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Dave’s Homemade Loop Antennas

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Article by N2DS Dave

Welcome!

Welcome of my homemade loop antenna or loop aerial pages. All the loops described here were designed and built by myself. The features are not real different from loop to loop. These loops are made to enhance radio reception in the broadcast, or medium wave (MW) band range. Some of the loops are just one coil, some have tuning capacitors and some have an extra coupling coil. Read on and discover the fantasy of loop antennas. Or fetish in my case.

A Word About Loop Antenna Design

All these loops involve a resonant tuned circuit made up by a multi-turn loop coil and a variable capacitor. If you are using one of my designs shown on these pages, you are all set to go ahead. But if you are designing your own loop antenna, please read on.

As just mentioned, a resonant circuit is made with the coil and variable capacitor. The old standard configuration to tune the medium wave band is a 240µH coil and a 365pF variable capacitor. These numbers are fine when using a small diameter coil, but are grossly inaccurate with a loop antenna coil.

This inaccuracy is due to a relatively large amount of self capacitance (also called distributed capacitance) built in to large diameter wire coils. Increasing the wire spacing doesn’t do a lot to reduce this extra capacitance.

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Dave’s Homemade Antenna Tuner

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Article by Dave N2DS

A tuner like this has appeared with some of my high performance radios, such as my #35 and #50 sets. This type of tuner has worked very well with the accompanying detector board to make a nice dx crystal radio. My aim was to put as much versatility into this tuner project. When litz is this expensive, you can only go around once.

There are 4 uses I have found for this tuner. (This is why I call it a multi-use tuner.) The first use is a front end for my medium wave dx crystal or tube regenerative radios. Second is using the 4 gang capacitor with a loop antenna as a high performance crystal radio. Third is a long wave tuner and finally a signal booster for a nearby radio. Please look at the circuit below as I describe the different uses.

The medium wave (530-1700 broadcast band) crystal radio or one tube radio is set up by opening the two brass link switches between the capacitor gangs. The coil switches should be closed or shorted. By connecting an antenna and ground, this device becomes an antenna tuner. The signal is inductively coupled to the nearby crystal set detector.

The second use is to connect the tuner to a crystal loop antenna. To reduce circuit losses, only the stators of the capacitors will be connected. The links between the capacitor sections should be shorted together. Between the two sets of stators, the loop is connected. This can be done by using the A and G terminals. The effective capacitance is 500 pf. There is no wiper arm loss when using this 4 gang capacitor in that manner. The links to the coil should be opened.

The third use is for tuning in long wave stations. To tune the upper end of the long wave band, short all 4 links. If you wish to go lower, you will need a coil with higher inductance. This is easy to connect with this tuner. Open the two coil links and connect and external coil to the two thumb nuts that are now available. You will have 1000 pf capacitance across the coil and in series with the antenna available. Additional fixed capacitors may be used if a lower frequency is desired.

Finally, this tuner makes a great signal booster for a near by radio. I have had some e-mails from web visitors wanting to know how to make their little transistor radio work better. I did this in the 60’s when I wanted to put a transistor radio on my bike. The signal was weak so I made a tuned circuit and connected it to a rod antenna. Open the links that are between the capacitor sections and close the coil links. Connect an outside antenna and earth ground to the A and G terminals. Tune in a station, then reduce the volume. Then tune the tuner for a peak. You will be surprised! Just think how your kids can blast the house with Radio Disney with the same 10 songs all the time. Who Let the Dogs Out!!

Ok, now for the heißen eisen, the construction details. My tuner is built on an oak board about 16 x 5.5 inches (40×14 cm). The variable capacitor is a 4 section, 500 pf per section. If this is going to be used as a dx tuner, please look around for a quality variable capacitor. That is one with at least ceramic insulators on the stators. Nothing will kill the Q faster than a crappy variable capacitor. The capacitor should be mounted on ceramic or styrene standoffs.

It is also important to note that the capacitor shaft is isolated from the vernier drive with a plastic shaft. This is very important as this reduces the hand capacitance. There is still some slight hand capacitance effects which would be made better by moving the capacitor further back.

