PRACTICAL MEASUREMENTS OF LONG WAVE PROPAGATION
Do you know what FARADAY ROTATION is? For those who don’t, Jonathan G1EXG explains all inside.
Plus JONATHAN G1EXG’S SHORT CIRCUIT PRESIDENTIAL PONDERINGS CHAIRMAN’S CHATTER RALLIES Superhet or SDR? Two new radios but which one is in tune with the way the market is heading? The Kenwood TS-890S is a superhet while the Yaesu FTDX 101D is an SDR.
Spring 2018
Worthing & District Amateur Radio Club Established 1948 Website: www.wadarc.org.uk
E-mail: info@wadarc.org.uk President: Chris Smith G3UFS WADARC meets every Wednesday at 7.30pm for an 8pm start in the Lions Hall, 21 Roberts Road, Lancing BN15 8AR. All who have an interest in radio communications and associate subjects, whether a licensed amateur or not, are welcome. WADARC can also arrange training for the radio amateur Foundation, Intermediate and Advanced licences.
The WADARC Committee 2017 – 2018 Chairman Alan Baker G4GNX Vice-Chairman Leslie Sampson G3JSU Secretary Andy Braeman M6RFE Treasurer Roger Ferrand G7VBR Raymond Ellett M6IKO Norman Jacobs 2E0RKO Ian MacDonald M0IAD Alex Slee 2E0UMD These Committee and Members have volunteered to accept the following responsibilities: Membership Manager Ian MacDonald M0IAD Ragchew Editor Roger Hall G4TNT Website Andrew Cheeseman G1VUP / Alastair Weller M0OAL Special Events Stations Peter Head G4LKW Online Content Coordinator Alan Baker G4GNX Outside Events Coordinator, Facilities and Bookings Norman Jacobs 2E0RKO Training Coordinators Alastair Weller M0OAL / Andrew Cheeseman G1VUP Exam Secretary Alastair Weller M0OAL Press and Publicity Coordinator Les Sampson G3JSU Quartermasters Andy Braeman M6RFE / Raymond Ellett M6IKO Club Calendar Coordinator Alex Slee 2E0UMD Weekly News Email Phil Godbold G4UDU, Alan Baker G4GNX, Jonathan Hare G1EXG
WADARC Club Nets (all times are local) 07.30
Sunday
3.725MHz ± QRM SSB
19.30
Monday
145.425MHz (V34/S17)
11.00
Thursday
7.106MHz ± QRM SSB
CONTENTS Editorial .................................................. 4 Presidential Ponderings .......................... 6 Chairman’s Chatter ................................ 8 Faraday Rotation by Jonathan G1EXG .............. 10 Practical Measurements of Long Wave Propagation by Ted G3EUE ..... 12 Short Circuits by Jonathan G1EXG .................... 18 Rallies ..................................................... 22
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EDITORIAL
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elcome once again to the latest edition of Ragchew. It’s been a while since the last one and that’s been for the usual reason, a lack of material to put in here. It seems to be either glut or famine, with some issues having almost more stuff sent in than I can use while others, like this one, have almost nothing. I don’t even have a relevant photo to put on the cover! I wouldn’t normally publish an issue with so little content but this one is labelled Spring 2018 so I really have to get it out while there are a few days of Spring left. In This Issue Ted G3EUE sent in an interesting article on measuring long wave propagation. He first had it published in early 1996 in the now defunct magazine Radio Bygones. I’ve reproduced it exactly as it was published then but, unfortunately, Ted only has a photocopy of the original article so the photograph and illustrations have not come out well but they’re still surprisingly clear. Jonathan G1EXG has two contributions in this issue. The first is a look at something I’d never heard of before, Faraday Rotation. You can find out what it is and why it is of interest on page 10. Jonathan has also supplied his regular Short Circuit column and this time he been taking a look at varicap diodes and he explains what they do and how you can use them. Also this month, as usual, our esteemed President and Chairman share their thoughts with us and then we finish this issue with a list of forthcoming rallies for the next couple of months.
