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This results in much reduced coupling to nearby conductors, so that losses and interference problems are reduced to the absolute minimum possible. The CobWebb can be easily mounted on a single 20 foot aluminium scaffold pole, fixed to the wall of the house with a couple of stand off wall brackets. The pole can then be pushed upwards to put the CobWebb up at 30 to 35 feet, or lowered so that it is at roof ridge height, to overcome any possible planning problems! All the other small multi-band commercial antennas that are available are less than optimum. The “broad band” folded dipoles and verticals have lossy transformers or terminating networks in them. These may provide a fairly low SWR over the full 2 to 30 MHz band, but so does a dummy load! Some trap dipoles have lossy traps and baluns, so that a nice 50 ohm match is produced on all bands. Others have no balun at all, the feeder cable will then need to be a particular length to reduce feeder radiation and provide a match. Doublet Antennas may have some gain on the higher frequencies, unfortunately every 3 dB peak has a 20 dB null in other directions! Other small “magic maths” antennas are available, but their performance is so poor that you can’t even hear them on the bands, to measure how far down they are! The many types of vertical antennas are best avoided, unless you have no neighbours, because of all the interference problems. The inherent losses and poor radiation efficiency of the mini-beams negates any so-called gain. Remember that if a beam has a gain of 4 dB over a dipole in free space, it will be DOWN on a dipole! It will also only “work” over a very narrow frequency range. A dipole or a CobWebb has a gain of about 5dB over a dipole in free space, (due to ground reflection) or 7dB over an isotropic radiator (7dBi) and will work equally well over the entire band. The CobWebb has no lossy components in it, so there are no power limit problems for the QRO operators. The low loss and consequent high radiation efficiency also makes it ideal for QRP! The G3TPW CobWebb Specification Covers all 5 Bands.  Gives a low SWR resonance on the 14, 18, 21, 24 and 28 MHz bands. The SWR at the band edges is mainly reactive, i.e. the resistive component is still near 50 ohms, so auto and simple ATUs can match it with low loss. Over 95% radiation efficiency on all bands! Have you ever seen this spec mentioned by other manufacturers? Omni-directional.  Talk to all the world, without the need for a rotation system. Absolute Minimum of EMC Problems.  Vastly reduced interference on both transmit and receive due to pure horizontal polarisation and confined electric field. 50 ohm Single Co-ax Feed.  Built in co-axial choke balun to prevent feeder radiation. Standard PL259 plug on end of short lead. Feedbox and resonators all pre-assembled. No Compromise Performance.  Full size half wave dipole on each band, without nulls! Fibre Glass Construction.  Flexible so no metal fatigue problems in windy locations. Simple Assembly.  Fix fibre glass sections together. All screw holes pre-drilled. All elements pre-tuned, just uncoil them and fix to spreaders. No adjustments needed. Small Size and Weight.  Only 2.6 metre (8.5 feet) sides and 6 kg (14 lbs) weight when assembled. 1 metre maximum length parts for low cost world wide delivery. Easily Erected.  “V” bolt fixing to mast of up to 58 mm (2.25 inch) diameter. Can be fixed to 20 foot scaffold pole, which can then be pulled up to the wall bracket with rope. 160 Km/hour (100 mph) Wind Survival.  As long as the mast/support can take it! The G3TPW CobWebb Design The most important design point about the CobWebb is that it is a completely horizontally polarised, confined electric field antenna, which provides maximum radiation efficiency and the absolute minimum of interference problems. TVI fears have encouraged many people to shy away from the HF bands, in favour of VHF, UHF or 160 metres. New stations often begin operating on HF using an end fed wire or a vertical antenna, a recipe for disaster, sometimes even on QRP. After starting in this way and getting involved with various EMC problems, it is often found that planning permission for a horizontal antenna is refused. You can’t really blame your neighbour for being concerned. If that small inconspicuous vertical or simple wire antenna causes so much trouble, what would it be like with the proposed mast and special horizontal antenna? The fact that the use of horizontal polarisation, particularly if it is from a confined electric field antenna like the CobWebb, would probably cure the breakthrough problems is very difficult to explain. During experimental work on a 5 band beam, using full size resonators on each band, it was noticed how well the driven element worked by itself. It also became obvious that a full sized dipole, up in the clear, worked far better than the multi-band minibeams! The CobWebb is a full size half wave dipole on each of the 5 amateur bands, 14, 18, 21, 24 and 28 MHz, for maximum performance. There are no lossy traps, stubs or loading coils, so there is no reduction of radiation efficiency on any band. Each dipole is bent round to form a horizontal square, to make the antenna omni-directional. Thus no expensive rotator is required. Each resonator looks like the “square halo” that is often used on VHF, for SSB mobile work using horizontal polarisation. The parallel but anti-phase “sides” of the antenna cancel the radiation that would normally be wasted as high angle radiation from a straight dipole and fill in what would otherwise be the nulls off the straight dipole ends. The resulting omni-directional pattern has many advantages over antennas with directional effects. Unless an antenna with nulls in it’s response can be rotated, it will be found that certain parts of the world will be very difficult to contact. The five “squares” are made from white PVC covered multi stranded copper twin cable which is supported by a horizontal cross, made from white fibre glass. Each element is folded and tapped for impedance matching, so that the antenna looks like 50 ohms on all 5 bands. The small size ensures minimum windage and the low weight means that TV type brackets and masts may be used for supports. There are no aluminium elements to corrode and cause high resistance joints, or snap off in the wind. The antenna is fitted with a co-axial choke balun at the common feed point, to prevent any current from flowing down the outside of the co-axial cable feeder. This balun is absolutely vital, to prevent any radiation or pick up of signals by the feeder. EMC problems can be just as bad as with verticals if this balun is not exactly right. The electric fields of the CobWebb are confined because the high impedance ends of each element are only a few inches apart. This reduces the coupling to nearby objects so the antenna does not need re-tuning for operation at different heights and locations. Other Multi-band