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In all cases below these antennas are suitable for both transmitting and receiving. Antennas suitable for reception on the MF and lower HF bands are discussed on a later page; while some are large, the Pennant and Flag antennas would fit into many backyards.
If you own a large property, a rhombic antenna is an option for an HF with a good gain, and a low angle of radiation, in a particular direction. They are more usually used for military communications; at the BBC's monitoring station, where several were used until recently to cover different regions; and in the past, for things like radio-telephone links between Australia and Pacific islands; or California and Shanghai. Each segment is around 1 to 2 wavelengths long, and they must be (at least) a half-wave above ground. Even at UHF, they are several metres long.
In some cases, for tasks such as HF (SW) broadcasting, they have been replaced by antennas such as curtain arrays. They do however have the benefit of relative simplicity, and broad bandwidth. You just need to stand four tall poles in a diamond pattern, and run wires between them.
An important feature is that there is often a terminating resistor at the far end of the antenna from the feedpoint. This make the antenna unidirectional (transmitting in the direction away from the feedpoint), rather than bidirectional. An alternative to the resistor, which reduces the efficiency of the antenna, is a resonant stub of balanced feedline.
With the new QRP addition to 60 metres the receiving gain of these antennas may be useful on this band. You should reduce power due to the gain of the antenna, but remember that you can compensate for feedline losses.
You can see drawings in the Wikipedia article, and follow links to the patents: Rhombic antenna
If you drive past a MW broadcasting site, in many cases you will see just one tower, but in some cases, especially in the US, there are two, or more, antennas in a line, or some other arrangement. The reason these arrays are used for MW in the US is that they have a very large number of MW broadcasters, re-using the same frequency, or on nearby frequencies, in close proximity. The pattern is determined by the spacing and feed method (in-phase or out-of-phase), and helps to "protect" the other stations on the same frequency.
One option is a half-wave spacing, which gives a figure-8 pattern. If they are fed in-phase, then the pattern is broadside to the line of the antennas. If fed out-of-phase, the pattern is along the line of the array.
The other option explored is to site the two antennas a quarter wavelength apart, and feed the antennas 90 degrees out of phase. This generates a cardioid, or heart-shaped, pattern. These have a null to the rear, with only a minor forward gain.
US broadcast station systems can have something like 9 masts, to generate complex patterns, in some cases switched in at night, along with a power reduction.
For HF these may fit a suburban yard unlike some of the models above, and are listed by the examiner under "practical" antennas.
These are a half-wave end-fed antenna, consisting of a single half-wave wire, or an odd multiple of a half-wave, such as 3λ/2. These are termed "end-fed dipoles", because, like a dipole they are a half-wave long overall. It is important to note that special feed arrangements are necessary, due to the very high impedance of such end-fed antennas. The name Zepp is from German "Zeppelin" airships. These used a resonant dangling wire antenna, a half-wavelength long, or 3λ/2, 5λ/2, etc.
It appears that, in the original diagram the second wire forms an open wire feedline. Part of the motivation of the design was to keep high voltages away from hydrogen potentially mingled with air, a very dangerous mix.
If you can read German, you can read the patent, dated 1909, German Patent: 225204, and see a overview of this with a brief translation, along with other interesting antenna patents, some mentioned below.
End-fed half-waves aka end-fed dipoles are fairly popular and the subject of much online discussion. A coax is run to a water resistant electrical junction box or similar, which contains an RF transformer with a very high impedance ratio. The wire then goes across the yard to a tree or pole. 1:7 turns ratio provides a 1:49 impedance ratio and thus transforms 50 ohms to 2450 ohms. 1:9 provides a 1:81 ratio. The voltage on the antenna terminal can be very high, and potentially dangerous.
The Extended Double Zepp (EDZ) is an antenna fed at the centre, often using 450 ohm open wire line. Overall it is 1.25 wavelengths long. Given this is 5-quarters, each side is 5/8, or 0.625 wavelengths.
