[Moon] Preamp on 144 MHz

[Bodo Heyl]

Oene is right, this is also my experience here.

Very simple, download VK3UM's EME calculator,
play with noise figure, sky noise etc. and you will find
out how important (or unimportant) the noisefigure
of the preamp for 2m is..

70cm and up is a different issue, of course..

73 de Bodo/DL2FCN


----- Original Message ----- 
From: "Oene Spanjer" <pa3cwn at tele2.nl>
To: "Moon" <moon at moonbounce.info>
Sent: Monday, April 30, 2007 11:44 AM
Subject: Re: [Moon] Preamp on 144 MHz


> Hello All,
>
> I recently got my SSB SP2000 out of the mast and experienced
> that especially at low elevation angles my receive has improved
> dramatically. Below 3 degrees I could not hear any EME signal
> anymore (not even big guns).
> The reason is off course terrestrial noise, which overloaded the
> mgf1302.
> On high elevation angles the mgf1302 did his job as now I have
> abt 1 dB loss in the cables and the receive consist of an old
> FTV107 transverter with 3SK51 fet.
> I came to the conclusion that filtering BEFORE the preamp is
> in my case much more important than the NF of the preamp.
> (I guess the old transcerter with 3SK51 has not that good NF
> figure)
> Therefore a GOOD and low NF is to prefer if some form of
> filter is before the preamp, because due to it's losses will degrade
> the NF a bit.
> So in my experience the terestrial noise is of much more importance
> than a NF difference of severeal tenths of dB only.  In areas
> where there is almost nil noise I can think of some difference,
> but in my opinion one can better choose for a cavity preamp with
> 0,5dB NF as for 0.2 dB without proper filtering.
>
> GL to All
>
> 73 Oene
> PA3CWN
>
>
>
> ----- Original Message ----- 
> From: "Peter Sundberg" <sm2cew at telia.com>
> To: <moon at moonbounce.info>
> Sent: Sunday, April 29, 2007 10:29 PM
> Subject: [Moon] Preamp on 144 MHz
>
>
>> Had a discussion the other day regarding preamps and noisefigures with a
>> friend, thought I'd take it to the expert team on Rainers Moon 
>> reflector..
>>
>> When I started EME on 144 MHz (only 22 years ago) the general concensus 
>> was
>> that a BF981 with 2dB NF was good enough. Reason given was that the
>> background noise was the limiting factor, and a better NF than 2dB was 
>> not
>> needed.
>>
>> Anyhow, modern designs that people use today range between 0.2-0.4dB NF,
>> and people seem rather determined to reach such numbers. Anything higher 
>> is
>> dismissed as more or less "non functional".
>>
>> Now my question to you experts; was the old 2dB NF a myth from ancient 
>> times?
>>
>> If so, what is the actual treshold where a lower system temperature in
>> theory (and practice?) has no effect on moon signals? Could it be that 
>> all
>> the work to achieve virtually zero NF on 144 MHz is just to increase the
>> confidence factor for the operator?
>>
>> On 144 MHz, given good antennas, cables and relais ahead of preamps these
>> days, maybe we are spending too much time worrying about the preamp NF.
>>
>> Then again, Lasse SM4IVE is talking about stacking two soundcards, maybe
>> that's more important..  :-))
>>
>> 73 de Peter SM2CEW
>> www.sm2cew.com
>> http://blog.sm2cew.com
>>
>>
>>
>>
>>
>>
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>
>
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