...PERFORMANCE CHECKS AT 436 MHz

Perhaps the easiest way to check the sensitivity of the radio telescope is to make peak-sun-to-cold-sky signal measurements and cold-sky-to-ground signal measurements at the observing frequency. The results of these two types of measurements for this 436 MHz radio telescope are shown below:

PEAK SUN TO COLD SKY NOISE MEASUREMENT

The image below of signal intensity collected by the radio telescope on 24JUL2014 using the Continuum mode of SpectraVue when the antenna is moved from a cold sky direction to point directly at the sun and then back to the cold sky direction reveals a difference of 16.6 dB from peak sun to cold sky at 436 MHz; during the time of the measurement DRAO reported solar flux at 10.7 cm wavelength was 100.2 SFU.

COLD SKY TO GROUND NOISE MEASUREMENT

The image below of signal intensity collected by the radio telescope on 24JUL2014 using the Continuum mode of SpectraVue when the antenna is moved from a cold sky direction to ground and back again to cold sky shows a difference of 5.4 dB between cold sky (47 degrees dish elevation angle in this measurment) and ground (-2 degrees dish elevation angle in this measurement).

One can estimate the noise temperature of the telescope by using the relationship

dB = 10 log (ground noise power level/cold sky noise power level) = 10 log (Y) (= 5.4, in this measurement),

where Y is commonly called the "Y-factor ratio", defined as

Y = (ground noise power level / cold sky noise power level) = (Tg + Trx) / (Tcs + Trx),

where Tg is the noise temperature of the ground, Tcs is the noise temperature of cold sky, and Trx is the noise temperature of the radio telescope. Then,

Y = 10 exp(dB/10) = 3.5

On the day of this measurement the ground temperature was 294 K (70 F) and cold sky at 436 MHz is approximately 45 K. The noise temperature of the telescope is then approximately

Trx = (294 - (3.5 * 45))/(3.5 -1) = 54 K.

Thus, roughly speaking, the current configuration of the radio telescope should allow for observations of sources that have emissions greater than a thermal-equivalent source at a temperature of 54 K.

The above noise measurments indicate that the radio telescope is performing reasonably well in terms of sensitivity. However, the cold sky to ground measurement does suggest that a bit more optimizing might yield even more sensitivity as the cold sky to ground measurement taken a few years ago yielded a value of 6.7 dB cold sky to ground with this feedhorn and a similar arrangement of LNAs. Nevertheless, the measurements indicate that the radio telescope as it exists now should be able to detect the stronger pulsars at least, e.g., PSR0329+54 and a few others perhaps.