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Tips from a TVDX−er's Notebook
November 1957 Radio−Electronics Article

November 1957 Radio-Electronics

November 1957 Radio-Electronics Cover - RF Cafe[Table of Contents]

Wax nostalgic about and learn from the history of early electronics. See articles from Radio-Electronics, published 1930-1988. All copyrights hereby acknowledged.

TVDXing was a very popular sport in the 1950s through about the 1970s. As the name suggests, it involved attempting to receive television broadcast stations from as far away as possible from your location - akin to Short Wave Listeners (SWLers) who used radios with the same objective. If you were around back when over-the-air TV was the primary form of broadcast (before or during the early years of cable TV), late at light you were likely able to pull in stations - especially UHF - that were sometimes hundreds of miles away. An antenna rotator increased the chances of doing so. Living near Annapolis, I definitely remember getting among others TV stations from Philadelphia, PA, and Richmond, VA. At the time I did not know there was such a thing as TVDXing - it was just a curiosity.

Serious DXers went to great lengths to claim success, as related in this 1957 issue of Radio−Electronics magazine. Studying atmospheric propagation tables, monitoring live reports via Ham radio, erecting high gain antennas, inserting preamplifiers ahead of the TV set, etc., was in the TVDXer's bags of tricks.

See also TV DX - July 1958 Radio−Electronics, Mac's Radio Service Shop: Television DX - September 1951 Radio & Television News, Tips from a TVDX−er's Notebook - November 1957 Radio−Electronics.

A frequent RF Cafe website visitor, who also happened to be one of those serious TVDXers back in the day (and a licensed Ham), told me a joke relevant to this article: "A woman called for a TV repairman and as soon as he took a look at the back of the set he noticed that the wires from the antenna weren't connected to the antenna terminal on the TV. He looked up at the woman and said 'I think I know your problem, these wires aren't even connected.' The woman replied, 'I knew that, but I figured the signal had come this far I thought it could make that little jump.'"

Tips from a TVDX−er's Notebook

Tips from a TVDX-er's Notebook, November 1957 Radio-Electronics - RF CafeBy Robert B. Cooper, Jr.

Types of dx reception and necessary receiving equipment and techniques

The field and hobby of television DX−ing have grown to such proportions during the past 4 years that the number of DX−ers currently twirling the dials is estimated in the thousands. For most of them the only contact with other weak−signal chasers is through the TV DX column appearing in Radio−Electronics on a regular basis (alternate months).

TV DX picked up in Fresno, California - RF Cafe

TV DX picked up in Fresno, California. Top, WBAP−TV, channel 5, Fort Worth, Texas, June, 1956. Center, KFEL−TV, channel 2, Denver, Colorado, July, 1955. Bottom, CHCT, channel 2, Calgary, Alberta, Canada, June, 1955.

Along with predictions of dx conditions and news of unusual loggings, we often receive requests for information pertaining to antennas, when to look for dx, receivers, accurate record keeping and many other phases of full−scale DX−ing. Here are a few tips for those who are interested in TV DX but may not know how to break into the field.

Receiving dx stations (those not normally seen at your location) is not nearly so much a function of the location of the observer and the equipment used as it is of being at the right place at the right time. In DX−ing circles many make use of a "timetable" (see table) to give basic information concerning the types of dx we might expect during various periods of the year. During a year's time seasonal weather changes and the position of the Earth in relation to the Sun and other heavenly bodies have pronounced effects on dx conditions.

Types of DX Reception

The most common form of dx is that denoted by the term "sporadic−E skip." Sporadic−E skip (abbreviated Es) affects the lower television channels (2−6), bringing reception to your location from stations on an average of 500−1,500 miles distant. Various forms of Es have been known to provide reception for distances as great as 6,600 miles, although this is exceedingly rare. Es is a result of the television signal being reflected from a densely ionized layer, called the E layer, of the ionosphere. This layer exists at a height of 60−70 miles above the Earth. Under normal conditions the layer's density is very low and very−high−frequency television signals pass through the layer and on into space, never to return. It is only during periods of freak ionization conditions that the layer forms (actually forming in spots and not as a whole layer) and causes low−channel television signals to rebound from it as if it were a mirror.