Antennas for the HF bands The Horizontal End Fed WireThis is the simplest and cheapest antenna of all. It will require a very good ATU to tune it up though! Very high voltages may be present at the feedpoint, dependant on the exact length and frequency in use. You will probably need to use a so called kilowatt ATU, when using 100 watts, to avoid arcs on the ATU tuning capacitors. Severe interference problems are common. The antenna is obviously unbalanced with respect to earth, so vertically polarised radiation will occur. This radiation will be either off the vertical feed wire connecting to the end of the horizontal span, or from the earth lead if the wire comes straight into an upstairs “shack”. RF in the shack problems often occur, RF feedback, RF burns to the operator if any metal is touched, and general EMC problems normally restrict these antennas to QRP operations. There is an obvious radiation hazard when using this type of antenna. The local field strengths produced can be way above the maximum permitted safety levels. DoubletAny long wire can be fed at it’s centre with a tuned open wire feeder. This should maintain balance to prevent vertically polarised radiation off the feeder and subsequent interference problems. Whenever a twin feeder system is used though, the antenna itself must always be exactly electrically balanced and symmetrical, any slight lack of symmetry will cause feeder radiation, with the dreaded vertical polarisation. It will require a high quality proper balanced ATU i.e. not an unbalanced one with a toroidal balun transformer added on the output! (The balun will only work efficiently over a limited range of impedances) As with any long wire antenna, the polar diagram will contain many deep nulls, in which directions communications will be difficult. This more than negates the few dBs of gain that doublets have on the higher frequency bands. Note Large spaced open wire feeder should not be used in the shack, or anywhere where people or animals may be able to come into close proximity with it. The fields will not cancel in line with the feeder (they only cancel broadside to the feeder), unless the distance is many times the wire spacing. Unless the small spacing twin is used, the RF radiation problems in the shack can be almost as bad as those with end fed wires. G5RVThis antenna is very cheap to make, but because it is only resonant on one band, it requires a very good ATU to tune it up on all the other bands. It is really too long to give consistent results in all directions on the higher bands, the polar diagram becomes very “petal” shaped with many deep nulls. It is far better to convert it into a doublet antenna and use open wire feeder all the way to a proper balanced ATU, rather than to use co-ax cable for part of the feeder. The SWR on this antenna is very high on all the bands (except 14 MHz, where it is only about 2:1 at resonance), so the use of co-ax can cause very high losses. The ribbon feeder normally supplied with commercial G5RVs is very poor mechanically, if it swings in the wind it breaks quite quickly. Vee Beams and RhombicsGreat, if you have got the necessary real estate! Radial terminated Vee beams and/or Rhombics, with switching to beam to any part of the globe. Shack in the middle of the 10 acre site, which is a Polynesian island, with only local girls for company! Ahh, this is paradise, but would you bother going on the air? Dream on!!  Log PeriodicsToo big and low gain for the size. Note the CobWebb has a “gain” of 7 dBi.  Trap DipoleTrap dipoles use tuned circuits to isolate sections of a dipole, such that electrically it looks like a half wave dipole (with a low impedance feedpoint) on each band. Four pairs of traps would be required for a 5 band dipole. If the inverted “V” configuration is used, then the feed impedance should be about 50 ohms. However the traps act as loading coils on the lower frequency bands, so the antenna becomes shorter than normal. This should reduce the radiation resistance of the antenna on the lower bands. The radiation from an antenna is determined by the product of current and length. If the length is reduced then, for the radiated power to remain the same, the current must be increased. The increased current for the same power must mean that the voltage will reduce. The shorter length should therefore cause the feed impedance to be much reduced. This should cause the SWR to increase, if it does not the traps must be lossy! Trap VerticalThis is in effect half of a trap dipole, fed against ground. They can give a good match, but being on the ground the signals will be attenuated by surrounding objects, particularly on the higher frequencies. If your ground has poor conductivity results will be very poor. Verticals can be elevated, using either radials or extra traps. They can then work very well, as long as you don’t have any neighbours. In an urban environment the EMC problems can be chronic. All vertical antennas suffer from another problem. They require good conductivity soil for many wavelengths around them to compete with horizontals. Even verticals that do not use a ground connection i.e. vertical dipoles or ground planes etc. can still be as much as 8 dB down on a horizontal dipole antenna, due to reflection losses. The difference between sea water and very poor ground is up to 9 dB for a vertical antenna, but only 1 dB for a horizontal. The Magnetic LoopThis is really just a short dipole that is bent and end loaded with a variable capacitor. There is no magic involved in the way it works, a standard “electromagnetic wave” is produced from them, as per any other antenna. It is not producing magnetic waves with special immunity to “Electric Field Interference”. It does have a confined electric field so that near field “capacitive” coupling to surrounding conductors will be reduced. There will be some reduction in performance on the lower bands, a well designed 5 metre circumference loop will normally work over the 14 to 28 MHz bands with a 50% efficiency on 14 MHz. To keep the efficiency this high, the loop will have to be made out of large diameter copper or aluminium, NOT co-ax!! The resultant high “Q” will mean that the loop will have to be continuously re-tuned, as the receiver is tuned round the band. The remote control system that is needed to do this can be quite expensive, also the tuning capacitor will have to stand many thousands of volts, even when only running 100 watts. For high power operation a vacuum variable capacitor is normally used, which is very expensive. A loop standing on the ground in the vertical plane will radiate a vertically polarised signal. The ground will absorb/reflect the horizontal component straight upwards. The vertical component at low angles to the horizon i.e. that required for DX operation, will have a sharp null in the response broadside to the plane of the loop. This can be useful for reducing interference, but it does mean that the loop will need a rotation system. To