THE "PERFECT" ANTENNA MATCHBOX
( ONLY AVAILABLE IN HAM HEAVEN )
Most People Expect Too Much from their Antenna Matchbox . . .
EVERY MATCHBOX HAS A "SWEET-SPOT"
(...but no Matchbox can do everything.)
DEFINITION of MATCHBOX "SWEET-SPOT" - The "Sweet-Spot" of a matchbox is the range in Frequency and Impedance where the INTERNAL LOSS of the matchbox when tuned for a good match to the 50 Ohm transmitter, is LESS THAN 10%.
Matchboxes can also find a "good looking match" outside of their Sweet-Spot. In fact they can usually obtain a good looking match to impedances quite a ways outside of their Sweet-Spot. The only problem is, when working outside of their Sweet-Spot, the matchbox internal losses go up. Sometimes WAY UP.
Often internal losses in a matchbox can reach 50% or even higher!
Pictured below is a Loss-Table of a TYPICAL MATCHBOX.
The green area represents its Sweet-Spot, where internal losses are less than 10%. The orange area is where the internal losses are between 10% and 35%. The red area is where the internal losses are greater than 35%.
- Many people consider the term "Matchbox" (or "Antenna Tuner") as a specific term and believe that all things called that must be more or less the same. NOT!
- In reality, the term "Matchbox" is like the word "Car". It can mean just as many different things as "car" means.
- A Porsche and a Corvette are both great cars.
- A Mercedes "S-Class" and a Lincoln Continental are both grest cars.
- Nobody expects the Continental to be able to do the same things as the Corvette, nor do we expect the Porsche to be able to do the same things as the Mercedes.
- Yet many people seem to think all matchboxes should be able to do everything! How Silly!
- Most people don't know or don't stop and think about how different the task of matching a 160m antenna is to the task of matching a 10m antenna.
- Component values for 160m may be has high as a few thousand pF and 50 uH
- Component values for 10m may be as low as 10pF and 1 uH
- It is virtually impossible to build one single matchbox that can meet both of those requirements effeciently.
- Most people don't know or don't stop and think about how different the impedance of different antennas might be.
- Some antennas such as a short 160m vertical might have an impedance as low as 10 Ohms or even less.
- Yet when trying to load an 80m dipole fed with openwire on 40m, the impedance might be as high as 2K or 3K Ohms.
- It is virtually impossible to build one single matchbox that can EFFECIENTLY match such a broad impedance range.
- When Joe Ham buys a matchbox and finds it won't match his favorite antenna, the first thing he does is blame the matchbox. He never once considers that he may have bought the wrong size shoes and that's why his feet hurt.
If Joe Ham really wants to match everything effeciently,
it may be that Joe needs to buy
two or three different kinds of matchboxes!
ALL GENERAL PURPOSE MATCHBOXES LOOK SIMILAR TO THE CHART ABOVE.
- Some are better on the higher bands, some are better on the lower bands.
- Some are better at lower impedances, some are better at higher impedances.
- NO MATCHBOX IS GOOD AT ALL OF THESE.
THE SWEET-SPOT IS DIFFERENT FROM ONE MATCHBOX TO ANOTHER.
It is wrong to say a matchbox is bad, just because it won't match "your" antenna. That matchbox was probably designed to match something else. You didn't buy a bad matchbox . . .
. . . YOU BOUGHT THE WRONG MATCHBOX !
If a Soccer Mom can't take her 4 boys to the soccer match becaue they won't fit in her Corvette Stingray, does that make the Corvette a bad car? (It's not the car's fault!)
The Trick is to find a matchbox whose Sweet-Spot matches the impedance
of the antenna you wish to match, on the bands you wish to use it on.
IF YOU DO THIS RIGHT, THEN YOU HAVE FOUND THE PERFECT MATCHBOX!
(...but it's only perfect for YOU; maybe not for the next guy...)
In this section of my web site, I will try to help you understand what is important for finding the perfect matchbox for your own personal antenna matchbox requirements.
We will use the ARRL's Antenna Tuner test results, which they have published in QST over the years. There is no need to guess at this, or to take chances with a matchbox. Most of the information is available from the ARRL. You only have to read it and use it for your purchase decisions.