of action to put into effect when needed may head off real trouble.
After hearing reports and settling old and new business, the president can turn the spotlight on the program chairman and enjoy what follows, Hes not completely out of the work harness, however, since adjourning the clambake is also his job. When the program is over and the discussion dies down, he closes the meeting officially. He can ask for a formal motion of adjournment, or if coffee and cookies are on the menu, he might call the host or hostesses away from the hot-plate to give serving instructions, At any rate, the session shouldn't just fade away with everyone thinking there may be something yet to come.
Technical programs are to some radio clubs like salt and pepper on a fried egg— a little is a "must" but too much is tragic.
The club that is organized with the sole purpose of holding technical sessions featuring lectures and theory discussions doesn't have to worry about balancing their programs, They merely stick to the by-laws and attract hams who enjoy the same thing. But a club made up of Novices and old-timers, builders and non-builders, YLs and XYLs. has quite a chore pleasing everybody at least part of the time.
The best approach to the situation is to look (he crowd over and see how many are interested in what, or even get a vote on it. If the entire membership prefers to tackle their ARRL handbooks at home with an each-for-himself spirit, you can plan accordingly. If several express a desire to see some instructional films or hear reviews of electronic trends, youd better include some movies and speakers along these lines. It's very likely that a vote will go 50/50 and the program chairman will seem to be right where he started. Although it looks like nothing has been accomplished by a genera! vote, at least everyone will be aware that there's a demand for variety and will, perhaps, accept the "bitter with the sweet^ without griping too much.
All right, so what do you do after some or all of the members have said "Let's have something educational/" As program chairman, you may not feel like preparing a discourse on the most efficient method of demodulating a sideband signal, but who says you have to? First of all, look to the clul) itself for talent. If vou ve heard that m the TV repairman on the back row is busy wiring voice booths in the high school's new foreign language training room, ask him to explain how electronics enables teachers to listen in on each student's progress. If Second-Row Joe is testing a homebrew quad on 10-15- and 20, see if he won't put his plans on the blackboard some evening.
Every club is loaded with specialists in various fields and some of them, surprisingly enough, won't require too much arm-twisting before agreeing to take a program.
When local talent has been exhausted, start scouting the community and neighboring clubs, too. Many electronic industries and businesses are happy to provide films and slides on their products that are right up a ham's frequency. They may even send an employee with screen and projector. Who cares if the company sneaks in some advertising; the club will benefit from seeing how transformers are made, receivers designed, or vacuum tubes manufactured. Representatives are usually happy to answer questions, and members like to get information from the "horsed mouth."
Don't overlook films and speakers available for the asking from the Red Cross, Civil Defense groups, and also the military. Some organizations welcome chances to appear before the public. By checking with them for program material, you're doing both your club and an outside group a big favor.
Admittedly, if you're in or near a large city and industrial area, programs may be easier to come by. Groups in the grass roots have to scratch their heads, especially if they meet more than once a month. In the midwest, several small clubs may exist within a fifty mile radius. What's wrong with the program chairmen of these clubs picking an SO meter frequency and swapping ideas once in a while. A speaker enjoyed by the Sangamon Valley Club might agree to go to another town. CoNege campus groups in particular could benefit by a sharing plan since student chairmen can spare little time from books to search for program material.
Another little chore for the chairman may involve the matter of money, A club with a fat pocketbook can nail down about any kind of program because they can pay the price. If your treasury hovers on the empty mark, it's even more challenging to locate people who will perform for nothing. In this day and age that may seem impossible, but, thank heavens, there are still a few folks left who will. A club member who gives a demonstration or leads a discussion probably won't expect anything in return, but an outsider should be offered the price of gasoline, if nothing else.
When a speaker has been found, the chairman still can't fold his hands and forget the job. A few days ahead he should
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find out what stage props or equipment the speaker will need and arrange to have them handy. Since the visitor may not know anyone in the audience, a thoughtful chairman will break the p re-pro gram ice early in the evening and make a few introductions to put him at ease.
Just keep in mind that if your speaker enjoys himself too, he might let you schedule him for a repeat performance next year. And counting chickens before they re hatched is good business for a program chairman. • . ♦ W5NQQ
Getting Your Higher Class License
Part V — Receivers
Operation of a ham station involves, basically, three major items of equipment— a transmitter, an antenna, and a receiver,
In previous sections of this study course for the new Advanced Class license examinations we have touched upon aspects of both the transmitter and the antenna ( as reflected in the FCC study guide questions). Now it's time to turn our attention to the receiver.