Dayton There were two interesting new radios announced at the Dayton Hamvention in May this year, the Kenwood TS-890S and the Yaesu FTDX 101D. I was particularly intrigued by the way Yaesu have decided to follow the current trend of basing their design on Software Defined Radio (SDR) principles but Kenwood have stuck with the tried and tested superheterodyne that has been around for years. I thought that battle had been fought and lost some time ago and the sales figures for the
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C superhet Kenwood TS-590S when compared to the SDR Icom IC-7300 seem to show that people who actually buy radios have been voting with their wallets and opting for SDR. This is even though it could be argued that current direct-sampling SDR architecture does not match the older superhet design when it comes to certain aspects of performance. The designer of the new TS-590S, Toshio Torii, was on the Kenwood stand and when he was asked why he’d chosen to stick with a superhet design, he pointed to the figures on the poster (3rd IMDR 110dB, RMDR 112dB and BDR 150dB) and said that he would never have been able to achieve them with an SDR. This seems to be borne out by a quick look at the specifications of some other radios. For example, the Reciprocal Mixing Dynamic Range (RMDR) is a good measure of HF radio Toshio Torii and his new TS-890S performance – the higher the number, the better a receiver is at distinguishing a small signal while a very strong signal is present on a very close frequency. Icom reports a typical RMDR figure for the IC-7300 is 97dB at 1KHz spacing. To put that into context, QST measured some similarly-priced recent transceivers and these are the figures they found: the Yaesu FT-991 75dB, the Yaesu FTDX-1200 81dB, the Kenwood TS-590SG 94dB and the Icom IC-7100 84dB. Compare those figures to the 112dB Toshio has achieved for the new TS-890S and it starts to look like he has a point. Finally If you have anything you’d like to contribute to the next issue or if you have any thoughts you’d like to share on the Superhet vs SDR debate, please do get in touch with me at ragchew@wadarc.org.uk 73, Roger G4TNT
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PRESIDENTIAL PONDERINGS
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i everyone, please forgive me for harping on about memories but I do believe that one’s memories are one of the most important things you can pass on to younger people. I suppose the recent Club talk by Brian Spilby reawakened my memories of doing the same type of job he was doing in the “Y” service, except that he was a Linguist, whilst I was a Wireless Operator. But before that time, I have very vivid memories of being a young lad during World War II. For a boy in those days, the adventures one could undertake were enormous. Manoeuvres As you probably know this area, Worthing and West Sussex, was a very important training area for the Army and therefore many what were called ‘Manoeuvres’ (that is, war training) took place on the South Downs. Now we, as young lads, could not let these Manoeuvres pass without finding out what was going on! After the Army had left the areas, we used to go in to search for anything that was interesting. We regularly used to find hundreds of spent bullet cases and sometimes, of course, live ones as well. However, the most prized finds were the Parachute Flares, both used and unused. The parachutes were small, about 18 inches square, and very well made and the best ones we found were the ones that had failed to deploy after they’d been fired from mortars. We would take them away, dismantle them and remove the parachute and the magnesium, which we then placed in a tin lid and set alight. The brightness of the burning magnesium had to be seen to be believed. Why nobody was ever injured surprises me even today! Camps Another example of those extraordinary times for us lads was playing and building ‘camps’ in bombed houses. I remember one in particular very clearly. It was when a row of terraced houses in Hadley Avenue, Broadwater, Worthing had been demolished by bombs. When it happened, I was asleep with my brother under the stairs in our Downlands
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C Avenue house, which was about 100 yards away. Those bombed out houses provided us with many happy days playing in them. But it also brought home the terrors of war. Other Memories Other vivid memories I have include riding on the back of a Sherman M4 tank up Charmandean Lane on to the Downs, courtesy of the Canadian Army and of riding in a Jeep along the Sompting By-Pass at the very fast speed at the time of 60 miles per hour!! Again, this was courtesy of the Canadian Army prior to D-Day. It was all good fun and never to be forgotten. Reservoirs? Thinking of those times, does anyone who lived in Worthing at that time remember two large Water Reservoirs being built to help Firefighters in Leigh Road and Broadwater Road, by Broadwater Church? They were very large, very deep and made out of concrete. They disappeared soon after the end of the War when houses were required. Well that’s enough reminiscing for now. I hope that this piece has not been too boring, but as I said at the beginning, memories are important things to carry forward to each generation. 73, Chris G3UFS
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CHAIRMAN’S CHATTER t’s supposed to be springtime with summer fast approaching but looking out of the window, you wouldn’t think so. A brief spell of heat, then it’s back to cool and rain again! Fortunately, that didn’t prevent some of you making the foray onto Mill Hill for WADARC’s first outdoor event of the year. I’m sorry I couldn’t make it – it was the XYL’s birthday and I prefer to stay alive! There are more outside events planned, including the usual foxhunts, a couple of barbecues and on-air events too. We’re also hoping that we can make a visit to an appropriate establishment (Bletchley Park maybe) to commemorate WADARC’s 70th birthday.