A 6:1 vernier dial drive is used to allow for easy tuning. Trying to tune the MW band in a half turn when using big litz is tedious at best. A one inch (24 mm) hole is punched in the front panel and the drive is attached with two small screws and nuts. Allow for the front panel or capacitor to move a little so as to reduce the binding. When the sweet spot is found, then the capacitor and front panel may be tightened. The dial is a round piece of thin styrene that is attached to the vernier. Made the dial as you please. I use Brother P-Touch labels to dress up my dial.

The switches are made up of brass links machined to span the distance between the two #8 screws. The panel material is styrene. Styrene has very good rf loss properties.

If you look at the switch drawings on the diagram, you will see a fixed side and a movable side. If the brass links are placed that way, the tuner will work as intended.

The coil form is a piece of 6x7x1/16 thick (152,5 x177,5 x1,6mm) styrene. There are 11 slits cut down to a hub diameter of 2 inches (5 cm). The wire is 660 strand, 46 gauge litz wire.

There is not too much more I can tell you about this project. If you have questions, please contact – Dave N2DS

Article originally available at http://makearadio.com

WSJT-X Site down: how to download.

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The official WSJT-X site is down from several days. The Website is hosted at Princeton Univeristy and it looks like it is under maintenance or relocating.

At time writing the only way to download the WSJT-X program is to access the SourceForge website where the files are maintained by the developing team.

Click here to download WSJT-X

Current stable release is wsjtx-2.5.4 while release candidate version is 2.6.0.

Six Meter Yagi Antenna

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A four element Yagi Antenna for 50 MHz band.

The reflector and the director elements can be mounted directly to the metallic boom, while the Driven element must be insulated from the boom.

The driven element is basically a simple folded dipole and foreseen a 4:1 balun. Usage of a folded dipole as driven element of the yagi antenna is almost common on VHF Yagi designs since it allow broading the SWR bandwidth.

If the broading is not so much important, the antenna can be directly feeded with a conventional dipole directly connected to a 50 ohms coax cable.

Mic Wiring Diagrams

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Article by m0ysu

Microphone wiring can be a real pain if you aren’t sure how to work out which wire goes where. On this page I will try to explain the basics and also give you the wiring positions for most CB radio’s

Basic Mics – These consist normally of three coloured wires and a braid/screen. The braid is the common wire for the TX/RX/Mod and is normally twisted around the modulation wire. If you get this in the wrong place you will be fighting an uphill battle. 4 pin mic sockets are about the easiest to sort out, the 5 pin din can be very hard to wire as there’s not much distance between the pins and can “short out” easily. Normally when I’m wiring 5 pins I put a sleeve on each wire to prevent this.
Back to 4 pin. Put the plug into the radio and look at the solder pins. Two of these pins will make the radio receive (sound) so find out which two these are by shorting a piece of wire across the pins with the radio on until you find the two that make sound. One of these pins will also be common to making the radio TX so that pin will be where the braid is soldered to. Once that is soldered on its pin touch each coloured wire on the other pin until the sound returns. Solder that coloured wire on the other pin. Next you need to find the TX pin. With the mike key depressed touch the other two wires breifly on the TX pin until you find the one that makes it TX. Solder that wire to the TX pin. Finally the modulation wire will go on the remaining pin. Often the modulation wire is the yellow one or it has the braid wrapped round it.

PWR Mics – These normally have 4 coloured wires and a braid. More often than not the black and braid twist together and go on the earth pin. The blue goes on the Receive pin. Sometimes but less often the blue and braid go together and the black is RX.
Below I’ve made this a bit easier so you shouldn’t have to do the above unless the wires of the mic do not correspond with the below.

