Sunday, March 31, 2019

Beach seat portable antennas

It's heading towards summer in the northern hemisphere. Beach weather. What if you want to operate from there? After all the proximity to salt water improves signals, and if you're away from urbanised areas you'll benefit from lower local noise as well. 

One problem is that if the weather is nice the beach will be popular. With other people around. So you don't want to take too much space, have people (and dogs!) trip over your antenna radials or make too much noise. Careful selection of antennas takes care of the former while CW (with headphones) and the more efficient digital modes look after the latter.  

The most important thing is not radio-related at all. It's to find a seat that's comfortable for you. After all you could be operating from there for an hour or more. I particularly like the seat pictured above. Whereas (for me) the curves in the one below make it so uncomfortable that I prefer being on the ground. 

 Then there's the antenna. It will almost certainly be some sort of vertical. A magnetic loop could work but it may be unwieldy. And it will require frequent adjustment if changing the frequency. An extendable pole with some sort of vertical is elegant and takes up next to no horizontal space. And you may be able to tie it to your seat. 

Possibilities include an end-fed vertical with an L-match antenna coupler. A 9 metre pole will allow one that's close to a half wavelength long on 14 MHz. Or you could try a vertical dipole. A difficulty with that is ideally you need to bring the feedline away from the dipole's centre. Or you could try a coaxial type vertical dipole where the lower element surrounds the coaxial feedline. 

If there's a support (eg a sign) that's 10 or 15 metres away you could tie off a wire there. Then you could use an inverted-L about 20 metres in total length. That will work well on popular bands like 7, 10 and 14 MHz. And likely higher. This is what I used in the video below to work CW and SSB USA DX from Australia. A horizontal dipole or inverted vee is also good but you'll need two supports apart from the central pole. 

Grounding is another consideration. Your seat may have a metal frame. That could be clamped onto (picture below). However that won't be big enough for the lower HF bands. Radials present a trip hazard but if there's a timber deck you might be able to have them underneath. Or even under sand if right on the beach. Though dogs are guaranteed to dig so be prepared for them to be uncovered. 

What about VHF/UHF? A small yagi for 144 or 432 MHz is light enough to be supported on a fishing pole. Provided it's 3 or more metres up it won't get in anyone's way. And, even though it's not far above sea level, the water side location may be favourable for tropospheric ducting as often happens over summer. 

These are a few ideas for operating from a beach seat. Have you done it? What's worked for you? Please share your experiences 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.

Saturday, March 30, 2019

Loading up the gutter

Living in a place where you absolutely can't have any visible outside antennas?

Poor you!

Still, where there's a will there's a way and hams have used almost any metal object as an antenna.

Including rain gutters around your house.

The first thing I'll say is they are a severely compromised antenna on both receive and transmit.

Unless you live in a multi-storey building they're not very high. Their proximity to electrical wiring and appliances inside means they will pick up a lot of noise on receive. And if you're near an AM broadcast station you may even hear signals that aren't really there due to harmonics generated by rectification caused by bad connections between sections.

As for transmitting, the same bad connections or dissimilar metals could cause a perfectly clean transmitter to radiate harmonics. The low height means poor performance. And their odd shape might cause unpredictable performance. You will need a wide-range antenna coupler to match it; the one built into your transceiver might not do it, unless you are lucky. Still, especially for efficient modes like WSPR, a gutter antenna should get you some results.

A rain gutter antenna is the type where you'd really want to read about others' experiences before trying one. Some are presented here:

* Experiences of rain gutter antenna with SG230 antenna coupler (commercial link)
* K5IJB rain gutter antenna
* N3VEM rain gutter antenna
* WB3GCK downspout antenna
* WMOG's results with rain gutter antennas
* W6NBC on rain gutter wire loop antennas (not loading up the gutter as such)

Have you used a gutter antenna? Or even worked someone with one? If so 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.

Friday, March 29, 2019

The discone for VHF/UHF

What is omnidirectional, comprises many elements yet has the same gain as a vertical dipole?

