Antenna Tuners - Necessary Evil or Just Evil? - Part I

Nearly every ham who operates HF has an antenna tuner, some have more than one. I do. There is a useful purpose for them, but, they have to be used properly to be an asset. Used improperly, and they can be more trouble than they are worth.

Let's start with the basic idea. If you have a properly designed and tuned antenna, you don't need a tuner. You might need a matching network, but not a tuner.

MFJ 949 Antenna Tuner

What's the difference?

The difference is radiation. What is important is getting your signal out of your radio and into the atmosphere. The objective is to push as much of your signal in the direction you want it to go as possible.

So, the antenna system has two functions. First, to efficiently induce electromagnetic waves into the air. And, second, to couple to the transmitter in a way that will make it happy. No tuner can help with the first function; that is dependent on the interaction of the metal components of the antenna and the atmosphere. But, a tuner can help keep the transmitter happy by allowing it to maximize the transfer of its power to the antenna metal.

Make no mistake, you cannot determine the effectiveness of an antenna by measuring the SWR. You could tune a lightbulb to 1:1 SWR pretty easily, but you won't make many contacts on a 100w table lamp.

Let's look at another example. What about using a tuner to allow a 6 meter dipole to be used on 80 meters? You could probably use a tuner to match the transmitter to the antenna, but a 6 meter beam may not be able to couple 80 meter RF into the atmosphere very efficiently. Just because you can match it doesn't mean it is going to radiate. In fact, in this example, the feed line may be doing more than the antenna elements themselves.

As an former broadcast engineer, I miss the Field Strength Meter in tuning antennas. SWR is not an important measurement in a broadcast transmitter, especially in one operating under 30 Mhz. There are things other than SWR that will indicate mismatch problems. But, measuring exactly how much of your RF is going in what direction is critical. So, broadcast engineers get off their duff, and head out into the world with a meter that measures the relative strength of your signal in various directions at various distances.

I will go into some techniques for measuring your radiation pattern in Part II, but suffice it to say that the key to using field strength measurements is maintaining a database of measurements. For now, just be aware of the value of knowing how your antenna systems interacts with the environment.

EmComm - The Prime Directive

It has been said many times in many places, but it bears repeating, the essence of amateur radio is emergency communications. Let’s quote from the FCC Rules, Part 97,

§ 97.1 Basis and purpose.
The rules and regulations in this part are designed to provide an amateur radio service having a fundamental purpose as expressed in the following principles: 
(a) Recognition and enhancement of the value of the amateur service to the public as a voluntary noncommercial communication service, particularly with respect to providing emergency communications. 

Couldn't be clearer, the Prime Directive for the Amateur Radio Service is emergency communications, EmComm. And, amateur radio has a proud history of serving the public in times of crisis. It is not necessary to recount all the times that ham radio has been a vital part of emergency response; it is so common as to be in danger of being taken for granted.

The question is, what are you doing to support the Prime Directive? Checking into weekly traffic nets is a good start, but there is far more you can do to support the cause.

What can you do?

For starters, make a plan. You should look at emcomm from two perspectives - as a giver of aid and as one affected by a disaster. Every ham has the potential to play either of these roles. A situation in a nearby community might need your support. You might be called on to go into the area and help with communications, or you might be asked to handle traffic or provide situation awareness information from your home.

Either way, you need to plan ahead. Pack a Go Bag, loaded with the things you might need. Don't wait until a disaster hits, do it now! Remember to pack not only radio gear you will need, but also things for your own sustenance.  I will detail my own plan in a future blog, but most of it is common sense. Just remember, you might find yourself in a situation where you need to be able to operate for 24-48 hours without outside aid. Hint, get, or make, some MREs.

Next, get your act together for when you might find yourself in a situation. Is your shack capable of operating without commercial AC? What about antennas? If your tower goes down, can you get back on the air? Make yourself some wire antennas - a VHF/UHF twin lead J-Pole can be very valuable and a G5RV for hf all wound up, ready for action, could be life-savers.

I will cover these topics in detail in future blogs, but don't wait on me, or anyone else for that matter. Get planning and acting now and you will be on the way to fulfilling the Prime Directive.

160 Meters - Size Matters

Drake L7 Linear Amplifier

Last year, I participated, or tried to participate, in the CQ Magazine 160 Meter contest. I used my Icom IC-756proIII radio into an inverted L antenna with a counterpoise. I ran barefoot with the 100w of the ProIII because my aging Drake L4B won't tune 160.

It was an exercise in frustration. Many of the weaker stations I tried to call couldn't hear me all that well, so multiple efforts were required. And, I just got buried by all the big signals.

This year, 2013, I bought a Drake L7, a later version of the L4B, that does full 1.5kw on 160. I like tube amps for a variety of reasons, but probably due to my background in broadcast engineering 35 years ago, the 3-500Z triodes were very common in drivers for AM transmitters. I know them to be efficient, hardy and, they glow. The only time solid state amps glow is when they melt down.

I had a much different experience this year, and worked nearly every station I could hear. I even tried a couple of CQs, and, at one point, had a bit of a pile up by stations wanting South Carolina. Same antenna, 9 db more power out.

Lesson learned - If you want to play with the big boys, you need big toys!

In Praise of Service Monitors

HP/Agilent 8924C Service Monitor

I like to fiddle with gear and antennas, so I have always dreamed of having a bench full of sophisticated, lab grade test equipment. What red-blooded tinkerer has not? My dream is to have a wide-band scope, an accurate RF generator, a multifunction AF generator, a wattmeter, frequency counter and lots of other gear. Throw in a sensitive receiver that goes from 30 Mhz to 1 Ghz, all modes, and you have the real deal. Oh, and a spectrum analyzer would be just dandy, as long as we are dreaming.

Trouble is, as you research the cost, each of these beasties can cost hundreds of dollars. And the amount of bench space they take up is mind boggling. Then, I discovered service monitors. A new one will set you back $25,000 and up, way up! But, after a bit of research, I found the HP/Agilent 8924C Service Monitor. This is an older piece of equipment, designed to serve the needs of the cell phone industry. It is computer controlled and has lots of features that are specific for the technical needs of CDMA cell phones.

8924C Display

But, but, but -- This baby is loaded with features that hams can use. In fact, it includes all the test gear I have mentioned so far, and a few others. It is programmable, so if you have a software bug (pun intended), you can create your own combinations.

Let me tell you what I have done with it in the few months I have had it. I fixed a UHF transceiver that was not putting out power. I set up 3 repeaters, including tuning the cavities. I have measured the output and frequencies of several dozen UHF handhelds I am working on. I also measured the sensitivity of the receive section. I plotted the SWR curve of a VHF/UHF J-pole antenna I built (needs some more work). And, just for kicks, I use it to tune around the HF, VHF and UHF bands, up to 1000 Mhz with great sensitivity. I can measure the tones generated by local repeaters.

Fantastic and unbelievable! What's that? How much did it set me back? $850 including shipping, and it weighs over 60#. There are variations of the HP/Agilent series of monitors, but the 8924C is the most complete. I did have to upgrade my input section, which was a maximum of 5w, to 100w (60w continuous). That cost another $125. I am under $1000 and it works perfectly. It is capable of doing much more than I am capable of doing with it. There is a learning curve, but there is lots of good info on operating these, including videos. Just plug 8924C into YouTube and you will find many good videos.
Here are a few:
Duplexer Tuning
HP 8920A Service Monitor and AW07A Antenna Analyzer
RX 40 meter band 7.075 Mhz SSB on HP 8920A Service Monitor
1 - RF Tools Antenna Return Loss.mp4