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BSEE - KB3UON
RF Cafe began life in 1996 as "RF Tools" in an AOL screen name web space totaling 2 MB. Its primary purpose was to provide me with ready access to commonly needed formulas and reference material while performing my work as an RF system and circuit design engineer. The Internet was still largely an unknown entity at the time and not much was available in the form of WYSIWYG ...
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|January 1955 Radio & TV News|
[Table of Contents]
These articles are scanned and OCRed from old editions of the Radio & Television News magazine. Here is a list of the Radio & Television News articles I have already posted. All copyrights are hereby acknowledged.
We are accustomed these days with stores having "no questions asked" return policies for just about anything. I once watched a guy successfully return a 4" PVC plumbing fitting that had clearly been smeared with glue in the coupling areas. Another time a guy returned a painting drop cloth that was full of paint, declaring that it wasn't what he wanted. The return counter bins of Walmart and other stores are always chock full of stuff. Such was not always the case, though. This episode of Mac's Radio Service Shop, mentions, among other things, how busy he and sidekick Barney had been right after Christmas doing troubleshooting and repair on various electronic equipment that had been received as gifts. Imagine receiving a radio for Christmas and not being able to simply return it to the store where it was purchased - even without a sale receipt. Nobody would stand for such a situation today!
Things were a little slow in Mac's Radio Service Shop. The holiday season was just over, leaving most people, if not actually broke, at least pretty badly bent. The Christmas radios, phonograph players, and TV sets that refused to play upon presentation had been taken care of in the hectic week between Christmas and New Year's Day. Now there was a lull that was welcomed by Mac's red-headed assistant, Barney, by the "office force" of the shop, Miss Perkins, and even by Mac himself.
The men had been busy most of the day checking and overhauling service equipment that ordinarily could not be spared from active use long enough for this to be done. Signal and marker generators were carefully recalibrated so that their dial readings - at least at the most essential frequencies - were right on the nose. The v.t.v.m.'s had their calibration controls adjusted so their pointers read precisely 1.55 volts when checking a fresh standard flashlight battery. On a.c. they were calibrated to read exactly with Mac's precision type 150 volt a.c. meter when connected in parallel with it across the line voltage. All multiplier ranges of these instruments as well as those of the v.o.m.'s were checked by measuring a wide range of known voltages on the different scales. The ohmmeter sections of both types of instruments were tested for accuracy by measuring several wirewound and precision carbon resistors.
The voltage calibrator used with the oscilloscope was examined to make sure its peak-to-peak voltage indications were accurate; then the vertical inches-per-peak-to-peak-volt sensitivity of the scope was measured at each setting of its step attenuator and with the fine attenuator set for both maximum sensitivity and at the half-way point. These sensitivities were compared with those measured some time before and arranged in the form of a chart pasted to the case of the instrument. As Mac explained, being able to preset the vertical amplifier to several known sensitivities frequently made it unnecessary to use the voltage calibrator at all. Usually a trace could be adjusted to a suitable size with some setting of the step attenuator and with the fine attenuator adjusted for either maximum sensitivity or at the half-way mark; then the peak-to-peak voltage could be determined simply by observing the height of the trace on the calibrated screen and translating this measurement into peak-to-peak volts by use of the chart's indication of the amplifier sensitivity obtained at that particular setting of the attenuators. Finally, square waves of various frequencies were observed on the oscilloscope to be sure that the frequency response characteristics of its amplifiers had not changed.
Out in the front office Miss Perkins had kept busy checking the advertising mailing lists against the customer records for the past year. The customers who had been into the shop in 1954 would receive a card thanking them for their patronage expressing the hope it would be continued. Customers who had not been heard from during this period would receive the "We've-missed you-is-anything-wrong?" card. Then there was the new prospect list that Miss Perkins constantly compiled from reading the wedding announcements, new-arrivals-in-town stories, etc. These were slated to receive the "Why-don't-you-give-us-a-try?" card.
At four o'clock, though, she neatly cleared off her desk and quietly slipped out the front door and into the restaurant adjoining the shop. Soon she was back with three huge steaming hamburgers covered with "the works" and with three bottles of Coke to match.
