[TowerTalk] HF Antenna Planning Questions

[K7LXC]

In a message dated 98-01-04 10:10:19 EST, crippel@exis.net writes:

> I am currently using an M2, 20M4 (20M, 4 el on a 46' boom) mounted on 
>  a 100' Rohn 25G tower.   
>  My thoughts are to erect another, perhaps shorter tower, or tall 
>  phone pole and add an M2 17-30LP7, 17-30mHz log perodic.  The cost 
>  v/s performance far outweighs the 1-2 db losses in advertised forward 
>  gain and 5 db shortfall in F/B over mono-banders.  I am also 
>  tentatively considering stacking a 40M3L, 3el 40M on a 30' boom 
>  under the 17-30LP7.  Since there is a harmonic relationship between 
>  40 and 15M, the jury is still out on that.
>  
>  My questions for the Collective Wisdom are:
>  
>  Any thoughts on using an LPA on 17-30 mHz?  Has anyone tried the M2, 
>  17-30LP7?

      Since you're willing to make some performance sacrifices by going to an
LP, I don't think there's a significant difference between any of the LP's
available on the market. It might get down to mechanical design.

     While not a big fan of the LP myself, many people are happy with them. My
main problem is that while you do get continuous bandwidth, it's not optimized
for the ham bands.

     The best argument FOR an LP was by Jay, W6GO, who felt that the big, fat
forward lobe from the LP makes it a good contest antenna. His mult/second
station uses one.
>  
>  Any thoughts about stacking the LPA over the 40M beam?
>  
     No reason not to. Go for it. I would recommend a ten-foot stacking
distance. You'll need something better than water pipe for this application. I
have a program that'll help you determine a suitable mast for any wind speed
and antenna loading scenario. It's the Mast Antenna and Rotator Calculator
(MARC) program. It's $9.95 + s/h from TOWER TECH. Catalog available also.

>  How about suggestions for most optimum height.  (I suppose I ought to 
>  get un-lazy and get the software out of the ARRL antenna book, load 
>  it and work the problem but I thought I'd first get some thoughts 
>  here).

       The higher the better? Yes, get out the software (including TA) and
start looking at arrival angles, etc.
>  
>  Anyone cost a phone pole v/s guyed tower?  I suppose you can get them 
>  80' tall which would yield 65' of so to work with considering 10-15' 
>  in the ground but 80' phone poles are not common.  The (35'?) ones 
>  are which is too short, IMHO. 
>  
     The cost of a good pole is not insignificant. Combine that with the cost
of getting a borer/setter rig in there and there isn't any cost advantage to a
pole. Combine that with the lack of antenna/rotator mounting  hardware and I
think it's a pretty good case for NOT installing one. On the plus side, a tree
or pole mounted antenna works like a bomb because there's no metal tower or
guywires to interact with it - electrically it's floating in space.

    BTW, I couldn't figure out what county you're in but Isle of Wight county
next door is an 85 MPH wind zone and within 100 miles of hurricane oceanline.
You need to take that into account for any antenna/tower installation. 

>  An 80' tower 170 or so feet behind my existing tower would work 
>  wonderfully for providing an additional support for E-W facing 
>  dioples but the co-ax run from the shack to the top would be in 
>  excess of 500'.  Even with 9913, 10M performance would suffer.  7/8 
>  hardline is too expensive for my budget and might not suit my 
>  lightning disconnection scheme (see below).
>  
      Siting the new tower in a usefull orientation is a great idea. 

    You need to go with some type of hardline. While the typical ham budget
might not afford new Heliax, the availability of cable TV hardline is well
documented.

73 and GL,  Steve  K7LXC

    TOWER TECH -- professional tower supplies and services for amateurs

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