Results on FSH3 analyser

Some vswr pics of the amp output on R&S FSH3 spectrum analyser with R&S vswr bridge . . .

-35dB/144.3MHz




















Output impedance: 51 + j1.8

Triode Control Board

The picture shows the triode board. A series transistor is being used for tx/rx switching. The grid voltage is regulated with a TL431 with a series transistor as well. The circuit was copied from other control boards. Ia and Ig metering and Ia and Ig trip function is included, using parallel resistors to improve reliability. In addition a control board using a PIC microcontroller is under development. The function of this board is to monitor and control the triode board signals, as well as inrush 
current of the HV transformer,  min/max Anodevoltage, min/max filement voltage and the blower and VSWR. Amp status information is displayed through 2 x 20 LCD on amp. Alarm status is displayed on 4 LED's.

Dish tune- and load capacitors

With the kind help of Mario ( PD0MNI ) I got me a set of brass tune and load capacitors.
As can be seen in the construction drawing, stationary plates were
foreseen. After calculation of the necessary capacity I considered
to leave the stationary plates out. Tune and load capacitors should
have capacity enough (ca 3pf for tuning and 6 pf for loading).
The load capacitor is also the (coaxial) outlet of the amp.
At the end of this a N-type connector is mounted.
Teflon isolation is used, to withstand large RF-current and reduce
losses.

Construction detail: anode line

The anode line is a sandwich construction, as can be seen in the construction drawing.
The inner part is a aluminum pipe 70mm wide (ext.) 5mm wall. The top part is
machined so that the GI46B anode cooler fits in. Some cooling paste is used to
assure good thermal contact. Teflon sheet (0.5mm) is mounted on the inner part,
to form an isolation for the High Voltage (2.2kV) on the anode. The outer part
of the sandwich is made of brass sheet (0.3mm) which is rolled thightly over the
teflon isolation layer. The sheet is soldered with silver-solder-alloy.

RF cavity details

This construction drawing contains the detailed sketch from my RF-poweramp.
It is based on examples I found on the internet and the cavity dimensions
were calculated and checked with known RF-engineers.

The design is based on a Gi46b which can be obtained from various suppliers.
The amp is intended to produce a solid 400-500W RF on 144Mhz, since 400W
is legal limit in Holland :(  

Enjoy this blog and let me know your comments.