[Moon-Net] LNA Relay

Magnus Lindgren sm6xma at gmail.com
Mon Sep 30 01:55:06 CEST 2019


Hi!

Be sure to have a relay with enough isolation, for two reasons: 1) So 
that the LNA does not get damaged during Tx. 2) So that the ~290K noise 
level from the 50 Ohm termination does not increase the noise seen by 
the LNA during Rx. Point 2 is important in order to reduce the system 
noise temperature and thus achieve a high G/T!

Please refer to my Master's Thesis which can be found at the following 
location:

"A 1296 MHz Earth–Moon–Earth Communication System – Theory and Practice"

http://publications.lib.chalmers.se/records/fulltext/217884/217884.pdf#pagemode=bookmarks

More specifically, the following sections are of interest:

4.6 Total system noise temperature at the terminals of an antenna
7.3.2 Coaxial protection relay
9.2 Transmitted power at the LNA input

73's


Magnus, SM6XMA/DL6XMA

On 28/09/2019 19:26, James C via Moon-net wrote:
> FWIW,  Besides the additional protection an iso relay provides, it also 
> ensures your LNA is always looking at a 50ohm impedance to deter self 
> oscillation. Something to think about anyway,. GL, 73 .-James K7KQA
> 
> On Sat, Sep 28, 2019 at 9:32 AM Stephen Hanselman via Moon-net 
> <moon-net at mailman.pe1itr.com <mailto:moon-net at mailman.pe1itr.com>> wrote:
> 
>     Vlada,
>     Are you suggesting that an isolation relay is not needed on a septum
>     feed?  That would make my 1296 system simpler, but I’m a bit worried
>     about my LNA
> 
> 
>     73's
> 
>     __ __
> 
>     Stephen Hanselman, KC4SW____
> 
> 
> 
>     Sent from my iPad
> 
>     On Sep 27, 2019, at 02:12, vlada via Moon-net
>     <moon-net at mailman.pe1itr.com <mailto:moon-net at mailman.pe1itr.com>>
>     wrote:
> 
>>     Hi Voja,
>>
>>     as regards LNA input protection, the transfer relay behave
>>     actually in the same way as a single port relay.
>>
>>     So, the level of protection just depends on the isolation of the
>>     particular relay and proper function of the sequencer or similar
>>     function circuitry.
>>
>>     Additional relay at LNA input is almost necessary in case of
>>     separate but close RX/TX feeds (like septum feed) with limited
>>     isolation in-between.
>>
>>     Optionally, if the relay isolation is insufficient or you are
>>     looking for a secured protection, you could use an additional
>>     protection directly on LNA input either outside or inside (like a
>>     power limiter used e.g. in spectrum analyzers or an antiparalel
>>     vhf Schottky diodes etc.).
>>
>>     However, al these units will obviously somehow (more or less)
>>     decrease the noise performance of LNA.
>>
>>     73, Vlada
>>
>>     OK1KIR
>>
>>     ______________________________________________________________
>>     > Od: "Vojislav Bandobranski via Moon-net"
>>     <moon-net at mailman.pe1itr.com <mailto:moon-net at mailman.pe1itr.com>>
>>     > Komu: "Moon-Net" <moon-net at mailman.pe1itr.com
>>     <mailto:moon-net at mailman.pe1itr.com>>
>>     > Datum: 26.09.2019 21:39
>>     > Předmět: [Moon-Net] LNA Relay
>>     >
>>
>>     Hi,
>>     does anyone have experience with using a transfer rf switch (with
>>     4 connectors) in LNA?
>>     Is it necessary to add another relay in front of LNA input for
>>     insulation?
>>     I mean simple rx/tx transition.
>>
>>     -- 
>>     73 de Voja/YU7C
>>
>>
>>     ----------
>>
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