Thursday, February 28, 2019

Are you a fan of the fan dipole?

Our first real post discussed the coax fed half wavelength dipole. It's a basic antenna building block and it's hard to go wrong with one.

A dipole's main limitation is that it's (largely) only a single band affair. That can be a problem at home with our transceivers covering numerous bands but our partners wanting few antennas.

The simplest way around that what is often called a 'multi' or 'fan' dipole.  You keep the one feedline  and balun (if used) but have multiple wires running off the centre.  Like a paper fan. The wires are cut for the bands that you want. Effectively parallel dipoles.

So if you had a 40 metre band 7 MHz dipole (20 metres end to end) and wanted to add 20 metres (14 MHz) then you add two shorter wires each about 5 metres long.  That's simple and foolproof. Although you may need to slightly trim the length of the wires due to interaction between them. Interaction is why you don't want them too close to one another.

Adding more wires gives more bands. But beyond three or four of them it gets a bit messy - like looking through a spiders web. And you can get more interaction, making trimming harder. So I suggest starting simple, cutting the shorter ones first to size.

Enjoy the following articles and videos on fan dipoles.

* M0MCX 40/30/20m fan dipole
* Multiband fan dipole by N4UJW
* Modeling a fan dipole for DX by W1DYJ
* How to build a fan dipole for Field Day (DX Commander's video)

If you haven't built a dipole before, I suggest starting with one band only. My article here

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, February 27, 2019

What coaxial feedline should I use?

It's no good having a zillion element beam atop a mast that pokes through the clouds if hardly any of the power from the transceiver makes its way all the way up to the antenna.  That can happen with bad coaxial feedline. Either because it's inherently lossy or due to damage such as water ingress.

Generally speaking, the higher the operating frequency and the thinner the feed line the greater the loss. Loss is expressed as a number of decibels for a given length at a particular frequency. 

Unless you're willing to compromise station performance you should do what you can to keep total feedline loss to 1dB or under. This means that at least 80% of your power will reach your antenna.

Ardent VHF and UHF operators, particularly those who operate weak signal moonbounce, will want to be even stricter. This is because they are operating so close to the noise level that every decibel counts.

Conversely those who operate low power mobile and portable installations may be more concerned about feedline size and weight than the ultimate performance.  And the lower power means that the power handling limitations of thin feedline do not arise. Still, you still want people to hear you so you can't be too cavalier about losses.

For the fill-in on feedline, here's some great items to read:

* Feedlines from the ARRL
* Which cable to use from
* Feeding the beast by N4KC
* 2014 Tech Study Guide - feedline and connectors

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.

Tuesday, February 26, 2019

Building manual HF antenna switches

Antenna switches are extremely useful accessories in the shack. You could either connect them to the transceiver so you can switch between two or more antennas (great for quick A/B comparisons) or to one antenna so you can do compare transmitted audio or reception on different transceivers.

A manual antenna switch comprises a flip or rotary switch with some antenna sockets. Leads need to be kept short and the whole thing needs to be in an earthed metal case. Connecting wires must be very short (to minimise stray inductance, capacitance and loss) while switch contacts must be heavy enough to withstand sometimes high transmit powers.

You can buy antenna switches commercially. But they can be expensive. But also beware some cheap antenna switches which can be very shoddily built (even if they claim they can do 1 kW!). At least if you build your own you can control what goes into your switch and the quality of workmanship. Things get more critical with higher power levels and higher frequencies. Although note that if using low power a lossy switch won't complain by arcing but it may still be losing valuable watts.

Anyway here's some manual coax switch ideas to get you started. Some amateurs use remote antenna switches but we'll discuss those in a later post.

ZL2IFB's simple instructions for building a manual antenna switch
PA0FRI coax switch
W5CYF's homebrew coax switch (Part 1 of video series - other parts follow)

The above are good if you're using coaxial feeders. If you're using open-wire feedline then a knife switch is what you want.

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, February 25, 2019

Homebrew 70cm (430 MHz) antennas

70cm is a good band for experimenting with antennas. Unless you need very high gain the antennas are small. This means that you can experiment without fear of wasting much material. And you don't need much room either.  Potential uses for 70cm antennas include FM and repeater work, long distance SSB contacts, digital modes and satellite communication.