An interesting tie-in is that the Zeppelins were built in Fredrichshafen, and it is possible to visit the Zeppelin Museum while visiting the largest Ham Radio event in the democratic world in this southern German city. The company is still making airships, now helium filled. They offer sightseeing flights. See: Zeppelin NT. There is a separate heavy equipment rental, generator, heat pump, and fuel-cell company.
There are several variations on the OCF or OCFD theme, with the version discussed by the examiner consisting of a dipole fed one-third the way along, using a 4:1 balun. These antennas allow operation of a range of HF bands.
A variation used by a friend is the Carolina Windom. Their version consists of a continuous horizontal element, connected to a single drop wire, grounded via the winding of a transformer, with coax feeding the other side of the transformer.
A standard dipole with quarterwave legs has a radiation pattern broadside, as long as it is higher than a half wavelength (as opposed to an NVIS antenna). An example is an antenna used on the 7 MHz (40 metre) band. If we use it at 21 MHz (15 metres), the third harmonic then lobes form at roughly 45 degrees instead. If the antenna had been built to listen to the 120 metre (2.3-2.5 MHz "tropical" band) then at 7 MHz there would be the 4 lobes, and at 21 MHz there would be more lobes, each aligned close to the direction of the wires.
If the antenna was a single end-fed wire I believe the energy is primarily projected forwards.
For 2 metres FM voice and AX-25 packet I built a quarterwave antenna from brass rod. This had a reasonable match at 70 cm, and allowed access to a nearby repeater. However, the lobes would have been upwards at around 45 degrees.
In the Technician section we discussed the folded dipole, for VHF and UHF, made from stainless steel or aluminium tubing. For HF a folded dipole can be made from parallel wires, totalling a full wavelength. These have an impedance of 300 ohms; and thus some form of balun is often used.
Construction is somewhat similar to ladder-line, with some form of spacer between the lines.
Note that many companies sell a variation with a resistor opposite the feed-point, as some sort of "miracle" wideband antenna, touted as needing no tuner. These are however not efficient, as energy is absorbed by the resistor. Perhaps their function is to transfer funds from the pockets of the gullible to those of the vendor, rather than to efficiently radiate signals?
This is a dipole antenna, designed by, and named for, Louis Varney G5RV. Also termed a doublet, the classic version is 31.1 metres, or 102 feet long. It is fed with ladder line or TV ribbon for 8 - 10 metres, depending on the impedance of the line. It is then connected to 50 ohm coax, either directly, or ideally via a 1:1 balun. The antenna may work on 14 MHz without a tuner, but can be used on several other HF bands, but certainly not all, using a tuner.
There are a range of modified versions, including the "half G5RV", the ZS6BKW, and the W0BTU; plus a version for 17 metres.
The article Wikipedia: G5RV, and linked pages, should provide enough information to build one, should you wish. There is certainly no need to purchase one.
A better alternative, and one suggested by G5RV himself, is to run open-wire line (typically 420 - 450 ohms) all the way to a balanced tuner in the shack. Some claim that he passed before he could get the design to where he wanted it.
It may not be the best antenna if you have the opportunity to build multiple half-wave dipoles, but it provides the opportunity to get on several bands if you have limitation on the number of antennas you can have.
One method of using a single dipole on two or more bands is to use "traps", these being a resonant parallel circuit. If we want an 80 and 160 metre dipole we would use traps resonant on a frequency such as 3650 kHz. The traps are placed around 20 metres from the centre feedpoint. The trap prevents signals from the transmitter on 80 metres reaching the remainder of the antenna, and thus the transmitter sees a resonant antenna while transmitting on this band; and while transmitting on 160 metres, it sees the full antenna.
Traps are traditionally made from either a large diameter (50-125 mm) coil, or a toroidal inductor; and a fairly high voltage ceramic, silver mica, or other capacitor. The alternative is a using coils of coax. Capacitors are often several tens to 100 picofarads.
The downside is that if we have a 160 metre transmitter which is generating harmonics, especially on 80 metres, then this antenna will radiate them well, as the harmonic sees a good antenna, whereas on a standard dipole, it would see a high impedance.