prevent low angle signals from being absorbed by surrounding objects i.e. shrubs, fences, trees, houses and the myriad of conductors around the QTH, it is obviously far better if the loop antenna is mounted up in the air. If it is mounted about 30 feet high then the horizontal radiation will be able to be used for low angle DX operation. The loop can then also be mounted in the horizontal plane to eliminate the vertically polarised radiation, and so reduce EMC problems. The small diameter loops made from co-ax or flat bar give very poor performance. They don’t need retuning as often as you tune round the band, because they are low “Q”, the problem is that most of your transmitter power will be dissipated as heat! The main advantage of the loop antenna is it’s continuous frequency coverage over the entire spectrum, by remote controlled re-tuning. This is ideal for military users etc. but against this is the cost, especially if you only wish to transmit on the amateur bands. Mini-beamsThese antennas are a very big compromise. They generally only cover the 14, 21 and 28 MHz bands, because of interaction effects with 18 and 24 MHz. A reflector resonance for 28 MHz will act like a director resonance for 24 MHz, a reflector resonance for 24 MHz will look like a director resonance on 21 MHz etc. etc. The result is a very expensive trap dipole! The gain that they are supposed to have is only over a very narrow bandwidth. They are very difficult to set up, most people just give up and feed them with an ATU. They need to be rotated, not because of a good front to back ratio, but because of the nulls off the ends of the dipoles! They are often rated for high power use, presumably what this means is they don’t actually catch fire when used with QRO, because they certainly get very hot! Broad Band VerticalsThese antennas use most of the applied power to produce a low SWR reading. The  fraction of power that is radiated can still produce some DX QSOs on the higher frequency bands though, it’s amazing what you can do with QRP on HF! If the guy with a 100% efficient antenna is getting a 59 plus 20 dB report, then the guy with the 1% efficiency will still get S9!! On the lower frequency bands these antennas are very good dummy loads! It always amazes me that if a 100 watt rig was only putting out 10 watts, most amateurs would be very upset, yet they will use a 10% efficient antenna and be quite happy. The reason is, of coarse, they can’t measure the radiation efficiency but they can measure the power/SWR.  Many radio amateurs seem to think that a low SWR means that all the power is being radiated, so you cannot really call the producers of these antennas “Con Artists”, they are merely producing what the radio amateurs say they want! They are even quite good for lack of TVI and general EMC problems, as they radiate such a small amount of the applied power!!! Caveat Emptor! Broad Band Terminated DipolesThese antennas also use most of the available power to produce a low SWR reading on the lower frequency bands. On the higher bands they only use about half of the power for this purpose, so about half of the power is actually radiated! Unfortunately, on these higher frequencies, the antenna will have lots of lobes and deep nulls as per a standard doublet antenna. The military have used this type of antenna in the past, because of its ease of matching over a wide continuous frequency band, but it really is just a waste of power to use it on the amateur bands. Crossed Field AntennasThese antennas don’t work! A little knowledge is a dangerous thing! The co-ax feeds radiate a little power, because they don’t have proper baluns on them! The metal bits radiate a little power because they are metal and have a small amount of RF current flowing through them! One guy on the internet has even offered a $10,000 dollar reward to anybody who can demonstrate one working! The so called “antenna design experts” who invented and patented the CFA have not claimed their reward!!!  A short length of wire and a parallel tuned circuit ATU will work much better! It’s a classic case of somebody inventing a theory and then trying to make the facts fit the theory!!  Parallel Connected DipolesThese antennas work very well. The dipoles need to be spread out so that the high impedance ends of the shorter ones are not affected by the longer elements. They can be arranged “maypole” style round a central support, so that they can act as guy wires as well as antenna elements. When arranged in this way the feed impedance will be about 50 ohms so they can be fed with 50 ohm co-ax, via a choke balun. This system works very well when out portable, the only problem is the vertically polarised radiation off the ends. This radiation fills in the nulls off the ends of each dipole, so that no rotation is needed but it can cause the dreaded interference problems. These antennas really need to be horizontally polarised for minimum EMC problems, but they then need a 75 ohm feed. They can be double gamma “T” matched to 50 ohm co-ax, as long as an effective choke balun is used. This is in fact what the G3TPW CobWebb antenna is! The dipoles are each bent into squares, so that they can be supported by a single horizontal fibre glass cross, rather than having separate supports for all ten dipole ends. Bending the dipoles into squares also eliminates the dipole end nulls, resulting in an omni-directional radiation pattern. Another major effect is that the electric field of the square dipole will not couple into the ground, or any other nearby conductors so losses are much reduced. Verticals and EMC (Electro-magnetic Compatibility) Whilst we have all heard that vertical antennas cause interference problems, I suspect that most people don’t fully appreciate why. I certainly didn’t, until I investigated the TVI problems that I had with my original 5 band vertical design. In fact I always used to say that verticals cause TVI because they put out such good signals at the low angles that we need for DX communication! It was only when I discovered that my vertical was causing lots of EMC problems with my neighbours, whilst my horizontal half wave dipole antenna at 30 feet was not causing any problems at all, yet giving a better signal in Australia, that I realised that it was the vertical polarisation that was to blame. It is obvious that vertical antennas will couple more power into nearby vertical conductors than horizontal antennas will. This causes much loss of radiated signal and also causes many EMC problems. If more RF energy is being coupled into a vertical TV feeder co-ax cable, then TVI is going to be more lightly. Interference will also be picked up from the TV, producing an increased background noise in your receiver. However I was not convinced that this was the whole story. My neighbours portable radio was also clobbered by the vertical but completely clear when I used my horizontal! The portable radio could be oriented in any plane, with no effect on the amount of