Take a look at this solution. Less expensive and provides the lockout
from the control unit.
Sent from my iPhone
On Mar 2, 2010, at 11:50 AM, Jim Lux <email@example.com> wrote:
> -----Original Message-----
>> From: Barry Fox <firstname.lastname@example.org>
>> Sent: Mar 1, 2010 11:40 AM
>> To: email@example.com
>> Subject: [TowerTalk] Budget 4-Pack?
>> I have two HF radios and 4 different HF antennas. I would like to
>> each rig on any antenna, while obviously locking out that antenna for
>> the other rig. The commercial products 6-Pack, 8-Pack, etc are way
>> over my budget. Anyone have a schematic for a "4-Pack" or similar
>> device they would like to share? Obviously relays are the way to
>> go, and I can get the RF relay switching part of it on paper but
>> not the lockout logic. Some sort of electro-mechanical exclusive-OR
>> gate array / diode matrix? Anyone been there and done that?
> I wouldn't trust lockouts in the relay drive logic (e.g. what
> happens if a relay sticks)..
> What's your port to port isolation requirement?
> one way to do it is to use a single pole double throw relay
> connected to the antenna that switches the antenna to one radio or
> the other. If a relay fails, you can't wind up connecting one radio
> to the other, although you can wind up with two antennas connected
> to one radio. (essentially it's a mechanical interlock)
> If you need more isolation, you can put a SPST relay in series from
> the radio to the port on the antenna relay (this would take 3 times
> as many relays).
> One problem is finding a good SPDT relay for RF. Because of the way
> relays are made, one set of fixed contacts is closer to the frame/
> coil than the other. One strategy is to use a DPDT relay, short the
> two moving contacts together, and then basically use the two halves
> of the switch in series. A failure that makes one contact stick,
> but not the other, is unlikely, and even so, it just "reverses" the
> sense of the switch.
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