Apollo commemoration - 6cm EME

Some of you may be aware Dean, VK6DSL, is working to get the 28 metre diameter dish at Gnangara, Western Australia, operational on 5.7 GHz EME to commemorate the Apollo 11 moon landings. Brian, G4NNS has been working to get Goonhilly GHY6 on air as GB6GHY as part of the celebration.

I thought it might be nice to try and get my 6cm EME system back on air to try and work them both. I haven’t used the 6cm system for about a year. As the local oscillator was not stabilised and the DB6NT MKU57 G2 transverter was located close to the dual (combined) power amplifier, if suffered badly from frequency drift due to heat. I never quite got round to modifying it for an external high stability LO source.

I viewed the new MKU57 G4 on the Kuhne Electronics stand at Friedrichshafen, last month, and decided I would buy one, especially as there was a small discount. 

To help things along I had been asked if I was prepared to sell my G2 and even my old G1. Of course!

The G4 has an external 10MHz reference input as well as a good internal TCXO. This should give me the frequency stability that I require. Doppler is bad enough to track without having to adjust for thermal drift as well.

I have decided fo locate the G4 away from the PA and LNA. That probably means at the back of the dish. That has several advantages.removing the transverter from that heat source and reducing the weight of the feedpoint equipment because I can also remove the control box and sequencer from the feedpoint.

Two low loss coaxial cables will connect the feedpoint PA/LNA/feedhorn. Both the high gain of the PA and the reasonable gain of the LNA  (a DB6NT LNA  - I don’t make one for 6cm) will enable me to run this arrangement with negligible receive system sensitivity loss and no transmit power loss.

One of the shortcomings of my previous arrangement was that the SSPA relied on simple conduction cooling to the aluminium frame at the feedpoint. Whilst this never led to any failures of the PA, a better cooling arrangement was a definite requirement.

With the transverter removed from the RF feedpoint frame I am now able to fit a 12V fan to blow air between the two PA modules that comprise the dual balanced amplifier. I found in test that I could increase airflow by cascading two identical 12v fans, one blowing into the other. In this arrangement the two fans tend to synchronise and definitely increase airflow. Whether it is twice a single fan is still unknown.....but it’s more than a single fan.

Sam