Topband: HMC580 instead of W7IUV preamp

[Andrew Ikin]

Rick N6RK Wrote Sept 9.


Snip<I've characterized this device and can tell you that the 1/f
corner is well below 2 MHz, because it is based on HBT
technology.  The devices that are good at VHF and noisy
at 2 MHz use MOSFET, GaAsFET, or ephemt technology.
JFET devices are also low noise at 2 MHz if they have a sufficiently
low channel resistance.>


Both amps, being single ended are likely to be susceptible  to second order 
IMD from BC AM band Tx. Whether one would notice much difference with a amp. 
with a less than 1dB NF versus the above mentioned types with higher NFs is 
debatable. The reason I say  this is; is that the Flag  has a high NF due to 
its termination resistance. With other antenna types the noise due to the 
loss resistance is a minute fraction of the antenna impedance. Hence, this 
noise resistance is mismatch to amp. input z. For example a very low noise 
JFet amp. (Wellbrook ALA100LN) when terminated with a loop antenna will 
provide a 6-8dB lower noise floor compared to the amp. being terminated with 
a resistance equal to its input z.

73

Andrew Ikin

G8LUG