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Venue Lions Hall seems to be popular as a meeting place so we intend to continue meeting there for the foreseeable future and it’s hoped that we will be able to get some antennas erected this year. There’s also been some talk of a cupboard for exclusive use, which means we should be able to keep some club equipment permanently on site. The idea of having a club shack has been shelved indefinitely as it’s proved to be more than the club can afford in rental fees. 70th Anniversary In my previous missive, I spoke about obtaining a special event callsign for the WADARC 70th anniversary but due to strange Ofcom rules, this has proved almost impossible and it probably wouldn’t suit our purposes. Instead, Edmund M0MNG will be operating our Club callsigns G1WOR and G3WOR as ‘GX’ calls, which we’re hoping will stir up some activity on most bands. What we now need is a special QSL card to celebrate our 70 years so I’m going to suggest we have a competition. Please submit your designs for a QSL card to a member of the Committee by the last day in July. The rules are simple – you can submit as many entries as you like but they must be your own work. Designs can be computer aided and they must
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include the words “Worthing and District Amateur Radio Club”, “WADARC”, “GX1WOR”, “GX3WOR” and “70th Anniversary Station”. All designs must fit on a standard postcard of 148mm x 105 mm (A6 size). Apart from that, you’re free to design anything you like but please remember that it should reflect the Club, it’s nature and location. If you have any ideas for a design, please do get in touch with a Committee member. Club Attendance Although WADARC currently has 58 paid-up members, most weeks meeting attendance is between 10 and 20 people. I believe this is not a good situation, especially when we arrange talks because having just a few people in the audience doesn’t give speakers much encouragement. I do realise that the current low sunspot count is not contributing to HF QSOs and this might be the reason why interest in amateur radio seems to have waned but surely that’s one good reason to come to Club meetings, to meet with like-minded people. Maybe we should turn the whole thing over to the internet and conduct meetings on Skype so nobody needs to get off their backside and travel a mile or two? C’mon folks, please rally round and support our Club and not just leave it to the faithful few regulars who turn up most weeks. I hope to see YOU at Lions Hall… 73, Alan G4GNX
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FEATURE FARADAY ROTATION Jonathan G1EXG explains Faraday Rotation and looks at why it is relevant to radio amateurs as well as anyone who communicates by radio.
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ack in 1850s, the great experimental scientist Michael Faraday was conducting experiments to investigate the idea that light was an electromagnetic phenomenon. The detailed theory behind it was provided later by James Clark Maxwell.
Electric and Magnetic Fields We now know electromagnetic waves are formed of electric and magnetic fields at right angles propagating outward from the source. For radio wave investigations, it is often taken as a standard that if the electric field happens to be parallel with the ground, we call the wave horizontally polarised but if the electric field is vertical to the ground, we say it is vertically polarised (in optics, however, the reverse classification is sometimes used).