interference received. Tests with a calibrated field strength meter showed that the field strength levels near the ground were very low from the horizontal antenna, and very high from the vertical antenna! The field strength meter needed to be up at a height of  about 20 feet before the field strength readings from the horizontal antenna were similar to those from the vertical. Reports from Australia showed the horizontal to be 3 dB stronger though!! The susceptible portable radio was substituted for the field strength meter. It became obvious that the ground was effectively “shorting out” horizontally polarised signals. It was found that at low heights the power fed into the horizontal antenna needed to be about 100 times (i.e. 20 dB) greater than that fed into the vertical antenna, for the same interference levels at a given distance. It was realised that if any electronic device with an EMC problem is mounted close to the ground (in terms of wavelength) then it will not receive horizontal polarised signals very effectively. Up to a height of about a quarter of a wavelength the ground will act as a reflector, so that horizontally polarised signals will only be received from higher angles. Below a height of about an eighth of a wavelength the ground will also provide a lossy dielectric path for the horizontal electric fields, and thus tend to short them out and/or dissipate them. Thus the ground will protect electronic devices from horizontally polarised electromagnetic fields. Vertically polarised fields will however be received very well, even if the susceptible equipment is actually sat on the ground. I decided to concentrate all my efforts on the design of horizontal antennas, to avoid all the hassle of  TVI, HI-FI and telephone breakthrough etc. I thought that it would be very anti-social of me to market a vertical antenna that would subject lots of radio amateurs, and their innocent neighbours, to EMC problems that could be avoided by the use of the correct polarisation.  Thus the CobWebb concept was born!! G3TPW  COBWEBB  F. A. Q. s (Frequently asked Questions) What is a CobWebb antenna and what is it’s gain? It is a very efficient horizontally polarised omni-directional antenna for the 14, 18, 21, 24 and 28 MHz bands, with a gain of 7 dB over an isotropic radiator (7dBi). Note that this is the same as a standard dipole, although a straight dipole will have sharp nulls off each end. A standard straight dipole has a gain of 5 dB over a dipole in free space! I notice that the specification of my standard large 3 element tribander says that it has a gain of 8.5 dB over a dipole in free space. This means that it has a gain of 3.5 dB over a dipole at the same height! How does it work? Technically the CobWebb is 5 separate full size dipole antennas, each bent into a square. This makes it very small (only about 8 foot square) but it is still full size! It has 5 separate double gamma tee matches to match each element to a common 50 ohm co-axial feeder, and has a built in air cored co-axial choke balun, to prevent feeder radiation. What is the secret ingredient. Why does the CobWebb work so much better than other antennas? Simply because it radiates all the power fed into it, and it also radiates in an omni-directional manner so there are no nulls. There are no lossy ferrites,  traps or loading coils to heat up, and each element is full size and made from 84 strands of 0.2 mm diameter pure copper wire with a plastic covering. The confined electric near field (caused by the high impedance ends of each dipole being close to each other) also ensures that the antenna does not couple to other electrical conductors i.e. telephone wires, power cables, television antennas or even the ground and lossy di-electrics such as trees and buildings. Thus the radiated power is not absorbed by nearby objects, it is all radiated into free space. Breakthrough and noise pick up are also reduced to an absolute minimum and the ground conductivity and height do not affect the antenna tuning. What is the maximum power that can be fed into it? Nearly all the power fed into the CobWebb will be radiated, so the antenna will not heat up and so limit the power rating. There are no ferrites used so no intermods are produced. It has been tested with 3 kilowatts of RF, above this level there could be a problem with corona discharge sparking at the ends of the elements as the air is ionised! How is it constructed? A single horizontal fibre glass cross supports all 5 elements. The feed-box is on the end of another solid fibre glass rod, such that the feed is in the centre of  one of the sides of the squares. Each rod is secured with “U” bolts onto a 0.25 inch thick aluminium plate. Another similar plate allows the antenna to be fixed to a vertical mast of up to 2.25 inches in diameter, with the “V” bolts provided. Plastic covered “figure of 8” section 84 strand copper conductor is used for the elements, which are secured to the fibre cross by the unique G3TPW system to prevent pre-mature  breakages! I’ve not seen any of your adverts for ages. Why don’t you advertise the CobWebb more? The last time we advertised in a magazine was in 1993! The CobWebb was last reviewed in a magazine in 1996 though. It is interesting to note that the magazines always asked us if they could review the CobWebb, we never had to ask them!! Of course the reviews in the magazines were very good adverts, but they only last for a month or two. We find that the 750+ antennas that we have sold are the best long lasting advertisements, literally being broadcast to the world every time somebody says, “And the antenna here is a CobWebb”. So are your antennas sold purely by word of mouth? Most of our sales do come from people who have received personal recommendations from existing users. However, the interest is mainly generated when people hear  stations using CobWebbs doing so well on the bands. The recommendations are normally received when the enquirer is trying to find out our address/telephone number!! This is, of course, a scale model made specially for your lectures. How big is the full size antenna? No, we only have full size CobWebbs! We don’t need a scale model of the CobWebb because it is so small. I must admit that even I am still amazed when I look at a CobWebb and realise that though it is so small IT IS STILL FULL SIZE!! A 33 foot dipole is a much bigger beast than a square with 8 foot 6 inch sides! Can two CobWebbs be used as a beam? Yes, but only by phasing them, i.e. they both have to have separate feeders. Parasitic elements will not work because the CobWebb does not couple to other nearby conductors! The maximum gain obtainable is less than 3 dB over a single CobWebb  and of course a beam rotator is needed. The phasing adjustments needed to provide optimum directivity across all the bands are quite complex and the phasing unit becomes expensive and difficult to operate. If you increase the antenna height by 50%, then the DX signals will increase by more