The answer is the discone antenna, widely used on VHF and UHF.

It's quite a big beast comprising a disc at the top and a cone at the bottom (hence the name). Although more often than not it's not a real disc and cone. Instead it's lots of elements radiating from the feedpoint to form what amounts to be the same thing electrically. They also often have a vertical element for lower frequencies.

At first sight the discone doesn't sound very attractive.

But if you want a general purpose wide band vertically polarised antenna for listening and local transmitting, then the discone could be just right.

If you've got a RTL2832 software defined radio dongle you probably got a short vertical antenna maybe 15 or 20cm high. They're useless. You might hear local FM broadcast stations if you're lucky. An outdoor discone fed with coaxial cable will be far better and allow you to receive a wide variety of VHF/UHF transmissions including aircraft, broadcast, amateur and more. In fact the discone has had a big surge in popularity since SDR dongles came out and people wanted an antenna that suited their dongle's wideband receiving capability. 

What about transmitting? They're not better than a dipole or ground plane. But their broadband capability is particularly useful in countries like the United States with many VHF/UHF amateur bands, for instance around 50, 144, 222, 432 and 902 MHz. You should be able to comfortably work through repeaters up to about 50km away with 5 to 20 watts output power on FM. Just make sure your transmitter's RF output is clean because if it isn't the discone will faithfully radiate any spurii due to its broadband nature.

You will need a stout solid mast to mount a discone. Particuarly one that operates much below 100 MHz. But if you've got lots of scrap metal, for example from an old TV antenna, the cost to build one is not high. They make a great reference antenna that provides a base level of performance against which you can compare your higher gain verticals and beams. If your other antennas are performing worse than the discone then you know something's wrong.

Here's some ideas for homebrew discones:

* Home made coat hanger discone
* Instructables discone plans for SDR
* WB4HFN notes on discones
* DIY folding discone (video)

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.


Thursday, March 28, 2019

Antennas for bicycle mobile

I've never gone bicycle mobile. I don't think I've even worked anyone whose been bicycle mobile.

It presents a formidable challenge. You're limited for space and weight. The bike's frame provides only a rudimentary ground plane for a vertical (which is most often used). And your station has to be easily operable while pedalling along.

2m and 70cm FM are obvious choices with repeater coverage and small antennas. Capability on 6 and 10 metres provides some variety during the summer sporadic-E season with great contacts up to about 3000 km possible. And at other times you might be able to work bands like 20 and even 40 metres with a suitable antenna.

Anyway, here's some ideas. Even if you don't go bicycle mobile, the tips might be useful for pedestrian mobile or even apartment balcony operating as well.

* ARRL's guide to bicycle mobile antennas (pdf)
* KS1G's bicycle mobile station (pdf)
* $5 antenna for HF bicycle mobile
* VK4MSL 40 - 6m bicycle mobile antenna
* Bicycle Mobile Hams of America

Let us know your bicycle mobile experiences in the comments below if you try any of the above.

PS: Want to get more from low power amateur radio? Minimum QRP is what you need. This top-selling manual covers the equipment, antennas, operating and strategy needed to be successful with low power amateur radio. Available for under $US 5 as an ebook. Or in paperback form (some countries). Click here to find our more and to see reader reviews.

Wednesday, March 27, 2019

Antenna ideas for the 30 metre (10 MHz) band

Amateurs into HF commonly have a beam covering the 20 metre (14 MHz band). Either a monobander or a tribander with traps. 7 MHz is often covered with either a dipole or vertical.

What about 30 metres or 10 MHz? That's easy if they have a dipole with tuned feeders and a good antenna coupler. Otherwise it requires modifying an existing antenna or putting up a new one dedicated for the band.

Is this worthwhile? At the current phase of the solar cycle there are times when 30 metres is open but 40 metres isn't. If you're into single hop communication of around 1000 to 1500km there are times when that is too short for 20 metres but signals are weak on 40 metres.