Note that these only appear as a distractor below.
Q stands for Quality Factor. High Q can be our friend when we want a good filter to resolve a weak Morse signal in a noisy band, but is our enemy when we want to use a single antenna to cover a whole low-HF band with good SWR. High Q reduces the bandwidth of the antenna.
Read more on Q in the Wikipedia article: Q factor
For various reasons we may not be able to use a quarter-wave antenna on HF, so some form of shortened arrangement is needed.
Helical winding up a fibreglass rod or tube is one option. Generally a half wavelength of wire is used. Some are single band. In the case of Outbacker for Hams, or Terlin for other users and agencies in rural and remote Australia, there are taps and a "wander lead". Often there is a metal rod or wire at the top, between 100 mm and 1.2 metres. A friend made one for 40 metres using a fishing pole which reached the 4.3 metre legal maximum. It has similar efficiency to a dipole. Lower cost 27 MHz CB antennas use a rod tapering from around 8 mm down, fitted with a ferrule with a 5/16" 26 TPI "Brass" thread. HF and some CB units often use a roughly 20 mm, maybe 25 mm blank, and the 5/16", or a 3/8" 24 TPI UNF thread, or often a 1/2 inch 12 TPI Whitworth (BSW). 3/8 may have the male on the antenna. The larger the diameter of the rod, the better the bandwidth.
Terlin / Outbacker uses an epoxy coating, others typically use heat-shrink of varying thickness.
Diamond in Japan had a rather complicated 7 MHz antenna which includes from memory 6 metres and 2 metres, maybe 10 metres and 70 cm too, I forget the exact details, although there were optional additional parts such as for 14 MHz, and 21 MHz (if the antenna does not work there already). They now have a single band 40 metre one 2.2 metres long. It consists of a base structure, around 50 cm of rod, 50 cm of fairly slim helical, and a bit over metre of whip. Both use an SO-239 base. These antennas need a solid ground connection, are somewhat heavy, have a fairly large wind load, all of which make them unsuitable for magnetic mounting.
M14 (14 mm) is used on some commercial HF whip antennas, for use on top of a coil or tuning unit. Some have a long coil over which a contact can move, driven by a motor under processor control; others use a relay based antenna tuner in a cube, which forms the base unit. It is important to ensure a good earth connection to the vehicle chassis or body, using a braid as necessary.
The the other end of the quality spectrum I had a cheap magnetic base and centre-loaded 27 MHz whip set. Shortly after I was licensed I worked with an engineer who as also a competent machinist. After measuring the 0.23-something inches in a micrometer the next trick is to determine likely thread sizes. 15/64" is not super common, multiply by 25.4 to get 5.9-something millimetres, which is very close to 6 mm making that a likely candidate. This is M6 × 1 mm thread pitch, although 0BA was a possibility, but the thread shape was incompatible. Test fitting a known nut or screw is one method, or using a thread gauge. He turned a ferrule, and drilled and tapped it for the M6 stud, and to take 1/8" plain brazing rod to make a 2 metre quarterwave. Eventually the cable on the base failed, and I re-threaded the ferrule for a regular base (5/16" BSB uses a 6.8 mm hole). See: Vertical Antenna for details.
And towards the other end of the spectrum literally, N connectors bases are used at 23 cm and for Wi-Fi / 13 cm. The only magnetic base I could find for a 23 cm antenna I bought was sold for W-Fi, and had a RP-SMA plug, although this could have been changed easily enough. Adaptors to BNC are quite rare, and I had to have it sent to the hotel I stayed at for Hamvention.
I saw one design for perhaps for 80 metres, with a varnished wooden pole some meters long, and maybe 5 cm in diameter, with half a wavelength of wire wrapped up it, closely spaced at the bottom, less so further up, and a say 30 cm wire at the top. Dried bamboo would also work well.
