Pager extension. Encyclopedia of radio electronics and electrical engineering

Encyclopedia of radio electronics and electrical engineering / Mobile telephony

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There were times when I had a pager. A handy thing, but, like any radio receiver, it has its own coverage area. Went beyond its limits - and the thing turns into a beautiful toy. It's a pity!

I myself live in Veliky Novgorod. But it happens, I go to the village, 50 km from the city. There my house is somewhere 6 m below the "average level". That is, this is a zone of potentially uncertain reception. My pager was POCSAG standard and worked at 159,5 MHz. According to the company, the effective range of paging is up to 35 km. In fact, when moving away already at 25 km, a lot of errors appear, and when moving away at 30...35 km, the pager simply "catches nothing".

I decided to connect an external antenna to the pager. The idea is not new, but there are difficulties in implementation. The first (not the biggest) is to assemble the antenna. This is not very difficult, since the operating frequency is written on the back of the pager. But the second problem is more serious - connect the antenna to the pager, because it does not have a socket for it!

Let's start with the antenna (Fig. 1). This is just a piece of aluminum wire with a diameter of 3 ... 4 mm and a length of 92 ... 93 cm (just half the wavelength). The top end (1 cm) of the wire is bent at about 90°, like a hook, to make it easier to hang. To the lower end, after stripping, the central core of a conventional coaxial television cable (75 ohms) is attached. Its braid is not connected to anything.

Fig.1. Pager Antenna

Fig.2. Wiring diagram of the antenna to the pager

The manufactured antenna was simply suspended in the attic of a residential wooden house by the load-bearing elements of the roof (non-metallic roof - slate). The cable from the attic descended into the house. At home, next to the cable, there was a grounding socket for a television antenna, which turned out to be very convenient. If you don’t have one, you can simply bury some metal object in the ground (for example, an old galvanized bucket), having previously soldered a wire of the required length to it. I don't think anyone will have any problems with this.

Then the most interesting part begins: how to connect the antenna to the pager. After all, as I said, it does not have an antenna jack. The solution is simple - use inductive coupling! The pager itself has a magnetic antenna (on a ferrite rod). So, you can simply wind several turns of wire on the pager with a certain orientation of the turns and connect the ends, respectively: one to ground, and the other to the central core of the coaxial cable.

But a pager wrapped in wire looks ugly, and it will be inconvenient to use it. I did the following. My pager is BUMERANG 2 (2-line). Its dimensions are just right for placement in a pack of regular cigarettes. The contents are removed from the pack and the lid is torn off. With an awl, two pairs of holes are pierced at the beginning and end of the bundle for attaching the wire. The wire is wound on a pack like a blank. The wire that I had on hand was enough for 6 turns. I distributed the coils evenly over the pack, the distance between the coils turned out to be about 1 cm (Fig. 2). This turned out to be quite enough. The pager worked at a distance of 50 km from the transmitter without a single error!

The design turned out to be very convenient: put the pager in a box - connected the antenna, pulled it out - turned it off. There are no connectors and wires, everything is simple and easy. But this seemingly simple design, I still finalized. In order to see if something came to the pager when you were not at home, you need to pull it out of the box, which means that at this time the message may be lost. To eliminate this shortcoming in the pack, you need to cut a window the size of a pager display and provide access to the main "Read messages" button. Now he came, pressed the button, looked out the window and read the messages without taking out the pager itself.

For other pagers, such as the RDS standard, operating on FM broadcast frequencies, you simply need to recalculate the length of the antenna. The frequencies of the FM transmitters are known - 88 ... 108 MHz. The average frequency is 100 MHz, respectively, the wavelength is 3 m, and the antenna length for this wave is 1,5 m. That's all! Good luck!

Author: I.Dziuba, Novgorod, E-mail: il@mail.ru; Publication: radioradar.net

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