Here are some ideas for 70cm antennas:

ARRL's ground plane antennas for 70cm (and other bands) - PDF
PA1CA 70cm quad loop
PG1N's massive list of 70cm antenna links
N8PR's simple 70cm yagis (PDF)
11 element 70cm yagi A project by VK3ZZC
Simple 70cm satellite antenna by ZS1AN
4 element handheld quad for 70cm video by LilBlighter
A bobtail gain antenna for 70cm One of my videos

PS: Puzzled about some of the terms you hear? This dictionary can help with over 1500 explained.

 Link to Ham Radio Dictionary

Sunday, February 24, 2019

Exploring balanced antenna couplers

Almost all the HF transceivers hams use cover 9 or more bands. It would be nice if our antennas did the same, especially if we don't have room for a massive antenna farm. One of the simplest antennas that does just that is the tuned feeder doublet. You put up a wire between two supports and run some open wire feedline down to the transceiver.

Provided it's longer than about 3/8 wavelength end to end on the lowest operating frequency it will perform well without much loss. Yes, you do get some funny radiation patterns with narrow lobes and nulls on higher bands, but you will be on the air. And if that worries you it's not to hard to put up another antenna for more predictable performance on a band like 10 metres.

There's only two problems with that. First of all the balanced feedline. You may have to make it yourself. Don't worry, we covered feedlines just over a week ago.

Then there's the antenna coupler. Some people feed tuned feeder doublets with a regular unbalanced antenna coupler and a 4:1 balun connected to its output. Yes that will 'work'. But it's not the most consistent arrangement and there may be significantly increased losses on some frequencies.

The solution is to use a balanced antenna coupler. These are not that common commercially. But you can build your own.  Some good ideas are presented below.

Link coupled antenna tuners Some ideas from W4RNL
Wide range balanced antenna tuner by W5JXM
QRP balanced antenna tuner by OZ1BXM
Symmetrical matchboxes many ideas from DJ0IP
W4MMQ Legacy balanced antenna tuner Very simple!
A balanced antenna coupler and multiband dipole One of my videos

Inductors can be made at home. But you will likely need to shop around for the variable capacitors required, most likely at hamfests.

PS: The items below may assist your experiments.  They are affiliate links meaning that I receive a small commission (at no extra cost to you) if you decide to purchase.


Saturday, February 23, 2019

The benefits of vertical dipoles for HF

We normally think of HF dipoles as being a  horizontal wire strung between two trees. Or, if only a single tall mast is available, an inverted vee with the feed point at the top.  This arrangement provides a horizontally polarised signal. If its height is sufficient there will also be directivity broadside to the wire which may or may not be what you want.

However, especially on the higher HF bands, a vertical dipole is worth considering.  There are several benefits. You get omnidirectional 360 degree coverage.  Their small footprint makes them suitable for narrow courtyards. And, especially if operated by salt water or over a conductive ground you get low angle radiation good for DX. 

The main thing you need apart from the wire and feedline is some sort of high support to hang it from.  This could either be a high tree branch or a telescopic fishing pole of suitable height.

Read some experiences people have had with HF vertical dipoles.

10 through 20 vertical dipole by KL7JR
Restricted space antennas - vertical dipoles by W5ALT
My experiment in building a vertical dipole antenna - instructable by KF5YKO
A short vertical dipole - space-saving design by ON4BAI
Testing a 20m vertical dipole by K1HMS
Demonstrating a vertical dipole on 14 MHz - one of my videos

With very low construction costs you will lose nothing by building a vertical dipole. And with simple adjustment and thousands of satisfied users you have a high chance of success.

PS: Into low power amateur radio? Covering equipment, antennas, operating and strategy, Minimum QRP is the book for you. Available in both ebook and paperback (some countries).

Friday, February 22, 2019

Field strength meters to build

Before we had antenna analysers or even VSWR bridges, amateurs often used small light globes to do antenna tests. Common checks involved measuring antenna current and field strength. After all the aim is to radiate the maximum signal for your output power and antenna arrangement.

