[TowerTalk] Multi-station antenna selection patch panel

krishna kanakasapapathi kkanakas at cisco.com
Sat Jan 18 17:54:59 EST 2014

Thank you all for the inputs. I think we now have a good deal of data to 
start an in-depth investigation.


On 1/18/2014 2:16 PM, Jim Lux wrote:
> On 1/18/14 4:07 AM, David Robbins wrote:
>> Agree, any to any gives lots of relays no matter how you do it.  but you
>> really don't need vacuum relays, most of the common switch boxes 
>> today just
>> used regular frame relays.  If you want to keep cost down by using 
>> off the
>> shelf parts try looking at the rcs-10 remote switches that do 8 to 1, 
>> I am
>> using them for my rx antenna switching:
>> http://wiki.k1ttt.net/2011%20Maintenance%20and%20Upgrade%20Blog.ashx#bevswit 
>> ch  and they work well... of course there is no lockout, you would 
>> have to
>> come up with that in whatever provides the control power.  I think 
>> k1xm was
>> working on something like that, but not sure how far it ever got.
> I think it's the port to port isolation requirement that is going to 
> drive the design..  Regular old power relays, if chosen wisely, will 
> probably work just fine, but you might need to come up with switch 
> architectures that cascade two or short unused ports, etc. to get 
> enough isolation.
> I doubt a single relay will get you 60 dB of isolation for instance.
> There's a fair number of posts to TT over the years with suggested 
> part numbers for the relays, and for such a big project, I'd go out 
> and get a few and rig up some test fitures before committing 
> (although, if you got a good deal on surplus and they cost $1/each in 
> that quantity...)
> Another aspect to consider is failure modes: if one of those dozens of 
> relays sticks or fails to change positions you don't want to be 
> blowing up radios with the output of the linear.  This is one of the 
> advantages of the various schemes where you have two SPDT relays in 
> the path: if one fails, you've still got the other one to prevent 
> disaster.
> I've found that it's the driving circuitry that is often the more 
> complex aspect.  Although.. these days, there are people selling nifty 
> computer controlled relay drivers AND decent software that can be 
> configured appropriately, so you probably don't have to spend hours 
> figuring out diode matrices.
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