Make a "super frame antenna" with your cabinet door

With the incomplete memory of the method described in an old electronic magazine, I want to use the method described here to make a "super frame antenna" with the periphery of the cabinet door. I do n’t know what the wire of this antenna is, and I do n’t know how many circles are needed, but I think this antenna must be quite “cool” because you can shake the cabinet door to change the direction of this antenna to where you need it.

By adding a variable capacitor, it should be able to make a very good broadcast antenna. Does anyone know the exact parameters?

At the end of July I did a careful mathematical calculation and came to the conclusion that if you are using a square cabinet door and a standard 0-365 pF adjustable capacitor, use approximately 80 feet (25 meters) The wire can just meet the requirements, (no need to worry about the area size of the frame antenna you choose)

The cabinet door is of course not square, so the length of this line will be slightly different (may be longer, but through my mathematical calculations, the difference is not too big, the specific data I remember is not too clear). You can make holes along the four sides of the cabinet door, and then insert a wooden stick, so as to make a loop.

Carefully separate each loop of wire (ideally keeping a 1 cm or wider gap per loop is ideal) to minimize the distributed capacitance of the loop antenna. If you don't do that, these additional distributed capacitances will affect the frequency response at the high end of the band.

There are companies that sell finished frame antennas. The self-made method I introduced can save you a lot of money. I have seen the finished tuned loop antennas sold for 100 dollars, but if I make them, it will cost up to 5 dollars.

BTW, the idea of ​​this door loop is very clever. I will use this method to make my frame antenna. The most troublesome thing now is to rotate the antenna and set the position without collapsing.

Receiver antenna feeder (1) (2)


Antenna feeder of receiver (1)

The antenna plays the role of transmitting or receiving electromagnetic waves in the radio communication technology. The excellent performance of the antenna often plays a multiplier role in wireless communication. In principle, the transmitting antenna and the receiving antenna are reciprocal, but there are differences in practical applications. An antenna with excellent transmission performance at a certain frequency must be a receiving antenna with excellent reception performance at that frequency, but any antenna that can receive it is not necessarily an excellent transmission antenna. Most of the articles and materials on research and discussion of antennas are focused on the aspect of transmission. In fact, there is also a lot of attention to the reception of antennas. This is often very important for our fans who focus on radio reception.


Generally speaking (except for the common antenna for transmitting and receiving), in order to highlight and emphasize the transmission effect, the transmitting antenna often uses a resonant antenna (narrowband antenna), while the receiving antenna often uses a non-resonant antenna (wideband antenna), even if the receiving antenna loop There is resonance at some frequencies, but the quality factor (Q value) of the antenna loop to measure the degree of resonance is relatively low. Such an antenna can basically be regarded as a non-resonant antenna. If you want to use the same antenna to complete the full-band reception, including V / U band, or even reception at frequencies above 1G, it is best to choose a broadband antenna specially designed by some manufacturers, and some broadband antennas can work at frequencies of 500KHz-1500MHz Within the range, but the broadband antenna (non-resonant antenna) receiving weak signals is always not as good as the narrow-band antenna (resonant antenna). As for taking a few meters of wire or other antenna as a full-frequency antenna to achieve full-frequency reception, it will certainly not have good results.


To measure the pros and cons of an antenna's transmit and receive performance, there are several technical indicators.

1. Antenna efficiency

Antenna efficiency is related to the conductor material, antenna shape, operating frequency, antenna length, and antenna erection height of the antenna.

1. Antenna material

Try to choose metal materials with good conductivity and low resistivity, such as silver, copper, aluminum, etc. Because the cost of silver wire is too high, it is best to choose electrical pure copper wire in practical applications. After smelting from copper ore, remove impurities, especially to reduce oxides, and then obtain electrolytic copper after electrolysis, and then draw into wire. This electrical pure copper has few impurities and very low resistivity. The wires and enameled wires produced by some regular state-owned wire factories belong to this kind of wire. Nowadays, some township enterprises or individual households often use electric wires produced by smelting recycled copper (recycled copper). This kind of copper wire contains more impurities and has higher resistivity. If it is made of this wire When the antenna is used, the effect of the antenna will not be very good, and it will often increase the white noise during reception, which is not conducive to the reception of weak signals. When making antennas with various wires, the receiving effect of wires with a large cross-section is better than wires with a small cross-section. Due to the skin effect of high-frequency signals, the reception effect of multi-strand wire is better than that of single-strand wire at the same cross-section. Aluminum materials are generally used in making Yagi antennas.

