ASSA Radio Astronomy Group

A few years back Robert Hart bought some large VHF Broadside Antennas at a stock-take sale. So during one weekend, he thought he'd just weld up a stand and see if I could use them as a simple radio telescope.

Using a WinRadio WR-3700e Wide-band receiver and small preamp, he  scanned the VHF spectrum within the antenna's designed frequency range for a radio quiet area where he could conduct a meridian drift scan of the sky.

After a week of scanning and logging, the quietest frequencies identified where 173.5Mhz on the low side and 232Mhz on the high side where reasonably clear of terrestrial interference.

The scans where conducted at a receive sensitivity less than 0.5uV, the bandwidth was 17Khz and was logged at 1khz steps, AGC (Automatic Gain Control) was disabled.

Here is an example of the 232Mhz interference scan, the purple line indicates the maximum signal strength detected over the 24 hours and similar the green the average and orange minimum. Note that over the 24 hour period, some RFI interference occurred at different times of the day. Nevertheless this could be reduced using a band-pass filter at a latter stage.

In the radio astronomy test he also connected the audio of the receiver to a computer using the sound card and logged the noise over 24 hours from 7pm to 7pm using the the famous amateur radio astronomer software Radio-SkyPipe and the results where not to bad for a first attempt.

The antenna was aligned approximately by eye to line up with the sun as it passed over, if there are any extraterrestrial objects it is difficult to verify, as no planning at all was attempted.

The next trace was recorded from 9pm to 9pm where the antenna was tilted directly vertical to zenith.

The last is an example of the noise generated by heat in the equipment without an antenna over a similar 24 hour period. Note that the noise floor has been amplified significantly.

Two 16 element VHF antennas where stacked together to form a 32 element collinear phased array and should in theory offer a gain over 20dbi and a beam width of appropriately 18 degrees.

Although the gain may seem low compared with other microwave radio telescopes examples the all important aperture size is over 4 metres square. In a region of the spectrum where that galactic noise is very bright compared to microwave.

Additional Observations at 173.5Mhz