http://www.boulder.nist.gov/timefreq...al/pdf/451.pdf

Can someone please comment on the following statements and questions?
Thanks.

1 The reflector and director element lengths and spacings of Table 1 are
good for a yagis where d/lambda is 0.0085 and boom is non conducting.

2 You make a correction to the lengths when d/lambda of your reflector
and director element diameters are other than 0.0085.

3 When you use a metallic boom, you have to make corrections to the
element lengths as per Table 10.

4 I take it that whatever you put in place for DE, all spacing and
reflector and director elements continue to remain correct. So you can place
whatever you want for DE, hertz dipole, folded dipole, gamma match, T
match, DE with 1/"4 dia tube or 1.2" dia tube -it does not matter,
parasitic element lengths once calculated need not be changed whatever you
DE you place in the design. Spacing always remain the same.

5 How do you go about designing for DE?

6 Do the element length corrections due to use of a metalic boom assume a
particular element fixing method? Such as through the boom or on top of the
boom?

7 The designs are maximised for gain.

8 What is the bandwidth of a NBS designed antenna?

9 Has anyone written a program specifically for an NBS antenna so you can
calculate the element lengths without relying on tables and graphs?

10 Once designed the NBS design will probably work very close to
parameters. But strictly speaking the antenna will only work very close to
parameters if the antenna is 3 wavelenghts above ground. But for reception
purposes on VHF, you can probably ignore effect of ground and no further
design is probably necessary. (Lets face it with most bought antennas for
receivimng, you just put them up. You don't start altering element spacings
etc.)

Richard wrote:
http://www.boulder.nist.gov/timefreq...al/pdf/451.pdf

Can someone please comment on the following statements and questions?
Thanks.

1 The reflector and director element lengths and spacings of Table 1 are
good for a yagis where d/lambda is 0.0085 and boom is non conducting.

Good for those particular yagi designs, maybe, but not necessarily good
for all.

2 You make a correction to the lengths when d/lambda of your reflector
and director element diameters are other than 0.0085.

Yes, you must do that for any yagi design.

3 When you use a metallic boom, you have to make corrections to the
element lengths as per Table 10.

That's Figure 10. Those corrections will only apply if you use the same
method as they did for mounting an element on a round metal boom...
which they don't specify in detail, so Fig 10 is almost worthless.

4 I take it that whatever you put in place for DE, all spacing and
reflector and director elements continue to remain correct. So you can place
whatever you want for DE, hertz dipole, folded dipole, gamma match, T
match, DE with 1/"4 dia tube or 1.2" dia tube -it does not matter,
parasitic element lengths once calculated need not be changed whatever you
DE you place in the design. Spacing always remain the same.

It does in the NBS designs; but not in most more modern designs.

5 How do you go about designing for DE?

Too big a subject - look it up teh basic principles and some practical
examples in various antenna handbooks, and then go and get your hands
dirty.

6 Do the element length corrections due to use of a metalic boom assume a
particular element fixing method? Such as through the boom or on top of the
boom?

No, they *demand* a particular fixing method! (See 3.)

7 The designs are maximised for gain.

As well as NBS could do it with the tools available to them at the time
(a hacksaw, mostly). Almost 40 years later - the work was actually done
in the mid-1960s - we have much better tools and wouldn't say those are
optimised designs any more.

8 What is the bandwidth of a NBS designed antenna?

With or without losses due to the bandwidth of the matching circuit?
You'd have to model it; but the NBS designs are not noted for being
wideband.

9 Has anyone written a program specifically for an NBS antenna so you can
calculate the element lengths without relying on tables and graphs?

I'm sure someone did, back in the MBASIC days - go search for it.

10 Once designed the NBS design will probably work very close to
parameters. But strictly speaking the antenna will only work very close to
parameters if the antenna is 3 wavelenghts above ground. But for reception
purposes on VHF, you can probably ignore effect of ground and no further
design is probably necessary. (Lets face it with most bought antennas for
receivimng, you just put them up. You don't start altering element spacings
etc.)

In order: yes; yes; it depends how on the particular yagi, the
particular installation, and how much performance you're prepared to
sacrifice; certainly lots of people do; but that doesn't make it right.



--
73 from Ian G3SEK 'In Practice' columnist for RadCom (RSGB)
http://www.ifwtech.co.uk/g3sek

"Richard" wrote in message
...
http://www.boulder.nist.gov/timefreq...al/pdf/451.pdf

Can someone please comment on the following statements and questions?
Thanks.

1 The reflector and director element lengths and spacings of Table 1
are
good for a yagis where d/lambda is 0.0085 and boom is non conducting.