2. The shape of the antenna

In order to improve the efficiency of the antenna, antennas of different shapes are often used in different wave bands. The LW segment is dominated by long wire antennas, the MW segment is dominated by long wire antennas and loop antennas, and the SW segment is dominated by long wire antennas, dipole antennas and Yagi antennas. The FM and V / U bands are dominated by Yagi antennas and whip antennas, and the microwave bands above 800M are dominated by plate antennas and parabolic antennas.

3. Working frequency

The efficiency of antennas working at different frequencies is also different. The efficiency of antennas generally increases with the increase of operating frequency. The efficiency of high-frequency antennas is generally higher than that of low-frequency antennas. Data show that the efficiency of long-wave antennas is 10% -40%, the efficiency of medium-wave antennas is 70% -80%, the efficiency of short-wave antennas is 90% -95%, and the ultra-short wave (FM, V, U) and microwave antennas The efficiency is 95% -99%.

4. The length of the antenna

When the effective length of the antenna is close to a positive integer multiple of its operating frequency half-wave (1/2 wavelength), the efficiency of the antenna is higher. If this multiple is increased, the efficiency of the antenna will be further improved, but the number of wavelengths (antenna length) The increase is not directly proportional to the increase in efficiency. As the diameter of the loop antenna increases, the antenna efficiency will increase, and as the number of loops of the loop antenna increases, the antenna efficiency will further increase. As the diameter of the parabolic antenna increases, the efficiency of the antenna increases more significantly.

5. Erection height

Generally speaking, the higher the antenna is installed, the better the effect. Of course, this height is relative, and the actual installation must be selected according to the environment and the cost of installation.
However, when the receiving antenna is used at a frequency above the V segment, it is not as high as possible. This is because at frequencies above the V segment, the vertical distribution of the field strength in the space is not uniform, and sometimes the antenna position is set lower. Instead, the effect is better than the effect at high places.


Antenna feeder of receiver (2)



Second, the directionality of the antenna

When we measure the performance of an antenna in transmitting and receiving electromagnetic waves, we must also understand another parameter of the antenna performance index-the directionality of the antenna, that is, the ability of the antenna to transmit and receive electromagnetic waves in various directions in a 360 ° space . In practical applications, we are mainly concerned about the ability of the antenna to transmit and receive electromagnetic waves in the horizontal direction, or require the antenna to have as large a capability of transmitting and receiving electromagnetic waves as possible in certain directions.


The theoretical basis of the antenna is the electromagnetic field theory. The Maxwell equation and simplified boundary conditions can be used to calculate and determine the results of the antenna transmitting and receiving electromagnetic waves in various directions. This result can be described by the antenna pattern expressed in polar coordinates. . The result obtained by calculation is often too ideal, and sometimes there is a large error with the actual antenna. Therefore, the products of regular antenna manufacturers are often obtained in the electromagnetic anechoic room through the method of actual measurement to obtain the pattern of this type of antenna. We can choose the finished antenna with the appropriate pattern according to our needs. Under amateur conditions, the pattern of the self-made antenna can refer to the pattern of known antennas of the same type.


