The ProblemMost general coverage receivers have adequate gain and you can hear the background atmospheric noise from the receiver’s bottom frequency limit of around 30 to 100 kHz up to their maximum frequency of 30 MHz: that is except for the “Medium Wave” range of 500 kHz to 1.620 MHz. The reason that most receivers … Read more
Recap on the ThyristorIn a previous article, I explained how a thyristor worked. This is a transistor-like device in which the current through it, (between anode and cathode), is controlled by the thyristor gate. However, unlike a transistor, the “through current” is not proportional to the gate current in a linear manner. Instead, the current … Read more
Electro-Magnetic radiation is not confined to broadcast, commercial and amateur bands, and figure 1 shows a significant portion of the electro-magnetic spectrum including the visible part. Particularly note the “fierce” logarithmic scales of frequency and wavelength. This is necessary to accommodate the huge range between “radio” waves and gamma rays in a single diagram. This … Read more
Some things can go faster than light, but not ‘material’ things. Three examples of these things are; the cutting point of scissors, the meeting point of lines as the lines go from crossing to parallel, and the phase of a wave. But these are imagined things, things in the mind. In the case of waves, … Read more
It would be no good removing the man-hole cover in the pavement and directly measuring the resistance between the metal pipes at either end of the plastic section, as these would be effectively shorted out by the surrounding earth, so I decided to simulate the real situation by measuring the resistance of a length of … Read more
Back In the hastily rearranged talk to the club on Tuesday, 21/11/06, Brian, G3YKB talked about many different methods of home construction of experimental or “one off” circuits. These included: conventional printed circuit board, strip board, “paddy board”, ugly bug, and others, and also how to make screened enclosures by soldering sheets of single sided … Read more
It has a similar layout to the alternators used for generating the country’s electricity supply, except that instead of having 6 poles for generating 3-phase 50Hz AC, it has 600 poles for generating single phase AC at 17,200Hz. It also rotates somewhat faster than the alternators supplying the national grid, and delivers 200 kW of … Read more
Back This is not really about amateur radio, but it is technical and it involves electricity. Have you ever got the Christmas Tree lights out from the box in which they had been carefully packed the previous year only to find that they no longer work? If so you will know that finding the offending … Read more
Back There has been some discussion on whether it is better to wind inductors as a torroid or as a solenoid on non magnetic material. Thoughts:-Magnetic lines of force add vectorially. They do not influence one another. Hence: The result of this is that the field near the centre of the solenoid is proportional to … Read more
AB INITIO PERFECTUS EST (or in plain English, this “From first principles” series is finished). This series of technical articles for the VARC Newsletter is now concluded. It has ranged over more than 3 decades and some 80 articles, although in the early days its publication in the VARC Newsletter was somewhat irregular. Its original … Read more
Back A dipole in free space, fed at its centre by a balanced feeder, can radiate all the RF power fed to it with no radiation from the feeder. Such a system is illustrated in figure 1. A dipole is a “resonant” aerial and its first “self resonance” is when its total length is approximately … Read more
The next VARC meeting will be at The Boot on Monday 17th of April. We welcome members and not members. You are cordially invited to join us for at The Boot on Monday 17th of April 2023. This is an excellent opportunity to connect with fellow club members, share your knowledge and your projects, and … Read more
My antenna is a 2m folded dipole designed by Dave Kimber, G8HQP. I followed his instructions like this: 2m Folded Dipole – a loft-mounted vertical folded dipole for the 144 – 146MHz band. Theory: A vertical antenna most appropriate for 2m. A fat dipole (therefore wideband) will have a lower feed impedance at resonance than a thin dipole … Read more
The annual VARC Antenna Shootout starts today and runs until the end of June. The theme for this year is ‘2-metre activity’ meaning that it can be any mode, any polarisation, and any power (within applicable licence restrictions of course). You can operate from any location but must use your own callsign and not the … Read more
