## Saturday, June 28, 2014

### QRP Power Meter and Dummy Load

##### Steve Yates - AA5TB

E-mail
Last Update: June 14, 2010

Many years ago I acquired a antique field strength meter and probe kit that did not function. However, the meter had a fast response time and a good enclosure and I thought it would make a good piece of test equipment. I designed the following circuit around what I had and it has worked out well for me.

The schematic below is of my QRP power meter and dummy (50 Ohm) load combination. The 50 Ohm load consist of resistors R2 through R5. The four 200 Ohm resistors in parallel combine to make 50 Ohms. I used four resistors because this minimizes the component lead inductance of the resistors as well as distributing the power dissipation. The meter is simply a current meter with a known internal resistance configured as an RF voltmeter. D1 rectifies the RF voltage across the load resistors and C1 charges to the peak of this rectified voltage. The capacitance of C1 is chosen so that the time constant of the RC circuit consisting of C1, R1 and the meter's resistance is long compared to the RF cycle. R1 is chosen so that when the RF power applied is 5 Watts the meter reads full scale.

The calculations are as follows:

The internal resistance (Rm) can be found by constructing the simple circuit below and performing the following calculations:

Adjust R until the meter reads it's full scale value. Be sure to start with R at it's maximum value to prevent damage to the meter. Solve the following equation to find the meter's internal resistance.

The formulae below are to convert the reading on the microampere meter to watts and back. Please note that the possible error caused by the diode's nonlinear response below about 100 mW has been ignored. The scale in the region of tens of milliwatts could be calibrated against a known calibrated power meter or signal source if desired. For more information regarding the very low power measurements with a diode detector you may want to check out "Square Law Diode Detectors in 50 ohm Systems" presented by Glen, VE3DNL.

## Friday, June 27, 2014

### Loop Antennas - Delta Loops and Square (Quad) Loops and more

Delta Loops for HF  -  "You'll love lower noise and relative gain over a dipole"
http://w5sdc.net/delta_loop_for_hf.htm
One Stealthy Delta - This HF antenna keeps a low visual profile while attracting plenty of attention on the air.
An excellent and amusing article by Steve Ford, WB8IMY
http://www.sgcworld.com/Publications/Articles/237qst0502.pdf
Random length multi-band delta loop antenna – A good antenna for when a dipole isn't enough by KC8AON
An Easy to Install Vertical Loop for 80-6 Meters by John Reisenauer, Jr. KL7JR
http://www.hamuniverse.com/kl7jreasyvertloop.html
40m-10m DELTA LOOP ANTENNA - GU3WHN
http://www.rsars.org.uk/ELIBRARY/ANTENNAS%20DOCS/40m-10m%20%20DELTA%20LOOP%20ANTENNA%20-%20GU3WHN%20iss%201.3.pdf
M0PLK Multiband Delta Antenna - By Arthur M0PLK (SQ2PLK)
H5ANX Mk4 Delta Loop Design by Sajid Rahim
http://www.eham.net/articles/10738
Multiband H.F. Delta Loop by IW5EDI:
SGC Stealthy H.F. Delta Loop:
http://www.sgcworld.com/Publications/Articles/237qst0502.pdf
KL7JR Easy H.F. Delta Loop:
http://www.hamuniverse.com/kl7jreasyvertloop.html

W6ZDO Portable H.F. Delta Loop Project:
http://www.fros.com/KI0GU/w6zodelta.htm
Loop Antenna Notes by "Yukon John" KL7JR
http://www.hamuniverse.com/kl7jrloopnotes.html
Build a Multi-Band Mono Delta Loop for 40, 30, 20 and 15 Meters by Jose I. Calderon (DU1ANV)
http://www.para.org.ph/membersarticles/DU1ANV/Multi-Band%20Mono%20Delta%20Loop%20ant.pdf
DL2HCB Multiband Delta Loop
The Delta Loop (Skywire) Antenna - Legends, Theory and Reality
http://dk5ec.de/deltaloop-eng.htm
Loop Antenna notes and ideas from Radioworks
Delta Loops by GW7AAV
http://www.cqhq.co.uk/2009_05_01_archive.html
Magnetic Loops:
Small Transmitting Loop Antennas (Magnetic Loop Antennas) by Steve Yates - AA5TB
http://aa5tb.com/loop.html

End loading can also help reduce the size of antennas, particularly useful for dipoles used on the  80m and 160m bands. An end loaded dipole will produce an antenna that is H shaped. There are several commercial designs available produced in designs that cover a single band and others that cover multiple bands. The version shown below is only 3 metres tall so will be suitable for very unobtrusive, low profile use. It is the ProAntennas Multi-band I-PRO: 20m 17m 15m 12m 11m & 10m which uses a capacity hat with some loading at the centre. http://www.proantennas.co.uk/

Other similar antennas were available from Force12 Antennas in the form of, amongst others, the Sigma 5 and Sigma GT5. The Sigma design used T-bars at each end of the vertical dipole for loading technique and off-center loading coils.  http://www.force12inc.com This was supplied supplied in the UK by Vine Antennas at one time http://www.vinecom.co.uk . Transworld Antennas also have produce antennaa using a similar concept - the TW2010 Adventurer and Backpacker http://transworldantennas.com