Magnetic Influence Faraday passed light through a special piece of glass. After much experimenting, he discovered that the polarisation changed angle (the angle rotated) when a magnetic field was present across the glass. We now know this as Faraday Rotation. The effect is dependent on a number of factors, including the nature of the material the wave is travelling though, in particular the way free charges in the material (usually the electrons) interact with the wave, the strength of the magnetic field and the square of the wavelength.
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C Faraday Rotation has implications for radio amateurs because our electromagnetic radio waves interact with the electrons in the ionosphere, which is immersed in the Earth's magnetic field, and the effect can change the polarisation of our transmitted signal.
VHF & UHF For line of slight terrestrial VHF or UHF communication we always need to make sure the receiving antenna uses the same polarisation as the transmitting antenna, otherwise the received signal can be very considerably reduced ca. 20-30dB. As previously mentioned, Faraday rotation is dependent on the wavelength so at UHF and microwave frequencies, where the wavelength is tiny, the effect is very small. Therefore, satellites can routinely send back reliable signals with 'fixed' polarisations to earth.
HF At the relatively long HF radio wavelengths, however, Faraday rotation is important. The waves launched from our horizontally or vertically polarised antenna suffer from Faraday rotation in the ionosphere. At HF this usually means people will not receive our signal with the same polarisation our transmitter antenna produced – in fact, it could arrive at any random polarisation. For communication via the ionosphere then, Faraday Rotation will mean that it's quite possible to have a contact with someone who is using a horizontal dipole even if you are using a vertical antenna. If you have the space, it might be interesting to be able to switch between a horizontal or vertical antenna to see if one polarisation dominates. But it's probably more likely that variations in Faraday rotation taking place from one moment to another, and over slightly different paths within the ionosphere, will mean that the polarisation will be continually changing at your receiving station. 73, Jonathan G1EXG
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FEATURE PRACTICAL MEASUREMENTS OF LONG WAVE PROPAGATION In early 1996, Ted G3EUE had an article on measuring long wave propagation published in the now defunct magazine Radio Bygones. He’s now kindly given me permission to reprint it in Ragchew and I’ve reproduced it verbatim. Unfortunately, he only has a photocopy of the original so the photograph and illustrations have not come out well but they’re still surprisingly clear.
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n 1905, Duddell and Taylor carried out measurements of field strength at short distances of about 60 miles from a spark transmitter situated on HM Telegraph Ship Monarch. Their readings were made at Howth in Ireland, the received current being recorded directly by a thermogalvanometer. It was noted that signal strength varied inversely as to wavelength and distance. Following those early experiments W. L. Austin (Austin-Cohen) HM Telegraph Ship Monarch carried out similar investigations which extended intermittently over several years. His measurements began in 1909 on damped waves and consisted of a series of measurements of the field produced by the Brant Rock station near Boston, Massachusetts. The receiver was on board the USS Salem. The results of these two series of experiments were used for many years as the basis for the design of early transmitting stations. Austin’s observations then extended to studying CW transmissions over much greater distance. The small value of the received current precluded direct measurements but readings were achieved by shunting a pair of telephones with a non-inductive resistance of such a value that the signal could only just be detected. The particular aerial current was
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C determined by producing a known current in the aerial and telephones which gave a signal of the same audibility for the same amount of shunt. Eventually it was concluded that the shunted telephone method was liable to large errors and was very difficult to work reliably. All later measurements indicated that signal strengths at long distances were much greater than had been calculated from the earlier experiments. A separate series of measurements in Italy at about that period were as much as 16 times the calculated values.
