The Homebrew Microwave Transverters

The 1st, and 3rd stage pre-amplifiers are modified KU band LNA's, the 2nd stage is a Down East Microwave kit.   The oscillator source is a California brick with a temperature controlled oven.  The mixer stage was also built from a Down East Microwave kit.
  The final output stage is capable of ~50 mw but is attenuated to a 3 mw level in order to safely drive a 100W I/P TWA for ~10W O/P.  The input frequency of the homebrew transverter is 435.5 MHz with attenuators installed between PA I/P and transverter. The transceiver has attenuators in the O/P to reduce the drive from 25 watts to a few milliwatts.   A simple 435 MHz pre-amplifier is used to overcome the loss of the attenuators. A diode switching circuit is used for TR switching on the I/P side.  A Transco SMA relay is used to switch between transmit and receive in the transverter.  The I/P to the first stage pre-amp is a waveguide, (centre top view below) and is connected to a large rotatable waveguide RF switch located on the front panel of the 100W amplifier, this allows switching between transmit and receive.  A three port circulator is located between the O/P of the TW tube, it's O/P connects to the waveguide RF switch.  A directional coupler, (bottom picture) connects to the O/P waveguide shown near the middle of the picture.  The directional coupler is used to monitor both the forward and reverse power.

10GHz transverter

Front top view

Back view

100W 10GHz amplifier

The 5.7GHz transverter top view

The 1st and 2nd stage pre-amplifiers are modified C-Band LNA's.   The mixer, oscillator and filter circuit boards (centre) were built from Down East Microwavekits.The crystal oscillator source for the mixer is in a temperature controlled oven and mounted in a separate enclosure (grey box on right side).  The output PA(upper left black box) was a commercial linear brick capable of 10 watts O/P.  The 2nd mixer stage, (not shown) runs at a frequency of 1296 MHz, the driver for that stage is a Yaesu FT-480R transceiver running on 144.0 MHz.  A couple of Transco SMA relays are used for switching between the I/P and O/P stages on xmt and rec.

The 5.7GHz transverter bottom view

Homebrew 2m 1KW Linear Amplifier


Top view home brew 2m linear amplifier

The 2M amplifier uses a pair of Eimac ceramic 4CX250B's. All of the plate tuned tank circuit is made from copper sheeting then silver plated using a product called Cool-Amp. The chimneys are not shown in the picture. The metering circuit is capable of measuring grid current, screen current, bias current and plate current. As well, it can measure screen voltage, bias voltage and plate voltage. An RF output detector is also incorporated in the metering circuit to aid in tuning. The tubes are forced air cooled with ~100 CFM. The amplifier can be driven with as little as 8 watts in linear mode. The homebrew power supply can deliver 1850V at 600 mA for 1KW I/P. The transformer originally only put out ~1000 VAC but we were able to get more power for our buck, by using a simple boost circuit consisting of a couple of smaller high current transformers. The booster circuit also allows us the ability to go from low to hi power at a flick of a switch.

Top view of tubes

O/P tank design

The output is tuned by using a capacity coupled vane which comes in close proximity to the output tank circuit, adjusted from the front panel. A PTFE rod with adjustable screw stops the output tunning vane from coming too close to the tank line and causing a short.

View of loop

Closeup of output coupling loop under tank circuit. The output coupling consists of a copper strap located under the plate tank and is tuned by a small variable capacitor located on the front panel.

Grid compartment

Neutralization is accomplished by means of a pair of small gauge wires which cross over from one tube to the other on the underside, then through the chassis to the top side. On the top side each of the leads from the grid has an adjustable copper tab that can be moved closer or further from the side of the tube.

Homebrew 1296 MHZ Transverter

The 1296 MHZ transverter consists of a SHF 1240K, 1240-1300 MHZ linear transmit/receive converter kit. The input frequency is 144.0 MHZ with only +10-13 dbm drive. Small RF relays are used to switch the I/P and O/P stages. The output stage uses a Mitsubushi RF power module M57762 with an O/P of ~18 watts nominal. That module is driven by an NEC SC1043 RF power module which is running at ~2 watts. The 1st stage pre-amp consists of a MGF1402 GAS FET followed by a 2nd stage Miteq AFS42 low noise amp. The +12V power supply is mounted separate from the rack unit.

View of mixer (centre) using stripline layout

Back view of transverter with heat sink visible and 1st stage pre-amplifier

Front view of transverter

Power Amplifier

The transverter drives a couple of forced air cooled 3CX100A5 triodes in grounded-grid (schematic) with ~1200V on the plates.

Front view of 1296 100W grounded-grid amp. (Mechanical dwg)