[Moon-Net] LNA Relay

vlada vlada.masek at volny.cz
Sat Sep 28 19:22:49 CEST 2019

Hi Stephen,
I suggest just opposite (see the bolded sentence) !
Sri for a bit complex formulation, but there were some solutions described in the past with a small "coin" reflector in front of septum feed, which increased isolation between TX and RX part by a kind "neutralization" between both parts of septum feed. 
This small reflector reflected a piece of radiated TX energy to the RX part with opposite phase, both created by the "coin" size and proper position.
However such sophisticated solution is quite sensitive to any change of arrangement in the close vinicity, so I think it is a bit risky.
Moreover a good quality isolation SPDT relay can be used to very handy testing of system performance by means of Zo/CS ratio, when one DT connector goes to RX septum and the other to a good quality Zo load.
The SP connector goes, of course, directly to the input connector of LNA.
It only need a simple additional circuitry allowing to control this relay when receiving, e.g. easy with a reversible button placed in operating place.
We are very happy with that RX performance test option on all bands from 432 MHz up to 24GHz.
73, Vlada
> Od: "Stephen Hanselman" <eme at kc4sw.com>
> Komu: "vlada" <vlada.masek at volny.cz>
> Datum: 28.09.2019 18:35
> Předmět: Re: [Moon-Net] LNA Relay
> CC: <ebvoja at gmail.com, moon-net at mailman.pe1itr.com>
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

Stephen Hanselman, KC4SW
Sent from my iPad
On Sep 27, 2019, at 02:12, vlada via Moon-net <moon-net at mailman.pe1itr.com <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
 > Od: "Vojislav Bandobranski via Moon-net" <moon-net at mailman.pe1itr.com <moon-net at mailman.pe1itr.com>>
 > Komu: "Moon-Net" <moon-net at mailman.pe1itr.com <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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