"Rubber Ducky" antennas for handheld radios consist of a springy coil inside a rubber sheath. In such cases, and those above the diameter and inter-winding spacing is very much less than a wavelength, and these are called "normal mode helical antennas", which radiate broadside like any other whip. They are also used as FM broadcast band receive antennas in many newer cars, which also receive DAB or DAB+ where available. They may pick up strong AM / MW signals above the vehicle's injection and/or ignition system noise, but work poorly.
Another is to use a single loading coil with rods or whips. While "base loading" is an option, centre loading gives the best performance. These were popular for 27 MHz CB whips, where the 2.5 to 3 metre length for a full-sized antenna was often inconvenient. For amateur bands, larger "bug-catcher" sized coils may be used.
One disadvantage of antennas shortened by the use of coils is narrower bandwidth than a full-length antenna. It is also important that these coils have low resistance, for good efficiency.
Part of the function of these coils is to cancel the capacitive reactance of a short antenna.
The centre loading coil is often a close-would coil of enamelled wire, rather than the open wound coils on stiff wire Australian UHF CB antennas, or old mobile 'phone whips; which act as phasing sections separating resonant sections. These antennas are sometimes termed "co-linear", as the elements are in a line.
Loading can also be used to build shortened dipoles, and similar antennas. The Buddipole, and various emulations are examples of these, which are designed to be used by portable stations, or temporarily set up in locations with restrictions. One of the smarter aspects is to have 560 mm of rod before the coils. They can be supplied as a Buddistick vertical (or I believe the Buddipole can be configured this way). Note that these are for stationary use, not on moving vehicles.
Chinese online markets now sell 5.6 metre telescopic antennas with an M10 (10 mm fine) thread on the bottom. These are similar to 16.9 foot 3/8" 24 TPI thread units from MFJ. They can be mounted on a loading or tuning coil. Note that 3/8 and 10 mm are within half a millimetre, but threads are incompatible. AliExpress sellers also have 3/8" UNC (16 TPI) to M10 adaptors to mount a metric base on a Manfrotto or other quality tripod with the head removed, sized as per ISO 1222:2010. You should be avoid using them in more than a light breeze. 32 TPI UNEF also exists, so avoid these.
If you are making your own portable antennas professional speaker stands are affordable and light weight. One example is the Pyle PSTND1 which extends to 2.1 metres or 6.8 ft, available via Element 14 as part 2833397. Turramurra Music has the Xtreme SS260, 1.85 metres or 6 ft.
Off the paper: Those above are not the Axial-mode helical antennas used from VHF to microwave bands. These generate circularly polarised signals. They receive CP signals only of the correct handedness, and linear polarised signals in any orientation. They are an alternative to the crossed Yagi's discussed elsewhere. They are popular for satellite use, including by the military and spy agencies. An operative can use a 200 MHz or 400 MHz radio to communicate a via satellite in geostationary orbit. A number can be seen in Canberra in VK1. Maybe they could even replace the innards of an Australian-style UHF CB also used in Indonesia and the Pacific with a Software Defined Radio capable of secure digital communications.
Wire and plastic pipe or another former can be used to make a high gain antenna for uses such as sharing Wi-Fi over a distance. Supports can also be 3D printed: Derek SCG: Building a 2.4 GHz WiFi helical antenna
One parameter in selecting or configuring an antenna is take-off angle. To "work DX", meaning make contacts with distant stations, we want a low angle of radiation, so that the signal reaches the ionosphere at the greatest distance, meaning the signal travel the greatest distance.
A vertical, especially a 5/8 wavelength generates a signal with low angle of radiation, especially if it is over a conducting surface, such as salt-water. Poorly conducting rocky ground typically results in a higher angle.
For horizontal antennas, the higher the antenna, the lower the angle of radiation. Factors, such as being on a slope, affect the angle. On a slope, the take-off angle on the down-hill side is lower than over flat ground.
Covered in other papers, in some cases we do want a high angle of radiation, such as NVIS.
