Remote Antenna Switching.pdf

Remote Antenna Switching

Why Remote Switching??

My original Remote Antenna switch was made specifically to select the various

driven elements on my Quad. This works extremely well, and was simple to

build. I then realised that remote switching for all of my antennae would have

a number of advantages.

1. A large reduction in the number coax "runs" from the shack to the

various antenna locations, thereby making a considerable saving in

cost, and complexity, of switching antennae from the shack.

2. A few runs of expensive, high quality "hard line" coax to the main

antenna switching points outside the shack, is CHEAPER than running

seperate runs of RG213 or similar, to each individual antenna all the

way from the shack.

3. If an electrical storm heads in your direction, it is comparatively easy

to unplug two or three coax lines and control cables and throw them on

the lawn before you hide under your bed..!!! Also, all unused antennae

have their coax feeds shorted to ground at the remote switch boxes.

4. It is easier to experiment with new, or temporary antennae, as you can

hook into a spare point at a remote switch, rather than run a temporary

coax all the way back to the shack...And of course, "temporary" set-ups

have a nasty habit of becoming permanent "eyesores"...

5. There is an overall reduction in general"clutter" in the shack, making

operating easier, and perhaps even earning the coveted "XYL seal of

approval"...

There are two disadvantages to "Remote Switching"

1. The cost of the switches....Negligable, if you build them yourself....

We're Experimenters....Right???

2. If you lose your electrical supply to your home, in a storm, or for other

reasons, you have no control of your antenna selection.

As regards the second scenario, I have always made a point of having an

emergency supply available. I have a standby 3KVA generator, and also a bank

of four large 12V automobile batteries wired in parallel. All my remote

switches use 24V DC relays, so I series a small 12V battery with the other four

to give me my emergency 24v supply. I have no preference for 24V relays

over 12V relays... I use 24V relays, purely because I have a good supply

of high quality relays which just happen to be 24V...

If you have a small antenna setup, with perhaps a tribander, and a Zepp, or

trapped vertical for the lower bands, then remote switching is not really any

advantage. If on the other hand, you're one of the lucky ones, and have lots of

space for lots of antennae, then you should probably take a look to see if it

can be of advantage in your situation.

In my own case, (I'm one of the lucky ones) I live in the country, on the coast,

and my site is approximately 1/2 an acre. I have permission from my farmer

neighbours to erect whatever antennae I like, in the surrounding fields, so

long as I do NOT interfere with the agricultural activities in any way

whatsoever. I have erected four large (45-60ft) timber poles at various

locations on the boundaries of surrounding fields. I have a 55ft tower at the

back of the house, and a couple of verticals in another corner of the garden. I

have a 4insOD plastic conduit running underground from the shack to the

tower...120ft. Another conduit to the Verticals about 80ft. But the run to the

60ft pole in the field is 900ft...Yes ...nine hundred feet..

I run three coax lines to these locations, and have one or more remote

switches at these three antenna sites. For instance, at the tower, one coax

line feeds the eight bands on the Quad (40M thru' 6M) and a sloper..Nine

antennae...One coax...one control line.

Simple Remote Switch..

The switch consists of two units, the control switch in the shack, and the

relay box at the remote end. The Control Box consists of a small Power Supply

providing 12V or 24V DC to suit whatever relays you are using. The " + " of the

DC supply is connected to the input of a rotary switch, and the output tags of

your switch are wired to a terminal strip mounted on the back of the box. A

multi-core cable is then run from the terminal strip to the Remote Relay Box

at the antenna site.

( Diagram of Remote Relay Box.. All unused antenna outputs are grounded)

Most of the surplus relays that I come across are encased in a clear plastic

cover, and have " OCTAL" bases. Others have flat metal "pins".Anything that

can handle about 240V AC, at about 10Amps, should be adequate for powers

of up to 1.5kW of RF. ( switching 50 Ohm coax).

You can use these "as is", soldering the wiring direct to the pins on the bases

of the relays. I prefer to modify my relays, because the long connecting wires

from the base to the switching contacts, are usually pressing against the relay

bobbins. This must induce RF into the bobbins, and probably introduce a bit of

distruption to our 50 Ohm line. I remove the bases and plastic covers. I also

remove the "flying leads", and solder a jumper between the two relay

switching "leafs". This shortens the RF path through the relay,and reduces any

extraneous coupling. Hopefully the drawing below will be adequate

explanation of the modification...

( Pic of remote relay switch box, with modified relays)

The MK2 Switch Box

Recently, I got some really nice new modern PCB mounting relays. They are

quite small and tidy, but the bobbins are well away from the contacts. The

Contacts are silverplated, and are rated to handle about 2kW at 240v AC. The

use of a PCB, really tidies up the wiring., and minimises anomolies in the RF

path... See pics below... The local contest station EI7M, recently used this

switch in "battle conditions", and hopelessly failed to do any damage to

it....C'mon guys... Your not TRYING!!!!

( FINDER type 40.31 S . PCB mounting 24V relay. They measure 1ins high by 1ins long

by 1/2ins wide..approx )

( Pic of relay box using PCB mounted relays, and PCB board chassis)

(Rough drawing of PCB layout)

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