4m noise

4m has always been  noisy here.

Using the arrangment in the previous blog, but on my IC7300, i was able to measure the noise level around my antenna.

In the worst direction (towards the house) the noise rose 18dB over the quietest direction. Not good!

I need to investigate what is producing that noise increase.

Now to repeat the measurement on the other  bands  covered.

Sam

Measuring noise using the IC9700

No, I didn’t get on the moon on 6cm for the Apollo EME commemorative event. Chesty cold knocked me for six. Just recovering. Courtesy of our  vistors from Australia........l

It did allow me time to consider how I could make continuum noise measurements using the IC9700 (on 23cm) when it doesn’t have an IF output in the usual sense. One thought was to try and use the 12kHz IQ IF output, but I failed to find any information on this or how it could be used with existing SDR software. I know it can be done.

I had played with using my SDR-IQ at audio (it goes down to 500Hz) to measure noise power in a defined bandwidth using Spectravue running on the SDR-IQ. This worked well, but I was not happy with the amount of amplitude ‘jitter’ on the trace.

I managed to find  a working HP3400 true RMS voltmeter at Friedrishshafen, to do the same measurement with a ‘proper voltmeter’!. Again flicker, because of the nature of noise and the restricted bandwidth, made this unsatisfactory.

Finally, I set up the IC9700 as a soundcard input to Spectravue (no SDR-IQ) and selected continuum mode. With a moderate amount of FFT and smoothing the trace is as stable as it was using the SDR-IQ on the K3 8.215MHz IF output. Not only, but the results agree very well with those previous  IF measurements.

Now I CAN use the IC9700 for EME noise measurements!

Sam

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