[TowerTalk] 20m stack switching question

[Grant Saviers]

Jim,

I have only a years experience with my 5 over 5 stacks but have observed 
that the top antenna only can be much quieter at times.  I haven't 
experienced heavy p-static but that is often cited as a reason to select 
a lower antenna, as is shorter paths.   Otherwise I'm in BIP mode except 
when antennas are in different directions for contests (all are 
independent on K0XG rings).  So, extrapolating that to a 3 high stack 
rotating tower, I would probably do top only, bottom only, and all.

What I've read agrees that BOP is pretty useless, so I bought stack 
matches without that capability.

Grant KZ1W


On 7/13/2016 9:27 AM, Jim Thomson wrote:
> A buddy has  3 x 20m monobanders, stacked at   172, 117,  62  ft.   Currently, all 3 are driven in  phase,
> via a L network.  ( 50 ohm to 16.66 ohms, consisting of a   shunt  317.7 pf  cap  from input  50 ohm connector to chassis, then
> a series .2646 uh coil. Coil goes from input connector...to the 3 x paralleled output connectors)   Its just a mess of  5 kv NPO  doorknob caps
> in parallel + some cu tubing.   Pretty straight forward.   In actuality,  325 pf was used... and slightly less coil.
>
> The plan was to install some relays, and  then be able to switch top, middle, and bottom.... and all 3 in phase.   We can pull that off
> with just  3 x  SPST  relays...and  1 x  SPDT relay.
>
> Then we thought, why not be able to use any 2 x yagis at a time, like  top + middle... middle + bottom.... and also  top and bottom.
> That could be done with a 2nd L network +  1 x additional SPDT relay.
>
> Ok, is it even worth it to be able to use any  2 yagis ??   For  DX, all 3 in phase work pretty good.   For local, say within 3000 miles, perhaps
> the lowest yagi alone would suffice?     I cant see  the top and bottom buying him anything..... vs  all  3 in phase.  I cant see the top and middle
> outperforming all  3 in phase.   That only leaves the middle and bottom..and even that is dubious... but we have zero experience with this.
>
> Even with the 4 x relays and just one L network box,  we could still easily select any 2 yagis..and use the 50: 16.66 ohm L network... however
> the swr  will not be dead flat, but it would be <  2: 1      25 / 16.66 =   1.5:1  swr.... which is still useable.
>
> Are we wasting our time ?   On a side note, the pair of 40m yagis, 180 + 89 feet, are also driven in phase.... with no provisions  for top + bottom
> switching.  However,  BOP  was added to the BIP.   Easily done with a switchable  1/2 wave of coax in either leg.  Then countless  hrs spent switching between
> BIP...and BOP.   BOP was a disaster.  Only once  was BOP a bit louder... and that was on 40M during the daytime..and just one station, aprx  200 miles away.
> Looking at some notes here and there, it appears that  BOP  has a higher take off angle than the lower 40M by itself...which ends up way too high.
>
> Latest plan is to be able to switch  top /bottom /both on the  pair of 40m yagis......and ditto with the pair of 15M yagis ( 127  +  79 ft) .  We could also add
> the BOP function, but after the 40M failed experiment, I think BOP is a total write off.
>
> Any thought on any of this  would be greatly appreciated.   BTW, all yagis are pointed in the same direction on a rotating tower.   In the original config,
> non rotable tower, tic rings were used on 40M + 20m.... then all ants could be pointed in different directions.  That came in handy at times, but the tic rings
> were a constant head ache.
>
> Jim  VE7RF
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