“Polish antenna”, “grid”, “dryer” - this well-known television antenna has received so many epithets. A specialist or an experienced radio amateur would be hard-pressed to call it an antenna, at best a dummy, or simply one of the brightest manifestations of the new time, under the slogan “Bloopers! FAQ is already there...” However, we live in this very time, the antenna is easy to find not only on the radio market, but also on any nearby one, it still “catch”, is not expensive and to save money it makes sense to try to adapt it for CDMA networks. And this can be easily done by getting a pretty good antenna for CDMA from an unnecessary Pole. How? See "more details"...

There is a possibility for this, since the frequencies of most CDMA operators are in the UHF range, close to the frequencies of television broadcasting, and the antenna is quite broadband. The gain of such a converted antenna is about 12-14 dBi. There is another argument in favor of this antenna. Non-ferrous metals have long been taken to collection points and materials for making a homemade antenna in the outback are very difficult to find, but a dryer - here it is!

So, let's start adjusting the “Polish antenna” for CDMA.

This converted antenna is suitable for CDMA800 (Intertelecom CDMA Ukraine). Many radio amateurs will say: “Why offer such an antenna for CDMA, when it is known that it is completely unsuitable for digital television? Since it is not suitable there, it means here too. The frequencies are nearby. Is it logical?” At first glance, it’s logical, but to make sure of this, let’s analyze our converted Pole in the 4NEC2 simulator. The results show that simple logic does not work and the antenna is quite suitable.

Having saved on remaking a Polish antenna, you should be aware that the plastic parts of such an antenna literally crumble under the influence of solar ultraviolet radiation in a couple of years. Paint these parts with automotive nitro spray paint and they will last longer. You can paint the entire antenna. Now this structure can really be called an antenna for CDMA...

If your antenna with an amplifier does not stably receive a DVB-T2 digital television signal, then often the problem is not that the amplifier is weak, but that it is not needed there at all. Yes, yes, after the advent of digital terrestrial television, the situation with signal reception has changed a lot in some respects and in many cases, the amplifier in the antenna simply becomes unnecessary, moreover, it becomes the cause of an unstable and sometimes completely absent signal.

I have already talked about the cause of this phenomenon and methods of combating it, so I will not repeat myself and will not explain why the alteration is needed, which I want to talk about in this note. Namely, how to convert the amplifier for the “Polish” antenna into a matching board.

What will you need for this? Actually the amplifier itself, maybe even a faulty one, a 3 centimeter piece of wire and a soldering iron. Task: Make a matching board from the amplifier board, which is not always available in stores.

Let's start remodeling

Amplifiers from array-type antennas have a balun transformer, and we will need it to match the antenna with the signal consumer. In the photo below, the transformer is circled in yellow. (A similar modification can also be made in amplifiers for other types of antennas)

There is no need to solder it, everything is much simpler. On the amplifier board, on the side of the radio elements, you need to remove the excess. Namely, unsolder the capacitor at the output of the transformer (marked with a red dot) and unsolder the strapping elements in the terminal circuit to which the central core of the cable is connected (marked in orange)

Attention! In amplifiers with other numbers, the number of elements and their location may differ, but the meaning remains the same, disconnect the transformer and terminal from the amplifier circuit.

This is how I did it! (Photo below) Of course, I washed all the soldering points with alcohol..... well, how did I wash it? — Rubbed with a thin layer, you know))) Although this is not necessary.

Final stage - Using a short wire, you need to connect the free output of the transformer to the terminal for the central core of the cable. That's it, the approval board is ready! You can install and try. And yes! Don't forget to use a regular TV plug instead of the power supply. The one with the separator from the power supply will not work.

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Introduction and theory under the cut. Please read carefully before asking questions and/or accusing me of incompetence.
There was a lot of information on the Internet about homemade external antennas for 3g modems, but I didn’t find anything helpful, that’s why I’m writing these lines. I am very touched by people who believe that 3g is a communication standard like GSM, but in fact it is just a generation. These same people are looking for drawings of antennas for a 3g modem... So these drawings are not there, or rather they are, but this is the same as coming to the car market and persistently demanding a carburetor for a passenger car without even specifying its model. So we will design the antenna for the CDMA2000 standard, whose operating frequencies lie in the range 821-894 MHz (and not 800 MHz as many people think). The antenna reviewed here is won't fit for operators MTS Connect, Utel (Kyivstar). Of course, I have come across proposals to catch the signal with a “nail” (aka quarter-wave vibrator), to make a can antenna (the only catch is that, according to calculations, you no longer need a can, but a whole bucket), the notorious Kharchenko antennas (a good option when the signal still exists, but the gain leaves much to be desired), etc.