K9AY Notes that: "I have come to the conclusion from my experiments, readings and observations, that a capacity hatted vertical dipole, a few feet over ground, is less compromised than a 1/4 w/l vertical of the same height fed against a less than perfect ground. Let's face it, most amateur's ground systems are mediocre at best. Also, the dipole is easier and cheaper to rig, and is two dimensional..Very important in my situation, as I cannot run out radials on my neighbours property.  Or, to quote W4RNL.."Since only a handful of hams can ever have 160-meter antennas high enough to yield a low angle DX signal, more practical are vertical arrays such as yours.  Vertical dipoles with hats (or Tees) save a plethora of wire needed by monopoles." http://www.dxzone.com/cgi-bin/dir/jump2.cgi?ID=7466

Information by K9AY

Information by K9AY

Interesting concepts from K9AY

### The Norcal Doublet

The Norcal Doublet Antenna:  http://www.norcalqrp.org/norcaldoublet.htm

The Norcal Doublet is a simple antenna that is 44 feet (13.4 metres) long, 22 feet (6.7 metres) per side. The Norcal pages report "...that the antenna would have basically the same radiation patterns on all bands from 40 - 10 meters. This would be very handy to have for field operation..... You will need the following materials: 50 feet of 4 core stranded computer cable; 1 #0 Fishing Swivel; 1 Cable tie; 2 pieces of fishing cord."
The antenna can be hung from trees or cheap telescopic 'roach' / Sota poles. Doubling the size would allow operation on 80 metres and even 160 metres by shorting the twin feed together at the transmitter end and feeding it against a good earth as a 'Marconi' type antenna.

## Wednesday, June 25, 2014

### The Moxon-Beam

The Moxon-Beam was introduced by L. Moxon (G6XN) in his book "HF Antennas for all Locations" (RSGB- Publications, Great Britain 1993). This beam is a 2-Element-Yagi with radiator and reflector and reduced size to about 75% of a normal beam. The 2-Element-Yagi with reflector has normally a 0,2-lambda-boom and an impedance of 50 W. The Moxon-beam has a 0,18-lambda-boom and still 50 Ohm. This is a good impedance for wire- beams.The ends of the two elements are bended backward (radiator) or forward (reflector) and act as a capacitive load. That is much better than inductive loading with coils. So we have greater bandwidth and lower losses.Through the reduced size we get a 0,5-0,7 dB lower gain than with a fullsize beam.

This type of a 2-Element-Yagi has an unbelievable F/B-ratio on the design frequency of >= 30 dB. That is higher than with any other 2-Element-Beam.

The gain is higher on the beginning of the band and lower at the end. The bandwidth for a SWR < 1,5 is great enough for the range of 28,0-28,7 and 21,0-21,45 MHz if the beam is built up with aluminium tubes. Wire-beams of the Moxon-type have a smaller bandwidth.

The design frequency should be for a frequency 1/3 from the beginning of the band, because the SWR raises more below the design frequency. For example look for the SWR of a tube-Moxon for the 15-m-band:

Designing a Moxon- Beam is very easy with a useful little program by D. Maguire, AC6LA with the name "Moxgen".

Moxgen generates an output file for "EZNEC" for modifications (e.g tapering) and shows you the dimensions for  building a wire-Moxon.

## Tuesday, June 24, 2014

### MINI ATU WITH TOROID

This ATU was designed in about 1990 to allow QRP rigs to be used with portable antennas. The unit had to be small and light weight. Generally I am against using ATU's at all regarding them as a cop-out for poor antenna design. However, when portable operation is considered, it is not always possible to erect the ideal antenna. This ATU was designed with idea of achieving a better match to an antenna that was nearly right.

A later version was tried which had an additional coil switched in and also a balun to accomodate twin feeder. I was never happy with this version, as it didn't seem to work as well as the simple version. When it was deconstructed in 2007 to do some loss measurements, it was discovered that a constructional error during the mod may account for this.

### ADRIAN KNOTT PROPOSES TUNED VLF ACTIVE ANTENNA

Hi to all! Today I found a very interesting project that using a small whip for hear the long VLF waves. Adrian Knot says that with this simple and inexpensive system you have good results, but suggests the using outdoor far from electric sources.
References: (http://www.hard-core-dx.com/nordicdx/antenna/special/vlfactive.html)

### Low pass filter subwoofer using LM324

This is a low pass filter subwoofer using IC 324 and some other components. which is mr Kunal Banerjee sent to me to publish on our site.It is very useful Thank you very much The Schematic PCB LAYOUT ORIGINAL The PCB layout original PCB SILK ORIGINAL The PCB Silk original The components list //Capacitor/////////////////////// ———————————— […]

### Putting up a Long-Wire Antenna

Fig. 2 Longwire antenna

I've actually used this kind of antenna. When I was a teenager, I used it with my old Realistic stereo receiver to improve its AM reception, and it did work. (My dad put it up for me.)

Note: RadioShack sells this antenna as a kit, catalog # 278-758, \$9.99 in their 2000 Catalog. You might also find it from other electronics suppliers. They sell the antenna wire as catalog # 278-1329, \$6.99 in the same catalog. The insulators can be ordered for shipment to your house through RadioShack RSU catalog # 12099248, \$4.79 + shipping in the 2000 Catalog.

Find two points, such as two poles (NOT utility poles!), or as most people will do, the corner of your house and a tree. Any safe places above the ground from which you can string this wire will do. Remember that not just the mounting places, but the "air-space" through which the wire will be strung must be free of obstructions, such as trees, and especially power lines. Whatever you do, don't put it on the same corner of the house through which your electrical service enters! First, that will be dangerous, and second, you'll pick up power line noise.

This antenna picks up signals best at right angles. It picks up worst end-on. Therefore, remember to orient the wire to pick up from the direction in which you are most interested.

Using an eye-hook at each point, attach a length of nylon rope. Tie the other end of the nylon rope to each insulator. The bare copper wire is strung from between the insulators, as shown in the diagram.

