Hi Friends:
Welcome to Tech-Talk. This is a series of articles that has appeared in my newsletters for the past several years. Until now, it has been available only to subscribers of the newsletter. I've decided to make it available to anyone who cares to read it.
My aim is to simplify some often complex topics to give you the information you need in an understandable format. I'll state right up front that I have no formal electronics training; nor was I born knowing all this stuff! When I was first licensed in 1989, I knew almost nothing about antennas, feedine, SWR, decibels, or DC Power. What follows are things I've learned by experimentation and observation, along with a good bit or reading.
These articles, and this entire site, are Copyright Quicksilver Radio. Please feel free to link to it, but please do not copy and paste it into other Web Sites.
Thanks and 73,
John Bee N1GNV
2. What is SWR?
Tech-Talk
Part 1
Hi friends,
As promised, here's the first installment in a series of discussions on SWR, antennas, feedlines, and related topics.
My aim is to give you some solid information based on facts, and to dispel some of the myths, old wives' tales, and just plain bunkum I hear regularly on the air and at Hamfests. No heavy-duty theory, and I'll keep the math to an absolute minimum. Some of the topics we'll explore include:
Part 1
Hi friends,
As promised, here's the first installment in a series of discussions on SWR, antennas, feedlines, and related topics.
My aim is to give you some solid information based on facts, and to dispel some of the myths, old wives' tales, and just plain bunkum I hear regularly on the air and at Hamfests. No heavy-duty theory, and I'll keep the math to an absolute minimum. Some of the topics we'll explore include:
3. You Can Tune an Antenna, But You Can't Tuna Fish
Tech-Talk
Part 2
Welcome Back!
Last month we talked about what SWR is. This month we'll explore why we care about it, and what we do about it. If you need to refresh, or are new to the list, previous installments are located below this one.
Modern transmitters are designed to operate into a 50-Ohm resistive impedance. We use 50-Ohm coax, a 50-Ohm antenna, all of our power radiates, and the transmitter is happy. But when the load is something other than 50 Ohms (in other words, the SWR is greater than 1:1, problems can arise. If the mismatch is bad enough, our solid state final amplifier stage can easily overheat and self-destruct. So our radios include a protection circuit that lowers the output power as SWR increases. The circuit generally kicks in at somewhere between 1.5:1 and 2:1 SWR.
So how do we lower the SWR and regain full output power? There are several ways.
Part 2
Welcome Back!
Last month we talked about what SWR is. This month we'll explore why we care about it, and what we do about it. If you need to refresh, or are new to the list, previous installments are located below this one.
Modern transmitters are designed to operate into a 50-Ohm resistive impedance. We use 50-Ohm coax, a 50-Ohm antenna, all of our power radiates, and the transmitter is happy. But when the load is something other than 50 Ohms (in other words, the SWR is greater than 1:1, problems can arise. If the mismatch is bad enough, our solid state final amplifier stage can easily overheat and self-destruct. So our radios include a protection circuit that lowers the output power as SWR increases. The circuit generally kicks in at somewhere between 1.5:1 and 2:1 SWR.
So how do we lower the SWR and regain full output power? There are several ways.
4. SWR Meters Can Make You Stupid
Tech-Talk
Part 3
Welcome to Part 3 of our discussion.
As promised, this month I have some rather eye-popping information for you. We're going to see why your SWR meter can lie to you. Or as another fellow says, "SWR meters make you stupid."
The material in this section was prepared using 2 programs from the ARRL Antenna Book CD. Roy Lewallen, W7EL's EZ-NEC antenna modeling program was used to get the basic antenna data. That info was fed into Dean Straw N6BV's Transmission Line for Windows (TLW) analysis program. If you like to play with antennas, both programs are great tools.