Occurring on all TV channels, but most pronounced on high−band (channels 7−13) vhf and on uhf, is tropospheric (abbreviated trops) bending or conveyance of television waves to areas beyond the radio horizon via the troposphere. The tropospheric layer exists immediately adjacent to the Earth, and the majority of our weather occurs in it. Trops is actually caused by sharp boundaries formed in weather fronts which act as a duct, carrying the signal to distant points. This form of reception occurs, for the most part, during the spring, early summer and early fall months of the year. Distances covered vary from 200−800 miles.

A form of DX−ing theoretically possible, during the next few years at least, is F2 skip. Like the E layer, the F2 layer of the ionosphere is often capable of reflecting television signals back to Earth during years of peak sunspot activity. The channels influenced most often by this form of skip are the lowest (2−4). The distances covered by F2 are enough to stagger even the most imaginative mind, beginning at 2,200 miles and working upward in steps of 2,000 miles at a time. This form of DX−ing promises to be extra interesting as it will provide us with the opportunity to view programs originating in other countries and even other continents!

DX Time Table - RF CafeLastly, we have what is commonly known as the DX−ers' form of dx. As sensitive receiver design developed to usable levels and antennas with higher gain were put on the market, alert observers began to notice a form of burst reception. Short bursts of reception could be obtained for seconds at a time during periods when no signs of dx were present. It was decided that these bursts were a result of meteorites entering the E layer of the ionosphere and burning up there. As the friction causes them to burn, they leave a trail of ionized gas. Thus, like regular Es, meteor bursts (or MS) could provide reception from stations 500−1,500 miles distant. As meteorites are entering the E layer at all times (though in varying degrees of .intensity), we are able to log distant stations whenever we wish. The only hitch in the scheme is the short duration of the bursts. It usually takes many bursts to identify the program material and a few more to identify the source. Lots of patience and a good deal of practical experience really payoff with this form of DX−ing.

Keeping an accurate log is a very important part of DX−ing. As DX−ers, we are able to provide scientists with a great deal of information not obtainable in any other way. TV DX is definitely freakish in nature and is therefore subject to explanation. However, as with many other occurrences in nature, information is needed before detailed study may begin. Radio−Electronics is providing without cost through the TV DX column specially prepared forms on which you may report your dx observations. When your reports are combined with those from other sections of the country, scientists get a broad view of dx conditions over the country as a whole for any given date. An accurate log is also important when you wish to write to stations requesting letters of verification for your reception. It is always best to include information as taken from the receiver screen or audio, referring to local advertisements, etc. This will help the station in verifying your report. Many DX−ers have verification letters from 100 or more stations.

Receiving Equipment

XEW TV, channel 2, Mexico City, Mexico - RF Cafe

XEW TV, channel 2, Mexico City, Mexico, seen in Temple, Tex., March, 1955. Courtesy Richard Lowry, Temple, Tex.

During the past 2 to 3 years the old−timers in the dx game have become increasingly aware of the fact that the newer television receivers are sadly lacking in many dx essentials. In fact, with the current drive to use multi−purpose tubes, etc. for receiver compactness individual set gain and stability have deteriorated measurably. Therefore, DX−ers usually recommend that newcomers in the game purchase a sensitive receiver having a cascode front end (cascode rf stage). Keeping your receiver in good electrical working order is very important. If you do a moderate amount of DX−ing, change the rf amplifier tube every few months. Other important tubes such as the detectors, if amplifiers, rectifiers, etc. should all be tested frequently and perhaps changed completely every year. Remember, the only difference between the receiver you use for DX−ing and the one your neighbor uses for normal home viewing is the shape you keep yours in.

Boosters are also frequently mentioned. Remember this simple rule: If your receiver is of late−model design, with a cascode type rf amplifier stage, boosters are of very little value. Receivers using pentode and triode rf amplifier stages will benefit greatly from a cascode booster stage.

When we approach the question of the correct antenna for DX−ing purposes (or just plain deep−fringe reception), we encounter a controversy. Some DX−ers prefer large−screen reflector arrays with dipoles situated in front for signal pickup. Others lean toward the various forms of Yagi antennas while still others like the collinear style. To provide optimum gain on each channel with a single antenna is an engineering feat yet to be accomplished. However, several compromises may be made to give fair to good gain across the spectrum and still allow the use of a single antenna for all−channel vhf operation. What is wanted is as much gain as it is possible to get, high front−to−back ratio and good directivity. Many DX−ers use 5−· or 10−element Yagis for channel 2 and then some form of all−channel for the rest. The reason for this is that both Es and F2 work up from the lowest channels. Thus, a good antenna system on channel 2 is a big help. If you have a local on channel 2, a similar system for channel 3 would also serve the purpose. Stacking Yagi antenna arrays pays off for weak−signal reception.

