[Moon-net] EME antenna/amp advice

Wed Aug 23 08:40:46 CDT 2006

Zdenek, Bodo, and all:

I would give a "Yes" to what Zdenek has said.  I have run 0.5 dBNF preamp
and then 0.15 dBNF preamp on my four 3WL 2m array and the latter preamp
wins...in the same real environment.

I think running the theoretical calculations is good for one's
confidence...using it will prove the validity or not.  I would lean to
lower NF as working for me.  Theory supports that as well.

Manmade environs can make a large effect on how well you can hear, but
nobody can determine this for you.  

73's Ed - KL7UW
PS:  I am continually promoting low-noise preamps to the local VHFers as
the "secret" to DX.  Every week I sit and copy easily many stations in an
SSB net that struggle to hear each other.  A few are begining to come to my
thinking.  When one finally tries using a mast-head preamp they are
"surprised" by how well they can hear...hmmm.

At 03:08 PM 8/23/2006 +0200, OK1DFC wrote:
>
>We have in OK (Czech Republic) one proverb. " Grizzle is theory, Green is
>tree of the Life". Why? It is simple. Before start of using my LNA in 144MHz
>system I was not able to work with many stations. I must to explain that on
>144 I am using only single Yagi. But with 0,16dB N/F LNA (Measured on HP
>Noise figure meter in the lab) I have worked now around 100 initials. I do
>not want to administer justice who is true and who is wrong. But practically
>without LNA is not possible to work seriously. I repeat the last word
>"seriously". I am sure that maybe 80% of "active" stations will say same.
>Here I must to repeat again "ACTIVE". Any articles in magazines are good to
>reading and to testing, but not all are valid to trusting without checkout.
>Solution is simple. If anybody trust WITHOUT, o.k. he can work without, I
>trust "WITH" and will work with. In this point is valid first sentence about
>Grey and Green. :-)))
>Best regards and looking forward to meet you all in Wurzburg.
>Zdenek - OK1DFC
>JN79GW
>www.ok1dfc.com <http://www.ok1dfc.com>
>QRV EME - 144 - 432 - 1296 MHz
>10m DISH - QRO
>
>
>
>-----Original Message-----
>From: Moon-net-bounces at list-serv.davidv.net
>[mailto:Moon-net-bounces at list-serv.davidv.net]On Behalf Of Bodo Heyl
>Sent: Wednesday, August 23, 2006 2:05 PM
>To: moonnet
>Subject: Re: [Moon-net] EME antenna/amp advice
>
>
>Leif, Kim, Oene & others,
>
>The background of my posting is, that I would like to
>know, whether:
>
>a) in practice(!)  the statement of DH7FB is right saying that using a LNA
>on 2m
>with the lowest possible NF is useless (except big arrays with a lot
>of connection cable and couplers in front of the LNA)
>DH7FB quoted by PA3CWN:
>
>DH7FB Frank wrote a nice article about that in the German Magazine
>Funkamateur and He explained in that, that only vy large arrays will benefit
>from Vy low NF figures because of the stacking losses are more with larger
>systems.
>These losses may in such situations exceed the 144Mhz  cold sky noise which
>seems 2.7dB,
>so if you add all the losses in your stacking to the 0.6 dB of your preamp
>you should be below
>this 2.7 dB and in my opinion you will be below that.
>
>unquote
>
>b) the statement of Leif, SM5BSZ, that on 2m a LNA with a very low NF is in
>any case
>useful.
>
>quote SM5BSZ
>The antenna temperature may be as low as 190K on 144MHz (optimum EME
>conditions). If we allow 5% of the noise at the output to be generated by
>the amplifier itself we find that the noise temperature has to be as low as
>10K.
>10 / (190 + 10) = 5% The performance loss compared to an ideal receiver is
>then 0.2dB which is a small number but not completely insignificant.
>unquote
>
>73 de Bodo/DL2FCN
>
>
>
>----- Original Message -----
>From: "Leif Asbrink" <leif at sm5bsz.com>
>To: <Moon-net at list-serv.davidv.net>
>Sent: Tuesday, August 22, 2006 10:57 PM
>Subject: Re: [Moon-net] EME antenna/amp advice
>
>
>> Hello Kim,
>>
>> > but only if the losses of the input circuit are extremely small,
>something
>> > that can be
>> > achieved in case input selectivity is unimportant.
>> >
>> >
>> > YES, but it is NOT in practice !
>> ?????????
>>
>> > The Loss of of an input circuit and its eqvivalent contribution to the
>NF
>> > itselves, can be calculated
>> > from the  NF itselves  PLUS the loss in the input LC !
>> > And according to the theory can this be calc. as the difference from the
>> > loaded Q / unloaded Q  !
>> >
>> > So its absolutely important to have  high unloaded Q and a low loaded Q
>!
>> Hmmm, would you not agree it is only important to have a very small
>> ratio loaded Q / unloaded Q ?
>> What about extremely low loaded Q and "normal" unloaded Q?
>>
>> > So all in all, inputselectivity is  VY dependend of this relationship,
>so it
>> > IS very important.
>> If we make the loaded Q = 3 (Equivalent to VERY poor input selectivity) by
>> having an extremely high L/C ratio we could have a modest unloaded
>> Q of only 300 and still have very low losses.
>>
>> 73
>>
>> Leif / SM5BSZ
>>
>>
>>
>> _______________________________________________
>> Moon-Net posting and subscription instructions are at
>http://www.nlsa.com/nets/moon-net-help.html
>>
>
>
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73's,
Ed - KL7UW  
=========================================
http://www.qsl.net/al7eb - BP40iq 
144-EME: FT-847, mgf-1801/1402, 4xM2-xpol-20, 170w
432-EME: FT-847, mgf-1402, 1x21-ele (18.6 dBi), 60w
=========================================