In the last part, the meaning of the equivalent noise temperature of an amplifier was given.
Whilst you will find that working in Teq has advantages for this analysis, amplifier specifications may not give Teq, but may give Noise Figure.
Continue reading Designing high performance VHF/UHF receive systems – Part 3
G/T is defined as the ratio of antenna gain to total equivalent noise temperature.
For clarity, lets define those terms.
Gain of an antenna is defined (IEEE 1983) as the ratio of the radiation intensity, in a given direction, to the radiation intensity that would be obtained if the power accepted by the antenna were radiated isotropically. (Isotropically simply means equally in all directions.)
Continue reading Designing high performance VHF/UHF receive systems – Part 2
A metric that may be used to express the performance of an entire receive system is the ratio of antenna gain to total equivalent noise temperature, usually expressed in deciBels as dB/K. G/T is widely used in design and specification of satellite communications systems.
G/T=AntennaGain/TotalNoiseTemperature 1/K
Example: if AntennaGain=50 and TotalNoiseTemperature=120K, then G/T=50/120=0.416 1/K or -3.8 dB/K.
Continue reading Designing high performance VHF/UHF receive systems – Part 1
I made a measurement of ambient noise on 144MHz this morning using the technique described at (Duffy 2009).
First step is to recheck the NF of the receiver. The TS2000 is getting a little tired, NF=8.3dB.
The technique calculates ambient noise from the variation in receiver output noise of a receiver of known Noise Figure with the insertion of a known input attenuator. The receiver output noise was measured using NFM (Duffy 2007) which allowed integration over 20s for high resolution measurement.
Continue reading VK2OMD ambient noise measurement 144MHz – 20140217