French Survey Around 75 years ago, governments and industry were taking a close look at the development of reliable long-distance communication. In 1919, the French sent the ship Aldebaran from Toulon to New Zealand to determine the law of propagation over land and sea. The transmitters were at Nantes on 9,000 and 11,000 metres with another at Lyons on 15,000 metres. Both stations used CW from arc transmitters. The principal results of the cruise were: 1. That signal strength at long distances was much greater than calculated expectations. Propagation of electromagnetic waves around the world did not follow an inverse distance law. 2. That fields produced by night transmissions were stronger but more variable than those produced by day; probably dependent on the variation of the height of the Heaviside layer. 3. That there was an unexpected increase in signal strength in the neighbourhood of the Antipodes, due, it was thought, to a convergence of energy towards the point diametrically opposite to the transmitting station. 4. That atmospheric interference increased with wavelength. On the whole, the results of the Aldebaran’s voyage seemed to throw doubt on the validity of the conclusions drawn from the results of the earlier Austin-Cohen experiments, especially for long distances.
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C Further Measurements In order to obtain further data on the controversial question of longdistance transmission, the Admiralty, in 1922, sent the battle cruiser HMS Antrim from Portsmouth to Sierra Leone. Measurements of field strength were made at the Signal School, RN Barracks, Portsmouth and on board ship throughout the outward and homeward voyages. The land transmitter was the Admiralty station at Horsea Island. The primary objective of the cruise was an attempt to determine experimentally the law of wireless propagation or wireless ‘visibility’ round a quadrant of the Earth’s surface. Other minor objectives were a study of diurnal variations in signal strength over sea and land, together with the determination of the minimum field strength necessary for reliable reception with modem receiving equipment. The complete investigation into the law of propagation involved four series of measurements in each of which only one of the four factors would be varied: distance; wavelength; transmitted current and effective transmission height. The latter two factors were respectively due to three different values of transmitting aerial current and the different effective heights of the two stations. The conclusions derived from the measurements made at Portsmouth and ship data were similar. The Horsea transmitter setup comprised a ‘T’ aerial supported between two 446-foot lattice masts. The 700-foot horizontal top consisted of two sets of 8-stranded wires on 39-inch circular spreaders 16 feet apart. Maximum centre sag was 70 feet. The downlead was 16 parallel wires on 14-inch circular spreaders. The earth system comprised a fan of wires 350 feet long in all directions. The effective height of the aerial system was 0.1 kilometre with 35 amps of aerial current except when changed for special tests. The ship’s receiving aerial was an inverted ‘L’ type. The horizontal top was 160 feet long, with an 80-foot downlead. The effective height was calculated as 0.016km. In order to obviate errors arising from the variations in field strength due to day and night travel, the route selected deviated as little as possible from the line of longitude through
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C Portsmouth, which meant that the time of day remained virtually the same throughout the voyage of about 5000km.
Test Methods The method of measuring signal strength was similar to that adopted on the cruise of the Aldebaran except that absolute measurements of received current were made. Other than for short distances, aerial current was so small that only indirect methods of measurement were possible. A portion of the signal from Horsea consisted of a series of sustained dashes of 5 seconds duration, followed by silent spaces of 10 seconds. The dashes were made audible by the use of a heterodyne wavemeter. During the silent intervals a local oscillator produced in the same aerial a known current, the value of which was adjusted until the pitch and loudness of the beat note were identical with those produced by Horsea. The aerial currents in the two cases were assumed to be the same. When the adjustments of the local oscillator were correct it was quite impossible to say when the signal from Horsea ended and that from the local oscillator commenced. It was considered that with practice the variations in aerial current due to errors of adjustment were much less than the variations produced by external natural causes. A prearranged 10-minute signal was sent from Horsea at 8 a.m., 1 p.m. and 9 p.m. as follows: Code call: 3 minutes Interval (i) Silent space: 1 minute Interval (ii) Sustained 5-second dashes and 10-second intervals (12 of each): 3 minutes Interval (iii) General message: 2 minutes Interval (iv) Code call: 1 minute Interval (v) The reception procedure was carried out as follows: Interval (i) was utilised by operator 1 to tune the station whilst operator 2 adjusted the heterodyne wavemeter so that the pitch of the beat note was the same as a musical reed. Care was taken that the coupling of the heterodyne wavemeter to the receiver was always the same. That was
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C determined by distance ‘d’ as shown in Fig. 1. Interval (ii) was used by operator 3 to tune the local oscillator so that the same beat note was heard without alteration of the heterodyne adjustments. During the interval (iii), operator 2 adjusted the current I for a given value of ‘D’ and also adjusted the distance ‘D’ for a fixed value of I so that the silent intervals were occupied by the beat note of the local signal. During the 5-second dashes, switch ‘S’ was closed and as many different combinations of D and I were read as the 3 minutes would permit. Coupling coils A and B were mounted coaxially so that B could slide along a calibrated scale of measured mutual inductance. I was varied by regulating the HT supply to the local oscillator. Another important control experiment necessitated swinging the ship through 360 degrees to see if any variation of signal strength resulted from the directional properties of the aerial. That correction was found to be negligible. The wavelengths used were 3,000, 4,000 and 6,000 metres. Antrim had a rough voyage, losing her aerial whilst crossing the Bay of Biscay to Gibraltar so that recalibration and control experiments had to be undertaken.