I settled on the “Wave Channel” type antenna, also known as Uda-Yagi. The advantages are a high gain, low windage, and a highly directional bottom, but the disadvantage is extremely significant - very high manufacturing precision is required. An oversized director will become a reflector, and an active vibrator will not resonate at the frequency we need. The more accurately you do everything, the better the result will be.

The base station is located only 3 km from my house, but the windows face the other direction from the tower and the signal leaves much to be desired. At first I wanted to make an antenna with 8 directors, but it turned out that ultra-precision is needed here because going 1mm will result in attenuation instead of gain. A 3-director antenna does not require such precision manufacturing, but has insufficient gain. Therefore, I settled on a 5-director wave channel, considering it the “golden mean”. The receiving and transmitting channels are quite far apart from each other, so the antenna was designed for the middle of the receiving channel, that is, at 881 MHz. At first I wanted to design the antenna for the middle of the range as a whole (859 MHz), but since the Yagi is a narrowband antenna, we will get a gain peak in the non-operating range and less gain at operating frequencies.

The Yagi calculator program was used for design.

What do we need:
- aluminum square profile with a cross-section of 10 mm (I bought it at the epicenter), non-aluminum will do, but it is still lighter, but does not affect the characteristics of the antenna in any way;
- aluminum rod with a diameter of 5 mm and a length of 1 meter (other materials are also suitable, including copper, which is even better, but aluminum is the best price/quality ratio);
- a copper tube with a diameter of 6 mm and half a meter long (the outer diameter is indicated, the wall thickness does not matter);
- bolts with a diameter of 3 mm 7 pcs.;
- cable with wave impedance 50 Ohm;
- adapters, connectors - everything is individual for each modem, as they say, “Google to the rescue.”

Separately about the cable. To you won't fit television cable due to its resistance of 75 ohms. More precisely, it can be attached, but due to inconsistency, the losses in the cable will most likely be greater than the antenna gain. I took 10 meters of RG58 cable, it is quite cheap, but the loss is 0.6 dB per 1 meter of cable, i.e. I personally lost 6 dB, despite the fact that the difference in the signal with and without an antenna is 20 dB. Therefore, it is not worth saving on cable.

From the tools:
- saw for metal;
- drill;
- three-point tap;
- drill 2.5; 5; 6;
- flat file;
- calipers (in extreme cases, a ruler will do);
- hands.

First the drawings:

Red indicates the reflector, blue indicates the active vibrator, and green indicates the directors.

Drawing of an active vibrator (dipole):

All dimensions in the drawings are indicated in millimeters. The distance between elements is indicated by centers.

Let's start production. We take an aluminum profile, retreat an arbitrary distance from its beginning (this distance is needed for fastening, I took about 10 cm) and make a through hole with a 5 mm drill. I recommend immediately making a hole with a drill of the smallest diameter possible, and then drilling it out with a 5 mm drill. This is necessary in order not to deviate from the center axis of the profile. Next, we retreat 68 mm (according to the drawing) from the center of the previously made hole and make a through hole with a 6 mm drill (this is exactly the diameter of the active antenna vibrator). Next, we make all the holes with a 5 mm drill to accommodate the directors.

We begin to manufacture the reflector and directors. Actually, all the dimensions are indicated in the drawing, I just want to give some tips on cutting. Cut the aluminum rod according to the drawing 2-3 mm longer, after which we set and fix the required length of the element on the caliper. We file the rods with a flat file to the required length, periodically checking the size with a caliper. If the element fits tightly between the jaws for internal measurements, then you can proceed to the manufacture of the next element.

The manufacture of a loop vibrator is quite complex. It is better to fill the tube cavity with fine dry sand to avoid tube fractures (I did without this, but it’s still better not to risk it). To make a circle, you need to find a pipe close in diameter and bend a copper tube through it. The rest is according to the drawing.

To fix elements in the profile cavity, I suggest this option. Having inserted the element into the profile cavity perpendicular to it from above the profile, we drill a hole with a 2.5 mm drill and cut the thread with an M3 tap and with a small three-point bolt we clamp the element on top (the main thing is not to overdo it because aluminum is a very soft metal). Maybe someone will come up with a simpler or more reliable option, but with my set of tools it seemed to me that this was the most successful method of fastening.