Using EZ-NEC, I "built" a 40 meter dipole at about 33 feet high. As expected, the SWR was about 1.6:1 at the center of the band and below 2:1 at the band edges. Then I opened TLW, specified 100' of RG-8X coax as the feedline and added the feedpoint impedance (77 -j13) calculated by EZ-NEC. TLW calculated the total loss in the coax as just under 1 dB. Most of that was the inherent ("matched line") loss in the coax. The slight SWR mismatch added just a 10th of a dB to the total. None of this was surprising; it's basic antenna theory. But read on...
Part 3
Welcome to Part 3 of our discussion.
As promised, this month I have some rather eye-popping information for you. We're going to see why your SWR meter can lie to you. Or as another fellow says, "SWR meters make you stupid."
The material in this section was prepared using 2 programs from the ARRL Antenna Book CD. Roy Lewallen, W7EL's EZ-NEC antenna modeling program was used to get the basic antenna data. That info was fed into Dean Straw N6BV's Transmission Line for Windows (TLW) analysis program. If you like to play with antennas, both programs are great tools.
Using EZ-NEC, I "built" a 40 meter dipole at about 33 feet high. As expected, the SWR was about 1.6:1 at the center of the band and below 2:1 at the band edges. Then I opened TLW, specified 100' of RG-8X coax as the feedline and added the feedpoint impedance (77 -j13) calculated by EZ-NEC. TLW calculated the total loss in the coax as just under 1 dB. Most of that was the inherent ("matched line") loss in the coax. The slight SWR mismatch added just a 10th of a dB to the total. None of this was surprising; it's basic antenna theory. But read on...
5. Ladder Go, Boys
Welcome to Part 4 of our discussion.
In Part 3, we discussed the advantages of using ladder line to greatly reduce feedline loss. You can reread it if you like, just below this section.
Using ladder line does come with a few challenges, however. Unlike coax, it cannot be coiled, run on the ground, or buried, without paying a price in performance. And most importantly, it does not like to be near other conductive objects. Ladder line is -- in theory, at least -- a balanced feedline. That means that the currents in each conductor at any given point are equal in magnitude (voltage) but 180 degrees out of phase. When that happens, the RF fields in each leg cancel each other out, and the line does not radiate. That's generally what we want. But...
In Part 3, we discussed the advantages of using ladder line to greatly reduce feedline loss. You can reread it if you like, just below this section.
Using ladder line does come with a few challenges, however. Unlike coax, it cannot be coiled, run on the ground, or buried, without paying a price in performance. And most importantly, it does not like to be near other conductive objects. Ladder line is -- in theory, at least -- a balanced feedline. That means that the currents in each conductor at any given point are equal in magnitude (voltage) but 180 degrees out of phase. When that happens, the RF fields in each leg cancel each other out, and the line does not radiate. That's generally what we want. But...
6. Losing Our Balance
Tech-Talk
Part 5
Welcome to Part 5 of our discussion.
In Part 4, we talked about practical installation of ladder line. You'll find that section (and all of the other parts) right below this one.
This month, we're going to take a first look at baluns -- what they do, why they are (sometimes) needed, and perhaps most importantly, how to pronounce "balun" so you don't sound like a lid.
Very simply, baluns match a balanced antenna -- like any typical dipole or loop -- to an unbalanced feedline, most often coax cable. Hence the name: BAL (as in balanced) + un (as in unbalanced) = BAL-un. Not "BAY-lin". "Not buh-LOON". BAL (rhymes with Hal and Sal) un (pronounced like the "en" in fallen. Now you know.
Okay, what do we mean by a balanced antenna?
Part 5
Welcome to Part 5 of our discussion.
In Part 4, we talked about practical installation of ladder line. You'll find that section (and all of the other parts) right below this one.
This month, we're going to take a first look at baluns -- what they do, why they are (sometimes) needed, and perhaps most importantly, how to pronounce "balun" so you don't sound like a lid.
