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

[Edward Cole]

Dave,

You received my recommendations, already, but I see that you are 
getting several folks that recommend shack install of the preamp.  I 
understand Jimmy's environment and it probably will not make a 
difference for him.  But I suggest a simple experiment that you can 
do to decide which is better for you.

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.

I use LMR-400 for my Rx line and suffer little over more expensive 
hardline (I use the hardline for the Tx).  My preamps are: mgf-1801 
0.15 dBNF, 16.8 dBG, 150-feet of LMR-400, DCI bandpass filter, 3sk48 
1 dBNF, 14 dBG, followed by FT-847 (internal preamp off ~ 14 
dBNF).  I calculate overall NF~0.8 dB.  I regularly get 3 dB lower 
numbers on JT65 tha stations with much bigger antenna arrays.  I will 
admit my location is fairly quiet.

Anyway try the test and decide if its worth it.

73 Ed

At 01:15 PM 11/29/2007, Dimitris Vitorakis wrote:
>Hi Dave
>
>I have my 2m preamp in the shack.
>TX/RX line loss is 0.45-0.5db including connectors and I lose 0.65-0.7db of
>Sun noise because of that.
>Nevertheless, I only recommend a mast mounted 2m preamp if in a really quiet
>qth, to see the difference effect.
>In my first 2 EME qth from the city of Athens, 5mn inhabitants, for 10 cw
>eme yrs i did not see any difference at all having the preamp mast mounted
>or in shack.
>In my 3rd, current qth, rx is optimized in all other possible ways except
>that. However, i know i can further improve my rx by bringing the preamp at
>the mast. It is far more quiet than a vy big city but still not an optimum
>eme qth. Most probably i will do that in the future, but other projects have
>priority.
>On 70cm my preamp is mastmounted. No other way to go about it, as roughly
>speaking any line loss is * 2.5 in additional nf and system temperature,
>when it comes to Sun noise...
>
>Given your well thought low feedline loss, if i were you, i would leave the
>preamp in the shack. For both 2m jt65 work which is forgiving, as well for
>2m cw work which is not, if you want to hear ''at the edge''.
>
>A word of advice: FSJ4 Superflex is a cable I would not recommend for
>rotating loops (in azimouth or elevation) as the shield cracks as time goes
>by. Better use LMR-600U. BPF must be placed after the preamp, hope it has
>good return loss and so does preamp output.
>
>73
>Jimmy SV1BTR
>
>----- Original Message -----
>From: "Dave Anderson, K4SV" <davek4sv at yahoo.com>
>To: "EME Reflector" <moon-net at list-serv.davidv.net>
>Sent: Tuesday, November 27, 2007 9:20 PM
>Subject: [Moon-net] How much gain and where should it be?
>
>
> > Hi Gang,
> >
> > Since I am new to EME I have lots of questions.
> >
> > I would like to know How much gain to have, and, Where should the gain be,
> > at the antenna or at the rig?
> >
> > I have a very nice M2 H frame with 4 2MXP20's.  It sits atop a 32 foot (10
> > meter) tower with clear visibility of the sky and I live on top of a hill.
> > It's feed with Andrew 7/8 Heliax with a few relatively short FSJ4
> > Superflex jumpers to connect all the pieces.  I am currently using a Icom
> > 910H radio, 8877 Amp and preamp located in the shack.  I get excellent
> > reports on transmit.
> >
> > The run of 7/8 Heliax and FSJ4 is no more than 85 feet when you add it all
> > up.  All connectors are Andrew.
> >
> > So my first question is
> > Where should I put the 0.3 NF Preamp and its Bandpass filter?  At this
> > time I have a single feed line with Polarity switching at the antenna.
> > The obvious answer is at the antenna, but, does it really make that much
> > difference considering my low loss?  Putting the Preamp at the antenna
> > requires antenna switching which induces more loss. In the shack the
> > preamp connects easily to the amp relays.  So should it be in the shack or
> > at the antenna?
> >
> > So how much gain is needed and/or required for maximum performance?  Is
> > there an optimum gain or convenient gain?
> >
> > If someone has played with a similar system layout or has completed tests
> > with the preamps I would like to hear your test results.
> >
> > Thanks in advance for all the replys.  I promise to share the results from
> > my questions.
> >
> > 73's
> >
> > Dave Anderson, K4SV
> > Tryon, NC
> > 828 777-5088
> >
> > www.K4SV.com
> >
> > _______________________________________________
> > Moon-Net posting and subscription instructions are at
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> >
>
>
>_______________________________________________
>Moon-Net posting and subscription instructions are at 
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73,
Ed - KL7UW
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