Not into contesting? 30 metres is a quite haven for you since contests are not run there. Then there are the DX prospects of 30 metres, especially if you are into digital modes. 30 metres can come into its own in the late morning when 40 metres fades out but before 20 metres comes in. And vice versa in the afternoon.

As for the antennas people use, a beam is out of the question for most. But there is a big choice of less visible wire antennas. These include dipoles, verticals and even beams. The usual rules apply. If you want DX go for a low angle radiator. Suitable antennas include a high dipole (at least 1/2 wavelength off the ground) or a vertical with good radials over a conductive earth.

Here are some ideas for 10 MHz antennas that other hams have found effective:

* K7EA 30m ground plane
* N2RIT 30/40m black box vertical
* I2NDT coaxial cable dipole for 30m
* ON8IM 30m bobtail
* M0MCX 30m rotatable delta loop
* N6JV 30m beam
* Eham discussion thread on 30m antennas

PS: Want more 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.


Tuesday, March 26, 2019

Joys of balcony HF whips

I lived in a second-floor apartment as a young graduate in Canberra. There was no access to the ground or roof but I did have a private balcony. On that I had a couple of antennas.

The most successful was a 1.5m long mobile whip for 28 MHz. Even though it was the bottom of the solar cycle I occasionally made DX contacts with a 12 watt Johnson Viking 352D converted CB. And it worked a treat during the summer sporadic-E season.

So I have some fond memories of balcony antennas. I've since moved to a larger place with land but no balcony. So I haven't used balcony antennas recently. But if you're an apartment dweller and want to get on HF then I can recommend them. Especially on 14 MHz and up where efficiency is reasonably good.

The simplest approach is to get some sort of mobile antenna mount and screw in monoband mobile whips about 2 metres long. Buy some for your favourite bands. Add at least two radials a quarter wavelength long for each band. You do need to swap whips to change bands but at least you're on the air. And, despite compromises with the whip length being significantly shorter than full size, you can get some good results especially if your balcony is in the clear and/or faces a useful direction.

Here's some accounts of other peoples' success with balcony whips on various HF bands:

* Long Reddit thread on balcony antennas
* UR5WCA balcony antenna for 7, 10 & 14 MHz
* Ham Radio on a very short antenna
* Buddistick balcony antenna (video)

Have you had success with balcony antennas? Or maybe some failures? Either way, please share your experiences 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, March 25, 2019

Lower noise with HF receiving loops

As important as you being heard by other stations is you hearing them. 

That's particularly the case in urban areas with ever increasing amounts of electrical noise.

160 metre DXers have long used separate receiving antennas to hear weak signals. However the benefits of this also apply on the lower HF bands.

While a shoddily built magnetic loop antenna might not be good for much apart from WSPR transmitting, it can perform well as a receive antenna. This is because signal to noise ratio, rather than efficiency, is most important in a normal environment with ambient RF noise. Loops offer the benefit of having deep nulls that can be used to null out noise if most of it is coming from a single source.

Loops can either be narrow band (like a transmitting magnetic loop) or wide band. Narrow band is good if  you want the loop to act as a preselector. This could be useful on the lower HF bands if you have strong AM broadcast stations nearby and your receiver's front end isn't very strong. However narrow band loops require some sort of variable capacitor which needs to be changed if there is a significant excursion in frequency.  Wide band loops don't have that constraint but don't offer selectivity. 

Another factor to consider is RF preamplification. Very small loops require this for good signal to noise ratio whereas larger loops don't as external pick-up is sufficient. Often the preamp circuitry is near the loop with DC power being fed up the feedline to it. This can be done using a technique similar in TV masthead amplifiers, that is to use an RF choke and capacitor to separate DC from RF. 

Here are some ideas on receiving loops: 

If you try any of these, I'd be curious to hear how you go. Please mention your experiences in the comments below.

