The Low Noise Preamplifier (LNA) is the first active component of the receiver chain. It provide the first amplification of the RF signal coming out from feed horn.
It is a critical component regarding the overall noise figure (NF) of the receiver, one of most important parameter in radioastronomy; infact, if the LNA has a gain >12-15dB it is a good approximation to assume that final NF of the receiver will be not so far from the LNA NF.
Herebelow there is a comparison between some LNA available complete and tested or in kit, at reasonable prices:
MODEL |
MANUFACTURER |
CHARACTERISTICS |
LINK OR INFO |
KU141AH |
KUHNE |
1350-1450 MHz, HEMT, NF=0.4dB,G=17dB |
|
1420ULNA |
DEM |
1420MHz, HEMT, NF=0.4dB,G=17dB |
|
1420LNA |
DEM |
1420MHz,GaAs FET NF=0.8dB,G=15dB |
|
WD5AGO design |
RAS |
1420MHz, NF=0.37dB,G=28dB |
|
DJ9BV design |
1420MHz, FHX35 PHEMT,NF=0.37dB, G=16dB |
DUBUS 4/1993, Kit available at DC3XY, Rainer Rainer-Jaeger@t-online.de |
Our choice was the last one, with the FHX35 PHEMT. It is the cheapest solution with excellent performances.
I can provide the Dubus article that describe the preamplifier to everyone who decide to build it.
Obtained the full kit, that is designed for the amateur band of 1296MHz, it is very easy to retune it for hydrogen line : it is sufficient to decrease the inductance value of the wire loop L1 , in the input circuit: 33 mm long instead of original 36 mm. After this simple modification we was able to obtain a gain of 17dB and a noise figure of 0.45dB at 1420MHz.
