[Antennas] Model this idea

[C.Whitaker]

de WB2CPN
Chris,
Perhaps you should have a look at how commercial
VHF and UHF stations populate those broadcast towers.
Generally, you can put 1/4 wave and other size stubs
all the way up and down the tower.
Like everything else, there's a lot more to this.
73  Clete
++++++++++++++++++++++++++++++++++++++++++
On 10/10/2012 9:29 PM, Chris Boone wrote:
> I have a possible project in the near future.putting 2 antenna (700 and 600
> ft high) and fed by separate cables of course (lower will be TX).
>
>   
>
> However, I was looking at the UHF side and though, HHMMM would be nice if I
> could make the mast carry three bands (VHF/220/UHF).
>
>
> Using the DB products elements (which I got plenty of) and a VHF Hiband mast
> (since it will be the longest and thicker/heavier than the UHF DB420 equiv),
> I came up with the idea of making the center of the mast the RF "center" on
> all bands.soo all dipoles mounted would be referenced from the center
> point..which means they will not try to occupy the same mounting area on the
> mast (the UHF elements are the most critical and will be mounted on the mast
> as a normal DB420 in omni mode with the top 8 bays 180 degrees (IE: Mounted
> in a N-S fro the top 8 and E-W for the bottom 8 dipole pairs).
>
>   
>
> This leaves the opposite directions available for the VHF and 220
> dipoles.the DB 224E 2mtr elements will go from the center up and down.since
> they use 1/2wl spacing (tip to tip) and so would the 220 elements mounted
> 180 degrees from the VHF elements but NOT in the same horizontal place so
> there should not be any interaction between them.
>
>   
>
> I can do a drawing on it but if you think about the DB420 then the DB224 in
> omni modes (where on the VHF model, the top two dipoles in this case would
> be looking E-W and the bottom 2 would be looking N-S..the 220 dipoles would
> 180 degrees away from the VHF dipoles and thus the dipole pairs would be 180
> degrees from the 2m dipoles and their field patterns would not be disturbed
> as the 224 and 244 dipoles will not try to overlap each other (but it may be
> close.but I have operated VHF/UHF arrays similar to the (the DB310 iirc)
> that works quite well.
>
>   
>
> BUT my BIG concern is tying all three of these antennas into one
> feedline.yes I could go with a cheap ham triplexer but one lightning shot
> and the caps, etc will be toast..I don't relish having to pay a tower crew
> everytime it gores POP.I was thinking maybe using some coaxial network (like
> the VB or RG series DB uses on the antennas) but not sure about matching
> 50ohms antennas on different bands into the feedline..On the transmit side,
> a simple power divider with ports at the right place MAY work..but I have
> issues with that.
>
>   
>
> Any comments or ideas on the matching side? At the  bottom I can use
> triplexer provided I don't try to connect high power transmitters and there
> is  possibility there may be up tp 5 channels of trunking as well as one or
> two conventional UHF rptrs..the VHF and 220 sides will likely only have ONE
> rptr on their port..BUT the possibility of adding additional channels is
> being looked at for later expansion..
>
>   
>
> Thanks for anything who wishes to offer some constructive comments and/or
> any modeling of this operation.
>
>   
>
> Thanks
>
> and how come NO one wished happy two way radio on 4th .10-4! Yeah I missed
> it too!! And commercial guys have used that longer than Chicken Banders.I
> even know one large company that uses the Q codes (QSL, QRT, etc) instead of
> the normal 10 codes!! YIKES ;)
>
>   
>
> Chris
>
> LMR list owner
>
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