|
The reader may be surprised with such a technical article’s title in a radio magazine, however, the desire to describe this radio communication system had appeared on board of this flight watching out the window endless expanses of the plateau tableland and Russian northern tundra.
Selecting the ideal place for the amateur repeater installation is not an easy task. Usually all the high-rise buildings are already occupied by the professional equipment and quite a little space remains on the mast for amateur antennas. What should a HAM living far from the tall buildings in the area do having only one communications tower?
The task becomes even more complicated if you want to install several repeaters. However, having a strong desire and this problem could solved. That's why I thought of the RR9KAB repeater, which is located in the QTH locator MP84VV on the 70 m mast. Curator of the repeater Igor Znamensky (UA9KDF) set the aim to consolidate the following receivers and transmitters on a single antenna: 2m-APRS on 144.800 and D -STAR repeater 145.175 and 145,775. The 70 cm repeater: Analog 434.900 (TX) and 433.350 (RX) and DMR 433.300 (RX) and 434.950 (TX).
As for today, all the callsigns and registration documents are received. Frequency distribution is the following:
Igor has approached me earlier and ordered the 70 cm equipment. After receiving the duplexer with TX-RX spacing 1.6 MHz, and having convinced of his quality work, I decided to go ahead and merge on a 2-band antenna all the remaining equipment. The harsh northern climate does not allow the antenna use in it’s factory version. Therefore, Anli 520 was taken and inserted in the optional fiberglass 54 mm diameter and 6 m long case. (Fig. 1).
Fig. 1
97m long 7/8 feeder cable is connected to the diplexer DIP 2 / 70-100, which splits the signal into two shoulders - 145/434 MHz (Fig. 3).
Fig. 3
Further multiplexing goes as follows. On 2m band each transmitter and receiver each has it’s own full reject filter.
If it would be a simple conventional repeater, the filter would have the only one notch pole in the AFC. But since we have two transmitters and two receivers system each filter must have two poles of rejection "for myself and the other guy." This frequency response can be provided by the 5 " diameter coaxial resonators - 5 full reject filters for the edge frequencies and 6-jar filter for the central frequency. As a result, we get such a diagrams (Figure 4, 5, 6). This is enough to provide maximum sensitivity of both receivers.
Fig. 4
Fig. 5
Fig. 6
The second shoulder of the system operates on 70 cm and is made according to the classic 2-channel scheme when the duplexer separates the receiving and transmitting shoulders, to which in each turn a reception radio panel and transmission combiner reception radio panel are connected. The frequencies of the two channels are close, there are only 30 kHz between them, so the addition of transmitters is implemented by a hybrid combiner. The receivers are connected through the active radio panel with preamplifier (Scheme 2, right-hand side).
Scheme 2
Despite of the sufficient losses in the system, radio communication distance is impressive: up to 90 km on the walkie-talkie and all the 120 km on the car! This is all with periodically working APRS transmitter - 1,5 W and analogue repeaters based on GM360 DMR3000 - 40 watts each. By the way, the APRS radius of action is 50 km.
The general view of entire system is depicted on Fig. 7.
Fig. 7
Interest in such a systems is quite high. But their cost is high too. In addition to a large number of cavities a lot of time for tuning is required - about 3-4 working days. However, our engineers have to cope with this task.
|
