I notice the model uses 2 inch diameter elements throught out, which
can't be correct. What it the taper schedule for the elements?
denis coolican wrote:
>I am planning on building an 80m yagi to cover the CW portion and hopefully
>retain good performance up into the phone band up to 3800. I currently have a
>4 el OWA design on a 76' boom that covers approx 3650-3975. It has been up
>for 6 years and performs well, but not into the CW portion. The new 80m yagi
>will not replace the one I have, but will be installed on a similar 150 foot
>tower. I am planning to use a 100 foot tower that I have as a boom (40"
>triangular lattice structure) with perhaps 5 full size elements as an OWA
>design if it has enough bandwidth. I am not interested in loaded designs with
>relay switching. The elements will be of the tapered pipe design, as is the
>Denis VE6AQ designed and we both built a 40m yagi 5 element OWA design on a
>59' boom that has wide bandwidth - about 400 khz - that if scaled would be
>adequate for 80m coverage. That would require a 118 foot boom, but I am
>hoping I can squeeze it down to use the existing 100 boom that I have. It
>isn't impossible to add another 20 feet but I don't have the matching tower
>section to do that so would like to avoid that if possible.
>As it correlates to current towertalk threads, the tower will be guyed with
>multiple screw in anchors. The guy wires (5/8 EHS) will be broken up with at
>least one insulator to reduce potential corrosion issues. The rotor will be
>at the bottom of the tower and I will be using 4" IPS sked 40 black (4.5" OD
>water pipe with welded flanges) for the mast. I have used this on the current
>80m yagi without any problems. The mast near the top will be something
>Some design innovations that I have thinking about include:
> having the elements winched into place to allow for modification and
> repair by lowering them to the ground.
> having a heavy steel 4 sided "pyramid" shaped structure on the top of
> the mast. A matching structure will be built into the boom, so that the
> antenna can easily be lowered (by crane) over the self guiding structure and
> simply set in place without any critical placement issues. It will be bolted
> down later for security.
>Anyway, the main issue at hand is the electrical design not the physical. I
>will have lots of time to ponder the mechanical aspects once it has been
>decided how much boom and how many elements are needed.
>A note from Denis Ve6aq
>I have modeled the 100 ft Yagi on EZNec and it can be downloaded from
>http://alfaradio.ca/ve6jy/downloads/ The spacing between the DE and D1 is
>0.025 wavelength and I noticed that some of the modeling programs give
>inconsistent results at these close spacings. I would like comments on the
>design and perhaps someone could run it on a NEC4 engine to see if the results
>are similar to what I have obtained. Comments would be appreciated.
>Denis with Ve6Fi
>TowerTalk mailing list
TowerTalk mailing list