For a parabolic dish gain is increases by 6 dB when the frequency doubles. Imagine a dish operating 1250 MHz. The wavelength is 24 cm. If you cut squares of sticky paper to this size and stuck them to the dish this is proportional to the gain. If you operated it at 2500 MHz the wavelength is 12 cm. You could also stick 4 times as many 12 cm × 12 cm squares to the dish surface, representing 4 times the gain, or an extra 6 dB of gain.
These pages have taken many, many hours to write, and then to edit with each update, plus the cost of the domain name. Thus a contribution would be greatly appreciated, via Ko-Fi, or using PayPal for any amount in the currency of your choice.
These are actual questions from the published Extra exam pool.
E9C01
What type of radiation pattern is created by two 1/4-wavelength vertical antennas spaced 1/2-wavelength apart and fed 180 degrees out of phase?
A. Cardioid
B. Omni-directional
C. A figure-eight broadside to the axis of the array
D. A figure-eight oriented along the axis of the array
Another way of saying half a wavelength is 180 degrees. At a point a half wavelength from the antenna the signal is at 180 degrees to what it is at the antenna. Thus, if we add a second antenna at this point, fed out of phase, we reinforce the signal along the axis of the two antennas. This reduces the signal broadside to the array. We therefore get a figure-8 pattern oriented along the axis of the array, answer D.
E9C02
What type of radiation pattern is created by two 1/4-wavelength vertical antennas spaced 1/4-wavelength apart and fed 90 degrees out of phase?
A. Cardioid
B. A figure-eight end-fire along the axis of the array
C. A figure-eight broadside to the axis of the array
D. Omni-directional
This results in a cardioid pattern, answer A.
This is essentially a circular pattern with a null in one direction, somewhat reminiscent of the cleft in the heart symbol, ♡. This is useful more useful for an AM broadcast station which is requires to "protect" another station on the same frequency, meaning they need a null in its direction.
E9C03
What type of radiation pattern is created by two 1/4-wavelength vertical antennas spaced 1/2-wavelength apart and fed in phase?
A. Omni-directional
B. Cardioid
C. A figure-eight broadside to the axis of the array
D. A figure-eight end-fire along the axis of the array
While the two signals would cancel each other along the line of the antennas, if we were a kilometre or so away from them, at 90 degrees, and could see the currents in the antennas, we would see them moving up and down in phase. We would also experience stronger signals than we would from a single antenna. The radiation pattern is figure-8, broadside to the antenna array, answer C.
E9C04
What happens to the radiation pattern of an unterminated long wire antenna as the wire length is increased?
A. Fewer lobes form with the major lobes increasing closer to broadside to the wire
B. Additional lobes form with major lobes increasingly aligned with the axis of the antenna
C. The elevation angle increases, and the front-to-rear ratio decreases
D. The elevation angle increases, while the front-to-rear ratio is unaffected
Lobes on a 1/4 wave wire are at 90 degrees to the wire. At 3/4 wavelength antenna are at roughly 45 degrees to the wire, and they get closer to it as the wire becomes longer, answer B.
While I forget the exact details, an electronics magazine included a reader submitted project for a 2 metres band antenna he set up while camping. It consisted of 5 wavelengths of wire, (around 10 metres) and radiated along the direction of the wire.
E9C05
What is the purpose of feeding an off-center-fed dipole (OCFD) between the center and one end instead of at the midpoint?
A. To create a similar feed point impedance on multiple bands
B. To suppress off-center lobes at higher frequencies
C. To resonate the antenna across a wider range of frequencies
D. To reduce common-mode current coupling on the feed line shield
Feeding them off-centre provides the ability to work on several bands, with a similar feed-point impedance, answer A.
The more affordable Remote Ham Radio stations use these, due to their multi-band ability.
E9C06
What is the effect of adding a terminating resistor to a rhombic or long-wire antenna?
A. It reflects the standing waves on the antenna elements back to the transmitter
B. It changes the radiation pattern from bidirectional to unidirectional
C. It changes the radiation pattern from horizontal to vertical polarization
D. It decreases the ground loss
It makes the antenna radiate in a single direction, answer B.