Warm cries of welcome greeted her as she stepped into the door of the service department, and activity there came to a grinding halt. Barney quickly wiped off the top of the service bench stool with the sleeve of his shop coat and proffered her the seat with a flourish that would have done justice to the offer of a throne. She perched herself graciously upon it with her high heels hooked over a top rung while the two men sat side by side on the service bench. For a little while all three munched away in the contented silence that is only possible among friends who know, understand. respect, and like one another.
Finally Matilda turned to Mac and said, "Mac, your wife called me before Christmas and wanted some suggestions about a Christmas present for you. I took a chance and told her I thought you might like a tape of pre-recorded music and suggested two or three sources of these. Did you find anything like that in your stocking?"
"Sure did, Matilda; and I thank you for saving me from the usual Christmas ties. She bought me two of Hack Swain's five-inch, dual track Musiken tapes recorded at 7 1/2 inches per second. The selections on these two tapes include piano, organ, and vocal numbers. Several of the organ selections are of the multi-track recording type that Les Paul and Mary Ford have made famous. All in all, these tapes are exactly what I wanted - to coin a yuletide phrase. Seriously, for a long time I've wanted to see for myself just how good pre-recorded ·tapes sound on my own recorder."
"Well," Barney demanded, "how do they sound?"
"Much as it pains me," Mac replied, "I've got to admit that a professional tape recording sounds better than anything I've been able to accomplish at home. Naturally, I expected this. After all, these recordings are made in studios with properly engineered acoustics; the recording equipment, including microphones, is the best obtainable; and the people doing the recording have considerable more know-how than most of us amateurs. All this shows up in noticeably improved fidelity, better signal-to-noise ratio, better microphone technique, and all around more pleasurable listening. I fully intend to buy some more pre-recorded tapes from various manufacturers. The fellow who has never heard one simply does not know how good the playback portion of his tape recorder can sound."
"Not to change the subject," Barney broke in, "but I'm wondering how you like the new TV antenna you put up at home back in September. You've had time to form an opinion by now, I suppose."
"I've formed several opinions about that experience," Mac said with a slow grin. "You'll recall I had a five-element channel 6 Yagi at the very top of a ten-foot pipe mast, while a two-bay, twenty-element conical was mounted below this. The mast and antennas were rotated on top of a forty-two foot guyed aluminum tower. The whole thing was put up three years ago last July 4th and has never been touched since."
"Hey!" Barney said, "that won't do.
A lot of the TV installers are telling their customers the feedlines should be replaced and the antennas cleaned every year."
Mac nodded. "I've been hearing that, too, and I was curious to see for myself in what condition I would find the antennas and feedlines. On top of that, though, the guy wires were getting pretty rusty-looking; and now that the station in Center City is putting in a pretty good signal, I was beginning to wonder if all that bird-roost was necessary up there in the air. The starlings seemed to think well of it, but the wife did not share their opinion."
"Were the guys right about the feedlines?" 'Barney pressed.
"Yes and no," Mac replied with a quizzical smile. "When I put up the tower, I used two different brands of flat feedline. Both looked equally good, and they cost the same amount; but when I laid the tower down in the yard, here is what I found: the line feeding the conical had cracked and crazed so badly that portions of the web were actually missing, allowing the conductors to assume various spacing. On the other hand, the line feeding the Yagi looked just as good as the day I put it up. Rolling it between my fingers so that it was forced into an arc with a radius of one-eighth inch or less did not cause it to crack or show any change whatever. The web material was smooth, shiny, and live-looking. In short, I couldn't see a thing about this line that would impair its performance. Out of curiosity, I carefully cut sections of both lines from side-by-side positions on the mast and mailed a sample of each to the two manufacturers who had made them. I asked for comments concerning the cause of the deterioration in the one case and the measured efficiency of the sample in the other."
"What did they say?" Barney asked eagerly.
