[Antennas] Model this idea

[Chris Boone]

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