Topband: Rx 4 square switching box

[K4SAV]

..."I'm trying to be careful with the grounds isolation, i.e. the 
verticals ground system not connected to the central box and feedline 
output through a separate windings xfmr."...

It doesn't hurt to connect the antenna ground to the central box at the 
antenna, and it's usually a good idea to do that.  However the feedline 
should be coupled thru a transformer as you said.

...."But could be also a good idea to keep the -12VDC of the 14 relays 
insulated from the metal box (and the combiner grounds) and thus return 
only to the shack through their own multi-wires control cable?"...

I would connect the control box to antenna ground, and isolate the dc 
ground for the relays from the antenna ground, but use caps to bypass 
both sides of the relay coils to antenna ground in the control box. The 
control cable can be a separate cable but I would add some ferrite 
common mode decoupling on it before routing it back to the shack.  
Inside the box is a good place to put this since the ferrite can be 
small because the wires can be small. You only need one ferrite, just 
add enough turns to get good attenuation.

Reasons:  You need dc isolation to keep ground currents off the relay 
coils.  You need the relay coils at signal ground potential to keep 
whatever noise there is on the control lines from coupling into the 
contacts.  Without the bypass caps, the common mode choke will have to 
be much larger since the impedance will be much higher.  With the choke, 
current into the antenna ground will be low and not enough to cause 
coupling by drop across the ground impedance.

Jerry, K4SAV

Luis Mansutti IV3PRK wrote:

>Hi friends,
>
>While building the switching box for my new receiving array .................
>  
>