1.2GHz

Our 1.2GHz equipment was renewed in 2001 in order to provide more power and better receiving performance. Because the distance between PA and antenna is critical even with good RF-cable we decided to mount the PA on the mast behind the dish.
There are several restrictions :
    - regarding the rough environment of our contest QTH only a solid state PA is suitable for a reliable operation
    - the operating voltage is 13.8 (max.15V)
    - preamp, Rx/Tx-Switch, sequencer and protection circuits also must be located in the outdoor unit
A new 1.9m dish completes the new equipment. The circuit layout is made by DL2ALF. All mechanical work including the dish is made by DL6AUI.

Technical data
Supply voltage :    13.8V    (max. 15V)
nom. Output :        80W
nom. Input :          2W
DC Input at P_max : 19A
Noise figure :         0.6dB
Rx gain :               20dB

Max. PA-Temp. :    50°
Max. SWR :           20W reflected power (respective SWR is ~1:2)

The design is as follows : we combine a 80W-module-PA by DL2AM with a preamp by DB6NT together with a transfer relay in a solid plastic box. A sequencer gives the right timing, over voltage, thermal and SWR-protection is included.
The PTT can be fed either via RF-cable or via a separate line. A transfer switch connects the unused part (PA or preamp) to 50Ohms. There is no RF-bypass in case of no supply.

See the top view of the PA box. From left to right : sequencer, DC-decoupler, PA, preamp, transfer switch (with cooling)

Some interesting details

1. DC-decoupling and attenuator
The DC-decoupling circuit removes the PTT voltage from the RF-cable. The polarity is switch able, so the "Preamp On" voltage provided by most of the SHF-transceivers can be used for PTT switching. A miniature SHF relay handles the Rx/Tx-switch. In the Rx-line a "always on" 20dB-attenuator is protecting the preamp from RF power even when no supply voltage is present. Because of 40dB gain of the preamp this protection does not have much influence on the noise figure.

2. Sequencer
The sequencer circuit is rather complex :

The several parts are :

    - 12/24V - transverter with TDA 2003
    - voltage inverter with ICL7660 to provide a negative voltage for the OPV
    - NE555-timers for PA and transfer switch
    - constant current source for the KTY10 thermo sensor
    - amplifier and trigger for thermo sensor
    - amplifier and trigger for SWR-sensor
    - drivers for Power MOSFETs and LEDs
    - auxiliary inputs for blocking the PA

The timing keeps both transfer switch and preamp away from too much RF. To prevent oscillations the power supply of the module PA is completely switched off during Rx. See the diagram below :



The NE555 timers are not only suitable for timers but also the integrated triggers can be used for the thermal and SWR protection circuits. An interlocking between the two timers gives some additional security. The HEMT-preamp, of course, is always on.

3. PA
The PA is a well known design by DL2AM. It uses 4 Mitsubishi modules M57762 to get > 80W at max. 15V DC. The necessary input is ~ 2W. A Power MOSFET IRF4905 is used to cut off the supply voltage during Rx. An extensive cooling with two switch able fans on the back of the PA secures a reliable operation during the summer contests.

4. Antenna
The new 23cm antenna is a masterpiece of DL6AUI ! You need a lot of mechanical experience to build such a 1.9m parabolic dish. The dish looks very professional. It can be divided into two pieces for transport. Special thanks to all om's for the extensive pre-construction discussions. See the new dish with the mast amplifier among these other dishes :

	dish in "transport" - position : The dimension is abt. 1.90m x 0.90m and can be easy mounted on a car or stored in a van.
	separating the sections : foam rubber pieces keeping the two sections on distance.
	putting together : the aluminium profiles of the two sections are screwed together and you can see the heart of the dish, a no corroding disc cut in the half. A lot of bolts will attach a second disk for more stability.
	the reflector is ready : the second disk with two mast clamps is screwed tightly.
	magic feed : it is made from a tin can witch contained pickled gherkins in former times.
	mounting the rig : the mast amplifier is mounted behind the dish.
	ready to go : antenna with rotor in working position.