Mention the antenna's pattern, but also understand the polarization of electromagnetic waves. The so-called polarization refers to whether the electric field component of the electromagnetic wave propagates parallel or perpendicular to the ground. In this way, there is a distinction between horizontal polarization and vertical polarization. The LM, MW, SW, FM, and TV broadcasts of public broadcasting stations basically adopt horizontal polarization, and amateur stations also adopt horizontal polarization in the HF section. The V and U segment communications of service stations (the radios and pagers we often use, including the V and U segment communications of amateur stations), AIR, GSM, CDMA, etc., basically use the vertical polarization method. To get the best receiving effect, the actual installation of the receiving antenna should be as consistent as possible with the polarization mode of the received electromagnetic waves, that is, whether the effective unit of the antenna is installed horizontally or vertically. However, for frequencies above 800 megabits, the polarization effect of the receiving antenna is not obvious, and the higher the frequency, the less obvious. In addition, when the signal field strength at the receiving position is high, the polarization effect of the receiving antenna is not obvious, and when the field strength is weak, the polarization effect of the receiving antenna is obvious. The loop antenna is an exception. The low-resistance loop antenna receives the magnetic field component of the electromagnetic wave. The high-resistance loop antenna receives both the magnetic field component and the electric field component of the electromagnetic wave. It is precisely because of the loop antenna structure and receiving principle Particularity, in actual use, we do not need to consider the polarization effect of the loop antenna, only need to consider the directionality of the antenna.
In addition, during the transmission of radio waves, after multipath propagation, it is often impossible to guarantee that the strict polarization mode will be maintained when reaching the receiving location, and some changes will always occur. For example, multiple short bounces between the ionosphere and the earth when short-wave radio signals travel, diffraction of radio waves as they pass through mountains and rivers, reflections of radio waves by tall buildings in cities, and so on. When it comes to the directionality of antennas, it can be basically divided into two categories, omnidirectional antennas and directional antennas.

1. Omnidirectional antenna

The directional pattern of an omnidirectional antenna is a circle centered on the location of the antenna, or an irregular circle. In order to obtain the largest possible radio coverage area, public radio stations can also be regarded as the completion of point-to-point communication, especially medium wave and FM radio, as well as television broadcasting, mainly to complete the coverage of the area. Its transmitting antenna is used Is the omnidirectional antenna. But the shortwave radio station is an exception. The antennas commonly used by our walkie-talkies (including various hand-held walkie-talkies and receivers), the sucker antennas and clamp antennas used by mobile radios on mobile vehicles are all omnidirectional antennas, and the whip antenna is also a typical omnidirectional antenna. The long wire antennas that our enthusiasts often use can also be regarded as omnidirectional antennas.

2. Directional antenna

The directional pattern of a directional antenna can be seen as the pattern of the petals of a flower with the antenna located at the core of the flower, but the petals of this flower may be only one, two, or a few, or these petals may be large There are small, wide and narrow, and long and short, these petals, we call it lobes. Different types of directional antennas have different patterns. Sometimes, in order to emphasize the effect of the antenna in a certain direction, we can use a directional antenna with long and narrow lobes. This is often done when performing anti-jamming reception, or for remote reception of medium wave and FM broadcasts. Shortwave public radio stations are used to complete cross-regional, cross-border, and inter-continental broadcasting. Its transmitting antenna often uses directional antennas. Directional antennas are also used by service communication stations for point-to-point communication in the V / U section. The half-wave dipole antennas, folded dipole antennas, diagonal-pull antennas, inverted V antennas, Yagi antennas, and loop antennas that we often use are all directional antennas. Sometimes we can also combine an omnidirectional antenna and a directional antenna to get a combined antenna with a special pattern, or we can combine several directional antennas with the same pattern to get an omnidirectional antenna .

Method for joining outdoor antenna and radio mast

I bought several Deshengpu radios, and after using it, I always find it difficult to satisfy my performance. Therefore, to pay attention to some high-end high-end popular radio, but its price is indeed prohibitive. But after "bubbling" more in the forum, a phenomenon was discovered. A few enthusiasts use high-end radios that are not even as good as the low-end Desheng radios! In fact, this is a question of whether the method of use is correct! Especially if there is an "appropriate" antenna and its connection method!


On the winter solstice of December last year, I was ordered to sweep my father-in-law's grave on the orders of my mother-in-law. Da Leng Tian was a little reluctant and took my R9700 before leaving. In the cemetery on the outskirts of the city dozens of miles away, I got an unexpected effect. The short-wave signal on the radio is surprisingly clear. The annoying and difficult to remove background noises on weekdays are all "smoke dissipated", that cool Ah left a strong impression on me!