PS: Into low power amateur radio? Minimum QRP is the top-selling manual on the equipment, antennas, operating and strategy of successful QRP operating. It's available for under $US 5 each in electronic form. Or you can get a paperback version. Visit VK3YE Radio Books to find out more. 

Sunday, March 24, 2019

The most gain for the least money - fixed wire beams

Do you want big-station performance for a small station budget?

Are you only interested in working stations in one direction?

Do you want an antenna that doesn't stand out?

If all three apply then some sort of fixed direction wire beam might be for you.

Especially if you have a large tree that you could conceal it in.

Compact options include a two element quad or delta loop. Or a two or three element yagi. If a yagi you could even have the elements drooping down a bit like two inverted vee.

Once you've got the basic antenna refined you could make it switchable in direction. That could be handy for long distance DX where there's the option of working long path and short paths. Switchable direction is easiest for three element beams as you leave the centre (driven) element the same and electrically lengthen or shorten the outer elements to make them a reflector and director respectively. Relays could be used for remote switching with a control line from the shack.

Another option is to do what Les Moxon G6XN suggests in his book HF Antennas for All Locations for two element quads and that is to feed both elements with open wire line and handle the switching in the shack.

Here are some ideas on wire beams of various types.

* N6IJ 75m 3 element delta loop wire beam
* M0MCX bidirectional switchable wire yagi
* VE3RGW field day wire beam for 20 or 40m
* VE3VN 3 element wire yagi for 40m
* 2 element wire beam with 4 switchable directions

If you build any let us know how you get on in the comments below.

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, March 23, 2019

Mega antennas galore!

I like to keep things practical.

That is to write about antennas that amateurs of ordinary means with ordinary amounts of land could reasonably buy, build and accommodate.

Sometimes though it's worth lifting budget and space constraints to see what amateurs can install.

You might never own such a station but it's great that they exist, especially when you work them from half way around the world with your QRP and dipole. 

Here's a selection of some of the biggest ham antenna installations you'll see anywhere.

* OH8X 160m 3 element yagi (write-up here)

* KC1XX 3 element 160m array

KC1XX's towers (and 80m beams) 

* 7J4AAL 5 element yagi on 80m (picture)

IW5EDI 3.5 MHz 2 element quad

* R7AB's 12 element 14 MHz yagi

* Hy Gain 14 element HF log periodic (video)

* W5UN's EME array on 144 MHz

PS: Want a return to reality to read about more achievable 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.


Friday, March 22, 2019

Fitting a dipole into a smaller space

Take the band (in metres) you wish to make an antenna for. Halve it.

That's the horizontal space you need to accommodate a flat top half wavelength dipole.

But you don't have that room on your property.

What do you do?

Some people are worried that if their dipole isn't quite straight then they will suffer much reduced performance.

This isn't so.

Unlike antennas like magnetic loops, verticals and critically coupled beams, where you do need to be careful to get design performance, half wavelength dipoles are very forgiving with what you do to them. 

Provided you have the centre two thirds relatively straight you can bend their ends to fit.

The ends can be lower than the centre. Ends don't have to be the same height. The only substantial difference is that the length that you obtain resonance on your desired centre frequency might be a little different.

Here's a few (but not all) possible dipole configuration options below. The black blob is the feed point.

Not all bent dipole configurations are equal. Impedances change and losses increase with extreme bending. Read the following links for what antenna modellers and experimenters have to say about this. 

* Bending the dipole (academic paper by Erwin B Daculan)

* KK4OBI's bent Dipoles
* W4RNL on folding bending and mutilating dipoles
* W5ALT's bent dipoles

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.


Thursday, March 21, 2019

The smallest HF portable antenna

As a rough rule the smaller the antenna the less efficient it is. That can be somewhat mitigated by making its bandwidth narrow by making it high Q like a magnetic loop. But even there losses become overwhelming when the antenna gets tiny. And a high Q antenna requires extraordinary quality of construction (eg thick low resistance elements and excellent connections) to deliver anywhere near its estimated performance. And short verticals require extreme attention to ground systems that are longer, bigger or heavier than the antenna itself.

