of Contents]These articles are scanned and OCRed from old editions of the
ARRL's QST magazine. Here is a list of the
QST articles I have already posted. As time permits, I will
be glad to scan articles for you. All copyrights (if any) are hereby acknowledged.
is a good old fashion Q & A session on Ham radio topics... with the emphasis on 'old.' QST
magazine published a couple of these columns in the 1960s, and this is the second in the series.
I didn't read anything that wouldn't be applicable today, especially if you have some vintage
gear. As with most such articles, there is something to be learned by just about anyone who deals
with electronics, especially in the RF realm. One particularly interesting part is where the author,
in response to a question about building and tuning your own radio, states, "Too many beginners
are concerned about making 'Chinese Copies' of [manufactured] equipment described, even down to
the same placement of nuts and bolts." Little did he know then that nearly every piece of equipment
purchased new by Amateurs nowadays would actually be made in China and not in the USA. ...
(this link goes to a Mork & Mindy video clip)
all available vintage QST articles
Beginner and Novice
More Problems - More Questions and Answers
By Lewis G. McCoy, W1ICP
The answers to some of these questions may prove helpful to you, both in time and trouble. It's
useful information, so read on.
Some time back, we had a question-and-answer article1
on problems that are common to
many newcomers. Since then, a new batch of questions has been collected, and the answers may be
of help to hams with similar problems.Q.
"I am using an 18-foot vertical antenna, ground-mounted on my front lawn where it is subject to
being touched or contacted by children.
How much of a safety heard is this if a person
touches it while I am transmitting? What is the danger, if any, at 75-watts input against what
it might be at one kilowatt, and are some bands less of a hazard than others?"
First and foremost, any antenna or feed line should be installed so as to be protected from
any physical contact. The antenna or feed line can present a very serious hazard. There is always
radio-frequency energy present on an antenna when transmitting. While r.f. is rarely present in
a degree that could be considered lethal, even at a kilowatt level, very severe r.f. burns can
For the benefit of the newcomer to amateur radio, r.f. voltages will not give you
an ordinary electrical shock but will cause a penetrating burn or actual "cooking" of the flesh.
Such a burn is slow to heal. The greater the power the larger the amount of r.f. energy present
on the antenna. However, it is possible to get a nasty r.f. burn even when running relatively
low power, such as 50-watts input, and on any band.
Still another hazard is that of getting
an electrical shock from the antenna. Fig. 1 shows the typical pi-network tank circuit which is
common these days. C1
is the blocking capacitor which permits r.f. to flow from the
plate of the tube to the pi-network tank circuit and thence to the antenna. C1
the plus-B voltage from being on the antenna circuit. If C1
should short out - and
it is not a rare occurrence for capacitors to short - the plus-B voltage will flow out the feed
line to the antenna. Anyone coming in contact with the antenna could be electrocuted.
method of protecting against this is to install an r.f. choke between the output lead and ground,
as suggested at RFC1
in Fig. 1. If the blocking capacitor shorts, the plus-B will be
shorted to ground via the choke and the fuse in the transmitter power supply will blow.
Build a fence around your antenna or put the antenna up in the air where no one can touch
it. If you are doing antenna work yourself, be sure the power is completely off in the rig. If
you have insurance, such as the home-owner's type, be sure to read the fine print. Certain restrictions
on amateur stations are laid down by the National Electrical Code and your insurance could be
void if you don't comply with the code. Your local library or building inspector's office will
have a copy of the wiring code so it would be a good idea to check. (Along the same lines, although
not pertinent to the question, if you have a tower and think you have it insured, you had better
check to make sure. In many homeowners' policies a separate rider is required for adequate coverage.)
Q. "None of the articles on
transmatches I have read in QST, the Handbook or elsewhere, have ever mentioned shielding of such
circuits. Photos invariably show a chassis and a front panel but no signs of an enclosure behind
the panel. This is surprising since stress is usually placed on shielding transmitters, especially
around the output circuits. Do transmatches require shielding or don't they?"
The answer is no, they don't.
It is true that transmitters require extensive shielding to prevent radiation of harmonics that
could cause TVI. Once the transmitter is shielded there is only one way for harmonics to get out,
and that is via the antenna terminal. Any harmonics coming out of the transmitter should be attenuated
by use of a low-pass filter. In such a case, it will make no difference if the transmatch is shielded.
There are no harmonics reaching the transmatch so there is no point in unnecessary shielding.
If you have harmonics that could cause TVI they must be kept enclosed within the transmitter and
suppressed with a filter.
the other hand, a transmatch is useful in suppressing the lower-frequency harmonics - those that
can cause problems by interfering with other services than television. Because the transmatch
is a selective circuit tuned to your operating frequency, it will present a load to the transmitter
that is optimum for the operating frequency but is not optimum for the harmonics. Therefore, harmonics
will be attenuated through the transmatch. But in either case, low-frequency or TVI harmonics,
the transmatch doesn't require shielding.Q.
"My rig was working OK, as I was making contacts. Now, all of a sudden, I can't work out at all.
Can you tell me what is wrong or what to check? The rig loads up into a light bulb OK and the
antenna seems to be the same."A.
There are several possibilities in such a case. First and most important is to make sure
that you are transmitting and listening on the same band. Believe it or not, many Novices think
they are tuning up on the right band when actually the output is on another. You can spend a lot
of frustrating time by calling on 40 while listening on 80!
One method of checking is to
use a wavemeter to make sure that you are on the right band. A recent QST article2
had the construction details for a simple wavemeter and s.w.r./output-indicator combination, which
leads us to another point.
