[SECC] yagi antennae question

[Scott Straw]

Gentlemen, Bridget, (and all other esteemed lurking YL's),

If you will indulge me a partially off-topic question, I feel confident 
that some of the best experts in the field of antenna theory and practice 
are found on this reflector ( would you like some popcorn with that butter, 
sir?)

Some of you know that I am a fireman with the City of Roswell, Georgia. I 
am also a computer experimenter and a ham radio operator (obviously).  I 
have always enjoyed listening to police and fire department radio traffic 
on scanners as well.  When you throw all of the mental disorders in to a 
blender, and press the "frappe" button, you end up with a guy who has put 
three streaming audio feeds out on the Internet, so that all the globe can 
listen to the Roswell Fire Department, Roswell Police Department, and the 
Fulton County Fire Department 
(<http://www.roswellfirescanner.com/>www.roswellfirescanner.com, 
www.roswellpolicescanner.com, and 
<http://www.fultonfirescanner.com/>www.fultonfirescanner.com).

The audio source is three simple hand-held trunking scanners with "rubber 
duck" antennae.  I am convinced that the RF output from the trunking 
transmitters is inconsistent, module to module,  because a conversation 
"thread" will be all over the map, field strength-wise.  One transmission 
will be s5+10, the next s3.  Since I would probably be wasting my time 
pointing this out, and since I don't have any gear to take measurements 
that would substantiate my allegations, My only resort is to optimize my 
reception.

When I explored using a common yagi antenna for all of the receivers, I 
discovered that I would have to acquire (buy) an expensive device that 
would shield the units from each other, lest the desensitize each other.

My next idea was, and is, to build a "passive repeater." I would like to 
build an 11 element yagi, cut to 855.5MHz, then  couple it to a vertical 
cut to the same frequency.  The odd 11 element number was arrived at 
because according DL6WU's program, the total boom length would be 35.36 
inches - a yardstick.

Now to show my ignorance:

1. Can I use a yardstick as a boom, or does the boom interact with the 
elements such that it needs to be a conductor?

2. I would like to use 1/8" dia. threaded rod as my elements.  Ideally, I'd 
drill holes at the appropriate places on the yardstick (measuring for them 
would be a breeze), then secure them with counterpoised nuts on either side 
of the yardstick. Can the 9 directive elements and the lone reflective 
element each be one continuous rod, or do the need to be two separate rods 
with a gap of some width to isolate them from each other?

3. This antenna design call for the driven element to be a folded 
dipole.   Bending  1/8" threaded rod into a "U" shape sounds like the 
hardest part of this project... and, supposing that feat can be 
accomplished, what does the stated value of 6.526" refer to? The distance 
from curve apex to curve apex? the total rod length? For a receive-only 
antenna, what other choices do I have for the driven element?

4. If I attach a straight wire (like a solid 12 gauge) to the center pin of 
a PL-259, and screw it to a SO239 tied to the yagi, what would be better: a 
1/4 wave, 1/2 wave, or full wave length vertical?  Is there a better idea?

Finally is this scheme a totally hair-brained idea, or does it have 
merit?  Is it a "level 8" project, not be attempted by beginners?

For those who are curious, here are the statistics generated by the program:

Program - ANTDL6WU.BAS
***** YAGI ANTENNA DESIGN DETAILS *****
DESIGN FREQUENCY                 855.51 MHz
LAMBDA (Wavelength)                 13.796 ins.
GAIN (With -15 dB side lobes)         12.27 DBD
NUMBER OF ELEMENTS                   11
DIAMETER OF ELEMENTS            0.125 ins.
DIAMETER OF BOOM  (O.D.)               0 ins.
BOOM LENGTH                           34.339 ins.
BOOM WAVELENGTHS                  2.49
BOOM CORRECTION FACTOR            0 ins.
TYPICAL BANDWIDTH                   11.98 MHz
HORIZONTAL BEAM WIDTH               30 degrees
VERTICAL BEAM WIDTH                    34 degrees
HORIZONTAL STACKING DIST.     23.454 ins.
VERTICAL STACKING DIST.          20.694 ins.
DIMENSIONAL TOLERANCE (+/-)    0.041 ins.

For those who might want to jump my case for throwing this "rabbit" into 
our discussion, I apologize in advance of your flaming replies.  I thought 
long and hard about whether to ask this question or to ask if it would be 
OK to invite Glenn Baxter (K1MAN) and Herb Schoenbohm (KV4FZ) to join our 
group.  This question won.


Scott Straw, KB4KBS

Living proof of "The Hiram Percy Maxim".... Scheduling conflicts, 
interruptions, and equipment problems will always manage to manifest 
themselves most profoundly around amateur radio contest dates.