There are however cases when people are willing to compromise antenna performance for the smallest possible size. They might be satisfied to be receiving 90% of the time. Or confine themselves to highly efficient non-QSO digital modes like WSPR. Or mainly transmit on bands like 10m where a short vertical will be more efficient there than on 20 or 40 metres.

Small whips, such as usable for the above purposes, were really popular around 2001. The timing was perfect. The revolutionary Yaesu FT817 had just come out. Although of mediocre capacity, its internal batteries had made it a truly portable transceiver.  The only thing missing was an equally portable antenna, preferably self-supporting without a need for a tree or pole. Although efficient digital modes hadn't reached their current development, the strong sunspot peak of the time made long distance contacts on 28 MHz possible. Even on SSB. Even with tiny antennas.

To meet this demand there were commercial products like the Miracle Whip. This was a small telescopic whip that allowed operation on numerous bands.  You'd adjust for maximum noise on receive and VSWR would be passably low for transmit (although note that low VSWR does not imply low loss!). It could be plugged straight in to the FT817 to form a small portable transceiving package. Receiving performance was acceptable, but due to its size the transmitting performance put it in the 'novelty antenna' class.

More recently, although sunspots are down, modes like WSPR have made ultra-small antennas useful for transmitting as well as receiving again. Here's some ideas if you wish to build your own or use those that are commercially available.

* Short pedestrian mobile whip for 7 to 28 MHz - basically my version of the Miracle Whip
* Some experiences with a Diamond whip antenna VK3YY VK1NAM
* AA3SJ short whip tuner
* SM0VPO short antenna
* G3YCC portable HF whip
* G4FON musings on the Miracle Whip design
* G7DIE portable 20m whip (video)
* PA1CA's look at the Miracle Whip

As long as your expectations for transmit performance aren't too high, projects like these are a lot of fun. And when signals are strong, don't dismiss the chance of transmitting success, even on SSB. Please let us know your experiences of these antennas, or if you have a favourite design, in the comments below.

 PS: Wish to explore other facets of amateur radio? These favourably reviewed books might help.

Wednesday, March 20, 2019

Various antenna masts compared

Height is might. Generally speaking the higher your antenna the better. Signal reports improve and, for horizontal dipoles, the radiation angle is reduced so HF DX becomes more workable. And on VHF/UHF a higher antenna lets you clear obstructions and increases your communications distance.

Unless you find a handy tree or wish to play around with kites, you're going to need some sort of antenna mast. It can be fairly light and flexible if you're just using end-fed thin wire antennas. On the other hand, if you'll be using heavier wire antennas or even beams it will need to be more solid.

Below are videos of various poles and masts I've used for portable and home operating.

Compact telescoping poles - how good for portable antennas?

Comparing a 9m fishing pole with a Spiderbeam 12m mast

5m aluminium antenna mast (sold by Jaycar, Australia)

12m Spiderbeam as home antenna support

Home station timber antenna mast

What can happen if using a mast to support a kite antenna...

... and how you can best use the bits remaining

PS: Antennas to suit these masts are covered in Hand-carried QRP Antennas. Available in electronic and paperback form (some countries) this well-reviewed book is a popular read amongst hams who go portable.

 Link to find out more about Hand Carried QRP Antennas

Tuesday, March 19, 2019

The magnificent Moxon

Want some gain and directivity but don't quite have the room for a 2 element yagi? This is where what we'll discuss today could be of interest.

Called the Moxon, it is a development of the VK2ABQ beam of the 1970s. Think of it like a 2 element yagi but with the ends bent in. That makes a horizontal Moxon narrower - useful if you've only got a small yard and need a small turning radius.  Or, if you're using it vertically you'd only need a shorter pole to support it. Yet the gain can be nearly as good, thanks to 'critical coupling' as explained in Les Moxon's book HF Antennas for All Locations.