And there's something solid about doing tests with a field strength meter, especially a passive type where it's only energy from your radiated signal that is driving the meter movement.  While basic field strength meters give only a relative indication, even this is useful when you are just aiming for a peak in the radiated signal.  Radio direction finding is another use for field strength meters, especially if you are very close to the signal source.

Unlike absorption wavemeters, field strength meters are not frequency selective. They can respond to signals on a wide range of frequencies. This means that you need to be mindful of strong local signal sources. For example there is a possibility that your meter could respond to stray RF if there is a nearby radio or TV station. Bear that possibility in mind if you see readings that don't make sense. 

Anyway here are a selection of RF field strength meter circuits.

Wide dynamic range field strength meter Good discussion by KA7OEI
Simple field strength meter Andy Collinson describes one with just 4 parts
No Fibbin RF Field Strength Meter Described by VE7NI in QST
Sensitive RF Field Strength Meter Video by ElectronicsNmore

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, February 21, 2019

Antenna ideas for the 12 metre (24 MHz) band

The 12 metre, or 24 MHz, band is probably HF's least active. Especially at this phase of the solar cycle. Many (most?) hams lack antennas for it and it lacks the diversity of modes and operating activities found on other bands like 10 metres. 

However, as activity on the nearby 27 MHz CB band shows, 12 metres is probably open more often than it might appear. A good check are the IBP CW beacons on 24.930 MHz. You could also try WSPR. Setting up a WSPR receiver would be especially welcome as there seem to be more stations transmitting than receiving there in recent times. 

The scavenger interested in 12 metres will be on the hunt for old 27 MHz CB antennas, which with a little lengthening could be set up on 24 MHz. Other options are to take the dimensions of a 10 or 15 metre design and scale up or down accordingly.  Or you could build your own from scratch.  Here's some ideas.

3 element LFA antenna for 12 metres by G0KSC
28 and 24 MHz 3/4 wave delta loop by KL7JR
Lengthening a cheap CB antenna for 12m by G1EXG
Low cost magnetic loop for 10 and 12m Video by RadioHamGuy

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, February 20, 2019

Portable tape measure yagis for VHF and UHF

If you don't want to spend big on aluminium tubing, or have no defunct TV antennas handy, an alternative material for yagi antenna elements are old metal tape measures.  Beams can be made super light weight and the element springiness makes them easy to pack.

This makes them ideal for fox hunt or ARDF hand-held sniffers.  Other applications include range boosters for handheld transceivers, contest beams for VHF/UHF field days and use for satellite communication.  They also make a great educational project to demonstrate antenna concepts like gain and front to back ratio for an amateur licence study class.

Follow the links below for ideas and inspiration:

KB9VBR tape measure yagi for 2m foxhunting
KB9VBR tape measure yagi for 2m foxhunting (video)
WB2HOL tape measure yagi optimised for 2m direction finding
ZL2APS tape measure yagi for 70cm
Testing a 2m tape measure yagi One of my videos testing reception of a satellite

The main disadvantage of tape measure yagis (especially those on 2m) is that in moderate to high winds their elements flex. This reduces their gain and directivity, and, when it's really blowing, makes them useless.  You may be able to reduce this by fitting some sort of line or string across the elements for bracing.

PS: Many other portable 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.

 Link to find out more about Hand Carried QRP Antennas

Tuesday, February 19, 2019

Five ways to test your new antenna's effectiveness

We all want our antennas to be as effective as they can be. That means that a change to it (for instance extra height or some more ground radials) has had the desired effect in boosting your signal. Or that a new one is better that an existing one in desired directions and at desired radiation angles. Sure, one can look at anecdotes from people who have built them or modelling data, but it's better to actually test it.

Here are five ways you can test your antenna's effectiveness on transmit.