Verulam Amateur Radio Club now has it’s remote station running from it’s site near Dunstable. This is running most HF bands and proving to be very successful. It is operating using the RemoteHams software, which is a free download from the Remote Hams website. Once downloaded you can search for VARC and access the radio. … Read more
Europe and the Falklands are seemingly the main activity on the 4 metres (70 MHz) band. America and Japan don’t have it so most big ham radio company manufacturers avoid it for the most part. (The Icom IC-7300 is the exception but only the European model.) VARC member Bob Houlston (GVPVB) sent an e-mail to Elecraft … Read more
SWLs may have a lot of fun monitoring the new FM voice repeater on the International Space Station. ‘I heard it on 21st May 2021 at 20:05 UTC for an 11-minute pass’, says VARC member Bob Houlston (G4PVB). ‘The Doppler effect is quite noticeable, so I tuned my receiver high to 437.810 MHz and gradually … Read more
In January, Ron White G6LTT, the club’s district representative spoke at the club’s virtual meeting. He was joined by Terry Baldwin G4UEM, also a representative. Ron described the changes now taking place, particularly with training and examinations which have moved online, including invigilation of exams, all of which can be booked and paid in the … Read more
VARC member Tim Price (G4YBU) took part in a radio interview on BBC Radio Surrey this morning discussing Summits on the Air (SOTA). Tim is one of the event organisers for SOTA. He was joined by RSGB Board Director Stewart Bryant (G3YSX).
Rhombic for 6m One thing I have fancied playing with for a long time is the Rhombic antenna. It has a very good directional gain and in principal is easy to construct. The problem is that on HF a Rhombic is extremely large. Even on 6m the antenna is pretty big! My idea for the … Read more
The antenna consists of: 1:1 Balun Lengths of copper brake pipe approximately 1m long pipe and secured into grooves in a length of wood. “Stingers” which can be moved to adjust the length and secured with grub screws. It is secured to the mast with a stainless steel clamp.
Years ago I bought a commercial but cheap HB9CV antenna for 6m. I think in terms of dB per gram of beam aluminium, these antennas are top-notch and great for /P. (I have had a lot of success with good DX with my 2m version.) However, rushing a first activation (contest) a few weeks after … Read more
Every year Verulam Amateur Radio Club holds an Antenna ‘Shootout’ Contest. The idea is to get as many club members as possible building their own antennas and then competing against others to see who’s antenna performs the best. Over the years we have had loads of really interesting submissions, from massive quads to tin-foil and … Read more
The VARC Lockdown Challenge was to make a 6m antenna from materials found at the home QTH. No sneaking off to local suppliers or mail ordering! A rummage through my garage found the following: Plastic rectangular-section conduit, two telescopic Band 1 TV antennas, SO239 socket, ‘U’ bolts and miscellaneous bits of wood. Unfortunately, no useful … Read more
I’m entering the Verulam Amateur Radio Club aerial contest 2020. I’ve built a Delta loop with bits stored at the back of the house. Items used are plastic electrical conduit and drain pipe, coax cable and wire. Wire length is approx 6 metres, the conduit is 2 metres long. The matching coax is approx 1 … Read more
Back In “radio science”, ‘Q’ stands for Quality factor. In a simple resonant or tuned circuit, (and indeed also in a single inductor or capacitor), Q is conveniently summarised as “the component’s reactance divided by the component’s resistance”. The higher the Q, the lower the loss in the component’s resistance. (In most tuned circuits it … Read more
Hello everyone, I am sure, like me, you have been following the news and government reports surrounding the coronavirus. While the risk to the general population is still perceived to be low, we need to consider the safety of our members, especially as some of us are likely to be in a high-risk category. Over … Read more
AB INITIO Back Puzzling facts As we approach the festive season of Christmas crackers, games and puzzles, it was thought once again that it would be appropriate to divert to something “Scientific” rather than strictly “Amateur Radio”. Everybody knows that the tides on the sea are due to the “pull of the moon”, but a … Read more
The Club’s ‘fox hunt’ is an annual event held on a club night. This year it was Peter (G0OIKs) turn to be the fox. The way the club organises this event is for the fox to find a spot within a few miles of St Albans where a station is set up. Every few minutes … Read more