"The manufacturer of the line that had gone bad did not try to cover up in any way. He frankly explained that a few years back his supplier of web material had run short of a special antioxidant material necessary to prevent weathering and had substituted another antioxidant without saying anything about it and without making sufficient tests. The result was that the line produced with this material weathered very badly. As soon as the situation was discovered, the company immediately stopped using the material, but not before many thousands of feet of it were already in use, causing great embarrassment and chagrin to the company.
"The manufacturer of the line that seemed to be in good condition reported it was just as good as it looked. Careful examination in the laboratory revealed absolutely no trace of deterioration. The only thing found was an insignificant amount of soot."
"Then it looks as though you can depend upon a good feedline to stay good for at least three years," Barney concluded.
"Whoa, now!" Mac cautioned. "Let's not jump to conclusions. All we actually know is that at my location this particular line would be good for at least three years and that changing it in less time than that would be a waste of money. You must remember, though, that we have no salt spray and little smoke or fog to contend with here. Most of the houses in my block are heated with gas. Along the ocean or in a heavily industrialized area or in some other spots with unusual conditions, it might well be necessary to change the feedline once a year."
"What shape were the antennas in?" "In general, they were in good condition. There were no loose elements, and the small deposit of soot on the insulators was unimportant when you consider it was actually in parallel with an impedance of 300 ohms. The steel booms of the conical were beginning to rust pretty badly. While this detracted from the appearance, I cannot see how it could impair performance. By the same token any corrosion that interferes with a proper electrical contact between the various elements of an antenna may easily interfere with its operation, but I greatly doubt that a corrosive coating on the surface of an antenna element makes a measureable amount of difference. In other words, I do not believe such corrosion acts as an 'insulator' serving, as some technicians seem to think, to prevent the signal from reaching the antenna. I am convinced my all-aluminum Yagi was performing just as well on the day I took it down as on the day I put it up, in spite of the fact that it no longer glistened brightly in the sun as it did at first.
"Incidentally, I might mention that the use of brass bolts is not sufficient insurance against corrosion. Most of these broke in two when we attempted to unscrew nuts from them. All bolts, connections, and so on in the new installation were given a good shot of plastic spray."
"What kind of an antenna did you actually put up?"
"I decided to try one of the new 'all-band Yagis,' as they are called. There are several different versions of this basic type. Keep in mind I was not attempting to put up a 'best' antenna.
What I wanted was an antenna that was light, simple, unobtrusive, and sufficient for the job at hand. The new antenna is doing all I expected and more. While I'm not willing to say positively it has as much gain on channel 6 as my trusty old Yagi - that's a good bit to ask of any broadband antenna - it comes so close the difference is negligible. On the other channels it seems to perform every bit as well as my old-fashioned two-bay conical in spite of the fact it does not weigh one-fifth as much.
"The front-to-back ratio - an increasingly important factor as more and more stations come on the air - is greatly superior to what I had before, even with the Yagi. I believe the reason for this is that I always had a certain amount of signal transfer from the conical lead-in, both directly and by leakage through the changeover switch, that impaired the apparent Yagi front-to-back ratio. On several occasions I have been able to tune in three different stations on the same channel, without interference, simply by rotating the new antenna. What's more, on a hot night a few weeks back I was able to pick up a station on every v.h.f. channel - something I never could accomplish with the imposing antenna array I had before."
"Then you're about convinced the antenna design boys have really learned something in the past three years," Barney suggested.
"Yep," Mac admitted with a grin, "I believe they have."
"Now that's settled," Matilda observed tartly as she gathered up the empty bottles, "what say we close up shop for the day?"
"The most intelligent suggestion I've heard yet this year!" Barney applauded as he shucked off his shop coat and reached for his hat.
Posted May 4, 2016
Mac's Radio Service Shop Episodes on RF Cafe
This series of instructive stories was the brainchild of no other than John T. Frye, creator of the Carl and Jerry series that ran in Popular Electronics for many years. Mac's Radio Service Shop began life in Radio & Television News magazine (which itself started as simply Radio News), and then changed its name to Mac's Service Shop after the magazine became Electronics World. 'Mac' is electronics repair shop owner Mac McGregor, and Barney is his eager, if not somewhat naive, technician assistant. 'Lessons' are taught in story format with dialogs between Mac and Barney.