I created this web page, not as much for you as for me. I wanted a place to store all my ham radio information, links, etc. This page is the result of my selfish effort. But, isn’t that the essence of the web – to share information?

Feel free to explore, comment and link to this blog. Or, better yet, contribute something!

Wednesday, March 20, 2013

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.

Monday, March 4, 2013

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.