ALTAI PWR MIC – black/braid= earth, red=RX, white=TX, Yellow=MOD
ASTATIC – blue/braid=earth, black=RX, red=TX, white=MOD, Yellow=Spare
SIRTEL ECHO MIC CBE 2002 – black/braid=earth, blue=TX, white=RX, red=MOD
007 POWER MIC – brown/braid=earth, green=RX, white=TX, blue=MOD
SADELTA EC 980 – braid=earth, green=RX, brn=TX, white=MOD
or braid=earth, black=RX, blue=TX, white=MOD

OLDER MAKE OF CB followed by plug reference

ACADAMY – 3
ALPHA 4000 – 13
AMSTRAD 900/901 – 1
ATRON CB 507 – 2
AUDIOLINE (ALL) – 2
BARRACUDA – 15
BINATONE 5 STAR/ROUTE 66/ BEAM BREAKER – 1
BREAKER 40FM CEPT – 1
CB MASTER 2040/2080 – 8
CHEIZA – 3
COBRA 146GTL/148/19/21 – 2
COLT 210/295/355/720 – 8
COLT 320/444/510/870/EXCALIBUR – 1
COMMTEL – 3
COMMTRON V111/CXX – 8
COMMUNICATOR – 1
DNT M40/B40 – 11
DOMINICO CONVOY 1 – 1
ELFTONE – 3
EUROSONIC EURO 2 – 5
FALCON FCB1281 – 1
FIDELITY 1000/3000 – 3
FIDELITY 2000/2001 – 1
FORMAC 88/120 – 1
GE 3-5804/3-5805 – 12
GECOL GT858B – 3
GRANDSTAND BLUEBIRD – 9
GRANDSTAND GEMINI – 10
GRANDSTAND HAWK – 1
GRANDSTAND HOMEBASE/WAGNER – 2
HAM CONCORD 2 AND 3 – 1
HAM EXPLORER – 1
HAM INT. UK/JUMBO/MULTIMODE/VIKING – 1
HARRIER CB/CBX/CBHQ – 1
HARVARD 400M – 5
HARVARD 402MPA – 1
HARVARD 420M – 1
HARVARD GOOD BUDDY – 4
HY-GAIN 5 – 1
ICOM ICB-1050 – 1
JWR MK2 – 1
JAWS MK2 – 8
KRACO KCB4030 – 1
KRACO KCB4004 – 2
LCL 2740 – 11
LAKE MANXMAN – 3
LEGIONAIRE – 4
MAXCOM 4E/20E/21E – 8
MAXCOM 30E – 1
MIDLAND 2/3/4/5/6/7001 – 1
MIDLAND 805 (PORT A PAC) – 14
MIDLAND 099 – 8
MURPHY CBH1500 HOMEBASE – 6
MUSTANG 1000/3000 – 1
NATO 2000/NATO 40FM – 1
NEW FORMAC 88 – 8
PEGASUS 7 – 1
PLANET 2000 – 1
PRESIDENT ADAMS/ANDREW J/AR144/AX144/DWIGHT D – 2
RADIOMOBILE CB201/202/205 – 1
REALISTIC TRC2000/2001/2005 – 12
ROTEL RVC 220/230/240 – 1
SAPPHIRE X2000 – 3
SAPPHIRE X4000 – 8
SCOOPER MKY440/550E – 2
SERPENT UK4000 – 1
SHOGUN (OLD) – 7
STALKER (ALL) – 2
SUN 401 – 1
SUPERSTAR 120/360/3900 – 2
SUPERSTAR 2000 – 1
TOKAI – 3
TRISTAR 727/747/777/797 – 1
UNIDEN UNIACE (ALL) – 2
YORK 861/863/869 – 1

Article by m0ysu originally available at m0ysu.com/micwiring.html

Compact 20m Yagi

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Article by M0DGQ

This yagi antenna is particularly suitable for those with small plots ( myself included ) who wish to use a 2 element 20m yagi. The design is by AB4GX, the original article is listed below ( PDF ). Here different materials have been used for construction as these are easy to obtain here in the UK other than this the design is essentially the same. The original design uses aluminium tube for the elements, common 2.5mm pvc covered wire is used here, this will reduce the useable bandwidth slightly but approximately 150kHz of the band is still useable – you will have to decide which part of the band the antenna is to be adjusted for. CW is my main mode on HF, so the antenna was adjusted for this section of the band. Here, both solid 6mm wire and 6mm mains earth wire were tried for the elements, however 2.5mm pvc covered wire ( stripped from standard domestic 2.5mm twin and earth cable ) is used in the final build as it is easier to use and cheaper. Four 4m telescopic fishing poles are used for the element wire supports, the final thiner section of the pole is disgarded. The wire elements are soldered directly to the loading coils and sealed with self – amalgamating rubber tape. The diameter of the fishing pole is approximately 23mm at the loading coil.