Antenna transmission line is also important. Keep the line in as good physical condition as possible. Of course, the best line is that with the lowest signal loss: 300−ohm open−wire line does an admirable job and 450−ohm open−wire line is also very good. A problem here is matching the 450−ohm lead−in with a 300−ohm receiver input and 300−ohm antenna. If open wire can be used, we suggest the 300−ohm version. If you have problems with your open−wire line continually shorting to the mast or tower as you rotate the antenna, try using the 300−ohm tubular uhf line. The loss is very low and the plastic insulation keeps out moisture, dust, etc. Try to use just one piece of line from the receiver to the antenna as splices create more signal loss.

Getting your antenna high above ground and he surrounding objects is also of prime importance. If you live in an area with many power lines, poles, high trees, etc., raising your antenna above them will really help reception. Giving the antenna a clear shot at the dx stations is the whole idea in back of raising it into the heights. Power lines, rooftops, trees and the like all add to the amount of signal absorbed or reflected before it reaches your antenna. As you raise it up in the air, your antenna begins to break into signal levels that have not been decreased by absorption. A height of 70 feet above ground is a good minimum height for serious DX−ers, although good results can be had down to around 40 feet. A good rule might be: Raise the antenna as high as guy wire, guying space, pipe, neighborhood policy and your pocketbook allow.

Rotating the antenna can and does make all the difference in the world. Remember, you are using a high−gain antenna with its power punch concentrated in the forward direction. It is designed to reject signals from the rear and sides. Anyone of the popular antenna rotators is recommended for dx reception from all directions.

When using a large Yagi antenna array be sure that it is at least four boom lengths ,above any surrounding objects like trees and rooftops. This will assure you of a proper radiation pattern. If you cannot erect a Yagi array so that it is several boom lengths from any objects at the same height, it would be better to try some other form of antenna.

DX Tips

Venetian blinds: Horizontal bars move across the screen, alternating black and white. This is a sign of two (or more) stations on the same channel, the bars being what is commonly termed a beat note. The blind effect on a channel normally clear of them is the tipoff that some sort, of dx is trying to appear. Careful orientation of the antenna will usually bring it in. If you are not able to bring the dx station through a local or sublocal station, find the antenna heading in which the interference is strongest and then check the rest of the channels for signs of other dx stations.

Frequent signal bursts on a clear channel: This is a sign of either a meteorite shower or the formation of a Es cloud. In either case you should stick around for the next few hours and make frequent channel checks.

Fringe−area stations lose their snow: This is a sure sign that good, trop conditions are forming. First, determine in which direction the conditions are improving and then check the channels for weak stations not normally seen. (As fringe−area stations become of "local quality," dx stations appear with "fringe−area quality.")

If you live very near transmitters, there is not much that can be done for reception of dx stations on the same channels as the locals. For reception on adjacent channels, special traps can be used to filter out the overload from your locals, thus leaving the adjacent channels for dx reception. These adjacent−channel traps can do a lot for reception of Es signals. If you live 20 miles or so from the actual transmitter site, you should be able to bring strong E−skip stations in with the help of a folded−dipole antenna to attenuate the local station. The dipole antenna consists of a length of 300−ohm line cut to a half−wavelength on the interfering channel. Fed with another length of lead−in in the usual manner, you have a very effective antenna for cutting out locals by cancellation. Mount the dipole on a piece of board and experiment with it at various heights to find the highest you can go before getting into the extra−strong local signals. By carefully orienting the dipole, you will be able to "phase" out the local and allow the dx skip station to come through.

From several experiments made in California, we have found the best height above ground for the dipole is around 20 feet. For this antenna, height above ground is the all−important factor. If you wish to use a single dipole for the five low channels, find a compromise length in the vicinity, of channel 4.

For the latest in dx information and predictions of things to come, watch Radio−Electronics' TV DX column.



Posted December 20, 2021

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