Use an insulated wire to connect to the copper wire at the end closest to your radio. Strip a couple inches of it and wrap it around the bare copper wire. For best results, solder this connection. This is shown in Figure 2.

If you string the wire from a stationary point (such as a house) to a tree, use this trick that my father taught me, and that Ham Radio operators use. You see, the tree will sway in the breeze, stretching the wire over and over, eventually breaking it. So on the tree, instead of using a plain eye-hook, put up a pully (such as a clothsline pully). Run the nylon rope through this pully, letting a few feet hang down, and tie a brick (or suitable heavy weight) to the end of the rope. This is what I have illustrated in the first diagram. As the tree sways in the breeze, the rope moves feely through the pully, and the weight of the brick keeps the whole thing taut.

Grounding: From the ground terminal on your radio (next to the antenna terminal) run a wire to either a copper cold-water pipe (PVC pipe won't work) or a copper ground rod driven into the ground.

Some safety notes:

1. Keep your antenna far away from power lines! If you, your antenna or your ladder touches a power line, you could be KILLED.

2. Remember that you will be climbing ladders or trees to high place. Observe every safety precaution. Never extend the ladder beyond the manufacturer's reccomendation. Never stretch to reach a point-- instead, move the ladder. Have the ladder on a secure footing, and have someone there to hold the ladder.

3. Make sure your antenna is in a safe place, high enough so people or pets won't walk into it by accident. (Plus, the higher up you get it, the better it works).

4. Use lightening protection! Make provisions to disconnect and ground the antenna when not in use. C. Crane Company and RadioShack offer lightening protection devices. However, disconnecting and grounding the antenna is still the best option. RadioShack sells a simple knife switch you can use for this. Screw it to the wall or table next to the radio, hook one side to the antanna, the other to a wire leading to a copper grounding rod, or the copper cold-water pipe leading outside of your house. (Remember this doesn't work if you forget to throw the switch!)

### Long Loopstick Antenna

Wound on a 3 foot length of PVC pipe, the long loopstick antenna was an experiment to try to improve AM radio reception without using a long wire or ground. It works fairly well and greatly improved reception of a weak station 130 miles away. A longer rod antenna will probably work better if space allows. The number of turns of wire needed for the loopstick can be worked out from the single layer, air core inductance formula:

### Magnetic loop antenna for 7-21 mhz

• Magnetic Loop Diagram

• Magnetic Loop antenna

This antenna has several advantages, not least being only 1 metre diameter! This loop relies on being horizontally polarised and receives only the magnetic wave, thus as most noise in the domestic environment is vertically polarised and electrical wave, it delivers low noise to your transeiver/receiver, which makes for nice clean listening. In addition any signal arriving in the direction of the loop end on will be nulled out, this can be useful to get rid of an interfering signal by simply rotating the loop leaving the desired signal in the clear. It can be used indoors with ease and works well at ground level which is not the case for long wire/dipole antennas at shortwave wavelengths.

So what are its disadvantages? Well its tuning is critical, such that for a small change in frequency the antenna will need to be retuned at the loop end. This is even more important for transmitting where a high reflected wave (swr) due to not being tuned correctly will damage the output stage of your transmitter! In addition due to the very high "Q" of the loop, very high voltages can build up on the loop tuning capacitor even with low amounts of power from your transmitter. It is for this reason I recommend this loop is used with a transmitter of no more than 8 watts, any more and the ordinary broadcast tuning cap will arc over with spectacular results. Of course should you wish, a higher spec/bigger air spaced tuning cap would allow higher power output transmitters to be used. Also I consider the use of remote tuning using a fairly high geared motor and insulated coupling on the tuning cap essential. For shortwave listeners manual tuning would suffice.

In setting up the tuning of the loop, connect to a receiver and tune to 14 mhz. Now tune the loop which as it nears peak tuning will cause a whooshing sound. Stop the tuning you should now hear good strength signals in your receiver. For tuning for a transmitter, 1st use receive method then apply low power and fine tune loop tuning and tweak gamma match for lowest swr.

Magnetic loop dimension details

• Diameter of loop 1000mm
• Diameter of tube 15mm
• Width of base 780mm
• Diameter of support pipe 42mm
• Loop end spacing (for tuner) 50mm
• Height of support 1590mm
• Nylon board 210x240mm
• Nylon board 240x70mm
• Gamma match width 310mm
• Gamma/loop spacing 110mm

Construction Tips

• Use a bicycle wheel with no tyre on to help form the curves of the soft annealed copper tube
• Clean the tube with wire wool before any soldering
• Use a 100 watt soldering gun for the joints, but use a small blow torch first to get the copper at temperature to take a joint
• Force some timber with the corners planed off down the plastic plumbing pipe this will stiffen the pipe as the loop is quite weighty
• Use inverted shelf brackets to support the mounting pipe and make a wooden frame wide enough to hold up the loop

### Two transistors fm wireless microphone circuit

This FM Wireless Microphone circuit Which adds a transistors in RF amplifier other one. So this circuit have two resonance circuits and also two trimmers. This cause have Higher efficiency And transmission far up.

Technical information.
• Used DC Power supply of 9V

• Maximum consumption current about 10mA

• Transmission frequencies in the 88 MHz.

• PCB dimensions: 1.64 x 1.54 inches.

• The working principle.

Figure 1 Two transistors fm wireless microphone circuit.
The microphone acts as audio receiver, then will through C2 into base of TR1. Which the transistor will serves to RF generator. And is a mixed audio signal into frequency generated. By have T1 is the RF adjuster then mixed to send to C5 to base,to amplify RF out to collector to sending out the antenna. At collector of TR1, TR2 will have a copper wire as coil to instead general coil to easy to builds.