The element support mounting brackets are made from angle aluminium and are secured to the main boom by U bolts, the pictures give a clear view how this done. The boom is made from aluminium tubing, mine is approximately 50mm diameter and a wall thickness of 2mm – 3mm. The coax feeder is soldered directly to the driven element and insulated with self amalgamating tape, a four turn loop in the coax acts as a choke balun. As per the original article, the antenna should be adjusted at the height it is to be used at, this is tedious but worth the effort. In use, mine resides at a height of approximately 13 metres and gives a 1:1 SWR at 14 Mhz to 14.1Mhz rising to roughly 2:1 at 14.2 Mhz so you will have to decide which part of the band you want to adjust it for.

The antenna has been in use for several months now and the results have been very good, JA VK VE stations have been worked with ease. One observation ; because the antenna has quite a high Q, when wet due to rain the antenna resonance and SWR does alter somewhat but is still useable. It will be interesting to see what happens when frozen.

Article by M0DGQ originally available at http://m0dgq.co.uk (now offline)

Sudden TVI Problems – Solved

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Recently my apartment building decided to change the TV antenna system because of the latest upgrade of TV broadcasting to the DVB-T2 (Digital Video Broadcasting – Second Generation Terrestrial) standard.

My 10-year-old samsung LCD TV stopped receiving signals during last summer. Surprisingly, my TV was known to support the new digital broadcast signal, and also the shutdown of the old systems was already in place.

I therefore agreed to the antenna change, proposed by some condominiums.

The antenna installer, commissioned by the building manager, instead of changing the antenna, as I would have expected, decided to change only the antenna preamplifier, leaving me the old amplifier as a souvenir, and the box for the new amplifier.

Magically, my old TV went back to tuning all DVB-T2 channels correctly.

So far only the good news.

I then wanted to test my radio to make sure of the job done, since with the precendete amplifier, I could only jam the TV signal in certain frequencies, and exceeding the 200 W PEP.

Instead, to my immense amazement, I found that with only 5W of power on any HF band I could completely cancel the TV signal.

Terrified by this, and in disbelief as to what was going on, I began to document myself on the net and ask colleagues and in the fari forums.
Following everyone’s advice, I first informed the administrator, requesting a review of the amplifier, and then wrote directly to the Belgian manufacturer, of the TV amplifier reporting the anomaly.

The amplifier in question, about which I do not want to give bad publicity, is one of those self-programmable ones, very small, and evidently unshielded. The manufacturer immediately replied to me asking about the power output of my transmissions and frequencies, and saying that he would inform the technical department.

In the meantime I asked the administrator, for a replacement with another product that was shielded, and in fact in the following days the antenna technician, replaced the product with a TERRA PA420T and the problems magically disappeared.
Of course, this cost me the antenna specialist’s intervention to replace the TV amplifier.

A few days ago, I was contacted again by the Belgian manufacturer, even proposing to do a test with the modified version of their amplifier, to see if they had solved the problems. Of course, I declined.

WSJT-X not decoding – Solved

Posted in Ham Radio Software, How to 1 Comment

I want to share a puzzling experience I’ve had today with WSJT-X but also JTDX on my Mac.

Both programs, suddenly stopped decoding signals, they were unable to decode any FT8 or FT4 signal even if they were correctly represented on the graphic screen.

I did apparently nothing to cause this, and any effort to change the audio setting did not solved.

I tried changing the settings of my TS-590S, connecting and disconnecting the USB cable. No google search returned a valid solution or any usefull suggestion, just some similar issues were referring to corrupted driver software on Windows, or some issues on FlexRadioi devices. Absolutely nothing on Mac.

Cause:

It was clear was an issue software, not an hardware one, signals in some way were getting into the mac but probably in a way not readable by WSJT-X.

By setting the built-in microphone as a device in WSJT-X and letting the Mac decode the signals, it turned out that the decoding function worked! It was therefore definitely a USB problem.

