[amsat-bb] Even more out the closet

[Luc Leblanc VE2DWE <lucleblanc6@xxxxxxxxxxxx>]

For those unbeleivers..

I perform some test and here is some answers

Undisclose commentators wrote:

>I usually see a little rise in the s-meter when I turn on the preamp with
>no signal tuned in.  If I remember you use an FT-847.  I would say that
>could mean the LNG-432 preamp has only about 10-12 dB gain and if that is
>true then it will not be enough gain to be used at the antenna.

I found a bad jumper coax line (N type to PL-259 to BNC) the coax was a RG-58... unbeleivable how 
theses fine mobile coax are lossy... I change the jumper line for a 6 inches run of RG-213/1 "dont 
know the meaning of the /1" with one adaptor N to BNC.

The S meter now show S3 of noise on SSB when the preamp is on. I don't know if your little rise was 
also of this magnitude? but  i feel it is not a so little rise here!

>Why I say that is because the output level will be dropped by then coax
>cable loss (0.7 and 1.6 dB) to asomething like 8.4 - 10.4 dB.  This will
>not result in overcoming your FT-847 NF completely.   

>Using math:  systemNF = 1.0 + 12/10 = 2.2 dB.  
>If the preamp had about 20 dB then 18.4 dB would be still left at the radio
>so:systemNF =1.0 + 12/50 = 1.24 dB

I am aproachnig the antenna feed point... These 3 noise s units are probably the ugly thing that 
all wants to be get rid of!.

> All of this, of course, assumes normal coax with a loss of perhaps 2.8 dB 
> per 100'. If you can afford super low loss coax, then you can put the preamp 
> in the shack. Just keep in mind, whatever coax loss you put in front of the 
> preamp DIRECTLY adds to the noise figure of the preamp. So a fancy 0.5 dB NF 
> preamp with 100 feet of LMR-400 in front of it now has a NF of 0.5 dB + 2.5 
> dB or 3.0 dB...which is very very poor  for a good gasfet preamp.

I'm still dont rely too much on the FT-847 meter to convert S units in real DB but it looks like i 
have around 18 db on noise and if i substract the .5db NF of the LNG-432 i end up with still a good 
17.5 noise?
Just let see now if theses 3 S units of noise will be also there when the preamp will be at the 
antenna? (Just to be curious) Could be i will be able to hear the favorite Martian...

Bottom line this is not bothering me too much right now as all the sat's signal goes under this 3 s-
unit at AOS and LOS where the sats are nor very workable.


to be continued...stay tuned


P.S. I can copy the TV control guys with their studio open mike system at full meter scale on 
450mhz. It was S9 plus 40 before. I will probably end this test session with the loss/NF 
spreadsheet.


"-"
"Its not democratic to try to impose democracy"

Luc Leblanc VE2DWE
AMSAT 33583
Skype VE2DWE
www.qsl.net/ve2dwe 
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