How to builds its.

As Figure 2 the components layout and wiring of this project. I am sorry for cannot show PCB layout to you.

Then Figure 3 FM wireless microphone circuit that assembly is completed.

Testing
To apply the 9 volts battery to the positive terminal (+9V) and negative (G terminal) for ANT point to connects to coil. They must be scraping the liquid coatings out the copper before soldering. Then FM radio stations to rotate positions 88 MHz using a plastic screwdriver to gently adjust the trimmer T1, Until it whistles howling out the radio.
Next Try speaking into the microphone.

However, if the experiment is no sound speakers. Turn the radio to about 100MHz. If this is not yet, turn the radio all the way to 108MHz and try again. Then, adjust T2 allows, in order to get more distance.

The components list.
R1, R2____________27K
R3_______________4.7K
R4_______________270 ohm
R5_______________220K
R6_______________470 ohm
ELECTROLYTIC CAPACITOR
C2_______________10uF
CERAMIC CAPACITORS
C1_______________0.022uF (223)
C3, C6____________0.01uF(103)
C4, C5____________3pF
C7_______________5pF
TRANSISTORS
TR1, TR2_________2SC458, 2SC828, 2SC945, 2SC1815

## Friday, June 20, 2014

### Antenna for 432 MHz band with 21 dB gain

Antenna Backscatter length 4L. Antenna is shown in Figure. The antenna has a gain of 21.4 dB
with respect to increased half-wave dipole. The excitation system consists of a vibrator and a reflector nine directors. Reflector antenna configured as a disc whose diameter is equal to one wavelength. The vibrator has a length KL / 2. The first director is spaced a distance from the vibrator W-D1 = 0,2 L, each next - at a distance of 0,4 L from the previous one. The lengths of all Directors are equal (length director depends on its thickness). Full length of the excitation system is 4L. Large M reflector antenna has a diameter D, = 4L. In front of him at a distance of 0.25L. placed another ring-shaped reflector, the external diameter of which is 6L, and the internal - 4L. Studies have shown that this antenna has a gain of 8 dB greater than the antenna Uda-Yagi length 8L. Height w reflector ring is usually 0,25 L. Research has shown that an additional effect on the height of the antenna gain. The second figure shows the dependence of gain for one value of the diameter D = 2,35 L. Additional strengthening is added to strengthen that implements regular antenna is Backscatter flat reflector. An antenna with a large gain value for the 432 MHz band encounters certain difficulties, especially associated with the manufacture of a reflector of a sufficiently large diameter, since in this case it is necessary to ensure the necessary rigidity of the reflector and the carrying beam. Advantages of this antenna: high gain, power and simplicity of the relatively small size of the antenna criticality.

### Antenna for 432 MHz band with 21 dB gain

Antenna Backscatter length 4L. Antenna is shown in Figure. The antenna has a gain of 21.4 dB
with respect to increased half-wave dipole. The excitation system consists of a vibrator and a reflector nine directors. Reflector antenna configured as a disc whose diameter is equal to one wavelength. The vibrator has a length KL / 2. The first director is spaced a distance from the vibrator W-D1 = 0,2 L, each next - at a distance of 0,4 L from the previous one. The lengths of all Directors are equal (length director depends on its thickness). Full length of the excitation system is 4L. Large M reflector antenna has a diameter D, = 4L. In front of him at a distance of 0.25L. placed another ring-shaped reflector, the external diameter of which is 6L, and the internal - 4L. Studies have shown that this antenna has a gain of 8 dB greater than the antenna Uda-Yagi length 8L. Height w reflector ring is usually 0,25 L. Research has shown that an additional effect on the height of the antenna gain. The second figure shows the dependence of gain for one value of the diameter D = 2,35 L. Additional strengthening is added to strengthen that implements regular antenna is Backscatter flat reflector. An antenna with a large gain value for the 432 MHz band encounters certain difficulties, especially associated with the manufacture of a reflector of a sufficiently large diameter, since in this case it is necessary to ensure the necessary rigidity of the reflector and the carrying beam. Advantages of this antenna: high gain, power and simplicity of the relatively small size of the antenna criticality.

### QRP Fan Dipole

The object of the exercise was to produce an aerial that would allow me to operate from 40 metres to 10 metres, specifically 40, 20, 17, 15 & 10 metres. The antenna was always going to be mounted in the attic as no external antennas are permitted at my QTH, the attic allows the antenna to 'beam' roughly northwest / southeast and the house is some 40 feet above sea level. Construction would be simplified by the fact that I intended to run a maximum of 10 watts which means that the antenna wires can be simply attached to the rafters. (Click on images for a larger version.)

### Vertical antenna

This type of antenna exhibits an omni-directional pattern, with a low radiation angle. The length of the radiator is calculated by using the formula 234/Frequency in Mhz, for feet, or 71.5/Frequency in Mhz, for meters to make a 1/4 wavelength, at the desired frequency. The radiator can be made entirely from 1" aluminum tubing, but can also be made from several sections of tubing of different sizes (Below 20M it is not appropriate to use 1" tubing). These could be fastened together using pipe clamps, after splitting the lower section about 1", across the circumference, along the diameter to facilitate clamping of the upper section.

The radiator is mounted on a reasonable length square wooden post which is buried in the ground or fastened to the roof. Large diameter pipe clamps are used to fasten the radiator to the wooden pole. At about 1/2" from the base of the radiator a hole 1/8" should be drilled into the aluminum pipe. This hole is used for a bolt onto which the coax center conductor is fastened.