There were several at the OTC transmitting station at Doonside in Sydney, aimed at different Pacific islands. It would be undesirable to have high powered signals also fired backwards across rural NSW and beyond, potentially causing interference to other users radio, so they would have been terminated, to make them unidirectional. It appear that the longwire is a reference to the beverage antenna.
E9C07
What is the approximate feed point impedance at the center of a two-wire folded dipole antenna?
A. 300 ohms
B. 72 ohms
C. 50 ohms
D. 450 ohms
This is 300 ohms, high than for a standard dipole, answer A.
As an aid-to-memory: To make an FM broadcast band receiving antenna, cut a length of 300 ohm ribbon to a half-wavelength, and short each end together. Snip one of the two wires at the half-way point, and terminate these to a length of ribbon going to the radio. This also worked with TVs with 300 ohm inputs in good signal areas. I suppose it would work via a balun to a digital set, if you wanted a specific physical channel.
E9C08
What is a folded dipole antenna?
A. A dipole one-quarter wavelength long
B. A center-fed dipole with the ends folded down 90 degrees at the midpoint of each side
C. A half-wave dipole with an additional parallel wire connecting its two ends
D. A dipole configured to provide forward gain
This can be considered a dipole with an extra wire linking the two ends, as described in the FM antenna above, answer C.
E9C09
Which of the following describes a G5RV antenna?
A. A wire antenna center-fed through a specific length of open-wire line connected to a balun and coaxial feed line
B. A multi-band trap antenna
C. A phased array antenna consisting of multiple loops
D. A wide band dipole using shorted coaxial cable for the radiating elements and fed with a 4:1 balun
This is a dipole usable on multiple bands. Its main feature is a "drop" of balanced feedline, such as TV ribbon, joined to 50 ohm coax, as in answer A.
E9C10
Which of the following describes a Zepp antenna?
A. A horizontal array capable of quickly changing the direction of maximum radiation by changing phasing lines
B. An end-fed half-wavelength dipole
C. An omni-directional antenna commonly used for satellite communications
D. A vertical array capable of quickly changing the direction of maximum radiation by changing phasing lines
This is an end fed dipole antenna, answer B.
E9C11
How is the far-field elevation pattern of a vertically polarized antenna affected by being mounted over seawater versus soil?
A. The low-angle radiation decreases
B. Additional higher vertical angle lobes will appear
C. Fewer vertical angle lobes will be present
D. The low-angle radiation increases
A benefit for DX-pedition stations activation remote islands, the low-angle radiation increases, answer D.
E9C12
Which of the following describes an extended double Zepp antenna?
A. An end-fed full-wave dipole antenna
B. A center-fed 1.5-wavelength dipole antenna
C. A center-fed 1.25-wavelength dipole antenna
D. An end-fed 2-wavelength dipole antenna
This is a large centre-fed antenna, 1.25 wavelength long. Each arm consists of a 5/8 wave element, answer C.
E9C13
How does the radiation pattern of a horizontally polarized antenna vary with increasing height above ground?
A. The takeoff angle of the lowest elevation lobe increases
B. The takeoff angle of the lowest elevation lobe decreases
C. The horizontal beamwidth increases
D. The horizontal beamwidth decreases
The take-off angle decreases, answer B.
This potentially makes the antenna better for DX.
E9C14
How does the radiation pattern of a horizontally-polarized antenna mounted above a long slope compare with the same antenna mounted above flat ground?
A. The main lobe takeoff angle increases in the downhill direction
B. The main lobe takeoff angle decreases in the downhill direction
C. The horizontal beamwidth decreases in the downhill direction
D. The horizontal beamwidth increases in the uphill direction
The take-off angle reduces in the down-hill direction, answer B.
E9D01
How much does the gain of an ideal parabolic reflector antenna increase when the operating frequency is doubled?
A. 2 dB
B. 3 dB
C. 4 dB
D. 6 dB
The dish might go from being 10 wavelengths wide to 20, and from 15 to 30 wavelengths high, so the dish covers four times the number of wavelengths squared. As we increase something by 4 times, a 6 dB increase applies, so it is answer D.
