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- Written by: ik1hge
- Category: Electronics and radiofrequency
- Hits: 50
After a long break in the 1990s, in the early 2000s I decided to return to amateur radio. Unfortunately, room availòability and roof access issues prevented me from using my trusty Kenwood TS-830M, which I bought when I was 15 or 16 with my life savings. So I decided to buy a so-called "quad-band" transceiver, a transceiver that covered all MF and HF bands, VHF (50 MHz and 144 MHz), and UHF (430 MHz). I then purchased a second-hand YAESU FT-100D from a well known shop in Asti (Italy), that many of us, Italian radioamateurs, are undoubtedly familiar with. It's a very comfortable radio to use, still valid today, with a few flaws, it's true, but also many advantages. Over the years, some problems have arisen, common to all devices of this type, including a problem with the optical encoder that controls the VFO. It happened that, when continuously rotating the VFO knob, the frequency would vary somewhat in spurts, that is, regularly for most of a complete rotation, then it would lock on one frequency and then resume varying normally. To solve this problem, the simplest thing to do is to replace the VFO's optical encoder, which I found to be a fairly simple operation, certainly within the reach of many radio amateurs with some familiarity with mechanical assemblies. This doesn't require extensive electronics knowledge, as long as you know how to unplug, and plug in back, a connector.
Required Materials
First, we need the spare part. I purchased it a long time ago from the Italian distributor of the Yaesu brand because it was easy for me to quickly get one for another purchase, but you can also buy it from any electronics component distributor. The price is more or less the same, just under thirty euros, if I remember correctly. Be aware that the model you purchase from a generic distributor may not have the connector pre-installed; if you're unable to find and install the connector yourself, buy the official Yaesu spare part, which, as I said, won't cost much more.
The encoder you need is this: COPAL RES20D50-201-1D (instead of COPAL, you might find the NIDAL brand; don't worry, it's the same thing). These encoders were originally made in Japan, but production recently moved to Vietnam.
That's all there is to it with the spare parts. As for the tools, you'll need a Phillips screwdriver. Hear ye hear ye: you don't need a soldering iron!
Recommendation
Hey, I know that when I start with recommendations, I'm as annoying as my old Aunt Rita; read them, don't read them, do what you want, just as long as if something bad happens to your radio, you don't come whining to me... When working on electronic boards, or even just getting within a few inches of them, you must wear primary electrostatic discharge protection, namely the infamous ESD wristband, which must be connected to electrical ground via a power resistor with a resistance between 1 MΩ and 2 MΩ. Furthermore, the surface you're working on must also be "ESD safe," meaning at least static-dissipative, and connected to electrical ground in the same way as the wristband. Finally, the surface should be smooth and soft so as not to scratch or damage the object you're repairing. In short, if you don't already have one, buy an ESD wristband and an ESD mat and connect them to the electrical ground. The resistor should already be included in the kit you purchase. Remember to wear the bracelet properly (the metal part in contact with the skin on your wrist) and always; don't be like me and put it aside at the first opportunity and then forget about it...
Caution: ESD-induced failures aren't always destructive; they often only cause "soft failures," failures that appear sporadically and under certain operating conditions, such as when the DX you've been waiting for your whole life calls your callsign. Again, don't panic: you'll certainly have another chance to connect that ATNO1 in another thirty years, plenty of time to even buy an ESD protection kit in China.
Step-by-step instructions
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- Written by: ik1hge
- Category: Electronics and radiofrequency
- Hits: 18866
We are now talking about a very interesting mounting kit, cheap but, unfortunately, completely undocumented. There are a few web sites managed by smart radio amateurs that make up for the lack of information while, in my small way, I am publishing some pictures of my assembly, together with some personal comments. This Chinese kit does not suite well to new bees but, if you are quite skilled with SMD components soldering, you can build the amplifier even if you are not an RF electronics specialist.
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- Written by: ik1hge
- Category: Electronics and radiofrequency
- Hits: 9230
Almost all of us know that "BAL-UN" is the acronym for "BALanced-UNbalanced", thus we grasp the role of the device that bears the name of "balun" - allow to connect a generator having an unbalanced output (asymmetrical in respect to a reference), as a radiofrequency transmitter with a coaxial transmission line, to a balanced load (symmetrical in respect to the reference), as a dipole antenna or a lot of other kind of antennas, but not a Ground Plane one. The use of a balun let us avoid some drawbacks that would arise if we connected the unbalanced output directly to the balanced input. Actually, a balun is normally bi-directional, i.e. it allows to connect a balanced generator (the same antenna, but now used to receive) to the unbalanced load (the coax connected to the input stage of the receiver), though this function is generally much less promoted in amateur radio literature.
Well, let's come to the point. I've just built a choke bal-un, or current balun (with 1:1 impedance transformation ratio, i.e. it's just a balun, not an impedance adapter). I just want to share the pictures that document my work, I hope that they might be useful to someone else and, why not, that someone will send me his comments and suggestions trough the "Contacts" module of this web site. Honestly speaking, there is nothing new in this article, it just talks about one of the several (thousands? Millions?) realizations of a HF choke. However, I'm sure that nobody would come to this unknown web site by chance, and that most of you are here because you are looking for instructions and pictures to be used as a starting point to homebrew your balun. So, read my article and also some of the other articles that you'll find around on the internet and in the literature. I spent a lot of effort in order to make a tutorial that suits to individuals who don't have specific technical skills, commenting and showing all the mounting operations, including the trivial ones...
Let's build a wide band choke balun for HF, with a good hope that it'll work on 50 MHz band too. We'll realize it with 11 turns of RG-142 coax cable wound on two overlapped toroids, brand Amidon model FT240-43. Why exactly 11 turns? The choice is based on experimental data published by G3TXQ (SK), who gave the figures for 9 turns; in order to compensate a part of the leakage flux due to the much higher stiffness of the RG-142, when compared to the RG-58 used by G3TXQ, which results in less tight turns around the core, I've decided for 11 turns instead of 9. This balun should withstand a power of few kW, but I would not know how to verify that, I can run only 100W
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Needed material and equipment:
- A piece of RG-142 coax, let's say about 1,3 meters. The price is between 7 and 11 Euros/m in a shop (I paid it 5 Euros/m at a fair)
- Two Amidon toroids FT240-43; price about 9-10 Euros each
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One panel mounting female UHF connector (or, if you prefer, panel mounting N type female connector); price starting from 2 Euros
Read more: HF choke balun homebrewing (1:1 current mode balun)
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- Written by: ik1hge
- Category: Electronics and radiofrequency
- Hits: 1996
DANGER: HIGH VOLTAGE MAY KILL YOU!
This article is not for beginners. Specific electrical/electronics education is required as well as experience in the field of medium and high voltage circuits..
Observe all suitable precautions and safety rules. If you are wondering what they are, it means that this project is not for you!