The radials should be slightly longer than the radiator. To facilitate multi-band operation at least four radials should be used for each band you wish to operate in, the radiator being cut for the lowest band. All the radials are then fastened, or soldered together, and a connection is made to the coax cable shield. The radials should be buried a few inches into the ground, and ideally spread out in a circle. An antenna matching unit is used for multi-band operation. Alternatively, in place of aluminum tubing, a PVC pipe could be used, with a 1/4 wavelength wire positioned inside as the radiator. Note: For this antenna the Antenna Matching Unit should be at the base of the antenna, for best performance, and can be remotely controlled.

### A on-shot circuit ideals

The digital circuit additional a circuits taht is very useful is On-Shots circuit or Also known as Mono-stable multivibrator circuit.

This behavior is the input trigger signal into just a single pulse,which is usually a lot of thin or narrow. And then this circuit will output is pulse out there. But width of the pulse width can be set to a value more or less. As needed with configuring the device in circuits. There are several characteristics of this circuit, which I gather is the following.

## Simple Monostable Multivibrator by IC CD4528

This the Simple Monostable Multivibrator circuit. That interesting by use IC CD4528 , be IC CMOS perform be Dual Monostable Multivibrator or One shot. When encourage at input make have a signal pecks at 2 output by have differently. Pulse duration and accuracy are determined by external timing components R1 and C1. Wide supply voltage range 3.0V to 18V. Separate reset available. Quiescent current e 5.0 nA/package (typ.) at 5.0 VDC.
Diode protection on all inputs. Triggerable from leading or trailing edge pulse. Capable of driving two low-power TTL loads or one. Low-power Schottky TTL load over the rated tempera-ture rang.

## Two-Stage Timer By IC Dual Timer NE556

This be Two-Stage Timer Circuit by IC Dual Timer NE556. Which 2 Timer both of build be One Shot. By wasp Trigger pin with GND. Timer1 work send pulse come out. enough be finished pulse. The this Timer2 as a result continue working replace. By the value Time bilateral control with R1,C1 and R4,C6.

## One-Shot By IC Quad Timer LM558

When mention the circuit One Shot friends at take an interest digital side may know good that how much is it valuable ? And I thinks one part as a result like to use IC 555 for this work. Because of good easy economize with. But in occasionally you want to use One shot circuit. Many the group usual use IC 555 many may don't economize. Try use IC LM558 , replace see. Because integrated one circuit replaces IC 555 get 4 usability not very differently follow the circuit. Use a formula calculate same T = 1.1 RC when friends know like this a time tries to use integrated number this circuit ? be lucky sir.

## Basic Timer By IC Quad Timer 558

Today I begs for to advise the circuit timer the foundation. By use the integrated circuit number LM558 (IC Quad Timer). Which the structure within like to have IC 555 4 within. If think in the sense of the price has already. As a result economize very that one. For the usability have no differently IC 555 highly very popular extremely. Can use do timer circuit well sir time value can change with change R1 and C1 follow a formula calculates T = 1.1 RC good easy. friends try induce try build play request have fun electronics circuit.

### A Tree Friendly 2 Meter Halo Antenna

Having purchased an all-mode, all-band (160m - 70cm) transceiver, I became curious about what 2-meter weak signal operations have to offer. I have a 5/8th over 5/8th vertical collinear antenna hanging in a tree at some 30 odd feet high, but I never heard anything on it, except on FM. The reason for that, I learned, is most 2-meter weak signal operations take place using horizontal polarization. Cross polarization is good for about 20 dB attenuation, which easily translates into the difference between perfectly good copy and inaudible signals. So I decided I needed a horizontal polarized antenna.

As is usually the case with antennas, there are a bazillion designs to choose from and none of them really fulfills all your requirements. I do not have a mast or tower, and I love to use trees for supports, so I wanted something that I could hang from a tree branch. Since I have no means to rotate the antenna, I required that the new antenna have an omnidirectional radiation pattern. It didn't have to be the best performer, because I just wanted to get my feet wet in this new mode of operation. There are few designs that would fit that bill. I settled on the Halo antenna because of its small footprint. This is important because larger designs would require a longer branch, with sufficient clearance in all directions, to hang from. The Halo I describe here has a diameter of only about 12 inches and can be hung virtually anywhere in a tree.

### The Halo Antenna

Halo stands for "HAlf wave LOop". The antenna is in fact nothing else but a half wavelength dipole with the legs bent in the shape of a circle. However, the ends do not meet, (especially near the end of the month) so technically it's not a loop. This loop can be fed with coaxial cable using a gamma match.

The Halo is certainly not a new design. Laurence M. Leeds and Marvel W. Scheldorf obtained a patent for this antenna in 1943. You can find their design at the U.S. Patent Office under Patent Number 2324462. Click on the "Images"-button to view the patent. You'll need a special browser plugin to access the patent. See the U.S. Patent Office website for more information on this.

Most Halo designs you find on the internet have moving parts. Often they require some sort of tuning capacitor and have a capacitor in the gamma match along with a slider construction that connects the gamma arm to the radiator. I prefer a design without moving parts so that the antenna doesn't get detuned easily when a bird decides the antenna makes a good resting place. I found the design that I describe here in a German antenna book "Antennen Buch" by Karl Rothammel, Y21BK.