I started to remember every possible change I had made in the hours before setting up the software and ended up remembering that I was playing with the RumLog Audio Router function the day before.

Well, this probably changed the way the sound cominf from my transceiver was sampled, making the decoding function unable to work correctly.

I did checked the settings of audio input on my iMac and tried to set to the default values.

At the end, i had also to reconfigure WSJT-X, by resetting audio settings by selecting a different audio source, and saving configuration and that restoring the USB audio Codec device and saving again.

This solved my issue.

70cm Quadruple Quad

Posted in HamRadio, UHF Antenna 1 Comment

Quadruple Quad

by Richard Price BSc. MSc. GW0VMW

A suitable high gain 70cms antenna for SOTA operation was sought that did not have the drawbacks of a long Yagi antenna, principally a narrow beamwidth and bandwidth. This is important as operating from a hilltop on a relatively under used band requires as broad a catchment area as possible combined with high gain and a minimum of turning.

This may be part of the reason behind the low level of use by SOTA operators. Despite this problem however, 70cms offers excellent prospects for summit to summit and longer tropospheric contacts.

This compact portable antenna for 70cms was developed from an original design published in VHF Communications May 1971 for operation on 2m. The Quadruple quad (Plate 1.) is basically four, closely coupled stacked quad loops, with another four (larger) loops mounted 1/4 wavelength behind as a reflector. The antenna has a quoted gain of 11-12db over a dipole and a front to back ratio of 23db with a very broad (100° approx) frontal lobe (Fig 2.)

Other very important criteria are the low weight (8oz), compactness (Plate 2.), speed of assembly (30 seconds) and a good match into 50 Ohm coaxial cable. After much experimenting the latter was achieved with a simple delta match feed system with a 4:1 coaxial balun. This produced an SWR of +/- 1.5 and is quite different to the original article, which used 60W coaxial cable!

Once constructed the whole antenna comprises of just 3 pieces to assemble, a 2-piece split boom providing rigidity for the folding antenna. Antenna can be mounted for horizontal or vertical polarisation.

Plate 1.

Quadruple Quad

Materials required.

2m x Brass tubing 4mm dia
6m x RG58 coaxial cable
0.75m x 20mm dia plastic conduit
1 x 20mm dia plastic conduit joint 57cm x 8mm dia fibreglass rod/tube 20cm x 14/16swg solid copper wire 24cm x RG174 coaxial cable
Choc block connectors
Plastic block
20 x 3mm brass screws

The main drawback with quad antennas has always been their complexity (3 dimensional) and difficulty in assembly/disassembly for portable operation compared to the Yagi. This design and my development of it have circumvented these problems.

The same design could easily be adapted for use on a regular quad antenna for portable use on virtually any VHF/UHF frequency. The secret to the compact folding nature of the antenna is the combined use of rigid copper elements inter-spaced with flexible copper braiding. The copper braiding is simply the screen from RG58 coaxial cable stretched and flattened by hand.

Copper and brass are used, as electrolytic corrosion between the metals is negligible and brass makes good strong solder joints. Plate 2. Dismantled and folded Quadruple quad antenna.

Critical dimensions

Spacing between Reflector and Driven element 1/4 wavelength (17.5cm) Driven element (length of brass tube) 17.5cm x 5
Reflector element (length of brass tube) 19.3cm x 5
Spacing between brass rods 1/4 wavelength 17.4cm

Length of braiding required 70cm x 4
4:1 Balun- 1/2 wavelength RG174 = 35cm x 0.66 velocity factor = 23.1 cm

Construction of the antenna is quite straightforward. First cut the brass rods to length. Next cut 3 pieces of fibreglass rod/tube about 19cm long and drill a 4mm hole each end spaced 17.5cm apart for the brass director and reflector rods to make 3 H shaped structures. Next cut 4 lengths of RG58 coax 70cms long and strip off the outer jacket and remove the tinned copper braiding.

Stretch the braiding and pull between thumb and forefinger to make a flexible flat strap. Push a brass screw through one end of the braiding and solder to the end of the brass rod from one of the H sections.