1. THE RANGE CHECK. The first way is probably what you did if you ever experimented with small transmitters like FM wireless microphones or toy walkie talkies. You'd have a transmitter going at home (keyed up by a friend or family member) and then go for a walk around the block to see how far it went. If you were lucky it might go say 10 or 20 houses.  When you were a bit older and had something bigger then you might do the same thing in a car with a mobile setup. Ideally you'd be driving in all directions to get an idea of when your signal fades almost to noise level and becomes unreadable. On VHF or UHF FM you could put together a range tester (some don't need soldering) then go for a walk or drive.

2. REPORTS FROM STATIONS. Here is where you get on air, make contacts and ask for reports from multiple stations. A single contact at a single time is not enough - conditions can vary so much that comparisons can be misleading. And S-meter readings on different transceivers are meaningless. Different transceivers indicate different things on the same signal and people may or may not have their RF preamp or attenuator switched in. You also need to get reports from stations over a range of distances and directions. That is because some antennas might be outstanding for DX but mediocre for closer in due to the angle of their main radiation lobe. Results by direction can also vary.

The best sort of test is an A/B comparison. That is you have both antennas up. During a transmission you use an antenna switch (like we discussed on 26 February) to switch quickly between the antennas while asking for reports. Preferably done on a group or net where there's multiple stations on. Because many hams are biased with what antennas 'should' and 'shouldn't' work well it's best not to disclose what antenna A and antenna B are until after the test.

Another test, if you can't have both antennas up at once, is to be active at a certain time each day to try to work the same group of stations. Both before and after you erect the new antenna. You might want to drop power so your signal becomes more marginal and any differences between what your antennas can do are magnified.

3. ONLINE SDRs. Not much activity around? Here's where you do your own tests. Find an online web SDR and listen to your own transmission, switching between A and B antennas as you do so. Try ones in as many places and on as many bands as possible.  Then repeat at different times on different days.

4. DIGITAL MODES. A great thing about digital modes like FT8 and WSPR is they give a dB signal to noise ratio of your signal. And in the case of WSPR you can leave your station to do its thing, coming back later to check results on WSPRnet. Look over results and average them to compare antennas.  Or you could try to standardise for conditions by checking your performance relative to other stations near you.  There are also more advanced WSPR-based antenna test tools like DXplorer.

5. CONTESTS. Contests are competitive. In the big ones there are multiple high power stations on the air. The signal reports won't be any value (they're all 5/9) but the fact that numerous stations in a particular part of the world can hear you well enough to get your callsign is. The big contests bring out people from all over the world so you can get an idea of your antenna's favoured directions.

Antenna performance on receive is another ballgame of fish. It may or may not be related to transmit performance. This is because on receive our aim is best signal to noise ratio rather than absolute maximum strength.

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, February 18, 2019

Big thick efficient HF magnetic loops for the lower HF bands

Magnetic loops are often thought of as being compromise antennas, used by apartment dwellers and others who lack the yard space for a full sized antenna. Many are fairly simple slapdash weekend projects, taking only a few hours to build. While contacts can certainly be made with such antennas, performance is often well below possible due to high resistive losses. 

These often arise from a combination of (i) inadequate loop length, (ii) poor choice and diameter of loop material, (iii) losses in the variable capacitor and (iv) high resistance connections, especially between the loop and the variable capacitor.  In addition compromised parts can mean that the loop handles only a fraction of the legal power limit.  Add the loop's losses with the reduced signal due to a restricted output power and suffer the consequences.  You may still do well on efficient digital modes like WSPR but you will likely be the weakest station in the group if on an SSB net.

It doesn't have to be like that. With time, money and effort you can build a heavier, more efficient loop that can take the legal limit.  Your signal will then be quite strong. In fact under certain circumstances you might do better than some with full-sized antennas.  That's even true on lower bands like 80 and even 160 metres.

Building a big thick and efficient HF magnetic loop is more than your average casual weekend project. But the results will be worth it. Here's a few resources from those who have succeeded in this quest.

VK4AMZ magnetic loop for 160, 80 & 40m
W7YV magnetic loop for 160, 80 & 40m
VK5SFA 160m magnetic loop design
VK5SFA's 160m magnetic loop videos
AI6TK 160 and 80m magnetic loop (YouTube video)

Even if you don't attempt one, these links should at least give you a renewed appreciation of what magnetic loops can do when attention is paid to minimising losses from all sources.

