RADIO HABANA CUBA
ANTENNA TUNERS:
Are They So Important?BY ARNIE CORO
Host of "Dxers Unlimited"SEND YOUR COMMENTS, QUESTIONS AND IDEAS DIRECTLY TO ME AT: arnie@radiohc.org
YES, THEY ARE.... as my first grade English teacher made the whole class repeat after her...
So.. repeat after me... Antenna tuners are important. As a matter of fact, a well-designed antenna tuner is my number one choice for the second item to be bought by a newcomer to the hobby, after the HEADPHONES!!!Now, how can someone who is just starting to learn about shortwave propagation, how to QSL, how to fight the high noise levels causing interference etc., tell what a "well-designed antenna tuner" is?
FOLLOW ME... and you will be able to either select a nice tuner from the many high quality, well built units now available in many countries... or, perhaps you may want to build your own following an article soon to appear here at this WEBSITE...
Let's say you want to buy yourself an antenna tuner. Then you should ask some questions about the future of your radio hobby activities...
In many cases, when consulted, I recommend buying an antenna tuner that may be used for transmitting too... as it is not too rare to have someone starting in the Short Wave Listening hobby to end up with an amateur radio license too...
And... tuners built for the typical 100 watt class ham transceivers usually have higher quality, more rugged components than tuners intended for the SWL 's.
One thing you will want when buying an antenna tuner is to be really sure it has a really wide matching capability... avoid tuners that have very few taps on their coils, and those that have taps marked only for the ham bands...
Today's typical antenna tuner uses a circuit which, honestly, I don't like at all.... It may be very convenient for manufacturers,it may match to reasonable loads... but the T, yes the letter T, network tuners are not as good as other types from an engineering point of view.
Now, this doesn't mean that they are not going to be extremely useful in most cases... BUT, the fact is that a PI network, form the Greek Letter PI (the famous 3.1416...) is a much better approach.
Antenna tuners using ROLLER COASTER variable coils are better than those using fixed coils with TAPS selected by a switch... BUT, once again, a ROLLER COASTER tuner will be much more expensive than the simpler tapped coil type.
For your first antenna tuner, your friend Arnie Coro will recommend a tuning range of from 3 to 30 megahertz... That will take care of 99 percent of your listening, leaving only the segment from 1.6 to 3.0 megaHertz without coverage.
A standard T network tuner for the amateur bands MAY or MAY NOT work on the international shortwave broadcast bands.. It will depend on the taps of the coil and the maximum and minimum capacity of the two tuning capacitors used in that circuit.
SO... you must look around for an ANTENNA TUNER that will offer full range coverage from 3 to 30 megaHertz, or in a somewhat smaller range from 6 to 30 megaHertz.
CONNECTORS AND CABLES: VITAL TO TUNER OPERATION
Once you have your antenna tuner, then you must install it between your receiver and the antenna system.
This is done with coaxial cables and connectors in practically all cases. Some single wire antennas like the Inverted L, connect to a single terminal at the tuner's input, but do require a GROUND CONNECTION to be made.
A coaxial cable fed TTFD, Dipole, Vertical, or any other type of antenna, connects to the tuner via a coaxial cable, so you must prepare the cable's end to use the same connector used by the tuner's input. >From the tuner's output to the radio, you must also run a coaxial cable, making sure that both the center conductor and the shield or braid are properly soldered...
If you don't do things properly, the antenna tuner's performance may be downgraded significantly. SO... be sure that the interfacing between ANTENNA and TUNER and between TUNE and RECEIVER is done properly.
For receive-only installations you can use the very easy to work with RG58U cable to go from the tuner to the receiver. For the antenna downlead, you may can use RG58U or RG59U for runs of about 30 meters (100 feet), and the heavier and less lossy RG213 or RG11U for longer runs.
HOW TO USE THE ANTENNA TUNER
You must learn how to operate the tuner... something that for the typical RECEIVE-ONLY installation is not very difficult at all...
The T network tuner has three controls, the input capacitor, the coil (either tapped or roller coaster) and the output capacitor... All you need to do is play with the three controls for best possible reception... which can be done in several different ways...
For example you may tune the receiver to an empty frequency, then select a coil tap or roller coaster position according to the frequency, and then play with the two capacitors to obtain MAXIMUM NOISE at the receiver...
You may also try this other way... look for a WEAK station, a really weak one, and play with the controls to obtain better reception... don't try this approach with a STRONG signal, as the subtle changes will not be noticeable.
Then, there is a much more "scientific" way of TUNING THE TUNER... which is only applicable to the amateur bands... You simply transmit a signal on the ham frequency and tune the tuner for minimum standing wave ratio, as indicated by an SWR bridge.
My experience shows that even the simplest of T network tuners will help shortwave reception quite a bit, helping to reduce and sometimes eliminate out of band signals from getting into the receiver's input circuits (the cause of some very upstetting crossmodulation problems ).
Antenna tuners may be designed for asymmetric input only... in which case, when you want to use a balanced feedline, a BALUN must be used. This means that the BALUN must be installed between the balanced antenna and the unbalanced antenna tuner input.
For the beginner's first antenna installation, I don't recommend using an open wire balanced line, do use coaxial cables and keep things simple.
Medium sized digital readout portables seem to benefit a lot when an antenna tuner is connected ahead of them... between the antenna and the radio... Receivers like the SONY ICF2010, the Grundig Satellit 700, Realistic DX440 and similar types show a significant improvement when even a very simple tuner is used. And the improvement is much more dramatic with still smaller and lower cost shortwave receivers... As a matter of fact, a simple T network tuner will allow you to use one of those extremely low cost radios with amazing results.
Havana, Cuba
21 December, 1997COMING UP HOW-TO here on the "Dxers Unlimited" WEB page:
"How to build Arnie Coro's PI network antenna tuner family all by yourself!"
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