E9D02
How can linearly polarized Yagi antennas be used to produce circular polarization?
A. Stack two Yagis to form an array with the respective elements in parallel planes fed 90 degrees out of phase
B. Stack two Yagis to form an array with the respective elements in parallel planes fed in phase
C. Arrange two Yagis on the same axis and perpendicular to each other with the driven elements at the same point on the boom and fed 90 degrees out of phase
D. Arrange two Yagis collinear to each other with the driven elements fed 180 degrees out of phase
Two yagis perpendicular to each other, with the driven elements at the same point on the boom fed 90 degrees out of phase, answer C.
This typically uses a length of coax linking the two driven elements, to provide the phase shift, often zip-tied to the boom, with the end formed into a U-shape. A few other similar arrangements are possible, including having the driven elements spaced some distance apart.
E9D03
What is the most efficient location for a loading coil on an electrically short whip?
A. Near the center of the vertical radiator
B. As low as possible on the vertical radiator
C. At a voltage maximum
D. At a voltage null
It should be at or near the centre of the vertical element, answer A.
E9D04
Why should an HF mobile antenna loading coil have a high ratio of reactance to resistance?
A. To swamp out harmonics
B. To lower the radiation angle
C. To maximize efficiency
D. To minimize the Q
Heavy, low resistance material in the coil minimises losses, answer C.
E9D05
Approximately how long is a Yagi's driven element?
A. 234 divided by frequency in MHz
B. 1005 divided by frequency in MHz
C. 1/4 wavelength
D. 1/2 wavelength
This is a halfwave, answer D.
What usually occurs if a Yagi antenna is designed solely for maximum forward gain? The F-to-B ratio often decreases, answer B
E9D06
What happens to the SWR bandwidth when one or more loading coils are used to resonate an electrically short antenna?
A. It is increased
B. It is decreased
C. It is unchanged if the loading coil is located at the feed point
D. It is unchanged if the loading coil is located at a voltage maximum point
The Q of the coil means that bandwidth is reduced, answer B
The upside is that efficiency at the frequency to which it is tuned to may be better, due to the coil.
E9D07
What is an advantage of using top loading in a shortened HF vertical antenna?
A. Lower Q
B. Greater structural strength
C. Higher losses
D. Improved radiation efficiency
Top loading increases radiation efficiency, answer D.
My understanding is that the capacitance between the top loading "hat" and the ground increases current in the antenna element, and thus the energy radiated. Things like centre, rather than base loading also increase current in the section before the coil. While bending the ends of a dipole half-wave along is a spoiler, dropping the last few metres of a dipole downwards because your yard a little narrow is OK, ideally done symmetrically.
E9D08
What happens as the Q of an antenna increases?
A. SWR bandwidth increases
B. SWR bandwidth decreases
C. Gain is reduced
D. More common-mode current is present on the feed line
High Q reduces bandwidth, answer B.
E9D09
What is the function of a loading coil in an electrically short antenna?
A. To increase the SWR bandwidth by increasing net reactance
B. To lower the losses
C. To lower the Q
D. To resonate the antenna by cancelling the capacitive reactance
Inductance tends to cancel capacitive reactance, and make the antenna appear resonant, answer D.
E9D10
How does radiation resistance of a base-fed whip antenna change below its resonant frequency?
A. Radiation resistance increases
B. Radiation resistance decreases
C. Radiation resistance becomes imaginary
D. Radiation resistance does not depend on frequency
As frequency reduces, the radiation resistance decreases, and the capacitive reactance increases, answer B.
E9D11
Why do most two-element Yagis with normal spacing have a reflector instead of a director?
A. Lower SWR
B. Higher receiving directivity factor
C. Greater front-to-side
D. Higher gain
Using a director provides more gain, answer D.
E9D12
What is the purpose of making a Yagi's parasitic elements either longer or shorter than resonance?