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 .

Sunday, February 17, 2019

The VK2ABQ multiband mini beam

Before the Moxon Rectangle became popular there was the VK2ABQ beam.

Like the Moxon, this was basically a two element yagi with the ends bent in to reduce turning radius. As originally presented, in a 1973 Electronics Australia magazine, the VK2ABQ had wire elements for 10, 15 and 20 metres. Its square shape make it look like a rotary clothes hoist.  Elements were bent in towards themselves, with large coat buttons providing the spacing.

This development was done before amateur access to antenna modelling programs and antenna analysers. Test equipment generally available then would have been little more than noise bridges, RF ammeters, signal sources and field strength meters.

The VK2ABQ allowed people who didn't have the room or money for the standard triband trapped beam to have something of almost similar performance in a smaller space for less. The antenna became more widely known through Pat Hawker G3VA's Technical Topics column in RadCom. The critical coupling technique it used was refined by Les Moxon G6XN to produce what we now know as the Moxon.

VK2ABQ as built by ZS1JHG
Modeling and understanding small beams (including VK2ABQ) by W4RNL
Vertically polarised VK2ABQ for 50 MHz by GW0GHF
Critically coupled antennas by VK6APH/G3WXO

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, February 16, 2019

Resistive antenna bridges

You're listening to a weak signal. There's fading, there's static, there's a station a little too close for comfort. But you can just about make out all of their transmission.

That is until the carrier appeared. Your S-meter swings wildly between S9+20 and S9 +40 as adjustments were made. When you thought it was over it appears again.  Followed by speech.  "Haarlo Harlo 1 2 3". Apparently oblivious of or uncaring towards the activity on the frequency.

All that could have been prevented if the other station used a resistive antenna bridge. This is a small device that allows your antenna coupler to be adjusted without radiating a signal.  True, they don't measure VSWR or RF power output. Nor do they replace an antenna analyser. But they are cheap, self-powered, and, if you wish to build one yourself, requires fewer than ten or fifteen parts. They also protect the transceiver's final from wild impedance swings that can occur when adjusting the antenna coupler.

A resistive antenna bridge is just a few resistors, capacitors and a potentiometer. Oh, and some sort of indicator that shows the null you get when you've tuned up correctly. That could either be an (increasingly rare) meter movement or LED. Or, if a voltage controlled oscillator is added, an audible indication.

 Here's a few bridge ideas if you'd like to build your own.

GQRP Club resistive SWR bridge by G3ROO & G4WIF (PDF)
Determine SWR with a resistive divider Circuit Salad
ZS6AZP's investigation of a resistive bridge
G0WQR resistive bridge with LED from Sprat
L-match antenna coupler with resistive bridge from my site
Inside a resistive antenna bridge my video

PS: The items below may assist your experiments.  They are affiliate links meaning that I receive a small commission (at no extra cost to you) if you decide to purchase.

Friday, February 15, 2019

The Bi-Square

Another rarely heard antenna on the air is the bi-square. Probably due to its size. And many prefer coaxial cable to the 300 ohm ribbon feedline that the bi-square normally uses.

If you think a single element quad loop (1 wavelength perimeter) is large, double its size to get an idea of the bi-square's dimensions.  But despite what it looks like from afar, the bi-square is not quite a real loop since it is split at the top.

Still, if you have one tall tower (at least 3/4 wavelength high) the bi-square may be worth considering. It's basically a bidirectional gain antenna. If you've already got the wire the construction cost is low. And you may be able to use some ingenious remote switching with relays to change the antenna into a large loop for other bands. 

Bi-square ideas and discussion here:

The bi-square array reappears N4LBJ's 18 MHz version
Bi-square radiation How they work via HA5CFJ (Hungarian)
Curtain antennas W8JI explains how the bi-square is related to the Lazy H
Bi-square for 2 metres Manageable dimensions up here. By KG4ZNC
28 MHz bi-square used portable My one and only bi-square test (video)

PS: Into low power amateur radio? Covering equipment, antennas, operating and strategy, Minimum QRP is the book for you. Available in both ebook and paperback (some countries).