In fact, the various broadcast signals transmitted in the sky are the same no matter where they are, it is just that our listening environment is different. In order to cope with the harsh listening environment of the modern city, many prawns have racked their brains and tried all kinds of ways. The ring-shaped anti-dry antenna made by Leowood recently at the broadcast forum is a wonderful masterpiece!


This article only wants to talk about a simpler antenna connection method, that is, to make some supplementary amendments to the outdoor simple soft antenna of Desheng Company. This method is especially suitable for lazy and stupid people like me! But it can completely receive unexpected results!


Production Method:
The radio takes R9700 as an example! The whip antenna on the machine is fully retracted! Use a thin and long round ballpoint pen with a diameter slightly thicker than the antenna rod. Take 1 / 4A4 printing paper (do not use copy paper, it is too thin, and the stiffness is poor), use a thin pen to roll the paper into paper The bobbin is 15cm long and sealed with double-sided adhesive tape. Then prepare a relatively thin 220-volt power cable, take a single strand, remove the outer layer (plastic skin or cloth cover), and retain the insulation layer that is in contact with the metal copper wire core. The length is about 1.5m. Wrap this wire from one end of the paper tube. The end of the paper tube is pre-sticked with double-sided adhesive tape to help fix the wire head. The wire is close to the wire during the winding process. The 1.5m wire is completely wrapped and left Out a terminal. After wrapping, evenly wrap a layer of transparent adhesive tape on the paper spool. The remaining terminal is connected to the outdoor soft antenna and fixed. Finally, the pen holder in the paper spool is drawn out, and the antenna is ready! It is very convenient to put the paper spool on the fully retracted antenna rod during use!


The soft antenna that Desheng Company configures for its radio is thin and short, mainly to prevent the signal from being overloaded, because it uses a direct-clamping rod antenna. In this way, on the one hand, the broadcast signal induced by the outdoor antenna is very limited. On the other hand, some contaminated electromagnetic waves can easily enter the radio through the directly connected connector.


The joining method used in this article is actually an "inductor capacitor", so that the external antenna part can choose a thicker and longer power line, 5-10m is no problem, it can sense more distant or stronger signals without overloading In general, broadcast signals are at higher frequencies, and it is very easy to pass through this "inductor capacitor". However, many polluting electromagnetic waves are relatively low in frequency, but it is not easy to pass this "inductor capacitor", which plays a good role in blocking. At the same time, because it is made into a spiral ring tube, it also plays a role in shielding indoor electromagnetic pollution!


Listening effect:
The noise of my R9700 has been greatly reduced, and the number of received radio stations has greatly increased. Deguang, Aoguang, Hanguang, Iranian Radio, Canadian Broadcasting, Russian Broadcasting, etc. I all received it easily during their broadcast time. That night, when I received Deguang on the 21m band, I thought it was a strong VOA signal. ! Before that, I could n’t easily receive these radio stations. The tall buildings around me were dense and the listening environment was poor. I always felt that I was not as good as a rookie. I was depressed! Complain that the radio is too low. In addition, I do not know what the reason is, I still have not received the BBC Chinese Channel easily? It may be that I have too little listening time and too little knowledge of BCL.


A little digression:
The performance level of the radio is different. Beginners, especially friends with limited economic conditions, do not need to pursue high-end machines. The key is to use the radio on the hand well, step by step! Learn more, explore more, and "bubble" in the forum, there will be gains! For example, the outdoor antenna joining method introduced in this article is fumbled from the summary of the window frame antenna manufacturing method introduced by netizens two tigers and the prompt of Shwx Jun.


Recently, I have carefully plucked some R333, and I feel that the radio effect is practical and reliable! Some people say it's too big, but I disagree! It is many times smaller than the tube radio 20 years ago. If it is really used for learning and satisfying the purpose of various BCL, it will definitely not feel that it is big! It's such a low price!
Xinxin students still have to be considerate to their parents, and the choice of radio should be based on practical economy! Like me, when we reach middle age, we have to consider more issues. At a certain stage, the principle of practical economy should also be used! But this does not hinder our love for BCL! Does not hinder our desire and pursuit of high-end radio! We will have better motivation to work! There is greater motivation to make money! Understand the investment direction of this life better! Laofan, shwx ... and so many heroes are waving to us!

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