Gary (KD9SV) kindly loaned me one of his 994 x5 preamps (sometimes called KD9SV VLN (very low noise) preamp) so I could compare its Noise Figure against one of my W1FB preamps as well as 2 of my W7IUV preamps in series on 160 meters.
Here is a link to a youtube video I created that demonstrates the differences in Noise Figure between the above mentioned preamps. http://www.youtube.com/watch?v=JpIiF1Hfovw The KD9SV 994 x5 preamp did in fact come out on top (best Noise Figure) and it's a commercially available preamp, whereas my W1FB and W7IUV preamps are home built. Nevertheless in my current application (pennants that are 51.6% the size of full size pennants) the W1FB and W7IUV preamp Noise Figures are adequate and I didn't notice improvement in my signal to noise ratio on 160 meters when using the KD9SV preamp. The lower Noise Figure of the KD9SV would allow me to use even smaller pennant receive antennas that would have more negative gain without harming my signal to noise ratio. I ran into a couple of interesting issues when working on this project. The biggest surprise was that the input impedance of my old HF rig (Kenwood TS-180s) was no where near 50 ohms on 160 meters (it actually measured 189 ohms). I added a transformer to the input of the Kenwood TS-180s to bring it closer to 50 ohms for my testing. Also as previously reported by Hardy (N7RT) a long time ago, the W1FB output transformer turns ratio is incorrect for a 50 ohm match, and I measured the output impedance of the W1FB preamp at 429 ohms. I subsequently added a transformer to the output to bring it closer to 50 ohms for my testing. *Noise Figure Comparison (average of two different measurement methods)* W1FB preamp: Noise Figure 3.3 dB higher than KD9SV 994 x5 preamp Two W7IUV preamps in series: Noise Figure 1.1 dB higher than KD9SV 994 x5 preamp Note 1: my W1FB preamp is not stock, as I made modifications to protect the MC1350 IC from damage when transmitting. Note 2: The KD9SV 994 x5 preamp was set at its maximum gain (41 dB) for all of my tests. *Summary* While I suspect (through my measurements) that the KD9SV preamp absolute Noise Figure value is not the very low 0.7 dB value listed on a commercial website, it's indeed a very nice adjustable high gain preamp offering a maximum gain of 41 dB and it has the best (lowest) Noise Figure when compared with my other two types of preamps. I highly recommend the KD9SV 994 x5 preamp if you're in need of a high gain preamp on 160 meters. 73, Don Kirk (wd8dsb) _________________ Topband Reflector Archives - http://www.contesting.com/_topband