The hardware of the PI6ANH repeater

Now lets take a closer look on the different modules in the opened repeater-box:

Left door from top to bottom:

• The blower (not too good to be seen) on the top pushes the warm air out, that gets pressed in by the lower blower. The speed of the two blowers is regulated by a temperature sensor. So the temperature keeps in narrow range during the seasons, which is very important for stable operation.
• The first row of boards (under the blower) is meant for 10 GHz. For the 10.4 GHz input of the repeater, we use an modified TV-Sat LNC (Low Noise Converter), which is assembled directly at a 10 GHz slot-antenna.

On the board itself a simple satellite tuner block (by Sharp / 27 MHz bandwith) with FM-Demodulation is mounted. The outcoming signal (baseband) is led to an FM-ATV Baseband-Processor, which finally puts out clear Audio and Video. The usually free-running satellite tuner gets a PLL (Phase Locked Loop), which can easily tuned to any frequency by dipswitches. A synch pulse detector (on the very left) watches the band permanently for video and switches the transmitter (with priority related to 23cm) on, if a 15.625 kHz line frequency signal is recognized.
• The middle row of boards consists of the blower-speed temperature-regulation and the color testpicture card. A picture of 128x64 dots is burnt into an EPROM,- meanwhile a new test-picture board is installed with 8 different easy programmable pictures, which get slowly scanned all the time. See some of these pictures in "General technical information". The hard- and software will also soon be introduced...
• The task of the board-row below to the bottom is for the sysop's (system-operator) remote-control and for general time steering. There is a 8-number DTMF decoder to shut the repeater down (signals are delivered by a crystal 2m handheld). With a 2450 Hz sinus carrier, the repeater can be set into a 10 minute test-picture mode. Additionally every full hour the repeater switches on for 10min automaticlly to give people without a HAM-licence a chance to adjust their receivers.

Right door from top to bottom:

• Easy to recognize is the power block module, which is designed for heavy duty. It is certainly secured against short-circuits and switches off when voltage rizes over 14V immediately.
• The next row shows the 1.2 GHz receiving unit with a high quality TV-satellite (tuner by Sharp with 16 MHz bandwith) with optimized threshold. (A 40dB Pre-Amplifier with more than 40dB gain and noise less than 1dB is mounted directly under the 1.2 GHz antenna). Left of the tuner is again a PLL-board to keep the receiver right on frequency. Annother ATV-Squelch (synch line detector) is installed,- now for 23cm.
• The line in the middle represents the FM-ATV Baseband-Processor unit for the TV-satellite tuner and several switching- and timer prints (for switching video between testpicture generator and 1.2 GHz input video etc...). So far we work with a 6 MHz audio subcarrier (instead of 5.5 MHz) to reduce audio-effects in the video. We plan to add annother audiocarrier, which transmits the audio from the 2m ATV-meeting frequency on 144.750 MHz.
• The most important block in the repeater is taking nearly 50% of the space in that door. It's the whole 2.4 GHz transmitting unit with a baseband processing unit for transmitting, the 2.4 GHz-oscillator locked with a PLL (SP 5070), the driver (2x MSA1104), the final two-staged 5W amplifier (MGF904 and MGF905), the coax relais, some protection circuits and a supervision for the locked PLL. A closer look on this is in preperation.

Receiving 2.4 GHz FM-ATV signals on long distance makes it necessary to fight for any dB, which might be available anywhere in the system.
The easiest way is still a good high-gain antenna (semiconductors with more than 5W HF on 2.4 GHz are still too expensive for the average HAM).

The "11-Element-Slot" - Antenna (very similar to the DC0BV slot antenna) had been recalculated to the repeaters frequency and to a 180 degree (halfsided) radiation pattern. So far, we only could measure (with commercial help) the gain in 0 degree direction and the SWR over the whole band.-

The results were very satisfying for us: 13 dBd gain with a (-3 dBd) bandwith of 40 MHz and a return-loss of more than 20 dB (!). The raw aluminium block has the sizes of 80x40x3 cm and is standard and should therefore be available for only a little money. A sketch with all lenghts and impedance transformations is in work. (Has anyone else experience with such antenna types ?)
Compared to the dipol groups (ca. 7dBd gain) we used before, it is an additional gain of 6dB (= 4x times HF-Power).

On the picture: DL4EBJ (Johannes) with 11-Element-Slot Antenna.

One easy way to receive the repeaters 13cm-signals is described in "QRV on 13cm FM-ATV" (still in German only).

Back to the Home Page