[TowerTalk] Multi-station antenna selection patch panel

Scott scottw3tx at verizon.net
Sat Jan 18 19:31:47 EST 2014

Thinking outside the boxŠhere is how I would do it:

My first thought for designing a multi station, whether it be
multi-single, multi-two, or multi-multi, is with regard to minimizing
inter station interference. I am willing to give up the flexibility of
switching any band antenna to any radio [(while simultaneously eliminating
a significant number of points of failure (read: electro-mechanical
devices)] to reduce inter-station interference

One set of (non-shared) antennas per band. Each band's phasing switching
at ground level instead of on the tower, A separate feed-trunk for each
band from the band-antenna to the radio room. In each band's feed trunk
are the filtering coaxial stubs and bandpass filters for the specific
band, an amplifier dedicated to that band, and finally a separate radio
for each band.

Clearly for a multi-single or multi-two this uses four more amplifiers
than if one employed a relay switching matrix.  But, is it really more
expensive to buy six mid-range amplifiers than it is to buy two
auto-switching amplifiers? Probably not if you buy several used AL1200's.
Or build six mono-band amps.

And when it's time to re-arrange the station for single-op simply put all
the radios on a u-shaped table and buy a professional grade audio mixer
from the music worldŠthey have units that can take 6+ audio streams and
switch/mix them in any combination desired.

73, Scott W3TX 

On 1/18/14 5:54 PM, "krishna kanakasapapathi" <kkanakas at cisco.com> wrote:

>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
>>> 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:
>>> 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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