Results Graphs of the results of the voyage indicated that for short distances, short waves gave the best signals, but that long waves were best for longdistance transmission. Readings also showed that the electromagnetic fields at long distances from the transmitter were much stronger than the authorities had been led to expect. Other results such as more effective night-time transmission and greater variation of field strength during the
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C day had been anticipated. Irregularities in signal strength which occurred when rounding the south of Spain, entering the harbour in the Grand Canaries and in the neighbourhood of Freetown were thought to be due to the proximity of significant land masses; particularly the mountains of Spain which contain a large percentage of iron ore. Data obtained by Antrim indicated that the average field strength varied from 44 to 112 microvolts per metre, which confirmed the order of magnitude which had to be obtained in order to achieve reliable and readable signals with a 7-valve HF amplifier and ordinary high-resistance headphones. An international conference in Paris at that time had suggested that a figure of 50 microvolts per metre was a suitable figure for communication. At about the same time that the Admiralty experiments were being carried out, the Marconi Company Figure 2 also made a series of measurements on board SS Dorset travelling to New Zealand by way of the Panama Canal and on the SS Boonah from Australia to England by way of the Suez Canal. The outstanding conclusion from the great quantity of data obtained was the support they gave to the diffraction theory between concentric conducting spheres; diffraction alone being quite inadequate to account for the results. Day and night variations and the phenomenon of atmospherics were also investigated. The resulting variation in the attenuation of short and long waves is shown in Fig. 2.
Reference L. S. Palmer, Wireless Engineering, Longmans, Green & Co. 1936
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G1EXG’S SHORT CIRCUITS Jonathan G1EXG takes a look at varicap diodes and explains what they do and how you can use them. SHORT CIRCUIT NO. 18: VARICAP DIODES A varicap diode is a type of diode that can be used as a voltage-controlled capacitor. It is useful for tuneable filters, amplifiers and in oscillators in radio circuits.
A diode is an electronic component that only conducts when the voltage is correctly applied to it, that is, when the cathode is negative and the anode is positive. When connected the other way around, the device is said to be reverse biased and very little current flows. There exists a region in the diode called the depletion zone which is effectively an insulated region between the junctions making the diode behave like a capacitor. The greater the reverse voltage the greater the size of the depleted region and the smaller the resulting capacitance. By varying the reverse voltage, you can, therefore, adjust the internal capacitance of the diode – you have a voltage-controlled capacitor. All diodes behave like this but by carefully controlling the diode fabrication process you can deliberately create a variable capacitor diode that has much better reproducible properties, a wider reverse voltage range, better temperature stability properties and less losses than a standard diode (better Q). These specially made voltage-controlled capacitors are called varicap diodes, varactor diodes, variable capacitance diodes or tuning diodes.
