Construction 1
LONG WIRES AND BALUNS - some thoughts on.As you dear reader may have seen on our news page some of our members have been operating their stations away from the ?main station address? and finding the long wire a means of doing so.Whilst it can be argued that this antenna is not the perfect solution (what is hi) it does have the advantage of simplicity and an easy and cheap way to erect a method to operate in the field so to speak.Steve M0ECS gave you his dimensions for a long wire and counterpoise and this was formulated some time ago by an amateur whose callsign is generally used to name this, i.e. the W3EDP.and I make no apologies for repeating it here.Long Wire is 84ft and counterpoise of 17ft. (At Cobble cottage I used 64ft for ?LW? which also tuned ok with same counterpoise as above) To use this set up one does need to incorporate a 4 to 1 balun between it and some form of antenna tuning unit. This writer uses a home brew version of said balun and an auto atu by LDG Electronics. (See ?Cobble Cottage? a radio station in our news column) A long wire I am sure most operators can provide so I will give a simple balun you can make to give that ?LW? a try.(note that co-ax connects balun to tuner)First up is the list of parts and the table for the Toroid you require. The parts you will need are few:1. Toroid, taken from table. 2. A length of enamelled wire sufficient to make the bifilar winding on your choice of Toroid. (on my version with a T80-2 I used 0.56mm.) 3. Two binding posts. 4. A co-ax panel socket 5.A small aluminium or diecast box. TOROIDNUMBER OF TURNSPOWER RATINGT80-22-60 Watts T106-2 16 100 Watts T130-2 18 150 Watts T157-2 16 250 WattsT200-2 17 400 WattsT200A-2 13 400 WattsT400-2 14 1000 WattsThe exact number of turns is not critical but the numbers listed in the preceding table should yield optimum results. The windings are bifilar, that is, 2 wires twisted together to form the lead outs as per figure 1. It is possible to exceed the power ratings listed above but the performance of the balun may be degraded during high SWR causing heating of the core. Construction should be on the lines as shown in the photo. The Toroid in photo is mounted on a small piece Perspex for stability
Items on Page * Dedicated Power Supply * SW xx+ series Enclosure * Long Wires & Baluns
The SW xx+ series ? EnclosureFor all those homebrewer?s out there this is my latest enclosure I made for that well known set of qrp rigs by Dave Benson K1SWL.This was my first rig made from Dave?s SW kits and whilst the original box I made was ok it was not big enough to accommodate a vernier control for the vfo.
This meant I then decided, after being given the aforementioned vernier by my good friend Steve to make this new enclosure. It had to be slightly larger and taller.As you can see from the photo?s I again included the K1EL keyer using a small chip and a few extra components on a separate aluminium plate fixed inside. I also fitted a fuse on the same plate and an on/off switch on the front panel. The switch, push button for the keyer commands, and the stereo socket for the paddle key are grouped together at the left on the front panel. The other control on the front is the audio gain.
If you intend making a SWxx+ rig and building your own enclosure then you will need a box to fit it into. Dave does in fact supply a purpose made enclosure for these rigs but I like to homebrew these hence the above.The basic size I ended up with was 120mm wide x 135mm deep and a height of 62mm. You will notice I used 2 mini couplings and positioned the 100k pot for the vfo near the rear of the unit but I see no reason why this could not be just behind the vernier. If you decide to do this you may need a little more width of the box to leave room for the keyer circuit.
That?s about it but if anyone is thinking of making their own enclosure for these nice little rigs I can be contacted by e-mail for more detailed measurements.Tony, GØPEH.
Dedicated Power Supply for Valve Receiver ? Steve MØCUTI had given thought for some time about building a dedicated power supply for a valve receiver that I had built a few years before. The power supply that I was using is a general purpose unit for all valve projects. The unit was of larger capacity than needed and also physically quite big. I thought that if I made a purpose built unit it could sit on the desk underneath the radio. The chassis of the radio was based on a stock aluminium box purchased from Sycom, measuring approximately 300 x 150 x 50 mm. I purchased a similar box which was perfect for the purpose and also thin enough that it did not make the overall height of the combined unit too high. I carried out some measurements to determine what voltages were required. It was found that the HT was 230V 90mA, valve heaters were 6.3v 2.5A and the signal meter driver required 16V 20mA. The only other consideration was to incorporate a small audio amplifier to increase the volume when weak QRP signals were not really strong enough to drive the loud speaker at reasonable volume. I noticed that the kit manufacturer Velleman made a small 7W solid state audio amp for about £7.00 that would fit nicely into the enclosure.
Some years before when thinking about making a regen receiver I came across the website of ZL2JJ who had made a nice job of a TRF receiver. I had remembered that he had used a dc supply for the valve heaters in order to reduce any possible hum. He used an LM338 5A adjustable voltage regulator to obtain 6.3V DC. I often wondered why commercial amp builders did not do a similar thing as it would be very easy at a manufacturers level. As the HT current requirement was only 90mA @ 230V I decided to obtain this by putting two 230 ? 12v transformers back to back, Maplin supplied just the job for about £5 a unit. I used a 2 x 9V 80VA toroidal transformer with a LM338 for the valves and a 15V fixed regulator for the meter driver and audio amp. Construction was fairly straightforward. I was impressed with the quality of the Velleman kit. I powered the unit up and set the 6.3V DC supply. I then proceeded to connect the radio. There was no reception and I noticed that the valves were not glowing, the LM338 also started to smell hot. After carrying out some checks I found that the dc resistance of the combined valve heaters was only 0.7 ohms this would require a DC current of 9 amps. This was a sharp reminder of the differences between ac and dc currents flowing in an inductive circuit. This also explains why manufacturers stick to ac for valve heaters. They would require larger transformers and thicker wiring to the valves. To overcome my mistake I obtained a second toroidal transformer 6V 80VA for the valve heaters and a small 2x 9V
7VA toroidal transformer which I managed to fit on its? end in the top left hand corner of the enclosure. I used the LM338 to give 13.8v for the audio amp and used the fixed 15v regulator for the signal meter driver.The HT dropped to 105V Dc when the radio was running, but this did not make any noticeable difference to the performance, if anything the radio seemed more stable than with the original voltage of 230VThe unit functioned very well with plenty of audio output for the loud speaker.I was intrigued at how ZL2JJ managed to power 5 octal valves with a combined current requirement of 6 Amps DC. The only remark he made was to use a heat sink on the LM338 so I suppose he must have just been on the limit of what the LM388 would deliver.
Swale Amateur Radio Club G4SRC
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