### Basic Design

The design of this antenna is very simple and straightforward. It basically consists of a half wavelength piece of copper tubing bent into a circle. Between the ends of the tube there needs to be a gap of at least 1 3/16". This is to minimize capacitive coupling between the ends. This antenna is fed by a coax feed line through a gamma match. The gamma match is constructed from 6 1/4" #4 or #6 copper wire. This wire is bent into an L shape. The short end of the wire is soldered on the inside of the loop at the point where the long end of the gamma arm aligns with the halfway point of the loop. See below:

You could feed the loop directly with 50 ohm coaxial cable as shown above. However, I added a 1:1 current balun (choke) to the original design. I did this to force all the RF current, on the inside of the braid of the coax feed line, to go into the antenna and not to come back down on the feed line on the outside of the coax braid. This will help keep the feed line from radiating, causing potential RFI problems and changing the radiation pattern of the antenna.

### Building the Halo

Building this antenna is like making the pieces of the puzzle first, and then putting the puzzle together. First you build the antenna itself, then the support boom, the choke balun, the mount, and finally, you put these parts together.

### The Antenna

Start out by cutting a string to a length of 41 inches. You'll use this to measure the correct tube length. Thick monofilament wire as used for garden trimmers works very well. Mark this wire at the halfway point. A piece of electrical tape will do fine. This is the point where you’ll later have to mark the copper tube and where the coax braid will get soldered to the tube.

You'll probably find the soft copper tubing material in a 10-foot length, coiled up in a bag. Fortunately, the coil diameter is about the same diameter as the final loop will be. So there will be very little bending involved to get the circle shape needed for the loop. Eyeball how much tube you'll need from the loop coil and cut it. Don't attempt to make an exact measurement yet. In fact, the measurement I give here for the main loop is deliberately somewhat too large anyhow. Put the part you cut off on a flat surface and now measure how much you really need using the string from the previous paragraph. Cut off the excess tubing. Use the string again to find the halfway point of the tubing and mark it. This will be the point at which you will later solder the coax braid. Make sure the tubing is shaped like a circle, and that the ends are at least 1 3/16" apart. To keep the ends apart, I cut a piece of hexagonal Bic pen tubing to length and put it between the ends. You can secure it with some shrink tubing, but don't shrink it until you're done with the final tuning later on.

Now build the gamma from a piece of #6 or #4 copper wire. Use the measurements from the detail diagram above and bend it as shown. Solder the short end of the gamma arm to the inside of the loop at the point where the long end of the gamma arm lines up with the halfway point on the main loop (as marked earlier).

### The Support Boom

To support the antenna, I used a piece of 3/4" schedule 40 PVC pipe. Lay the antenna on the pipe and cut it so it's just a bit longer than the diameter of the loop. Now drill holes through the pipe to mount the antenna. On one end of the pipe you need two holes approximately 1 15/16" apart for the main loop and the gamma match to go through. Make sure you drill the hole for the tube very close to the end of the PVC pipe. This will make it easier to solder the coax braid onto the copper tube. Also be careful not to drill the hole for the gamma match all the way through the pipe. The gamma match only goes in halfway through the pipe and will not come
out the other side.

On the other side of the PVC pipe, drill a hole in the same plane as the first two holes for the piece of plastic tubing (hexagonal Bic pen) that is being used to keep the ends of the main loop apart. Next, drill the holes necessary to mount the SO-239 (panel mount) connector.

The last hole you need to drill is for mounting purposes. This hole needs to be drilled in the middle of the PVC pipe, all the way through. Make absolutely sure that this hole is perpendicular to the plane of the antenna. This hole needs to be the size of a bamboo skewer you can buy at the grocery store (sold in a bag of 20 or so). This skewer is later used to mount the antenna. You can use something else if you like as long as it's thin, strong, sturdy and straight.

### The Balun

Even though the original design does not call for a balun, I decided to add a 1:1 current balun in order to prevent RF currents from flowing back onto the outside of the coax braid, perhaps causing the feed line to radiate, create interference and change the radiation pattern of the antenna. The balun I built for this antenna consists of 12, 1/2" long, type 43 ferrite beads that slide over a short piece of RG-58 coax with the outer jacket removed. The hole in the beads I used was not big enough for the coax to slide through with the outer jacket intact.

The length of the piece of coax needed for the choke can be measured from the end of the boom where the gamma match is to the farthest edge of the SO-239 connector, plus about 3/4". The balun itself is about 6 inches long. If you use a different size of beads, just make sure you have enough beads to make a 6-inch long balun. You can secure the beads with some shrink tubing or electrical tape. This should be enough to make an effective balun for VHF that can handle up to 100 Watts of power.

One side of the coax should be prepared so you can solder it to the SO-239 connector. You can already solder the connector to the coax if you wish. The other side needs to be prepared so that the braid will reach the middle of the loop, and the center conductor meets the gamma match. Do not cut the center conductor to length. Instead, only remove the insulation from the center conductor so that it can be soldered later to the gamma match. Leave the excess wire intact. Put some shrink tubing or electrical tape around the braid to insulate it, except for the very end, of course.

If you do not have any ferrite beads available, you can construct an air core choke balun instead. There are several ways to make one. One method is to wind about 7 turns of the feed line on a coil form made from 3/4" PVC pipe. Place this choke near the antenna. If you prefer the choke to be part of the antenna, then you can wind 7 turns of the coax going from the SO-239 connector to the gamma match around the PVC boom.

### The Mount

Since I've chosen to hang this halo from a tree branch, I needed to find a way to mount this antenna onto a rope coming down from a branch in such a way that the antenna itself will remain in the horizontal plane. I came up with a method that will use gravity to hold the antenna perfectly horizontal.