All elements must be centered and perpendicularity with respect to the traverse (boom, as the bourgeoisie like to call it) checked.

Let's start soldering the reduction cable and matching loop. Cut a piece of RG58 cable 132 mm long. We remove 10 mm of outer insulation from each side of the cable piece, being careful not to damage the braid. Then we expose the inner insulation and twist the foil and braid into one bundle, fold the piece into a loop, connect the braids on each side and solder well. We strip the internal insulation to 8 mm. I think the rest is clear from the picture:

We solder the central cores to the ends of the active vibrator at the point where it breaks (15 mm in the drawing).

Some clarifications. Before you change or throw out anything from the design, it’s better to ask in the comments so that later there are no reviews “but it doesn’t work for me.” I made everything very accurately according to the calculations, but still the minimum SWR turned out to be not at a frequency of 881, but 885 MHz, which was quite acceptable for such frequencies. If you make it inaccurately, the effect will still be there, but not the maximum. At the transmission frequency (average frequency 824 MHz), the antenna performed very poorly, so I recommend that you still place the modem in the area of ​​best reception, because it feels like an internal antenna is used for transmission, not an external one.

I almost forgot about the tests. AxesstelPst EvDO BSNL program was used to evaluate the result.
The modem is simply plugged into the USB port:

Connecting the antenna:

What do we have? The signal is -62 dB, for comparison, if you are standing 20 meters from the BS, the signal will be about -40 dB, -105 dB is almost a complete absence of signal. The DRC Requested parameter is also interesting. 3.072 Mbps means that the modem is requesting the maximum possible speed and the BS station will give us the speed depending on the network load. The specific speed depends on the database load, i.e. further increasing the signal level will not improve the speed. The speed in the morning and in the evening will naturally be worse:

Good luck making it. I'm waiting for questions in the comments.

We live on the edge of a small village. Faced with the need for the Internet at home, we began to study what modern infrastructure offers in this sense.

It turned out that the most affordable and easiest way to connect to the World Wide Web is a GSM modem, inexpensive versions of which are often called a USB whistle. Such a modem is inexpensive, widespread and works well, but only in the area of ​​reliable signal reception of a cellular network base station. In the city, please be kind, but outside of it, it greatly depends on how developed the mobile network is. Often a modem requires a good external antenna raised to a certain height. Models of devices with connectors for connecting an external antenna are considered a kind of professional communication device and cost ten times more.

To work, you will need a minimum set of radio installation and plumbing tools, and a little patience. For working with small items, a special visor with magnifying glasses or a lamp with them is very useful. Make sure you have good lighting.

However, even in a simple “USB whistle” there is a technological connector for an antenna inside the case and you can use it. Some modems have access to the antenna connector, some do not; in the latter case, you will have to modify the plastic case, which will void the device's warranty. The antenna connector of a budget modem is very flimsy in design and is installed directly on the printed circuit board using the surface mount method. That is, it only holds on to the rations.

Only a sufficiently thin (flexible) coaxial cable should be connected to it, otherwise there is a high probability that the thick and rigid cable will break the connector. Thin cables have increased HF losses and should not be used for the entire feeder. In principle, there are adapters - a modem connector - 15...20 cm of thin cable - a larger connector for connecting a good external antenna cable. Such an adapter allows us to solve the problem of mechanical load on a weak connector, but we find ourselves tied to a specific connector at the output of the adapter, which is unreasonable in the case of a homemade antenna; moreover, such adapters are extremely rare on sale. It is also worth remembering that each additional connector, even each solder on the cable, introduces RF attenuation.

My connection option - I picked up a fairly flexible television cable in the store - without a foil screen, the central core is copper (soldered well) and multi-core (flexible). The connection looked like this.

A piece of thick tinned copper wire (resistor leg) is soldered to the central core. Its thickness is such that it fits tightly into the nest. The cutting area is insulated with a thermal tube.

The pin is inserted all the way into the connector and the twisted and tinned cable braid is soldered to the “ground” of the antenna socket.

The soldering area is insulated, and most importantly, the thin area on the cable is reinforced with several layers of thermal tube. Now all that remains is to try it on and, if necessary, file the plastic case so that it closes properly, with our modification. You will have to handle it carefully.

That's it, the modem is connected.

Let's move on to the calculation and manufacture of the antenna.

