Kamis, 20 Desember 2012

Tentang SWL

About SWL

SWL or shortwave listening is the reception of public broadcast or amateur radio ham stations in the frequency range 1.8 to 30 MHz (160m to 10m band), also called SW (shortwave) or HF (High Frequency) bands. The combination of receiver, antennas and propagation make SWL an exciting and often technical challenging hobby.This page explains how you can receive shortwave international broadcast, ham and utility stations with a good digital shortwave receiver in the price category of 200 Euro or $250, how to considerably improve its reception by constructing an external wire antenna, how to eliminated noise by properly feeding the antenna to your receiver, and how, when and at what frequency to capture the many stations. With only little technical skills you can build the complete antenna system for less than 100 Euros or $120.
Once you master the basics of SWL, you will enter the exciting world of radio signals that travel around the earth. You will receive the most exotic broadcast stations, capture conversations between radio amateurs from all over the world and get to know the ideal time and conditions to catch the most remote stations.
It is up to you how difficult or expensive you want to make SWL. You could compare it with fishing: catching a powerful 300.000 Watts broadcast station is pretty easy, even when it is located at the other end of the world. Catching smaller stations or amateur radio ham stations, transmitting with a mere 50 Watts, located thousands of kilometers away, can be a true challenge.
Sangean ATS 909X
My Sangean ATS 909X Shortwave Receiver (click to enlarge)
Most SWL's also log the stations they received. This way, they can easily analyze when and at what frequencies they can search for a particular station or radio signals from a particular country. Each new station or country is another trophy for their SWL log. Many SWL's also send signal reports, called SQL cards, to the stations they captured. By reporting the quality and readability of the signal at their location, they help the ham radio amateurs or broadcast stations to assess the quality and performance of their equipment and antennas.
Radio amateurs and some broadcast stations respond to these SQL cards by sending their own QSL card to confirm the signal report. These SQL cards come in all kinds of own designs and colors, but all carry a standard formatted signal report (RST or SINPO). SWL's and ham amateurs often collect SQL cards from all over the world. Amateur radio organizations offer free world-wide SQL postal service to their ham or SWL members. You might consider joining a local amateur radio organization. I'm a registered SWL myself (ONL11714 at UBA Belgian Amateur Radio Society) and whenever I get the change and time, I love to surf the radio waves!
For many ham radio amateurs, listening to shortwave stations was their first acquaintance with amateur radio and a first step towards their ham license. Indeed, SWL is an ideal introduction into ham radio because you get familiar with the ham bands, radio propagation and procedures. However, there are just as many SWL's who never become radio amateur but continue to enjoy discovering the world through radio waves all their live. On the other end, many radio amateurs continue to SWL once in a while, all their live, to sharpen their receiving skills or test new antenna designs.

Selecting a Receiver

There are many shortwave receivers on the market. Unfortunately, many of them are not suitable. Don't buy those 50 Euros or 60 dollar analogue or digital world receivers that promise you the world. They don't! If you're lucky, you will capture a few strong shortwave broadcast stations and some medium or long wave stations. That's it. So, what are the requirements for a decent shortwave radio?
You need a digital tuned shortwave receiver with full coverage of the HF shortwave bands from 1.8 to 30 MHz. Full coverage means that you must be able to tune anywhere in the whole frequency range (many shortwave radio's only tune broadcast bands and skips utility and amateur bands). If you intend to SWL on ham stations, it is essential that, apart from AM, you have SSB (single side band - both LSB and USB). You should be able to set the frequency manually, both from its keyboard and from a rotating tuning dial that includes a fine tuning function. Without SSB and fine tuning it is impossible to capture ham stations, since they do not use the normal AM signal. Its memory - the more the better - should store frequency, fine tuning and mode (AM, LSB, USB). A gain control, to amplify weak signals or attenuate over-modulation or heavy interference, and DSP (Digital Signal Processing) are definitely recommended and sync detection would be really nice.
Finally, your receiver must absolutely carry an external antenna connection (without, you cannot connect a balanced line or transformer). The laws of physics regarding radio waves and antennas are simple: you need large antennas for shortwave (much larger than your FM radio needs to capture music stations) and without external connection your antenna options are very limited. Don't despair, it's easy to construct simple wire antennas that greatly improve reception! We will explain all of this later on. There are several excellent shortwave receiver on the market for a reasonable price from manufacturers like Sony, Sangean, Grundig or Degen. Of course, you could also buy professional receivers from companies like Icom, Elecraft, Yaesu or Kenwood, but this will quickly bring you in the +1.000 price category. It's not my goal to promote one specific radio or brand and it's up to you to select one.
For SWL, I personally use the Sangean ATS 909X which is an excellent and well build radio with all required features. Its reception sensitivity is superior in his price category (I paid 199 Euros) when hooked up to an external antenna. Now, on some Internet forums you'll find people saying the 909X is great, and others saying it is deaf on shortwave?! Well, my SWL logs and videos show that the 909X is far from deaf, but again, don't believe you will receive remote weak ham stations with your whip antenna, whatever brand of radio you buy. Apart from being a great shortwave radio, the 909X provides superb FM reception and sound quality (with RDS/RDBS/PS/PTY/CT), LW and MW bands and plenty external connections (antenna, aux in, rec line out with remote, headphone) and an external power supply with good EMI suppression . The batteries are automatically charged inside the radio. If you have questions about the 909X you can contact me through my web mail.

The Antenna

Most good portable shortwave receivers come with an external antenna. Such antennas are usually a reel with a wire of some 6 meters (20 feet), connected with a 3.5 mm jack to the receiver. This short external antenna will already improve reception considerably and will enable you to capture many broadcast stations and ham stations. However, don't expect miracles with a whip or a short external antenna inside buildings.
If you really want to improve reception on the HF bands, you can easily make you own so-called end-fed longwire (random-wire) antenna. Take a 21,5 meters (70 feet) long thin (0.5 or 1.0 mm) enameled copper wire or any isolated flexible electrical wire and solder it to the tip connection of a 3.5 mm jack. If your receiver has no such external antenna jack (it really should) or you don't have the proper jack, you can connect the wire to the whip antenna with, for instance, an alligator clip. The difference will be remarkable!
Unfortunately, such antennas, directly connected to the receiver, will also increase the reception of noise, especially when used indoors. Buildings are infested with interference signals from TV, computer, light dimmers and many other electrical devices and the electrical wiring acts as a perfect antenna to spread that interference (and the neighbor's interference, thank you) all across your and other buildings. Simply use the whip antenna on your receiver, walk around the house and hold the antenna near working electronic devices. You will understand what we're talking about.
Nevertheless, this simple 21 meters long wire will already make a huge difference. If you don't have the free space to place a large fixed antenna, this is the best option for you. Please note that such simple antenna wires, permanently fixed in open air, can suffer from a buildup of static. Connecting a static charged wire could damage the receiver. It's good practice to connect the jack of such wire antennas a short moment to a grounding or a large metal object to bleed any static before connecting it to your receiver. Prudence is a good habit.
At the bottom of this page you'll find a video of my 909X receiving 40 meter band ham stations with such an antenna, only 2 meters (6 feet) above the ground! Not bad at all, but if you happen to have a nice garden, keep on reading and make yourself happy with a good antenna.

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