Thursday, February 14, 2019

Making your own open wire feedline

One of the most versatile multiband HF antennas is a doublet fed with open wire feed line. The antenna's length is not particularly critical provided it is longer than about 3/8 wavelength on the lowest operating frequency.  With a good balanced coupler this arrangement will provide low loss coverage of maybe 8 or 9 bands. 

Some find it difficult to find suitable open wire feedline. What you need must be able to withstand the weather and have a characteristic impedance between about 450 and 800 ohm (not critical).  Its wire thickness also needs to be suitable if you run high power.  You may be lucky and find some commercially at a reasonable price. Or you may not. And even if some could be ordered, you may have the urge to make an antenna that requires it today!

Fortunately it's fairly easy to make your own open wire feedline. Techniques vary.  Spacers can be made from a variety of non-conductive low RF loss materials. You may even be able to fabricate your own if  you have access to a 3D printer. Enjoy the links below for some ideas:

Feeding  your station QST article on various feedlines
Home made open wire feedline by W1AEX
Home brew light weight open wire line by N5ESE
Open wire Ladder Line Includes accounts of testing by DJ0IP
Some old notes on parallel transmission lines by W4RNL
Why use ladder line by KV5R
Making open wire antenna feedline One of my videos

PS: The items below may assist your experiments.  They are affiliate links meaning that I receive a small commission (at no extra cost to you) if you decide to purchase.

Wednesday, February 13, 2019

Pedestrian mobile HF magnetic loops

OK, I admit it, this is one of my hobbyhorses. Most of the links presented below are from my website. But it's a fun novelty aspect of amateur radio, not only for yourself but the people you work. And the construction of antennas light enough to carry for long periods makes you even more aware of the trade-offs between efficiency and weight.

A pedestrian mobile magnetic loop can occasionally give 10 000 km plus contacts. However up to 3000 km is much more common, especially at the current phase of the solar cycle. While I've tried coaxial cable and even mains flex for the radiating element, aluminium strip seems to provide the best trade-off between lightness and efficiency.

A bit like having different camera lenses for different jobs, I suggest having at least two loops.  a larger loop is best for the 40 - 10 metre range.  While a smaller loop is more convenient if you just want 10 and 6 metres.  Descriptions of these and other loops are in the links below:

Alexloop portable loops Loops to buy if you don't wish to build your own
Portable HF transmitting loop antenna  A 14 - 30 MHz collapsible PVC pipe loop by N5IZU
Portable HF magnetic loops Presentation Notes by WD6DBM (PDF)
Ultralight ped mobile mag loop for 40 - 10 metres When you want the very lightest
A better ped mobile mag loop for 40 - 10 metres A little heavier but a lot better
SummerLoop mag loop for 15 - 6 metres Just the thing for the summer sporadic E
Low cost magnetic loop for 10 - 12 metres YouTube video by RadioHamGuy

PS: Magnetic loops (and many other 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 and pedestrian mobile.

 Link to find out more about Hand Carried QRP Antennas

Tuesday, February 12, 2019

Using salt and vinegar to clean corroded wire

No antennas today but you should still find the post useful.

It deals a problem we all have with outdoor wire antennas. Wire corrosion. 

This is a video demonstration I made of cleaning corroded wire.

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.

Monday, February 11, 2019

The HF folded dipole

Today's antenna, the HF folded dipole, doesn't seem to be that widely used among amateurs.

Maybe because it needs twice as much wire. Instead of just one wire split in the middle at the feedpoint, folded dipoles have two closely spaced wires joined at the ends. One wire is split at the feedpoint while the other is continuous. On the other hand having all of the element at ground DC potential is sometimes seen as an advantage with users lauding its quietness as a receive antenna.

Folded dipoles have a 300 ohm impedance.  Unlike other types of dipoles and verticals this makes them unsuitable for directly feeding with 50 or 75 ohm coaxial cable without a 4:1 balun. On the other hand the higher impedance can be beneficial for long feed line runs as loss is lower. Why? High impedance means relatively high voltage and relatively low current. The voltage drop caused by a given line resistance is less significant at higher than lower voltages. For a similar reason this is why electricity grids operate at many thousands of volts over their long distance transmission lines before being stepped down to the normal domestic AC voltage.