than they would by phasing 2 antennas! I’ve heard that different antennas suite different locations. Will the CobWebb work at my QTH? YES! The ground conductivity for many wavelengths around an antenna will affect its performance. Vertical antennas that use a ground connection can be as much as 20 dB down on a dipole. Verticals that do not use a ground connection i.e. elevated feed vertical dipoles or ground planes etc. can still be as much as 8 dB down on a horizontal, due to reflection losses. The difference between sea water and very poor ground is up to 9 dB for a vertical antenna, but only 1 dB for a horizontal.The CobWebb is not affected as much as other antennas by trees, buildings, power lines, TV aerials feeders and telephone wires etc. The poorer or more cluttered that your QTH is, the better the CobWebb will perform, compared with other normal ants, including a straight dipole! These are the reasons why CobWebb antennas so often out perform other antennas, they are not affected by the nearby environment so THEY WORK AT ALL LOCATIONS. How do I mount it? The CobWebb can be mounted on a vertical pole of up to 2.25 inches in diameter. It can be added to existing antenna installations such that the mast goes straight through the CobWebb. A 20 foot scaffold pole makes an ideal mast, this can be fixed to a wall with a couple of stand off brackets. Do I need planning permission for it? Most people don’t bother to apply, if they are just mounting a CobWebb on a 20 foot pole. The pole can be slid down through the brackets so that the CobWebb is below the roof ridge height. This meets the standard “not above the roof ridge” planning restriction; it can then be gradually pushed up to the optimum height of 33 feet! Will it stand the high winds at my QTH? CobWebbs are in regular use in the Falklands and on Ascension Island. They have stood up to gales that have destroyed many other antennas. Most of the breakages that have occurred have happened when either the mast has come down, or the antenna has been dropped. Even then the antenna can be quickly and cheaply fixed because the short 1 inch diameter fibre glass joining tubes break, and the antenna simply folds up. These joining pieces can be easily changed in a just a few minutes. If the wires do get broken they can be repaired with choc block screw connectors or crimp connectors, or we can supply new wires. How does the CobWebb minimise the chance of TVI and breakthrough problems? The pure horizontal polarisation and use of a choke balun reduces the chance of breakthrough to the absolute minimum possible. The confined electric near field (caused by the high impedance ends of each dipole being close to each other due to being bent into squares) also ensures that the antenna does not couple to other electrical conductors i.e. telephone wires, power cables or television antennas. Are there any complicated adjustments to be made during installation? None at all! The CobWebb is not detuned by nearby objects, including the ground, because of the confined electric field. Thus the CobWebb can be pre-tuned and matched during production, so that it works at any QTH and any height! cobwebb Home build a Kenwood PG-5G cable. Posted in Homebrew Leave a comment Parts List P1 9 pin D socket with shroud.P2 8 pin mini DIN plug.Some 4 or 5 core shielded cable. Making Up Following the pictorial guide (right), solder wires between the relevant pins on each plug, not forgetting to slide the Mini DIN plug casing onto the cable before you start. The diagram is colour coded as well as having the pin numbers marked on it, for example the Red connection goes from Mini DIN pin 5 to pin 3 on the 9 pin D socket. Plug views are of the mating surfaces. If you have a 5 core plus shield cable, solder the shield to each plugs’ metal casing. If the cable you have has 4 wires and a shield use the shield for the Mini DIN pin 4 to pin 5 on the 9 pin D (Ground) After checking the soldering is good and there are no shorts or stray whiskers, assemble the shroud and cover around the plugs and you’re ready to go. Connecting to a PC without a serial port This cable should work with USB to Serial adaptors. Kenwood Microphone Home build a Kenwood PG-5A cable Posted in Homebrew Leave a comment This lead is the audio data cable for some of the Kenwood Mobile transceivers. It is also available as part of the PG-5H kit where it is supplied along with a PG-5G lead. Parts List P1 & P2 3.5mm stereo jack plugs.P2 6 pin mini DIN plug.Some “figure 8” shielded cable or similar 2 core plus shield cable (An old PS/2 mouse lead could be used with a little ingenuity). Making Up Following the pictorial guide (right), solder wires between the relevant pins on each plug, not forgetting to slide the Mini DIN plug and the 3.5mm plug casings onto the cable before you start. The diagram is colour coded and some method of telling the 3.5mm plugs apart is advised:The Red connection is the Recieved Audio Signal.The Green connection is the Transmit Audio Signal.The Black connection is common ground. After checking the soldering is good and there are no shorts or stray whiskers, replace the covers on the plugs and you’re ready to go. If the plug covers are the same colour you may want to label the leads accordingly. Kenwood Microphone The $4.00 Ham Radio Satellite Antenna Posted in UHF Antenna, VHF Antennas Leave a comment Article by Dave Tadlock Simple, inexpensive and lots of fun! Here is an easy to make home brew antenna that can get you on the air working satellites or be built for use as a portable hand held antenna to extend the range of your HT. It’s a dual band 2m/70 cm yagi antenna made with common materials and cost very little to make. Also, the antenna is fed with only one coaxial cable and does not use a duplexer. For many decades radio amateurs have built antennas with wood and wire and have had great success using their home brew creations. This antenna was built in the same tradition and I am pleased to say that I made my first satellite contact using such an antenna. To make this antenna I only needed to buy just a couple of items. Everything else I had on hand. I had to buy the wood for the boom, two 1-1/4″ long machine screws (although I bought 4 total) and a package of small wire nuts to place on the ends of the elements just for a bit of safety. Since I already had the screws, coax and connectors I spent less than $4.00 to make this antenna. I have well gotten my money’s worth out of it and have thoroughly enjoyed using it! Construction & MaterialsThe antenna is made with a 1×2 pine/spruce furring strip for use as a boom and steel coat hangers for antenna elements. I used two trim screws to hold each parasitic element in place and stainless steel #6 machine screws with matching hardware for the driven elements. Although the dimensions shown in the diagram are for use with steel coat hangers, you can experiment with other materials such as welding rods, stainless steel rods, etc. The first step was to mark