Without such an indicator it is possible for a rig to be tuned
up in what appears a normal manner when, in fact, there is no power going to the antenna. You
could have an "open" or "short" in the feed line and not know it, if you have no means of checking.
The simple device mentioned above contains a reflectometer which monitors both the standing-wave
ratio and the output. If something goes wrong in the antenna or feeders, the s.w.r. should show
a change from the normal reading. On the other hand, if something happens in the transmitter,
this would show up as a change in the output, as indicated by the meter in the device. We highly
recommend the use of a combination instrument that shows which band you are tuned to, the match
in the system, and the output, because by simple elimination you can quickly pinpoint your troubles.
Q. "I recently passed my amateur
exam. I have been a CBer and I was wondering if it is possible to use my CB beam on an amateur
band. It is a 3-element job with the elements in a vertical plane."
While this isn't a common question,
the answer is worth passing along to hams who may have an opportunity to pick up used (or new)
CB antennas at a bargain price.
The CB frequency assignments are very close to the amateur
28-Mc. band, being centered around 27 Mc. As one goes higher in frequency, a half-wave antenna
becomes shorter. In this case, 27 Mc. is lower in frequency than the 28-Mc. band so any CB antenna
can be shortened to work on 28 Mc. The formula for figuring the dimensions of a 28-Mc. beam is
First decide on the portion of the band in which you plan to do the most
operating. Let's say it is around 28.6 Mc. Divide 28.6 in to 468 to give you the length in feet
of the driven element. The director should be made 5 percent shorter than the driven element and
the reflector 6 percent longer. The spacing between elements does not need to be changed but it
is a good idea to make the elements horizontal to the earth. Most fixed stations on 28 Mc. use
horizontally-polarized antennas and you'll probably get better results if you mount your antenna
horizontally.Q. "I would
like to build the Super-Duper 75-Watter described in...QST. Please send me step-by-step wiring
information and pictorial drawings of the unit. I am afraid to attempt to build the rig with only
Variations of this request keep popping up. Unless specified in an article, we have no pictorials,
layout drawings, or step-by-step information. If you want to do that kind of construction it is
better to buy a kit. Kits usually come complete with pictorials and step-by-step instructions.
Here is the important point: A Novice must acquire a certain amount of radio knowledge if
he wants to stay in amateur radio. In order to pass the FCC exams he must acquire some "know-how"
in radio circuitry. One of the best ways of acquiring this knowledge is by building a piece of
gear, trouble-shooting it, and getting it working. Too many beginners are concerned about making
"Chinese Copies" of equipment described, even down to the same placement of nuts and bolts. Don't
be afraid to change the layout. Don't be afraid to make substitutions. And above all, don't be
afraid to experiment. The worst that can happen is a burned-out component or a blown fuse. The
important thing is that you will learn.Q.
"I have an s.w.r. bridge and its dial is calibrated in watts along with s.w.r. I am completely
confused because I am reading 70 watts output with 30 watts reflected, and I am only running 60
watts input. What goes on...will the 30 watts coming back damage my rig?"
No, the 30 watts won't damage
the rig. This is a complicated thing to explain because a certain amount of knowledge is required
about reactance, phase, and transmission-line and antenna theory. The subject is treated in detail
in "The A.R.R.L. Antenna Book."
However, here's a simple analogy: If you go into a radio
store to buy a four-dollar capacitor and hand the clerk a ten-dollar bill, you get six dollars
back. The six dollars coming back doesn't hurt your pocketbook. It just hasn't been spent. The
same thing is true of the reflected power in the above question. If you subtract the 30 watts
from the 70 watts you'll find the remainder is 40 watts. This is the total power the transmitter
is putting out and is actually going to the antenna to be radiated.
Still another way to
look at it is that with 60 watts input it would be pretty darn difficult to get 100 watts output
(70 forward, 30 reflected). The actual output is the difference between the two, 40 watts.
Q. "I am building the two-band
receiver described in last month's QST and am having a difficult time locating all the necessary
parts. None of the local radio stores seem to stock parts. Where do you suggest I look?"
Without a doubt this
question (or a variation of it) is the most common one. At one time, radio stores carried a fairly
complete line of parts, or would order them for you. It has become increasingly difficult to obtain
components, at least on a local basis. Not only do the stores not stock components, but the manufacturers
who make the parts a ham would want have become less numerous.
you like building, you will almost certainly have to order parts by mail. Although some distributors
still stock a fairly wide range of components, no one distributor is likely to have everything
you need. It is suggested you write to the large mail-order houses and obtain their catalogs.
Take a current issue of QST and go through the index of advertisers and write those that have
catalogs or flyers available. You can, of course, write to those closest to you, but if you want
a complete "availability file" it is a good idea to write to them all. Some of these concerns
have two catalogs, a general type and another larger one for industrial users. Also, nearly all
manufacturers of amateur equipment and components have catalogs and usually, they are happy to
send them on request. If you cannot find a component in a distributor's catalog you can look it
up in the manufacturer's catalog and write and find out who sells the item. In some cases, you'll
find the manufacturer will sell direct.
We might add that at the ARRL, in any projects
that are staff constructed, every effort is made to use parts that are readily available. However,
even then it may be that a certain part is not easily obtained. That's why it is a good idea to
have a stock of catalogs on hand. Also, as we stated in the previous question and answer, don't
be afraid to substitute components. 1: McCoy, "Is One of These
Your Problem?", QST, May, 1966.
2: McCoy, "The Wavebridge," QST, July, 1966.