[TowerTalk] Antenna switch isolation?

Jim Thomson jim.thom at telus.net
Sat Jun 5 23:03:23 PDT 2010


Date: Sat, 5 Jun 2010 23:48:56 +0700
From: "Martin Sole" <hs0zed at csloxinfo.com>
Subject: Re: [TowerTalk] Antenna switch isolation?

Back to my switch project it seems clear that layout is critical as may be
the choice of relay to minimise coupling. Whilst I think I have a stray
coupling problem there also seems to be quite a few variables at play.

Martin, HS0ZED

p.s. This switch box is for my quad project, feeding the loops ONE at a
time.

##  OK... since this appears to be a 1 in  3-5 out box... for a quad... then
why do u require all the isolation??    My Array solutions 1 in 6 out box  uses
6x DPDT relays.   They use  3/4" wide Cu  strap..exactly  5/16" above the chassis.
This forms  a 50 ohm strip line.  Input is at far left... and outputs 1-6  are to the 
right of this.  COM  of each relay is connected to the center conductor of each coax
connector [7-16 din].  ALL  NC  contacts are connected to  the grnd buss.. which is just
more 3/4"  wide cu strap..running the entire width of the box.    ALL the  NO contacts
are connected to the hot 2 kw buss. [ more cu stap].   Far left hand side of this hot buss is 
connected to the input connector. 

## in  normal operation... any relay that has it's coil DE-energized.. [ not operated] 
has it's ant center conductor grnded !   Any relay operated  has  it's ant center conductor
fed to the  input hot buss.    There really is no port to port isolation per se.... since all unused 
ports are dc grnded.   They have also paralleled all contacts to increase power hanndling by 4 x .

## I also have the AS  6 pack box... uses 12 x relays.   They have the diagram of it on the AS site.
These box's  use 12 x  3PDT  relays.   The 3rd set of contacts is used to control the ..'master-slave' 
function.. so which ever of the 2 x ops gets the ant 1st.... locks out the 2nd op.  There is loads
of isolation with the remaining  contacts.    Each of the 6 x ant  ports  has a PAIR  of  3PDT relays.

## If you just require a remote switch box to save on coax... and toggle  ONE xcvr between  a bunch
of DE's  on your quad... then almost anything will suffice.   Isolation in that case is a non issue. 

later........ Jim  VE7RF






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