the boom for the elements using a tape measure and a carpenter’s square. Some planning ahead of time on paper allowed me to make room for an extra 70 cm director just past the last 2 meter director. In starting from scratch I began by marking the 2 meter elements on the straightest 1 x 2 x 8′ long furring strip that I could find from the lumber yard. An equal spacing of 12-3/8″ is what I used for the 2 meter band so that I could add an extra director to give the antenna a little extra gain over a three element yagi and still have a fairly short antenna. That would make the 2 meter yagi antenna length just over three feet long not including the handle. At first I marked five 2 meter elements on the boom instead of four but after thinking about it I decided that the extra mark was a good spot to cut off the boom. This made the wood boom 50-3/4″ (128.9 cm) long. Starting from the director end of the boom mark the boom as follows. A mark at 1-1/4″, 13-5/8″, 26″, 38-3/8″, and 50-3/4″ (3.2 cm, 34.6 cm, 66 cm, 97.5 cm & 128.9 cm). Use a carpenter’s square and mark a straight line across the boom at each mark. This will also help to square the coat hanger elements. Cut the boom off at the 50-3/4″ (128.9 cm) mark. Also along each line, mark the center of the boom. Doing this will simplify adding the elements. Flip the board over, and again starting with the director end of the boom, mark the 70 cm elements as follows. A mark at 1″, 6″, 11″, 16″, 21″, 26″ and 31″ (2.5 cm, 15.2 cm, 27.9 cm, 40.6 cm, 53.3 cm, 66 cm & 78.7 cm). After using the square to mark a line across the board, mark the center of the boom along each line. The next step in preparing the boom is to mark the two holes for the feed-point. The feed-point is located at the 26″ (66 cm) mark on the boom. From the center mark on the boom, measure out 3/8″ (9.5 mm) in both directions and mark for drilling two holes. The spacing between the two marks should end up being 3/4″ (19 mm) apart. If you are using #6 hardware then drill two 9/64″ holes through the boom to attach the dipole elements. Once the boom is marked and the holes are drilled the handle can then be shaped. At the end for the handle trim a little wood off the edges and/or use some sandpaper to smooth out and form a nice handle. Using 80 grit sandpaper will make short work of this. Four coat hangers will have to be straightened to make the 2 meter elements. If you don’t want to straighten all of the coat hangers to make the 70 cm elements then you’ll need at least seven more coat hangers. Straighten the coat hangers and cut to the size shown in the diagram. After cutting the directors and reflectors use a marking pen and mark the center of each element. Cut the coat hanger wire for the driven elements a couple of inches longer than needed. Bend a loop in one end of the coat hanger wire large enough to wrap around the machine screw. Then measuring from the end of the loop to the end of the element, cut the dipole half to the length shown in the diagram. After making the four dipole halves use sandpaper or a file to remove any enamel or vinyl coating from the ends of the coat hanger elements where the leads are attached to the two halves of the dipole elements. The enamel coating on the parasitic elements does not need to be removed. The dipole elements are mounted to the boom using #6 stainless steel hardware. A flat washer is first placed on a #6 x 32 x 1-1/4″ machine screw. Next goes on the 2 meter element, then the assembly is placed through the hole in the boom. On the opposite side the 70 cm element is placed over the machine screw, then the coaxial cable connection, followed by a flat washer, split lock washer and a nut. If you cannot get the leads from the coaxial cable to stretch straight across the feed-point then use the shortest length possible. The leads can be connected using crimp on ring connectors or by wrapping the coaxial cable leads directly around the machine screws between two flat washers. To mount the reflectors and directors to the boom I used some 3/4″ long self tapping trim screws. You may instead use any screws with a large head or a screw with a flat washer. Line up the center mark on the parasitic elements with the center marks on the boom then fasten each element using two screws. You may pre-drill two partial holes 1/8″ from the line on the boom for the screws that hold the elements to the boom. Add a plastic wire nut (twist on wire connector) to each end of all the elements. The coaxial cable feeds the dipole driven elements at a 90 degree angle. The cable is run along the boom and brought back past the 2 meter reflector then secured with either a plastic tie or vinyl tape. The antenna will not work properly if the cable is allowed to hang down near any of the elements. Tuning the Antenna f the antenna is built as shown then it should not need much tuning if any. Tuning is of course by adjusting the lengths of the dipole elements making them either shorter or longer as needed. Check the antenna outdoors with an SWR meter or analyzer. If you notice a big problem then most likely it is the connection at the antenna feed-point or possibly the UHF connector (PL-259 or BNC connector). Parts List 1 each 1 x 2 x 8′ Pine/spruce furring strip. 8 to 11 each Steel coat hangers. 18 each Screws with large pan head (or screws and flat washers). 25-pack Plastic wire nuts 2 each #6 x 32 x 1-1/4″ Stainless steel machine screws. 2 each #6 Stainless steel nuts. 2 each #6 Stainless steel split lock washers. 4 each #6 Stainless steel flat washers. 2 each #6 Crimp on ring connectors. 4 to 12 feet 50 ohm Coaxial cable with UHF or BNC connector. Originally available by KG0ZZ at amateurradio.bz/4_dollar_satellite_antenna.html DXSpotter by YO8SAW Posted in Ham Radio Software Leave a comment I’ve been using DX Spotter by YO8SAW for several years. The software, whose last built was 1.3.106 has now been dismissed and it is no more supported, but I still have installed on my PC. I Find it very essential and usefull to track latest spots with easy filtering features. Even if it now the best on it field, it is part of my toolbox. Some of the main features: Can connect to DX Spider and CC Cluster types of nodes Can be minimized to the system tray and issue alerts for desired spots Supports spot filtering based on DX band, callsign, country, active DXpeditions and worked/new countries Supports three types of alerts: color change, sound alert, icon and balloon popup Reconnects automatically if the connection is interrupted Can be set to start automatically at Windows startup Retrieves previous spots when connection is established Send spots View details about spotted callsigns, such as DXpedition information Statistics – see how many spots have been processed, displayed or how many triggered an alert CAT through Ham Radio Deluxe Tune rig to spot frequency Automatically detect split operation and set rig to split mode Read rig frequency and use it when sending new spots Automatic update of country