building a good compact antenna for 40 metres will not be wasted.

30 - 12 metres

As wavelengths get shorter the variety of possibilities increases. If you don't have the yard length to install a full sized dipole it may be possible to fit in one with its ends bent up to form a square. 
Several dipoles on the one crosspiece can provide multiband capability. Look up 'cobweb antenna' for designs. Alternatively flagpoles can be a quarter wavelength on some of these frequencies so be a workable antenna if loaded against buried radials. An antenna coupler at the bottom (preferably automatic or switched) could allow operation on several bands with the one element.

10 metres

The existence of the 27 MHz CB band has been a real boon for the antenna experimenter active on 28 MHz. Many CB antennas such as ground planes or verticals can be modified to ten metres with very little work being required.

If building from scratch, a wire ground planevertical dipole or delta loop are worth considering. A good thing about 10 metres is that their dimensions are starting to get small enough to be concealed in a tree.

If you have less room consider a modified fibreglass CB mobile whip mounted on a gutter, roof or balcony. This is effective for both local and overseas contacts and occupies very little space. Longer whips give the best performance; a 1.5 metre whip or longer is suggested. Good height and a clear outlook are desirable. The ground system can either be a metal roof, gutter, railing or one or two 2.5 metre long radials.

Once installed, the whip is trimmed (using a hacksaw) to make it resonant on 28 MHz. To avoid over-cutting, saw off small pieces at a time (no more than 1 cm) and check the standing wave ratio (SWR) at the antenna after each cut. If the antenna is too long, you will find that its SWR is lowest at 28.1 MHz and gradually rises towards 28.6 MHz. Continue trimming the antenna until the SWR is lowest around 28.4 MHz. It will rise either side of this frequency but should be acceptably low over the most active SSB section of 10 metres. When you've finished, you will probably have sawn 8-10 centimetres off the antenna.

A horizontal dipole is another possibility. This could either be nested with dipoles for lower bands (noting the risk of interaction) or supported on its own poles or trees five metres apart. Unfortunately extra wires or more supports can be ugly; a consideration for amateurs wishing to keep their station low-profile. Even though people think that open wire feedline is ugly, it's actually

Those with sizeable balconies or a backyard could try a horizontal dipole. The space required is about 5 metres. If fed with open wire line, the dipole should also work on 21 MHz with the addition of an antenna coupling unit.

A yagi or quad is normally out of the question for unit dwellers. However if you have a small courtyard, the possibility of installing a VK2ABQ miniature beam antenna for a few decibels of gain should not be discounted.

Two metres and 70 centimetres

The helical antennas supplied with handheld transceivers often perform poorly around the house.
A good step up is a simple vertical dipole that can be hung behind a curtain or in a similar inconspicuous position. They are best near a window facing the direction of interest.

Or, when outside, hang it from a tree branch for better coverage on VHF. This should be sufficient to provide access to local repeaters and nearby simplex contacts. Simple vertical antennas are particularly useful when omnidirectional coverage of a local area is desired, for example during club nets or local contests.

For permanent use some sort of outdoor vertical antenna mounted on the balcony or roof is desirable. A small 1/4 or 5/8 ground plane can be fitted on top of a TV antenna (move the antenna down the mast) or on the toilet's exhaust pipe.

The main challenge will probably be to get the feedline into the house. RG58 is better than RG-213 (or thicker) in this regard, but is lossier, particularly on 70 centimetres. This is why feedline runs need to be kept short, with thought given to equipment and antenna placement.

What if gain is needed? It's a toss-up between a tall collinear vertical (for FM work) or a yagi. Both have their mounting problems. A tall vertical may be unwieldy for supports (eg TV antenna 'hockey sticks') designed for lower antennas. Whereas a vertical yagi requires a non-metallic mast (or at least its top section) to avoid interference to its radiation pattern.

Beams also introduce the problem of rotating. It may be possible to do this by hand if the support mast extends to the ground. Or, if you can't be bothered with a rotator, a 2 element vertical yagi could be a good compromise, especially if you're near the edge of a city and most stations are repeaters are in a favoured direction. This is because a 2 element yagi has a broad front lobe and a substantial rear response.

At least two antennas are needed if you wish to use both FM and SSB on VHF / UHF. FM vertical and SSB horizontal. Luckily horizontal beams for 2m and 70 cm look exactly like TV antennas so should attract fewer objections.


The above comments, have, I hope, given several ideas for the amateur wishing to establish a low-profile amateur station. With recent improvements to propagation conditions, there will never be a better time to set up a station than right now!
PS: I have written five books on various facets of amateur radio. They are available in electronic or paperback form. Find out more here.

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