The Commission's list of 51 suggested study questions contains six which deal directly with receiver operation, and they range from extremely detailed to extremely general. These questions (numbers are those assigned in the study list) are:
9. How can receiver sensitivity and selectivity be improved?
26. A superheterodyne receiver having an intermediate frequency of 455 kHz is to be adjusted to receive a signal on 3900 kHz. What frequencies can the high frequency oscillator be set to, to give a beat signal at the intermediate frequency?
33, Define the shape factor of a crystal lattice band-pass filter,
39, What functions does a variable-mu tube perform in an rf amplifier stage in a receiver?
41. How do noise Hmiters operate?
48. How does automatic gain control operate? When can it be used for SSB operation? CW operation?
Most receivers, these days, are superhets, and it's presumable that in the absence of any qualification to the contrary any question on the actual exam which deals with a receiver would assume that a superhet is involved.
However, non-superbets are still used for several special purposes. Therefore, although most of our discussion this month will concern the superhet, we must also cover non-superhet receiver types as well.
Following our usual practice of paraphrasing the FCC questions into more general questions covering (but not limited to) the same subject matter, lets re-frame the receiver portion of the study guide.
One of the first questions we ask must be. Mow Does a Superhet Differ From Other Receivers' I lie answer to this will adequately distinguish between supcrhets and all others.
Any superhet, whether it be a four-transistor broadcast band squawker or an ' ultimate" digital-tuning communications job, can be broken into four major portions as shown in Fig, 1, These offer us our remaining four questions.
Following the path any received signal must travel wev first ask, "How Does The Front End Operate?"
Superhet question number 2 (question number 3 of this installment) will then be. "What Does The if Strip Do?"
We follow this immediately with a look at filters in general—"Why Filter?'", before our final theme, "How Does The Detector Section Work?"
Noise Hmiters, automatic gain control, and the like are ah accomplished by the detector portions of most receivers—although AGC must also be involved with the if strip. Since we will be looking at the receiver as a functioning entity (except for the audio section. which we will ignore at this point), you may have a bit of difficulty relating the more detailed parts of the FCC study list to our questions.
To answer FCtl question 9, you'll need to know about the front end and the if strip. Question 26 involves only the front end. Question 33 is handled in the discussion of filters. Question 39 involves both the front end and the if even though the question as stated by the Commission would involve only the front end. Question 41 involves only the detector circuits, while question 48 requires a knowledge of front end, if, and detector for an adequate reply.
How Docs a Superhet Differ From Other Receivers? Unless you've worked your way up through a crystal set and a one-tube blooper (regenerative receiver to you young squirts) you may not have a real appreeia-
tion of the superhet. hat is, of course, unless vou've served your time with a Sixer
J w or woer and the constant hiss of their super regen circuits.
The function of any receiver is to convert the rf energy transmitted upon some specific frequency into audio energy. The various types of receivers are all capable of performing this function. Some, however, perform it more capably than others.
All receivers can be compared w ith regard to their performance in three basic characteristics; sensitivity, selectivity, and stability. Sensitivity measures how weak a signal may be received, selectivity measures how well undesired signals are rejected, and stability measures the receiver's capability for staying on the desired signal without readjustment, The lowly crystal set will perform the basic function of a receiver, provided that the rf energy carries amplitude modulation, but it ranks low in all three characteristics. Sen-sit ivity is poor since all the audio energy produced must be supplied directly by the rf energy received. Selectivity is poor because only one or two tuned circuits are available to reject undesired stations. Stability is moderate, and is of little consequence since selectivity is so poor in the first place.
The next step up from the crystal set (not counting such modifications as the one-tube grid-leak detector, which is hardly ever encountered these days) is the regenerative receiver. This makes a single active element (tube or transistor) serve double duty as both an rf amplifier and a detector-
Sensitivity is much greater and selectivity is also improved because of positive feedback, which increases the sharpness of the tuned circuits. Stabilitv however, decreases;
almost any movement near a regen will require retuning.
The regen has one capability lacking an the crvstal set or other detector-onlv receivers: it can be adjusted to receive CW as well as AM by throwing the circuit into oscillation and mistuning it a kilocycle or so from the desired signal. The local oscillation and the incoming signal mix in the receiver to form an audible beat note,
11 le addition of rf amplifier stages between the antenna and the detector improved the performance of non-re gen receivers and make them able to compete with regenerative circuits; this is the TRF (tuned radio frequency) receiver which was used to a
surprishiglv great extern as recently as the
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