When you built the PVC boom, you drilled a hole in the middle for a skewer. Now imagine you put the skewer through the boom, put the support rope alongside of the skewer and then tie the rope to the skewer with some wire ties. If you'd hold just the rope above the skewer and boom, the boom would just dangle in all kinds of directions and stay far from being horizontal. However, if you'd make a small loop in the bottom end of the rope and hang a weight from it, you'll see that the boom stays perfectly horizontal. See the diagram below.

### Putting It All Together

Take a piece of pen tubing, or whatever you chose to fill the gap in the main loop, and push it in the PVC boom.

Next you can join the antenna with the boom. Take one end of the antenna and guide it through the hole next to the hole for the gamma match in the PVC boom. Slowly move the tubing through the PVC support pipe. You'll notice some resistance because the loop is round and the holes through the pipe are in a straight line. This causes some friction. With a small amount of force you'll see that that the tube will go through the pipe quite easily. Stop when you reach the gamma match. Do not push the gamma match into its hole in the boom yet.

Bend the end of the braid of the coax that goes inside the boom at a 90-degree angle. Just over 1/4" from the end should be sufficient. This will make it easier later on when you solder the braid to the tube. Also bend the exposed center conductor at a 90-degree angle about 1/4" from the end.

Slide the coax inside the PVC boom through the hole for the SO-239 connector. While you do this make sure that the end of the center conductor kind of scrapes on the inside wall of the pipe, on the side where the hole for the gamma match is located. At some point you'll notice that the wire will get caught in this hole. Pull the wire through the hole with needle nose pliers while you continue to slide the coax inside the pipe. Stop when the insulation around the center conductor appears at or through the hole. If you bend the wire a bit at this point, it will stay in place.

Solder the center conductor to the gamma arm. You can cut off the excess wire, but I simply bent the remaining wire along the gamma match. Or, wind it around the gamma match, just in case you have to do it again. Now slowly push the gamma arm in the hole of the PVC boom. If it doesn't quite fit, you can cut a tiny wedge out of the hole where the center conductor passes through the hole. Stop when the gamma match reaches the middle of the pipe and the center marking on the copper tubing is in the middle of the PVC pipe.

When you look into the pipe you'll see the braid near the copper tube on the inside of the pipe. Pre-tin the copper tubing at the halfway mark. Make sure this mark is in the middle of the pipe. Now you can solder the braid to the tube.

If you haven't already soldered the SO-239 connector to the coax, then do so now. Push the remaining coax into the boom and fasten the
SO-239 connector to the boom.

Slide a piece of shrink tubing over each end of the antenna. Mate each end of the copper tube with the piece of pen tubing protruding from the support boom and slide the shrink tubing back a bit so it covers the piece of plastic tubing also. Do not heat the shrink tubing yet. This will hold the ends in place. You can also use electrical tape to do this. Just make sure the ends of the copper tubing stay flush with the plastic tube.

### Mounting the antenna

The antenna is now finished and we're ready to mount it for testing and tuning. Find a place where you can hang the support rope, like a tree branch. Make sure that there are no metal objects nearby, as they will detune the antenna. You can tune the antenna at a different place than the final destination if you wish.

Put a wire tie just below the middle of the skewer. This will prevent the antenna from sliding down the skewer. Secure the bottom half of the skewer onto the rope with two or three small wire ties. Make sure the skewer cannot slide along the rope. Drop the bottom end of the rope through the loop of the antenna and push the skewer all the way through the support boom from the bottom up. You may have to wiggle it a little bit when you're halfway into the pipe in order to get past the coax inside. Once the skewer is all the way through the support boom and the boom is resting on the wire tie on the middle of the skewer, you can fasten the top half of the skewer to the rope with two or three wire ties.

Your antenna can now dangle freely from the rope. You'll see that the antenna does not really stay horizontal yet.

Make a small loop at the bottom end of the support rope and hang a weight from it. I used a brick. Even if the antenna is going to be mounted very high up in a tree, try to keep the weight near ground level. This serves two purposes. First, if for some reason the weight would fall, it will not fall on top of someone and no one will run into it. Second, it will keep the whole system very stable in the wind. If the weight would be higher than just a few feet of the ground, the wind would catch it also and start swaying the weight. Not only is this dangerous, it will also take a long time before the system is stable again once the wind drops.

Of course you could opt not to use a weight and simply tie the bottom of the rope down. However, that makes the whole mechanical system very inflexible. The rope would move back and forth over the branch when it's swaying in the wind, and eventually the branch might be cut.

If you later find that the rope and weight are swaying too much, you can minimize this with a guide rope that is tied to, say, a post, or the trunk of the tree, and goes around the support rope. The guide rope will then allow the support rope to move mainly in the vertical direction.

Once finished, the antenna should look something like this:

### Testing and Tuning

Before you test the antenna, double check you made all the right connections. When you use an ohmmeter to check the connections, you should be measuring a short (zero ohm resistance) between the center and outer connections of the SO-239 connector. This antenna is what is called "DC grounded", which may help reducing static buildup on the antenna.

Now you can attach a 50-ohm coaxial feed line to the antenna to test and tune it. Use a wire tie to attach the feed line to the skewer. This will make the feed line run along the support rope and help stabilize the system. If you plan on weatherproofing the antenna, then read the part on weatherproofing below first before you tune the antenna.

I borrowed an antenna analyzer to tune the antenna, but you can also do it with just an SWR meter. When you use an SWR meter and cannot find a near 1:1 SWR anywhere in the 2 meter band, you need to make note of three SWR measurements. One at 144 MHz, one at 146 MHz and one at 148 MHz. If you find that the SWR is lower at 144 than at 146 and 148 MHz, then you know the antenna is tuned below the 2-meter band. If you find that the SWR is lower at 148 than at 146 and 144 MHz, then you know the antenna is tuned above the 2-meter band.