Antenna type, “log-periodic” was selected, the accepted foreign abbreviation is LPA antenna. Its features are high gain and a very narrow (sharp) radiation pattern. In addition, with sufficiently careful manufacturing, the antenna will not require adjustment, which cannot be done without specialized RF measuring instruments.

We prepare the necessary materials and tools. At the first stage, we need to cut two strips of one-sided foil fiberglass 10mm wide, 1.5-2mm thick, and long - according to calculations. We will also need trimmings of “bare” copper wire with a diameter of 1.5-2.5 mm, which can be removed, say, from a cable for internal electrical wiring. Well, accordingly, a soldering iron, rosin, a ruler and wire cutters.

We cut elements of the same size, 5-10mm larger than the longest vibrator, referring to the calculations made. We mark the location of the antenna elements on the improvised “boom”. Next, we carefully solder them, without overheating the substrate, and use wire cutters to bring them to the required size. It should be remembered that we are dealing with RF with its skin effect (propagation of currents in a thin surface layer), in this sense, “cold solders” and heavily scratched surfaces should not be allowed. It is good practice to use a special flux with glycerin to obtain a mirror-like surface for soldering.

Now, you need to rigidly fasten the finished “booms” opposite each other at the calculated distance and close the rear parts with a jumper. A coaxial cable is connected to the front ends - the central core is at one end, and the shielding braid is at the other.

My version of the antenna is on a polypropylene pipe. A suitable piece of pipe was sawn on a circular saw to obtain flat areas convenient for attaching the boom halves. They were attached with adhesive tape. At the back of the antenna there is a place for the modem - initially it was decided to shorten the antenna cable as much as possible, place the modem near the antenna and perform the reduction “digitally”. The plastic pipe was taken a little longer to obtain a convenient dielectric “handle”.

Another angle of the antenna, the seats of the boom halves and the cable connection are visible. I recommend that you get acquainted with a possibly more successful antenna design.

The finished antenna was taken outside to test its functionality and secured at the end of a long ladder with wire.

Due to the inconvenience of orientation, it was necessary to make a rotating unit. Some metalwork, cutting stainless steel, welding work.

The rotating unit turned out to be somewhat cumbersome, but unlike a similar satellite dish unit, it allows you to orient the antenna much more accurately.

The turning unit is welded to the mounting plate at an angle of just over 90 degrees (so that water can drain). During work, we ran out of stainless electrodes, so we had to use regular ones - hence the painted welding seams. In the photo above, the unit worked on the roof in different places, with different antennas, for about two years and generally proved to be reliable and convenient.

In the photo, an antenna with a USB modem is installed on the roof gable. The rotation angles allow you to orient the antenna towards a cell tower in a neighboring village (~5 km).

In a sealed box next to the antenna, the modem and the modem power supply. In general, the entire connection diagram looks like this.

The problem with long USB connections is the drop in supply voltage on long and relatively thin power wires (the principle of operation of the device via a USB port - including powering the device from the port itself). You can lengthen the USB cable within reasonable limits in two ways - increase the cross-section (reduce resistance) of the power conductors or power the device from your nearby power supply. The goal of both methods is to ensure that the supply voltage on our device is as close to five volts as possible. Plus.

Increasing the cross-section of the supply wires has already been tested during test activations of the antenna “on the stairs”. There was a connection and access to the network, but it did not work stably - it was interrupted periodically.

To place the antenna with the rotation unit, another place was chosen - the pediment of the roof of the house. The distance to it is somewhat greater and it was decided to place the power supply “at the top” - near the modem, eliminating the possible cause of failures. The “long” USB connection was made of two thin coaxial cables (central cores - two data lines, screens to a common wire).

What happened was the placement on the roof gable (access from the flat roof of the woodshed via a short ladder) and the general configuration of the equipment, which subsequently made it possible to conveniently experiment with different types of antennas. At that time, it was possible to connect relatively stably to the GSM (2G), sometimes WCDMA (3G) network. The antenna itself performed well. Some painstaking manufacturing (many precise dimensions) pays off in the absence of tuning and high gain. The antenna also has a low windage and is not very attractive to birds.

Looking ahead. The reason for the unstable operation of the modem turned out to be the long USB cable, despite the well-being of the device’s power supply. Perhaps it was a matter of the type or even the type of modem, because there are descriptions of similar “extension cords” and larger footage on the Internet.

The manufacture and testing of two more types of antennas will be described separately.