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C Types Type BB112 V149 BB212 NTE617 MV104 MBD102
Cap Range (pf) 20-520 20-500 22-620 34-39 37-42 few pf
Applications (1-8V) mw / short wave radios (1-8V) mw / short wave radios (1-8V) dual varicap dual varicap, FM tuning dual varicap, FM tuning varactor tripler (see text below)
Varicap diodes are much smaller and more convenient than a mechanical system such as a variable capacitor driven by a motor or servo system, for example, they respond faster and take far less power. You can conveniently use varicap diodes to create resonant circuits in filters, oscillators and a range of other radio related applications. The varicap capacitance is controlled using a DC voltage but one potential problem (no pun intended) is that the RF voltage itself might modulate this reverse bias voltage, creating unwanted detuning and distortion (see below). To reduce this problem, the RF levels in the circuits should usually be kept quite low so varicaps tend to be used in input stages, preamps and oscillator stages but not in power amplifier stages, for example. Two varicap diodes can be used back-to-back (in series) to half the voltage across each device but, unfortunately, doing this also halves the capacitance range possible. These double varicaps are often packaged in a three lead 'transistor' style case (for example, the well-known BB212 uses a T0-92 case) with a common connection on the centre pin.
Circuits The first circuit below shows a dual-varicap tuned oscillator circuit (in this case with the two varicaps wired in parallel) that can be used in voltage controlled oscillators (such as a spectrum analyser) and frequency synths such as transceivers and so on.
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If you couple an audio signal from a microphone into the varicap control voltage line (AF i/p on the diagram), you can create frequency modulation and at high frequencies (where the capacitance change required is very small), even a standard diode (for instance, 1N4148 or 1N4001 and so on) can be used.
Loop Tuner In a previous Short Circuit column, I described a simple receiving loop to help reduce local noise pick-up. It used a variable capacitor to tune it. Here, I show a varicap tuned version. The diode is attached close to the loop and it can conveniently be tuned using a control voltage cable from the shack, so there is no need for a costly and cumbersome waterproofed motor driven capacitor and waterproof box to be fitted outside with the loop. To ensure good reception, you need to make sure that the long varicap control voltage wires do not act as an antenna, introducing rogue signals into the loop circuit. As very little current flows when the diode is reverse biased, a simple resistance, capacitor (and inductor) circuit can be used to effectively decouple the control cable wires (but it needs to be fitted
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C close to the loop and varicap tuning diode). You can also use the coax to feed the DC varicap diode control voltage if you make up a suitable decoupling circuit.
Microwave Generators The distortion created in a varicap circuit by large RF voltages can actually be put to good use to create harmonics. This allows varicap diodes to be used as frequency multipliers (e.g. triplers) to create SHF and microwave frequencies that would be difficult, costly or impossible to generate with current transistors. 73, Jonathan G1EXG
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RALLIES SPRING 2018 JUNE 1st-3rd – Ham Radio Show, Friedrichshafen Messe, Friedrichshafen Airport, Germany 3rd – Spalding DARS Rally Holbeach Community Sports Academy, Pennyhill Lane, Holbeach PE12 7PR 10th– Ipswich Radio Rally Kirton Recreation Ground, Back Road, Kirton IP10 0PW 10th– Junction 28 Rally Bowls Hall, Alfreton Leisure Centre, Alfreton, Derbyshire 17th– West of England Radio Rally Cheese & Grain, Market Yard, Bridge Street., Frome, Somerset BA11 1BE 24th– Newbury Radio Rally Newbury Showground, next to Junction 13 of M4
JULY 1st– Barford Norfolk Radio Rally Barford Village Hall & Green, Barford, Norwich NR9 4AB 7th– Stockport Radio Society Rally Walthew House, 112 Shaw Heath, Stockport SK2 6SQ 7th– Bangor & District ARS Annual Rally Donaghadee Community Centre, Parade, Donaghadee BT21 0HB 15th– Cornish Radio Amateur Club Rally Penair School, Truro, Cornwall, TR1 1TN 22nd– Finningley Amateur Radio Society Rally Hurst Communications Centre, Belton Road, Sandtoft, Doncaster DN8 5SX 29th– Chippenham & DARC Rally, Electronics Fair & Car Boot Sale Kington Langley Village Hall & fields, Church Road, Kington Langley SN15 5NJ
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