You will probably find that the antenna is tuned somewhat below the 2 meter band. I deliberately listed the measurement of the main loop slightly too large which results in a lower than desired resonance frequency. Cut a tiny bit of each end of the copper loop until your antenna resonates near 144.200 MHz. That is the SSB calling frequency in the U.S.A. Of course you'll have to decide at which frequency you want the antenna to be resonant. The 1:1.5 SWR bandwidth of the antenna is about 1 MHz.

Since the gamma match is fixed, you will probably not be able to get an exact 1:1 SWR reading. More realistic is 1:1.1 to 1:1.3. Don’t let this scare you. SWR readings other than 1:1 are perfectly fine as long as they do not go much higher than 1:1.5. At that point many rigs will throttle back the power. If you really cannot sleep peacefully if the SWR isn't perfectly flat, then by all means desolder the gamma match from the loop and solder it at a different point until you've found that serene 1:1 SWR spot. I will warn you though that things can get messy real quick while it really isn't worth the effort.

If you find yourself in the position where you cut too much of the antenna ends in order to find that elusive 1:1 SWR, don't panic! There's an easy solution. Solder a half inch or so piece of solid copper wire (#14 will do) to the inside of each tube end as shown in second diagram on this page. The wire ends protruding from the copper tubing will fit inside the plastic separator tube. This will help maintain a clean look of the antenna while you get a second chance at tuning the antenna. Now simply cut small pieces, like 1/16" or so each time, off of each wire until the antenna resonates at the desired frequency.

When the antenna is tuned you can heat up the shrink tubing around the copper tube ends so that everything remains in place.

### Weather Proofing

You can weather proof the antenna by filling all holes and gaps with RTV, or silicone sealant. Care should b
e taken when you want to seal the end of the boom where the ends of the loop meet. Putting RTV in that side of the pipe will detune the antenna. Make sure the sealant only goes to the inside of the PVC tube, and don't be tempted to put any sealant on the loop ends. The reason for this is that there is some stray capacitance between the loop ends. By adding sealant you change the dielectric between the tube ends, and therefore the value of the stray capacitance. This in turn changes the resonant frequency of the antenna. So it is better to seal this end of the support boom first before tuning the antenna if you plan on weather proofing the antenna.

If you feel that you need to seal the area around the small piece of spreader tubing, then use something like a very thin layer of nail polish. Also, if you want to make the loop very shiny, use some very fine steel wool to polish it.

### Conclusion

I described how you can build a Halo antenna for two meters that does not require a mast, has a very low part count and can easily be built with a minimum of tools. This project description may seem more complex than similar ones you can find on the internet, but that is simply because most other plans leave out a great deal of detail, especially in the area of construction. I like to include the lessons I learned along the way when I built the antenna.

This article also described a unique way to mount these types of antennas on a rope. This makes the antenna an attractive alternative for use in the field where the usual support structures may not be available or for those folks who, like me, do not have a tower or mast. Of course you can mount the antenna on a mast with a U-bolt if you wish.

I have built a 2 and 6 meter version of this antenna, mounted them on the same support rope and feed them with separate feed lines.

The 2 meter Halo is mounted at 24 feet, and the 6 meter Halo is mounted at 20 feet high. As you can see, the Halo makes for a stealthy antenna even though that was never one of the design goals. If you really want the antenna to blend in with the background, paint it light gray or light green, and add some random black strokes here and there. When you break up any symmetrical lines and patterns, any object can be made invisible against the background.

These Halo antennas allow me to dabble a bit in VHF weak signal operations given the restrictions mentioned in the beginning of this article. While the performance of this type of antenna is limited compared to other types of antennas, I'm rather surprised with the DX contacts I’ve been able to make with a modest 50 Watts of power.

If you have any questions or suggestions, please do not hesitate to drop me an email.

73,
--Alex, KR1ST

### WIRE DIPOLE ANTENNAS

The dipole is one of the most important and popular antennas, it forms the basis of many other different types of aerial which are directional and have gain in certain directions.

The dipole in its basic form consists of two identical lengths of wire with the feeder connected in the middle as in the diagram above. It can be any number of electrical wavelengths long. The most popular is the half wave dipole, normally thought of as a single band aerial.  Although it has little gain, it can be easy and cheap to construct, and they often prove to be the ideal solution with amateur radio operators who are only interested in one particular band .

HORIZONTAL

SLOPER

The wire dipole is normally mounted horizontal, vertical or sloping between two supports, but it can be erected in many different shapes such as the inverted-V or a Z shape. On the lower HF bands the the lengths become rather long so it is sometimes necessary to bend the antenna to fit the average garden.

INVERTED-V

The formula to calculate a half-wave dipole (in feet) on any HF frequency is 468/frequency in MHz. This is total wire length tip to tip, or 234/frequency in MHz for each element length. For example = If you want the antenna for 40 meters, choose the centre part of the band or centre part of the frequencies you want to work, 468/7.05 MHZ = 66.3 feet. It is better to make the wire slightly longer and then trim the wire to resonance. Make sure you trim the same length of each end.

In free space the feed point impedance is 78W so it is a good match to 75W coax. However when erected in the garden or over the house the impedance changes and it is acceptable to use 50W coax cable.

Although it is not essential, it is best to use a 1:1balun. This is connected between the two elements and the feeder cable. This ensures the correct operation of the antenna. It does not provide any impedance match, but it will balance the load by causing equal but opposite phase currents to flow in the conductors reducing radiation on the transmission line.

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