If resistors are installed at certain places a folded dipole can be made to operate over a wide HF frequency span without an antenna coupler. Performance-oriented amateurs don't like this due to the extra losses introduced.  Commercial and military users, who primarily use HF for strong-signal single hop communication, often prefer versatility and usability over efficiency.  For them a broadband folded dipoles, such as a T2FD, may be more appealing than it would to a distance-oriented amateur DXer or efficiency-minded QRP enthusiast.

I haven't worked with folded dipoles so can't speak from practical experience. But these people have so their accounts are worth reading.

Folded dipole antennas Video by W1GV
Notes on the terminated wideband "folded dipole" Evaluation by W4RNL (PDF)
Terminated Tilted Folded Dipole by PA0FRI - Dutch
The folded dipole W8JI finds negligible benefits in using them

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 .

Sunday, February 10, 2019

The single element HF wire vertical delta loop

Only got a single high support? Don't have quite enough room for a dipole? After a loop style of antenna with a reputation for low noise reception? Or want something that can easily be changed from vertical to horizontal polarisation?

If so then the single element delta loop could be your saviour. It's a simple antenna to build comprising a wire approximately one wavelength perimeter. Feed it at the bottom centre for horizontal polarisation or down the side for vertical.  If you've got two supports you can have it pointing to ground (with a higher average height) or if you only have one you can have the apex pointing up.  The latter is particularly convenient for portable operating where you can use a telescoping fishing pole mast to hold it up.  It doesn't matter very much if it's not quite an equilateral triangle.

A single element delta loop doesn't have a lot of gain. Possibly a shade over a half wave dipole. But in its vertically polarised version it can give good low angle radiation, particularly if near salt water.

A challenge with the delta loop is how to feed it.  That's because its impedance is quite a bit higher than 50 ohms. It's not quite like a ground plane (about 35 ohms, but higher if you droop the radials) or a half wave dipole (about 70 ohms, but lower if you make it an inverted-vee). Options include using a matching section (a quarter wavelength of 75 ohm coax multiplied by its velocity factor), some sort of transformer or open wire feed with a balanced antenna coupler.  Open wire feed will allow the loop to work on multiple bands down to about 70% of the design frequency. The links below will give some good ideas on feeding this antenna.

40 - 10 m delta loop Comprehensive article by GU3WHN (PDF)
Multiband mono delta loop by DU1ANV (PDF)
$10 No transmission line delta loop Eham article by KE7WAV
Vertical delta loop Elmer Hour beginner guide from the Villages Amateur Radio Club (PDF)
Amongst the Kilowatts Part 1 I describe and demonstrate a 14 MHz portable delta loop (video)
Amongst the Kilowatts Part 2 More on my 14 MHz portable delta loop (video)

Start reading, start watching then start building. They're so cheap that you could even make several.

PS: Looking for even more things you can do with amateur radio? 99 things you can do with Amateur Radio can help. Available in both electronic and paperback.

Saturday, February 9, 2019

The quarter wave ground plane

Those who got their start with 27 MHz CB will be familiar with the ground plane. It consists of a radiating element a quarter wavelength long connected to the coaxial feedline's inner.  Connecting to the braid are two, three or four radials a quarter wavelength long.  These may be horizontal, or if you want a better match to 50 ohm coaxial cable, droop down at about 45 degrees. Ground planes can be made either of wire (on the HF bands) or aluminium tubing (on VHF bands like 2 metres - 144 MHz).

The ground plane is a vertically polarised omni-directional antenna. This makes it good for communicating with mobile stations.  That includes working through repeaters such as available above 29 MHz.  On frequencies lower than that ground planes are preferred over low dipoles for long distance contacts due to their lower angle of radiation.  This is particularly so near the coast due to the beneficial effect on radio signals of large salt water bodies.

