[Moon-net] How much gain and where should it be?

[Leif Asbrink]

Deve,

> Mount your preamp temporarily very near your antennas (use a 9-12v 
> battery to power it).  And just listen to eme signals for a day or 
> two.  Forget about transmitting (in fact disconnect the Tx coax so 
> you do not have an accident with your preamp).  I think you will be 
> pleased by the improvement in reception.  If not then you lost only a 
> couple days and tower climb.

If you try this, I suggest that you compare quiet sky (Leo)
to one of the major galactic sources. Do it one day (night?)
with the tower mounted preamp, the next day with the
amplifier in the schack.

In a good location, quiet sky could be something like 200K
and then 0.6 dB of cable attenuation would produce thermal
loss and degrade your system by nearly 1 dB. Use the VK3UM
calculator to find sky coordinates and to see what the
Y-factors (noise floor changes) really mean in terms of
noise figures and losses.

It is difficult to impossible to hear if a signal changes
in amplitude by 1 dB. However, if you really do the 
experiment of finding out the percentage of correct
copying a good CW operator can make, you would find that
a single dB would lower it from something like 75% to 50%.
It could easily mean the difference between QSO and no
QSO in (random) EME because the time to receive an unknown
call sign could easily become twice as many periods
(to many for the other station)

Only VERY marginal contacts would be affected by 1 dB,
but if you consider how big the cost is for 3 dB
(twice the antenna size) you might be willing to 
have 33% of that improvement for a reasonable effort.

BUT in case your noise situation makes the difference
much smaller, put the preamp in the schack.

(In all cases make sure the gain is high enough to
overcome the noise of the next stage unless you have
problems with very strong signals)

73

Leif / SM5BSZ