[TowerTalk] Stacking dissimilar antennas - correction

[Michael Lamb]

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From: 	Henry G Chapoton[SMTP:chapoton@smtp-gw.gdls.com]
Sent: 	Wednesday, July 22, 1998 9:39 AM
To: 	kq2m@eci.com
Cc: 	towertalk@contesting.com; n4kg@juno.com
Subject: 	re: [TowerTalk] Stacking dissimilar antennas - correction

Hello All:  I am sorry, but I think I have come into this thread at a late date, but I wanted to weigh in anyway.

I have played the stacking game for many years, especially on VHF.  I started using the standard 1/4 wave RG-11 70 ohm Wilkinson power dividers for up to 4 yagis on an H frame.  I have since used the M2 4 port power dividers that work great on VHF.

When I decided to stack six tribanders on a 190 ft. rotating tower, obviously I could not use the same old power divider technique because what is a 1/4 wave on 20 meters is a 1/2 wave on 10 meters!  First, I used the SAME yagis spaced the same 30 feet distance apart all the way up the tower.  Then I divided the antennas into pairs; an upper, middle and lower pair.  I used exactly equal lengths of RG-213 coax from each antenna of a pair to a 25:50 ohm UNUN physically located between the pair of antennas.  I now had three of these UNUNs on the tower.  I brought equal lengths of RG-213 coax to a centrally located "Stackmaster" switch box that allows me to select any combination of pairs of antennas.  That is accomplished using a 22 2/3 ohm UNUN for matching all three or any two pairs to nearly 50 ohms.  The UNUN is bypassed for any single pair.

So, if you are careful to keep the feedlines the same length (either
measure the same physical length off the same reel, or better yet,
measure with an antenna analyzer) and use broadband UNUNs, you can
even stack tribanders.

My inspiration for the triband stack was an article by Dean Straw and Fred 
Hopgarten (sp?).  For HF operation, I simply would not consider using the 
1/4 wave matching sections anymore because like someone already 
pointed out, the match will be different at one end of the band from the 
other.

73/Mike, N7ML

PS Does anyone have an idea of how I can reformat my Microsoft
Exchange e-mail?  It looks fine on my end, but I understand that
it does not word wrap properly when it is sent out??????  Please 
respond directly so that we don't take up space on the reflector.
Thanks.


     
     Bob:
     
     Change those references to "1/4 wave multiples" to "ODD multiples of 
     1/4 wave".  Usually a good place to put a 1/4 w. of 75 ohm (or 
     whatever) for matching, along with equal lengths of 1/2w. multiple 50 
     ohm for the balance of length req'd to the switch box.  If you don't 
     require the impedance transformation, just use odd 1/4 w. mults of 50 
     ohm. 
     
     Greg
     na8v

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