Moxons can be built either from metal tubing or wire. The latter needs some sort of support frame such as bamboo or fishing poles. Their main shorcoming is that some dimensions are critical, in particular the separation between the elements. That means that you need supports to be the right spacing or the correct amount of tension applied. They're mostly a single band antenna, though if you are willing to spend the time adding and optimising each wire element they can be made multiband as well.

Here's some Moxon links to peruse:

* DU1RZ multiband wire Moxon beam
* KD6WD Moxon antenna project
* Multibanding the Moxon Rectangle by W4RNL
* Handheld 2m/70cm satellite antenna using a Moxon on 2m
* VP9KF Moxon antenna calculator
* Portable QRP with a Moxon (video)

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.


Monday, March 18, 2019

Tuned counterpoises for HF vertical antennas

We all know how important it is to have a good counterpoise for a vertical antenna. Especially if you want to work long-distance DX. But sometimes you don't have the space for a full sized counterpoise system. For instance you might be operating from a public place like I often do from local beaches.

Here's an alternative. It's a small tuned counterpoise. It's explained and demonstrated in the video.

These notes on ground tuning units by Alex VK2HAS based on work by G4AKC are worth reading. (pdf) There's also VK6OP's video, again inspired by G4AKC.

PS: Thinking of more things you can do with amateur radio? This book can help. Under $US 5 as an ebook or available in paperback as well. Many favourable reviews.

Sunday, March 17, 2019

A little more gain: Ideas for 4, 5 or 6 element yagis on 2m

Two weeks ago I mentioned how good a two element yagi was on a gain for weight basis. Compared to a half wavelength dipole one could nearly triple one's effective radiated power and get better results on receive with just one extra element.

Nevertheless there are still times when you need a little more gain. When you're just on the cusp of readability an extra two or three elements can make your signal perfectly readable. That really counts if working aircraft scatter with low power or in events like VHF field days where your score increases greatly when more distant stations or grid locator squares are worked.

Bigger yagis can be difficult on HF. But on 144 MHz a 4 to 6 element beam can easily be carried places by hand. This is particularly so if you are operating from somewhere already in the clear that doesn't require you to carry a large mast as well.

4 elements will give you about 8 dBd, 5 elements will give about 9dBd while 6 elements will give close to 10 dBd. All are a noticeable increase compared to the 5dBd of 2 elements.  Even the lowest of these, ie 3 dB up on what you had before, may increase your transmitting range by 50% or more. Not only that but the higher gain will let  you work more closer in stations, including those running lower power and/or inferior antennas.

Interested? Some practical ideas for 144 MHz 4 to 6 element yagis are here:

* DK7ZB 4 element yagi
* IZ2UUF 100 gram 4 element yagi
* VK1AD portable 4 element yagi
* 4 element yagi dimensions (my own video - watch others linked to it)
* VE3SMA folding 5 element yagi (pdf)
* M0UKD 6 element yagi
* M1GEO 6 element yagi

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, March 16, 2019

Super-quick portable antennas

This weekend in Australia is the annual John Moyle Field Day. Amateurs around the country will be going portable to try to work each other. Antennas will important to their success.

Convenience as well as performance is a consideration. When you're tired at the end of a field day there's nothing worse than having to spend hours dismantling your station. Especially if you're forced off the air early due to an approaching thunderstorm.

Wouldn't it be good if your antenna was so engineered that it can be put up and taken down in a few minutes? That's very possible, particularly for the portable QRP operator. Here's some tips.

* Wire antennas only - no towers or heavy beams.
* Just use one antenna for HF. Preferably multiband. A good antenna coupler to allow this is worth its weight in gold.
* Inverted-vee dipoles or end-fed wires are convenient as they only require one high support. Link dipoles provide low-loss operation provided you aren't changing bands too often and your centre support allows easy lowering.
* Make your antenna as light weight as possible. That may mean avoiding antennas with heavy traps, or thick coaxial feedline. Then you can just use thin tree branches or telescoping fishing poles as supports. As shown in the videos below these can be very fast to erect.
* End-fed antennas are quick to pack up as they have little if any coaxial feedline.
* Light masts supporting little weight also don't require guy wires. Another time-saver.
* Choose a site with metal, such as jetties or fences, to clip on to for your earth system. That saves energy carrying and time in rolling out wire radials.

