[tripelo]

Interesting project, Bob.

Originally Posted by bobsgarage

... even with modeling software that the results are purely empirical.

Yes true.

Many models that I have seen, especially at UHF, fail to account for everything that can affect results.
Partially because NEC2 makes it difficult and partially because of failure to appreciate small details.

What modeling can do (if the model is accurate) is to provide insight and guidance.
Insight into how parameters affect results. Vary this, to see effect on that.

Here's a list of my current questions.

a) What should the director spacing be?

Unless one is seeking the last 0.1 dB of gain, small variations in director spacing are not critical.

Start with existing factory spacing, or the wide spacing could be OK.

b) What can I use to join the donor section?, there will be a gap and I can't find the right size square box tubing to sleeve the boom on the outside or inside. .655" ID .710" OD or 16.350 ID 18mm OD

Have used round aluminum tubing to sleeve inside of these booms

DX Engineering sells 6063-T832 that should be strong enough for this application.

https://www.dxengineering.com

Another option would be to omit one director and shorten the boom appropriately to use factory couplers.

c ) Vertical stack or side by side? With either, what should the spacing be?

Optimum spacing depends on antenna aperture (related to gain) and desired channels.
Higher gain and Lower channels would indicate wider pacing.

Maybe maximum spacing would be about 7 feet.

Wide spacing tends to increase gain and raise sidelobes.
Conversely, closer spacing yields lower gain and a better overall pattern (less sidelobes).

Vertical spacing behaves much different than horizontal spacing.
There is more coupling between antennas stacked vertically,
this affects antenna impedance, usually in a undesirable way.
Wider spacing vertically tends to minimize the undesirable coupling.

For performance of vertical stack to be mostly predictable, in terms of gain and pattern,
the antenna should be high above ground (preferably about 10 spacings high or more).
This height helps to make each antenna see the same signal.

Horizontal stacking is less afflicted by mutual coupling.
And, each antenna essentially sees the signal relative to ground.

d) Will the "u" between the booms disrupt the signal if it's below the reflector?

If mast mounted relatively close to reflector, not much affect on gain.

It can affect the pattern by filling nulls.

Given that you have provided some vertical spacing with the U-pipe;

The further away from the driven element toward front of antenna,
the more likely horizontal pipe is to interfere.

For horizontal metal, more vertical spacing and further back is better.

The idea is to minimize exposure to the antenna aperture.

e) Should I use any of the rear section? Directors etc...

You could cut the reflectors and make directors of them.
Probably need a longer boom to effectively use more directors.

Subquestion, why do the Y10 7-13 have two dipoles? since I have extra could it be used somehow?

The Y10-7-13 has two dipoles (driven elements) to achieve sufficient bandwidth to cover channel 7 thru 13.

High band VHF (Ch 7-13) is considered moderately wideband for a Yagi antenna.

The Y10-7-13 was designed before modern computer modeling was feasible.
Computer modeling helps with designing Yagis for wideband performance.

The additional driven element in the Y10-7-13 actually cost a small amount of gain,
that was a tradeoff.

Driven elements generally are not as effective as parasitic element in increasing antenna gain.


Question:

What is the bending strength of your 1 & 3/8 exhaust pipe?

Comment: There can be a strong rotation force due to wind,
trying to rotate the U-pipe and antenna assembly downward.
Need sturdy non-rotatable mast to U-pipe mount.

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