A. Wind torque cancellation
B. Mechanical balance
C. Control of phase shift
D. Minimize losses
You will notice that the options for a two-element yagi are a reflector or director. Thus a rod or tube around 5% longer than the driven element will reflect the signal, one about 5% shorter will reinforce the signal in the forwards direction. This is down to the phase shift in these elements, answer C.
Two deleted questions relate to station grounding. The best conductor for minimising losses in a station's RF ground system is... Wide flat copper strap.
The second asked which would provide the best RF ground for a station, with an electrically short connection to 3 or 4 interconnected ground rods driven into the Earth. These should be spaced 1.8 to 2 metres apart. If this spacing is maintained, more rods, and having more strings of them is better. While a connection to a metal water pipe was a wrong answer, metallic piping should be bonded to the ground system. This is additional to radials which can be run around towers, or as a counterpoise at the bottom of a single-ended sloper or inverted-L, etc.
Helical 27 MHz antennas are often available at Hamfests flea-market sections for between a few dollars, and at the the end of the day, "Just have it, I don't want to take it home". They are typically around 1.5 metres or 5 feet long. They have a copper wire wound over a fibreglass rod secured with a thin plastic film referred to as Polyolefin, although most heatshrink is made from this. The plastic can be cut away, and the wire unwound, leaving it soldered or welded to the ferrule.
Now you have a solution in search of a problem. Cut the wire to a calculated half wavelength of the frequency of interest, and wrap it back onto the rod, maybe use a little tape or a rubber band to hold it in place while you test SWR. I had hoped to get a 6 metre antenna at around 50 cm, the same as a 2 metre quarterwave, but could not get a match with wire on less than 70 or 80 cm of rod. I didn't complete the project, but I suppose a few drops of CA / super-glue could hold the windings while the rod is cut to length, and heat-shrink fitted. A small end-cap is needed.
While some Australian designed HF antennas may have constant windings, it is more usual to start fairly tight, and slowly increase the spacing. The final turn might be over several or 10 cm, depending on the band.
While maybe you could solder a little extra wire and try 12 metres, more likely candidates are 10 metres, 6 metres, likewise, 5 metres, and 8 metres in Europe*, or licensed agency low-band VHF. 4 metres at 70 MHz and licensed channels in the 66 to 88 area have this as an option, although with a quarterwave a metre long, potentially unnecessary unless you need to avoid hitting low-flying garages, etc. But if you want a 20 to 30 cm antenna for 2 metres it is worth trying. Remember that sensitivity will be lower than a full sized antenna.
*The Republic of Ireland (Éire) agency has given Amateurs 40-44 MHz (8 metres) and 54-69.9 MHz (5 metres), as they no longer need it for broadcast, commercial communications, or government uses. More slender 8 metre bands are available in various ITU Region 1 locations, and beyond. Others have beacon licences. GB3MCB is on 40.050 MHz and 60.300 MHz using FT8 and CW at 5 Watts under a Innovation & Research Licence. See: GB3MCB Beacons. They also have beacons on 28.215MHz, 6m, 4m, and on up to 10 GHz. Slovenia has S55ZMS on 40.670 MHz. Denmark has OZ7IGY on 40.071 MHz.
Meanwhile 9A0BFH in Croatia is on "70.022,00 kHz", meaning 70,022.00 kHz to English speakers, as they reverse the use of dots and commas in some countries. This is also 70.022 MHz.
There are LIPD class licence bands in Australia for 40.25 - 40.66 MHz at 100 mW, and 40.66 - 41.00 MHz at 1 W; and a global ISM band from 40.66 to 40.7 MHz, with periodic radiators permitted under Part 15. Aldi has had kids' walkie-talkie pairs on 40.68 MHz occasionally. 100 mW is permitted in the 70 to 70.24375 MHz LIPD band. WSPR or the like may work one one of these bands. ACMA may also allow a club or the like have a Scientific Licence in non-ham spectrum between 30 and 88 MHz for beacons and the like.
On to: Antennas 3 - Transmission Lines
You can find links to lots more on the Learning Material page.
Written by Julian Sortland, VK2YJS & AG6LE, February 2026.
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