2 You make a correction to the lengths when d/lambda of your reflector
and director element diameters are other than 0.0085.

3 When you use a metallic boom, you have to make corrections to the
element lengths as per Table 10.

4 I take it that whatever you put in place for DE, all spacing and
reflector and director elements continue to remain correct. So you can
place
whatever you want for DE, hertz dipole, folded dipole, gamma match, T
match, DE with 1/"4 dia tube or 1.2" dia tube -it does not matter,
parasitic element lengths once calculated need not be changed whatever you
DE you place in the design. Spacing always remain the same.

5 How do you go about designing for DE?

6 Do the element length corrections due to use of a metalic boom assume
a
particular element fixing method? Such as through the boom or on top of
the
boom?

7 The designs are maximised for gain.

8 What is the bandwidth of a NBS designed antenna?

9 Has anyone written a program specifically for an NBS antenna so you
can
calculate the element lengths without relying on tables and graphs?

10 Once designed the NBS design will probably work very close to
parameters. But strictly speaking the antenna will only work very close to
parameters if the antenna is 3 wavelenghts above ground. But for reception
purposes on VHF, you can probably ignore effect of ground and no further
design is probably necessary. (Lets face it with most bought antennas for
receivimng, you just put them up. You don't start altering element
spacings
etc.)


Further:

Reason why I looked at technical note 688 was because I thought I could
avoid using models in antenna computer programs. As far as I can see in
4nec2 and Eznec you *cannot* input boom data. So, I thought following note
688 I can more easily design an antenna because it includes a table so you
can take account of the boom. The test people obviously constructed the yagi
designed for maximum gain and used a boom to figure out the boom
corrections. This is dandy or looks good when somone like me does not want
to spend ages designing.

The way it reads is that if you follow note 688 you can easily design your
own antenna.

But, as always I get stuck with DE. Whether looking at note 688 or when I'm
messing with 4nec2.

I see now that in the original test yagi, DE was a 1/2 wavelength folded
dipole with the test element diameter of 1/4" matched to 50 Ohms with a
double stubb tuner. There is not enough information as to the construction
of the folded dipole to be able to replicate one to use as DE. Who knows if
468/f was used to get length for DE, who knows what the spacing between
the elements of the folded dipole were.

Yet, I think whoever wrote note 688 expects a "designer" to put almost
whatever he wants for DE, and is expected to keep the calculated dimensions
regarding the parasitic elements.Obviously that is how note 688 reads. The
problem is this though isn't it, it's okay if DE is in the clear of any
parasitic elements, because then there is no influence on DE and you can l
look in textbooks to calculate what the dimentions should be etc etc. DE
would be a simple dipole on it's own in free space or whatever. But of
course in a yagi DE is immersed in the fields created by the parasitic
elements which influence a lot of things to do with DE. So how on earth can
you design DE and establish Z etc without some sophisticated mathematics
that take into account the effect of the parasitic elements on DE. Could you
(whoever is reading this) know what to do with DE?. Could you calculate Z
and dimensions for DE just looking at the information given in note 688?

(I think it's possibly implied that whatever DE is, it ought to be a folded
dipole - maybe. Not a simple hertz dipole for instance.)

Anyway reasons why looking at note 688 is a ruse: I'm wanting a wideband
antenna and I'n not sure if a design for 159 Mhz will have a bandwidth of 6
Mhz. I wanted NOT to use a folded dipole so an NBS design is no good. And
can you actually make a design relying on the procedure in note 688 anyway.
Possibly though a basis of a model in an antenna program.

All this is part of my learning curve BTW.

"Richard" wrote in message
...


Yet, I think whoever wrote note 688 expects a "designer" to put almost
whatever he wants for DE,

I'm not really sure about that. Maybe this is not expected, rather perhaps
there is an implication DE ought to be a folded dipole.

"Ian White, G3SEK" wrote in message
...
Richard wrote:
3 When you use a metallic boom, you have to make corrections to the
element lengths as per Table 10.

That's Figure 10. Those corrections will only apply if you use the same
method as they did for mounting an element on a round metal boom...
which they don't specify in detail, so Fig 10 is almost worthless.

That's why Iasked the question could I could appreciate this issue.

4 I take it that whatever you put in place for DE, all spacing and
reflector and director elements continue to remain correct. So you can
place
whatever you want for DE, hertz dipole, folded dipole, gamma match, T
match, DE with 1/"4 dia tube or 1.2" dia tube -it does not matter,
parasitic element lengths once calculated need not be changed whatever
you
DE you place in the design. Spacing always remain the same.

It does in the NBS designs; but not in most more modern designs.

5 How do you go about designing for DE?

Too big a subject - look it up teh basic principles and some practical
examples in various antenna handbooks, and then go and get your hands
dirty.