As you've probably seen from my videos, a good combination that meets all the requirements for a quick portable antenna is an end-fed wire (approx 20m long) supported by a 9m telescoping fishing pole. An antenna coupler allows operation on multiple bands between 7 and 28 MHz. 3.5 MHz is also possible but efficiency is poor unless you have a good ground system. Or, if 7 MHz isn't required you could just use the pole to support a vertical.

Three minute portable antenna

Two minute portable antenna

Have any other time-saving portable antenna ideas? Please leave them in the comments below.

PS: Want to get more from amateur radio? These books written by Peter Parker VK3YE could be of interest. Available in electronic and paperback form (some countries) they have proved popular among amateurs worldwide.

Friday, March 15, 2019

One wire, two (or more) bands: The HF trap dipole

Do you need a basic antenna that works well on a handful of frequencies? Just want a direct coax connection to the transceiver without twiddling an antenna coupler? Or maybe you're short of space and need something that's not quite full size?

If so then a trap dipole might be the answer. It's a dipole that can do multiple bands. How many? I've seen trap dipoles that claim five or six bands. But they get complicated with interaction between wire lengths and the component values in each trap.  Whereas a two band trap dipole is much easier to build. It would make an excellent second antenna project after you've succeeded with a single band dipole.

A two band trap dipole is shown above. Ignore all the parts from each trap outwards. What you're seeing is a regular half wavelength dipole operating on the higher frequency band.

If you were just to add more wire to it then that dipole's resonant frequency would move down. You don't want that. So you place a parallel tuned circuit, called a trap, on each leg. The traps act as  insulator on the higher frequency band. Then you can add more wire on the outside of each trap without spoiling performance on the higher frequency band.

Like all tuned circuits, the trap's behaviour changes with frequency. It no longer acts as an insulator on lower frequencies. If you get the value of the trap right, along with the length of the outer portion of the antenna element then the antenna will also resonate on a lower frequency. All while still operating perfectly on the higher frequency.

Another reason why you might use a trapped antenna is that because the inductor in the trap operates as a loading coil it allows the antenna to be shorter end-to-end than a full sized dipole. This entails a performance compromise including narrower bandwidth than a full-length dipole. However it may be the only way you can operate on a particular band if space is limited. Also, if you only operate CW or digital modes, the narrow bandwidth probably won't be a limitation.

You don't necessarily have to have your trap resonant inside an amateur band. Some designs specifically have traps resonant outside it. And with careful design it's possible to get more than two bands from one pair of traps.

How do you make a trap? There's several ways. You can buy them pre-wound so you don't have to. A common approach is to wind the required inductance on some plastic pipe. The capacitor required can be put inside the pipe. The capacitor needs to be a low loss high voltage type for best performance and power handling. Other trap designs use coaxial cable for both the inductor and capacitor.  Very small traps, such as used for portable QRP station antennas use iron powder toroids for the inductors. You'll find ideas in the links below.

* Online trap dipole coil calculator
* W8NX 1.8, 3.5 and 7 MHz trap dipole
* NU3E attic multiband trap dipole
* VK1HW 3.5 and 7 MHz trap dipole
* K0BXB 7 and 14 MHz trap inverted vee
* Trap dipole for 7 and 14 MHz (video)
* AD5X 18 and 24 MHz trap dipole (pdf)

PS: More antennas are covered in Hand-carried QRP Antennas. Available in electronic and paperback form (some countries) this well-reviewed book is a popular read amongst hams who go portable.

Thursday, March 14, 2019

Work low band HF DX with the half-square

Earlier this month we featured the bobtail curtain.  This is an effective antenna for low HF band DXing.  The main drawback is its length.  At 1 wavelength this is too much for most peoples' backyards.