Measure 17.5 cm along the braiding and attach the next brass rod and then the next H section and so on. Remember the only difference between the reflector and driven element is the length of the brass rods. Note :- The brass rods are allowed to rotate in the fibreglass and can be prevented from moving from side to side with a blob of solder on each side of the rod.

The feed-point was made, by cutting the centre of the middle driven element brass rod. An insulated plastic block was inserted and a delta match feed with 4:1 balun soldered to the element (Fig 2).

Quadruple Quad

Fig 2. Delta match and 4:1 coaxial balun feed (modified from Orr & Cowan 1990).

I used chocolate block connectors for the 4:1 balun and 2.5m of RG58 coaxial cable for the feeder reduce losses. The plastic boom is all that is required to make the whole structure rigid and was made from 2 pieces of 20mm plastic conduit with a joint near the middle. Make the joint first and then make a notch in one end for the fibreglass tube to clip in.

Cut to the required length so that when you make another notch in the other end you have to flex the fibreglass over. Another notch will need to be made halfway along to clip the middle tube in. Attachment to a walking pole/mast can be made using whatever method you prefer.

Fig 2. Horizontal radiation pattern of quadruple quad compared to a dipole (VHF Communications May 1971).

On air tests revealed that the antenna is very much directional and outperformed all my other 70cms antennas except my 17 element Yagi.

The light weight and compactness means I have no worries about carrying it around in my rucksack and it can very quickly be deployed for action.

Website originally available at mw0idx.co.uk:80/quadruplequad.html
Author: GW0VMW

1:4 Current Balun

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Article by N5ESE

Here’s yet another handy little Altoids QRP project. This makes a great travel companion to the 1:1 current balun and is intended to aid in tuning a balanced antenna or feedline that has a high impedance (100-600 ohms). I’ve even used it successfully to tune a 20 meter, 1/2-wave vertical with 4 radials, placing it directly at the bottom feedpoint of the vertical, feeding it with 50-ohm line (RG-58), and letting my Elecraft K1’s automatic antenna tuner do the rest.

The classic 1:4 current balun’s circuit looks like so:

This version, shown below, is wound with 10 turns of RG-174 mini-coax on each of two FT114-43 ferrite cores.

Measurements using my MFJ Antenna Analyzer showed that the SWR rose gradually from 1.1:1 at 21 MHz to 1.25:1 at 30 MHz (into a 200-ohm dummy load).

Construction-wise, an isolated BNC is used at the input (Amphenol 31-010), though a garden variety BNC connector (non-isolated) mounted directly to the Altoids box could as easily been used. I grabbed a piece of 3/32″ thick PC board that I had laying around as scrap, peeled off most of the copper, but left some copper traces to ease wiring. The PCB would also serve as the “mounting plate”, mounting the completed toroids with hot glue. To preserve balance, attention is given to keeping all lead lengths symmetrical; that is, all the leads on toroid 1 are identical to toroid 2, and the length of the wire from any junction to the input and the output connectors, is identical for both toroids. Standard banana plug binding posts were used for connecting the feedline to the balun’s output. It is assumed that the transceiver or antenna tuner will be earth-grounded, to provide a path for bleeding static charges on the antenna.

In operation, a female-to-female BNC adapter is mounted on the BNC jack of the balun, and the balun is then mounted directly onto the BNC jack on the rear of the transceiver or antenna tuner. Alternatively, mount the balun at the feedpoint (assuming the feedpoint is 100-400 ohms), and feed using a half-wavelength of coax. While throughput losses were not measured, it can be assumed that the balun will be lossy for impedances much above or below the intended matching range (100-600 ohms), or outside the intended frequency range (1-30 MHz). Also, I believe the balun is readily usable at 10 watts applied power, but that it may be good to somewhat higher levels. Use at higher levels has not been analyzed nor tested.

I used this balun between my K1 and 1/2-wave vertical to help match the antenna. Without it, the K1’s automatic antenna tuner could not find a match below 5:1. With the 1:4 step-up balun, the K1 managed a 1:1 match, and 30 QRP contacts were made in dreadful band conditions during the 2002 Flight-of-the-Bumblebees contest, with contacts up and down both coasts. Needless to say, this balun is a keeper.