database It’s free! https://drive.google.com/file/d/1l9ZV11vVRPXliVxb98uB5Q4NsWrZnHtl/view?usp=sharing dx cluster DXSpotter Windows The Hentenna Posted in VHF Antennas Leave a comment While browsing through my new copy of Simple and Fun Antennas for Hams one day in the Spring of 2003, I discovered an interesting looking design, with an interesting name – the Hentenna. The versions described were made of wire and cut for 6 meters, although it was suggested that the design could be used on other bands as well. l was looking for a 2 meter antenna to use for a second rig, and I thought I could adapt this design to 2 meters easily. Some Hentenna BackgroundThe Hentenna is a loop style antenna developed by Mr. Tadashi Okubo JH1FCZ, Mr. Someya, JE1DEU and others in Japan in the 70’s. It was first described in the US in a Feb 1982 QST article by Koji Sugihara, JJ1UMS and Shirow Kinashita, JF6DEA/KE1EO wrote about it in the ARRL Antenna Compendium Vol. 5. The gain is approx. equal to a 3 element tribander, JH1FCZ reported 5.1 dBd in 1972, yet it is small compared to a beam. 1It looked like the type of antenna I wanted to try on 2 meters, small and with some gain. However it also looked like it was a little complex to build for what I had in mind.DESIGN GOALSI wanted it to be very easy to build, broad banded, and inexpensive, all good antenna attributes. It looked like a good candidate for a “plumbers delight” copper pipe project. A major consideration was to build it so it required no tuning of the feed point. So I scaled the dimensions for 2 meters and began to experiment. Several prototypes were constructed of ½” copper water pipe and fittings purchased at the local hardware store, empirically arriving at the final dimensions below.BUILDING ITI recommend building the ½” copper pipe 2 meter Hentenna to these dimensions: LEAD Technologies Inc. V1.01 Overall length = 40 inches Overall width = 12 ¾” Feed point = 7 3/16” to center line of T connectorYou’ll need one 10′ piece of ½” copper pipe, four right angle elbows, two tee’s, and two end caps from the hardware store, total cost about $12. With the dimensions below you can just jam it all together, apply the heat and solder and it will work just fine. Or you can be a little fussier and adjust the dimensions perfectly before soldering. I used a tubing type cutter; it’s much easier and more precise than a hacksaw. Use a propane torch and apply the heat to the fittings so the solder wicks into the joint, sometimes referred to as “sweat soldering”.Cut the pipe as follows:2 pieces 31 13/16” for the long side pieces above the Tee’s 2 pieces 6 1/16” for the short side pieces below the Tee’s 2 pieces 11 1/2” for the two end pieces 2 pieces 5″ for the feed points.Use lead/tin rosin core solder, and shine up the ends of the pipe and the insides of the fittings before soldering. I just laid it out on the garage floor to keep it flat and applied the heat. Be sure to wear safety goggles since concrete may “pop off” little pieces when overheated.The caps go on the end of the feed tubes and the distance between them will be around 3/4″. Solder the coax braid to one cap and the inner conductor to the other; just tack them on, ugly style. There’s no tuning involved; the position of the tees takes care of it for you!TO B OR NOT TO B (Balun that is)A balun probably should be used to preserve the radiation pattern. But while experimenting with the prototypes, I discovered that any metallic objects inside, on or near the loop had major effects on the match. So I just stuck the coax on without a balun and it seems to work just fine, in a practical sense, at my QTH. INSTALLING ITHere are several things to consider when installing this antenna.1. Use a non-conductor for the mast. I used 1 ¼” schedule 40 PVC pipe.2. For the vertically polarized version, tape or cable tie the coax to the middle of the end piece nearest the feed point, NOT the mast. Let it hang over the end some then attach it to the mast below the antenna. Side mounting the antenna may be a better option.3. Use non-conducting hardware to attach it to the mast. Steel or brass hardware has a really detrimental effect on the match. During the course of experimentation I’ve used nylon bolts, tape, cable ties, and wood dowels. Nylon boltsare by far the best mechanically and the easiest to install.NOTE: The signal polarity is perpendicular to the axis of the feedline.4. For a vertically polarized signal for repeater use, the 40″ dimension must be horizontal to the Earth. Typically this is the orientation for working FM mobile and repeaters. See the top picture at the right.5. For a horizontally polarized signal for ssb or CW, the 40″ dimension must be vertical to the Earth. See the bottom picture at the right. Article by WA0ITP originally available at http://www.wa0itp.com/hentenna.html A Cost Effective Current-mode 1:1 Balun Posted in Antenna Theory Leave a comment describes a 1:1 balun. Introduction A cost effective current-mode 1:1 balun can be constructed from a length of coax and a rod typically used for a broadcast antenna loop-stick, some electrical tape, cable ties, a length of PVC water-pipe and some connectors. The balun is formed by winding several turns of coax on the ferrite rod. Principle The operating principle is that the inner conductor and the inside of the braid act as two opposing bifilar windings with substantial inductance inserted in the outside of the braid. Differential current passes through such a transformer with little insertion loss as the opposing windings of the transformer mode effectively eliminate the winding inductance. If you want to run an unbalanced differential current through the transformer then substantial inductance will be present. Thus the current balun suppresses common-mode current. Since current flowing on the outside of the braid, is referenced to ground it must flow through the impedance resulting from the winding inductance formed by the outside of the braid and the core. This inductance will reduce the current if the impedance is high enough. The same principle applies in the common-mode choke where two or more wires pass through a ferrite core. A typical example is seen in the ferrite chokes clamped on the monitor cable of computers. High permeability cores can be used for current-mode baluns or common-mode chokes as there is not net magnetic field around the bifilar winding even though substantial currents are flowing. Construction A ferrite rod is easier to wind and cheaper than a toroid. At 160m I found that I needed 30 turns of RG58 U/C to ensure that I obtained equal, but opposite current, in each leg of an asymmetrically mounted dipole. To place 30 turns you will need to wind more than one layer across the core. The turns can be held by insulation tape and by applying two cable ties on the ends of the last layer. One end of the coax is terminated in a connector while the braid and centre conductor are split out and used as the balanced feed at the other end. You should