Very simply, baluns match a balanced antenna -- like any typical dipole or loop -- to an unbalanced feedline, most often coax cable. Hence the name: BAL (as in balanced) + un (as in unbalanced) = BAL-un. Not "BAY-lin". "Not buh-LOON". BAL (rhymes with Hal and Sal) un (pronounced like the "en" in fallen. Now you know.
Okay, what do we mean by a balanced antenna?
7. And Regaining It
Tech-Talk
Part 6
Welcome to Part 6 of our discussion.
Last time, we started to look at Baluns. Recall that their purpose is to help to match a balanced antenna (like a dipole) to an unbalanced feed line (like coax). They do this by choking off RF current trying to flow down the outside of the coax shield, forcing equal and opposite currents to flow on the center conductor and the inside of the shield. Baluns can be easy to make...
Part 6
Welcome to Part 6 of our discussion.
Last time, we started to look at Baluns. Recall that their purpose is to help to match a balanced antenna (like a dipole) to an unbalanced feed line (like coax). They do this by choking off RF current trying to flow down the outside of the coax shield, forcing equal and opposite currents to flow on the center conductor and the inside of the shield. Baluns can be easy to make...
8. More Unbalanced Ravings
Tech-Talk
Part 7
Welcome to Part 7 of our discussion.
I was going to start talking about coax this time, but I received two questions from readers that I think bear answering here.
Rich from Connecticut asked "If my coax is 50 Ohm, and I'm connecting it to 450 Ohm ladder line, doesn't that mean I should use a 9:1 Balun? Back a long time ago when I was in school, 50 x 9 = 450, and I don't think that's changed". His math is correct, but...
Part 7
Welcome to Part 7 of our discussion.
I was going to start talking about coax this time, but I received two questions from readers that I think bear answering here.
Rich from Connecticut asked "If my coax is 50 Ohm, and I'm connecting it to 450 Ohm ladder line, doesn't that mean I should use a 9:1 Balun? Back a long time ago when I was in school, 50 x 9 = 450, and I don't think that's changed". His math is correct, but...
9. "Coax"-ing the Best Performance
Tech-Talk
Part 8
Welcome to Part 8 of our discussion.
We've talked quite a bit about ladder line over the past several months. And it certainly has its advantages, in many cases. However, a lot of folks prefer the simplicity of coaxial cable ("coax") and to be sure, 99.99% of modern radios have a coax connector for the antenna. So we'll take some time discussing coax -- what's available, and what are the advantages/disadvantages of each.
As with most things, selecting the proper coax means balancing several often conflicting factors. The most significant are size/weight, loss, cost, and convenience. Other considerations are power handling, flexibility, and the type of installation. Here are some things to consider...
Part 8
Welcome to Part 8 of our discussion.
We've talked quite a bit about ladder line over the past several months. And it certainly has its advantages, in many cases. However, a lot of folks prefer the simplicity of coaxial cable ("coax") and to be sure, 99.99% of modern radios have a coax connector for the antenna. So we'll take some time discussing coax -- what's available, and what are the advantages/disadvantages of each.
As with most things, selecting the proper coax means balancing several often conflicting factors. The most significant are size/weight, loss, cost, and convenience. Other considerations are power handling, flexibility, and the type of installation. Here are some things to consider...
10. The Death of Ham Radio?
(not exactly) Tech-Talk
Part 9
Welcome to Part 9 of our discussion.
This month I'm taking a break from the Technical discussion. I have some thoughts to share that I hope you will find interesting and useful... or at least, thought-provoking.
I think most of us have heard some old-timer whining about the death of Hamfests, and Ham Radio in general.
Don't you believe it, my friends! Here's why....
Part 9
Welcome to Part 9 of our discussion.
This month I'm taking a break from the Technical discussion. I have some thoughts to share that I hope you will find interesting and useful... or at least, thought-provoking.
I think most of us have heard some old-timer whining about the death of Hamfests, and Ham Radio in general.
Don't you believe it, my friends! Here's why....
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