RF Grounds

How many times have you heard Hams refer to an "RF Ground". It's as if there's some mythical connection to which you can connect and that will magically absorb RF and dispense with it in a way that affects nothing else.

What I really find surprising is the "lengths" (literally) Hams will go to connect their stations to these magic RF grounds. It's as if the laws of physics that govern RF and conductors are suspended when you call it a "ground". Simply connect a copper strap or heavy gauge wire to this "RF ground" and stray RF is a thing of the past. Never mind how many wavelengths it is to that single 8' ground rod or how much inductance there is at the operating frequency.

Hey, it's an RF Ground!

Counterpoise

How many of us would spend good money and time to setup an antenna and only bother to do 1/2 the job? Well, it seems that many of us do.

Enter the "counterpoise". It's the "other" half of many antennas you don't have to worry much about--right? Just make it about 5% longer and toss it out on the ground (earth this time guys) and you're set, right? -- Wrong.

The ugly stepchild of many an antenna is actually part of your antenna, so don't insult it by calling it a "counterpoise". That part of your antenna will contribute loss, affect your antenna's pattern, and will inject noise into your receiver.

Let's all honor the dignity of both sides of our antennas!

Half-wave End-Fed

Nope, I didn't miss anything in the name of this section. The "Half-wave End-Fed" antenna is really a myth in and of itself.

You've seen the adds and heard the claims--you don't need a counterpoise (there's that word again) with this type of antenna because it's fed at a "High-Z" point on the antenna. It's as if the minimal current at that point in the antenna negates all good sense. If you think there's nothing on the "back-end" of the antenna feed-point, why do you even bother with the antenna at all. Hey, it's a "High-Z" point in the antenna!

If you haven't sorted it out by now, let me spell it for you. There is no such thing as a "Half-wave End-fed" antenna because you simply can't feed it against nothing. Since you need something more than nothing, the antenna is more than just a half-wave length of wire. If you think it's Ok because it's High-Z, then what the heck is the deal on the "antenna" side of that feed? Same rules apply!

So, should it be called a "Half-wave and a Half End-fed", a "Half-wave and a bit more End-fed", perhaps a "Half-wave and a quarter End-Fed" (or is that really a "Half-wave End-fed and a quarter)"?

Remember that "counterpoise"? If you still think there's really a functional "Half-wave End-fed" antenna, then read the part about a counterpoise above.

(Half-Wave End-fed epilogue)

I know, you know people who have been using these antennas for some time and perhaps you've used them yourself. You know it works and you're convinced I'm all wet on this because you don't have any more antenna than that. Well you do, it's your transmission line, your radio, the power cable connected to it, and even YOU if you're holding the microphone or the radio. But wait (I love that), you have a common-mode choke or balun at the antenna, so what does the transmission line have to do with it? The answer is simple, it's (you guessed it) that very High-Z that seems to make it a magic antenna that's convoluted your intent to isolate your feed-line. I'll let you sort it out.

Antenna Tuners Don't Really Tune Antennas

If I hear one more Ham say "Antenna tuners don't really tune antennas, they just make the radio think it's OK", I'll scream. If that was the case, then the same is true of the loading coil at the base of your antenna (or perhaps in the middle) and of the tank circuit at the output of your tube amplifier.

Oh, but those are different situations you say. Really? So if I put a shield around that loading coil at the base of the antenna does that now mean it's not really affecting your antenna? If I move it a few inches or feet away from the antenna elements is it really something different? If I move it all the way back to the transmitter, is it now something really different? You make the call.

The key is in the transfer of power and matching the source to the load (antenna). If you ever adjusted the Load and Tune on your amplifier while watching a power output meter you know what I'm talking about. If all antenna tuners do is make the transmitter happy, then tell me why the amp's tank circuit isn't an antenna tuner.

OK, perhaps the term "antenna tuner" is a problem. Might be better to call it an "antenna system tuner" or a "complex impedance matching device". But then Hams like confusing terms (grounds, counterpoises), so what the heck!

Send your cards and flames

I just started this section, so I haven't had time yet to add Hamisms for other areas of Hamdom. They're in there rolling around in my head, but the couch is calling to me. So are some people on the radio, but there's one basic law of Ham radio most Hams don't know -- You don't always have to answer when someone calls you on the radio!

Chuck - N8DNX

Ground Mobile Radio to Chassis

Here's one I really don't understand, and it involves more than what the title implies.

The statement usually comes something like this. "Don't forget to ground everything to the car chassis including the antenna and radio." Really? Why would one do that?

When I ask that question often the response relates to chassis being the best ground in the vehicle or something about being the closest to the actual ground under it. The problem is that doing this violates all the basic principals at work in a Ham station.

Sure, the chassis might be a good DC ground but that really doesn't have much to do with RF, does it? If you've read some of my comments above, you already know that I advocate RF staying at the antenna where it can radiate. So what does running a ground wire from the antenna to the chassis accomplish when it has length, has inductance, and presumably has current? I'll tell you what it does, it creates an additional RF path and radiator that becomes another part of your antenna and does so in an unpredictable way and therefore may actually impair operation. It also encourages RF to flow on the chassis and everything the "ground" wire passes and therefore to couple into other cabling below the vehicle.

Next, what does grounding the radio to the chassis do? It provides yet another means for stray RF to find a way into the inside of the vehicle and to the body of your radio. Why would anyone want that? It does this in ways that are highly unpredictable because with RF everything changes with frequency. Things could be perfect for weeks, months, or years, but then all of a sudden there's problems. Could it be that the operator hasn't worked that frequency before?

What to do, what to do... The first thing is to consider what constitutes the antenna. If you have a whip antenna of some sort, the vehicle is the other half of your antenna (and it's an active half at that). What part of the vehicle do you want to be that part of the antenna? Unless you have a sporty fiberglass go-fast car (in which case all bets are off), it's the outside of the vehicle body. That, along with the whip, is where the RF should go and from where it should radiate and not cables running around pretending to be "grounds" and the things to which they connect.

My advice is to make sure as much of the outside of the vehicle is bonded together (for RF), that the coax feeding the antenna is terminated is some way to the OUTSIDE of the body, and that any other cables running away from the antenna or near it have chokes to prevent RF from doing nasty things. That includes the transmission line and antenna control lines where they leave the antenna and the power cables for your mega-power after-market driving lights (or for some hams, extra emergency flashers). And where those cables enter the vehicle, please... please... please put chokes on them to keep the RF out of the vehicle.

One last note on connecting the coax shield to the body. Try to do that on an OUTSIDE surface and definitely don't run that ground down into the trunk to tie onto so nice spot INSIDE the vehicle. If you ask why, you're not listening. I know, it's sometimes hard to do that without putting a big ground bolt through the paint on your fancy new car, so look for things like luggage rack mounts or perhaps even something on the body lip just under the edge of a trunk or door and MOUNT YOUR ANTENNA THERE!

Now for the test question:

When is a ground wire not an RF ground? ... When it has length and there's current!