If you like the concept but don't have the space, consider the half-square instead. It fits in the same space as a flat top half wavelength dipole but puts out a vertically polarised low angle signal. This makes it a good DX antenna for bands like 40 or 80 metres.  Radiation direction is towards and away from you.
The drawing above shows the half-square fed in a top corner (doesn't matter which one) with coaxial cable. This should be brought away from the antenna to avoid interaction. Or you can keep both corners joined and feed at the bottom if you have an antenna coupler or tuned circuit that can handle the high impedance.  Although it will no longer operate as a half square, an external coupler allows the antenna to operate efficiently on other bands as an end-fed.

The bottom of the vertical elements of the half square can be quite low to the ground.  Only 1 or 2 metres is OK. This low height requirement makes the half square more attractive than many other low band HF antennas, especially for DX working.  Construction is super simple with two appropriately spaced supports. Just keep it as symmetrical as possible.

Interested? There's more in these articles and videos:

* AF6EF's half square instructions
* N4DJ's 3.5 MHz half square (video)
* N6LF's article on using half squares for DX (pdf)
* Commercially available 14 MHz half square
* Half square on 10 MHz (one of my videos)
* Waters edge portable DX 14 MHz half square (another of my videos)

PS: Enjoy these well-reviewed books on various amateur radio topics. They're available for under $US 5 each in electronic form. Or you can get them in paperback. Visit VK3YE Radio Books to find out more. 

Wednesday, March 13, 2019

Vertical HF pedestrian mobile antennas

This day last month I talked about magnetic loop antennas suitable for HF pedestrian mobile.  They're a good choice, especially if you want something that can null local noise and isn't so high that it can get caught in tree branches. And  you don't have issues with having to find a ground or counterpoise.

However a loop can still be a compromise, particularly on the lower HF bands. You might have a handy park or field with no overhanging trees. Or be near a beach like I am, with salt water nearby to greatly improve the signal.  Especially if you can walk in the water, as I am about to do in the photo below.

In these circumstances a vertical might be a better antenna option. It could either be made of an old telescopic antenna (likely with a base or centre loading coil), aluminium sections (that screw or slide together) or, as I prefer, thin wire supported by a fishing pole in a backpack. A 5 metre height is practical and gives you a full sized half wavelength on 28 MHz or a quarter wavelength on 14 MHz. It's long enough be efficient on all bands above 10 MHz, with a centre loading coil permitting good results on 7 MHz as well.  That's just one approach.

For more on this and other peoples' pedestrian mobile vertical antenna efforts enjoy the links below:

* Wadetenna for pedestrian mobile 7 to 50 MHz (article and video demonstrations)
* WA3WSJ's Amateur Radio Pedestrian Mobile Handbook (pdf)
* G3XBM's Pedestrian Mobile HF DXing
* G4AKC HF bicycle and pedestrian mobile
* 80m pedestrian mobile antenna experiment by Martin Gillen
* Small (but inefficient) hand-carried pedestrian mobile vertical antenna (video)

PS: To support The Daily Antenna, please start your Amazon shopping here . 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.

Tuesday, March 12, 2019

Audible antenna tuning indicator attaches to VSWR bridge

Don't like squinting at a meter movement when you're trying to adjust an antenna coupler?

Why not make it audible?

That means the pitch drops to nothing as you approach 1:1 VSWR.

Here is a simple 555-based voltage controlled audio oscillator (designed by Drew Diamond VK3XU) that can be connected across the meter movement of a VSWR or resistance antenna bridge. The meter still works but you get a tone as well.

Watch the video to find out more.

Want a self-contained unit without the meter movement? Here you go.

There's other applications for this as well. For instance you could try it in a Wheatstone bridge circuit to measure resistance, capacitance or inductance. Or any other application where you are adjusting a meter for a null. You might even be able to save money by removing the meter movement altogether and just rely on the tone.

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