Designing for Construction Error - how to hedge a design?

[AD7N]

I want to make my 2m and 70cm Log Periodic design as rugged as possible, which means making it as immune to construction error as possible. My software tool uses a Differential Evolution technique rather than classical LPDA designs, which makes it very easy to optimize for particular antenna parameters.

One of my key design parameters is ease of construction, which I want to optimize for ease
I would rather sacrifice .5dBi antenna gain if it made the antenna more resistant to construction error.

My current approach is to design for "maximum stability". This means designing for consistancy over a band vs designing for peak.
Making sure the the gain curves, the impedence (real & imaginary), phase and F/B are as flat as possible across the two bands.

Also, I've been including a huge "safety factor" by designing extra bandwidth beyond the band edges, so the antenna is more broadband than needed.

Is this good design philosophy to hedge against construction error? Any other parameters to "optimize for ruggedness"?

[AF6LJ]

I like your conservative approach and am looking forward to seeing what the Zed experts have to say.

[AD7N]

Bump - any hints?

I found I can run a sweep through different values to test how sensitive each element length/distance is.

[WX7G]

You design philosophy is excellent.

[AF6LJ]

I am by no means an expert in antenna design however as I said you have a very conservative approach. I would think i would go ahead with it.

[NA0AA]

Hm interesting question. I've let this simmer for a bit. You have two issues: First is an optimal design - that's all up front and does not have much to do with building them - however, when it comes to describing your antenna and constructing it....that's another step.

My experience with building stuff, even with kits, is that the author of the instructions has assembled that antenna too many times and fails to notice the holes in the manual.

When you require the builder to drill things and measure things make darn sure the specific needs are illustrated. For example, with a folded element, make sure you are clear if the element is made from "36 inches of wire" OR "After bending into loop, the overall length of the folded element is 18 inches"....When in doubt, illustrate! Never assume your reader knows what a technical word means or how to calculate '0.2 pf' in gamma match....

When measuring a boom, using total lengths is often easier - IOW, start from end of boom, measure 2" drill for reflector, 20" drill for driven element, 36" drill for first director, 42" drill for second director - you see, this way you don't have to hold the tape measure at each hole and try to match a spacing....

A helpful note in the instructions is tolerances: "Note: Deviations of up to 1/16" have little or no effect on antenna performance"....

My advice would be to have a couple of teen amateurs build it from your directions, then have 'em tell you what's wrong, then send it for another peer review.

If you had not noticed, I hate bad instruction manuals.

I would also say that with respect to assembly: I would always choose the more durable assembly method, although if it was mechanically complex or required special tooling to build that way, I'd rethink it - anything for a homebuilder that requires more than hand tools will greatly limit your market.

[AD7N]

I am by no means an expert in antenna design however as I said you have a very conservative approach. I would think i would go ahead with it.

I appreciate the support! From the replies it looks like I've got most of the design bases covered.

KG6WOU - your comment on instruction readability is very valid. Nothing is more annoying than cryptic, complex, error-laiden instructions!

[KE5MC]

...or missing steps & dimensions. Which could fall under cryptic or not...

Mike

I appreciate the support! From the replies it looks like I've got most of the design bases covered.

KG6WOU - your comment on instruction readability is very valid. Nothing is more annoying than cryptic, complex, error-laiden instructions!

[AF6LJ]

Hm interesting question. I've let this simmer for a bit. You have two issues: First is an optimal design - that's all up front and does not have much to do with building them - however, when it comes to describing your antenna and constructing it....that's another step.

My experience with building stuff, even with kits, is that the author of the instructions has assembled that antenna too many times and fails to notice the holes in the manual.

When you require the builder to drill things and measure things make darn sure the specific needs are illustrated. For example, with a folded element, make sure you are clear if the element is made from "36 inches of wire" OR "After bending into loop, the overall length of the folded element is 18 inches"....When in doubt, illustrate! Never assume your reader knows what a technical word means or how to calculate '0.2 pf' in gamma match....

When measuring a boom, using total lengths is often easier - IOW, start from end of boom, measure 2" drill for reflector, 20" drill for driven element, 36" drill for first director, 42" drill for second director - you see, this way you don't have to hold the tape measure at each hole and try to match a spacing....

A helpful note in the instructions is tolerances: "Note: Deviations of up to 1/16" have little or no effect on antenna performance"....

My advice would be to have a couple of teen amateurs build it from your directions, then have 'em tell you what's wrong, then send it for another peer review.

If you had not noticed, I hate bad instruction manuals.

I would also say that with respect to assembly: I would always choose the more durable assembly method, although if it was mechanically complex or required special tooling to build that way, I'd rethink it - anything for a homebuilder that requires more than hand tools will greatly limit your market.

Very good ideas; I have trouble explaining to someone how to do something that is complex because I tend to leave out steps or when doing troubleshooting by phone I sometimes leave out why I am asking something be done...
Sometimes I want to say "just do it, I will explain later".
I usually take the time to explain and that sometimes throws me off of what was in my mind...