Hi to everybody,
I need schematic of an antenna switch witout control cable, for selection I
must use coaxial cable.
It will be placed on the mast. I found something interesting on ham
newspapers but . . I lost it. via internet I try but if you use some search
tool (ie. google) you are sure to find all but not what you are looking
for.
Thanks in advance.
Nike

It's easy to drive one or two relays, to select one of two or three
antennas. Use a capacitor at each end to feed RF through, and a choke
at each end to feed DC through. For the two-relay case, from the
control end of the coax, apply no DC to energize neither relay, or,
say, +12V to energize one relay, or -12V to energize the other. At the
mast end, use a series diode after the choke to each relay, in opposite
directions. Obviously, use 12V relays. Omit the diodes for only one
relay. If the run is very long, it's better to feed the DC as a
current--the rated current of the relay--to account for resistance of
the line. One way to do that is to use, say, 24V and put a series
resistor (appropriate power rating) at the power supply end, equal to
the nominal relay coil resistance. That can also protect somewhat
against the effects of a DC short across the line. Pick capacitors
that work well for the RF frequency you're using, and have low
reactance (say less than 5 ohms) at the lowest frequency of interest.
Pick chokes that have high impedance over the range of operating
frequencies, say 500 ohms minimum. If you don't have much experience
building RF things, check out some references for RF construction
practices. Without that experience, don't expect to get good
performance much above 30MHz.

try this site www.vkcorner.com or http://www.vkcorner.com/forum/index.php
"nike" wrote in message
...
Hi to everybody,
I need schematic of an antenna switch witout control cable, for selection
I
must use coaxial cable.
It will be placed on the mast. I found something interesting on ham
newspapers but . . I lost it. via internet I try but if you use some
search
tool (ie. google) you are sure to find all but not what you are looking
for.
Thanks in advance.
Nike

In article , nike
wrote:

Hi to everybody,
I need schematic of an antenna switch witout control cable, for selection I
must use coaxial cable.
It will be placed on the mast. I found something interesting on ham
newspapers but . . I lost it. via internet I try but if you use some search
tool (ie. google) you are sure to find all but not what you are looking
for.
Thanks in advance.
Nike



What K7ITM suggests is using DC blocks to put a DC control voltage on
the coax, and take it off again at the mast end. You can build your
own with a choke and a capacitor (both components well chosen), or you
can buy them already made. Depending on the company, they're called DC
blocks, line isolators, or bias tees.

These building blocks have three connections; a RF-only connection, a
DC connection, and an RF-plus-DC connection.

Key parameters include DC current carrying capability (which is also
affected by the coaxial cable you use), and SWR/insertion loss on the
RF side.

For low frequencies, SGC (http://www.sgcworld.com) sells DC Coaxial
Line Isolators (SGC catalog 54-70) good from 1.5 MHz to around 250 MHz,
handling up tp 1.5 amps at 25 volts.

At higher frequencies, Minicircuits makes Bias tees good from 1 MHz up
to the GHz range. You can often find these on eBay.

You can also find RF switches (relay and diode) on eBay.

--
Namaste--