Ground planes are one of the best antennas a beginner amateur can build. Especially for bands like 10, 6 and 2 metres. Connecting one to a 2 metre handheld transceiver will greatly increase its communication range compared to the standard 'rubber duck'. And on 10 and 6 metres, even when there's no sunspots, a ground plane will help you work stations thousands of kilometres away over summer.

Check out these practical ground plane links:

Build a Portable Groundplane Antenna Improve your 144 MHz signal - ARRL PDF
Simple ground plane for 2m/1.25m/70cm From N1GY
20 metre three wire ground plane Practical article by KK5JY
10 metre ground plane antenna Video from KG0ZZ
Simple ground plane vertical Video tutorial on a 7 MHz ground plane by W1GV

Find a high support such as a fishing pole or tree branch. Then just get an SO239 socket and some wire to make your own ground plane hanging from your support. Even if radio conditions are poor and you're not hearing many signals, WSPR can give a clue as to propagation and how the ground plane is working relative to your others. 

PS: Puzzled about some of the terms you hear? This dictionary can help with over 1500 explained.

 Link to Ham Radio Dictionary

Friday, February 8, 2019

The coax-fed horizontal dipole

Just about the simplest antenna to make is the humble coax-fed half wavelength dipole (usually shortened to 'dipole').  As someone once said, it's hard to make an antenna that performs much better than one but easy to make one that's inferior.  It's a great choice if you're starting out in ham radio.

In its basic form it comprises two quarter wavelengths of wire connected to some 50 or 75 ohm coaxial cable. Take the band's wavelength in metres (eg 20 metres, 40 metres, 80 metres etc) and divided it by two. That's approximately the dipole's end-to-end length.  There are better formulas out there but you are still likely to need to trim it to your desired centre frequency during testing.

A high dipole (more than about 1/2 wavelength up) gives a low radiation angle, good for DX. A low dipole pushes more radiation at high angles.  While not so good for DX, high angles may be just what you need for close-in contacts on bands like 80 and 40 metres. Its radiation pattern is bidirectional. Like a figure 8 with maximum radiation broadside to the wire.

You can make a dipole from wire, or, especially for VHF and UHF, solid tubing. It can be erected horizontally or vertically, depending on the desired polarisation. And if you run out of room or only have one tall mast, it can droop down from the centre, forming an inverted-vee.  Or, with two non-metal end-masts it could droop down and even bend in at the ends to save space to form a shallow inverted-U.

Anyway enough from me, here's some great dipole links to peruse.

Antenna Here is a Dipole All the basics here in this great ARRL article (PDF)
Feeding Dipole Antennas Part 2 of the above from the ARRL (PDF)
Your first antenna - the half wave dipole A dipole starter from the RSGB
Optimising a coax fed half wave dipole Solid know-how from VK2OMD
Making and using a simple 40m dipole Popular David Casler YouTube video

Build a dipole from information in the above and you can't go wrong!

PS: Dipoles (and many other 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.

 Link to find out more about Hand Carried QRP Antennas

Thursday, February 7, 2019


If there is one topic that unites radio amateurs of diverse sub-interests it is probably antennas.

Whether you are an apartment-dwelling digital modes devotee, acreage-living big gun DXer, or  cross-country mobileer, you're going to need one (or more) effective antennas.

The choice is almost endless. Not only the type of antenna you use but whether you buy pre-made, assemble a kit or build from scratch. Information is essential to choose something that best meets your needs.

The Daily Antenna will provide one post per day on a particular antenna type, accessory or related technique.  Posts will be concise, running to a few paragraphs maximum.  I will often include links to articles, blogs, forum posts and YouTube videos. Linked items will have been vetted by me and considered to be of good quality.

Who am I? I've been a licensed amateur for over thirty years. For most of that time I've been building QRP gear and antennas.  Not having a lot of yard space at home but with large expanses of sandy beach nearby I'm heavily into portable and pedestrian mobile operating. I maintain a popular YouTube channel and write books on amateur radio topics. Further information about me is at:

vk3ye . com website
VK3YE YouTube channel
VK3YE Radio Books on Facebook
VK3YE QRZ profile

I wish you happy reading and encourage your participation through the comments section.

73, Peter VK3YE

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.

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