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Re: [TowerTalk] Budget 4-Pack?

To: Jim Lux <>, "Tower and HF antenna construction topics." <>
Subject: Re: [TowerTalk] Budget 4-Pack?
From: Gregory Fischer <>
Reply-to: "Tower and HF antenna construction topics." <>
Date: Tue, 2 Mar 2010 13:58:39 -0800
List-post: <">>

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 <> wrote:

> -----Original Message-----
>> From: Barry Fox <>
>> Sent: Mar 1, 2010 11:40 AM
>> To:
>> Subject: [TowerTalk] Budget 4-Pack?
>> I have two HF radios and 4 different HF antennas.  I would like to  
>> use
>> 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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