use coax with adequate breakdown voltage to avoid damage when operating into mismatched loads. Housing The balun can be housed in PVC water pipe. Cut a section large enough to make two end pieces which can be flattened with the aid of the hot air from a hair-drier or heat-gun. The circular end-sections can be cut with tin-snips. I drilled a hole for a panel-mount connector in one end and used banana connectors for the balanced feed on the other end. The end sections should be inserted inside each end of the pipe and held in place with the PVC glue. I have found hot-melt glue adequate and easily removable. Extra protection is obtained for the ends if you leave an overhang by inserting the ends further into the pipe. My balun has survived several four-wheel-driving desert trips and is still intact and operating after five years. Ralph Holland 1996 4m Slim Jim Antenna Posted in VHF Antennas Leave a comment This 4m Slim Jim is cheap and easy to build yet it greatly out performs the more usual dipole due to its low angle of radiation. An SWR of 1:1 is obtainable across the 4m FM band with simple adjustment. The photograph and PDF diagram show the construction, however a brief description is also given. The spreaders are made from plastic knitting needles; two small holes are drilled about 10mm in from each end of the spreader to accommodate the aerial wire. Suitable sized holes are then drilled in the fishing pole to mount the spreaders. The spreaders are then glued in position using a two part epoxy. The telescopic fishing pole sections are also glued to each other using epoxy. Once the glue is set the antenna wire is then threaded through the spreaders according to the diagram. RG-58 is connected to the matching section but not soldered yet, just wrap the braid and inner around the aerial wire. Raise the antenna at least 3m above ground and clear of any objects (walls etc), apply a few Watts of RF and adjust the feed point to give a 1:1 SWR (slide the RG58 up and down the matching section). When the correct feed point has been found, solder the feeder connections. I dabbed some yacht varnish over the connections and the first couple of inches of the coax to stop water ingress down the feeder.Mount the aerial as high as possible; due to the construction materials the wind resistance is very low so it should survive the worst of any storms. N.B. I did try making a 4m slim Jim out of 450 ohm ladder feeder from a diagram posted on the web, however i could not get it to work correctly (maybe the two conductors in the ladder line are too close for 4m use. Barry Zarucki M0DGQ Article originally available at http://www.m0dgq.co.uk Understanding Solar Indices Posted in How to Leave a comment By Ken Larson, KJ6RZ Long distance HF radio communications is made possible by a region of charged particles in the Earth’s upper atmosphere, 30 to 200 miles above the Earth’s surface. This region is called the ionosphere. Continue reading→ Rewinding Power Transformers: Considerations and Step-by-Step Guide Posted in Homebrew Leave a comment Transformers are essential components in many radio projects, often accounting for a significant portion of the overall cost. However, since they can usually be reused in various ways, salvaging power transformers can be a cost-effective approach. Assessing Power Handling Capability The weight of a power transformer provides a clue to its power handling capability. For unpotted transformers, those weighing 15 pounds (6,8 Kg) or more generally fall within the kilowatt (KW) range. For example, an 800-volt, 20-pound transformer in a voltage tripling circuit should be able to intermittently power 1,000 watts of RF. Testing Salvaged Transformers When testing salvaged transformers, always use a variac or place a light bulb in series with the primary. Wiring color codes can be found in the appendix of most electrical and electronic handbooks, including Orr’s great reference. Considerations for Rewinding Transformers Power transformers can be used directly or rewound to power tube filaments or provide various specific voltages. When deciding whether to rewind a transformer, consider the following factors: Cost of purchasing a replacement: If the required secondary is readily available and inexpensive, it may not be worth the effort to rewind the transformer. Complexity of the secondary: With experience, practically any secondary combination can be rewound. However, the time required for a casual builder to reach that level of experience may not be practical. It is encouraged to limit ambitions to single secondary windings. Methods for Rewinding Transformers There are two methods for rewinding a transformer, both based on the same principle: Complete disassembly method: This involves completely disassembling the transformer, replacing the secondary winding, and then reassembling the laminated core around the coil form. This method produces tighter windings and more predictable results. Partial disassembly method: This requires replacing the secondary winding without disassembling the laminated core. It is limited to situations where sufficient space exists between the windings and the metal core, and when only a limited number of secondary turns makes this method practical. Step-by-Step Guide for Complete Disassembly Method Remove the mounting bolts and carefully pry the laminates apart using a knife or narrow-bladed screwdriver. Keep track of the manner in which the laminates were assembled to facilitate reassembly. Remove the coil, wound upon a phenolic or treated cardboard form, without disturbing its size or shape. Carefully remove the secondary winding one turn at a time, keeping a written record of the total turns. Calculate the turns per volt ratio by dividing the total turns by the secondary voltage. Consult a wire table to ensure the selected wire size can handle the required current. Wrap the new secondary turns in the same direction as those removed, using craft or wax paper between layers. Reassemble the laminates in the same order as when disassembled, using C-clamps or a vise to aid the process. Insert the mounting bolts, apply a coat of varnish, and compress with C-clamps until dry. If the core seems loose, shim it with small wood wedges or cardboard and apply a coat of varnish to hold them in place. By following these steps and utilizing the wealth of information available in handbooks related to wire capacity and projected performance, you can successfully rewind transformers for your radio projects. Happy winding! IW5EDI Simone Licensed Amateur Radio operator in 1996 as IW5EDI, active member of ARI Firenze and ARRL Class 1970, married with two childrens, love experimenting and antenna home-brewing. IT System Engineer, recently started having fun with morse code and Raspberry Pi IW5EDI Simone This Blog is mainly dedicated to Amateur Radio (Ham radio) and contains external articles and personal esperiences. What is Amateur Radio ? 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