Whenever anyone produces a design for a yagi, who has built a practical
model, whether a test model like NBS did, or whether a model built by Joe
Ham, then the DE is already designed. Most people who want to build a yagi
don't want to design from scratch, they just want to be presented with a
design methodology that's simple, that allows for some slight variation in
materials or method of fixing.

So the design methodologies that appeal a

Copying exactly someone else's design.(No design involved)

Trying to design with Technical Note 688. (Looked promising at first).

Taking someone's design and adjusting for variation in element diameter and
boom size using some program or other. (This involves ELE.EXE I think).

Taking a model and designing with that with a program. But I've got the
impression, rightly or wrongly, that going this route is getting away from
the concept of "simple design methodology". I think that stems from my
inability to have noted these programs allowing boom parameters to be
inputed, and I'm totally in the dark about DE in these programs.

All the really simple methodologies have as starting point a practical
proven design. All one is doing is making certain kinds of alterations:
frequency, boom size, element diameters, and if you really want to
adventurous, alter element fixing method, but that could be an alteration
too far. That's the only things I'm interested in messing with. And I'm
looking for the design methodologies that allow me to make these kinds of
alterations. I'm not really wanting to be in the business of designing DE or
spending hours experimenting.

I've yet to determine whether I can classsify using models in an antenna
program as being a "simple design methodolgy" given the kinds of alterations
I might want to make.

6 Do the element length corrections due to use of a metalic boom
assume a
particular element fixing method? Such as through the boom or on top of
the
boom?

No, they *demand* a particular fixing method! (See 3.)

This is a key to understanding for me.

"Richard" wrote in message
...

I've yet to determine whether I can classsify using models in an antenna
program as being a "simple design methodolgy" given the kinds of
alterations I might want to make.

The point being of course that if someone gives me a model, what do I know
about the practical construction associated with that model. Does the model
file (NEC or EX file) include data about element fixing method for
instance. Probably not. So unless I can input these practical parameters
into the program, and these paramters serve to make alterations to the
elements, diameter and spacings, how can I arrive at a practical design
having followed a "simple design methodolgy".

This is why Technical Note 688 looked so promising at first. The design
methodology is simple and you can input details or alterations concerning
the boom size and element diameters and end up with a practical design in
no time at all. There are apparant problems with Note 688, as you say with
Table 10 being possibly practically useless without there being a detailed
specification of element fixing.

"Richard" wrote in message ...
"Richard" wrote in message
...


Yet, I think whoever wrote note 688 expects a "designer" to put almost
whatever he wants for DE,

I'm not really sure about that. Maybe this is not expected, rather perhaps
there is an implication DE ought to be a folded dipole.

I doubt I would use a folded DE myself. More work... Normally, I
would just use a grounded DE, but in your case, you need to consider
how you would tune the antenna. IE: gamma match, etc...If you have no
radio that transmits, or an antenna analyser, it might be tricky..In
that case, probably the simpliest method would be to use a split,
carefully cut dipole DE, and hope for the best. The dimensions,
spacings, etc, are critical yes, but I don't think as critical as you
think. IE: I don't really worry too much about element mounting
methods, etc, when I build a yagi. Almost anything you slap together
should work pretty well as long as you measured carefully. When I once
made one for that purpose, I didn't have a transmitter. And I did use
a gamma match. I had no decent way to tune it up. So I just
guesstimated, and tuned the match for max signal, noise, etc..I don't
know how well it came out as far as the match, but the antenna worked
great.
A simple fast way to design an NBS yagi for any freq, is to use the
eznec demo. It has a NBS yagi as a demo, and it can be easily scaled
for any freq. MK

"Mark Keith" wrote in message
om...
"Richard" wrote in message
...
"Richard" wrote in message
...


Yet, I think whoever wrote note 688 expects a "designer" to put almost
whatever he wants for DE,

I'm not really sure about that. Maybe this is not expected, rather
perhaps
there is an implication DE ought to be a folded dipole.

I doubt I would use a folded DE myself. More work... Normally, I
would just use a grounded DE, but in your case, you need to consider
how you would tune the antenna. IE: gamma match, etc...If you have no
radio that transmits, or an antenna analyser, it might be tricky..In
that case, probably the simpliest method would be to use a split,
carefully cut dipole DE, and hope for the best. The dimensions,
spacings, etc, are critical yes, but I don't think as critical as you
think. IE: I don't really worry too much about element mounting
methods, etc, when I build a yagi. Almost anything you slap together
should work pretty well as long as you measured carefully. When I once
made one for that purpose, I didn't have a transmitter. And I did use
a gamma match. I had no decent way to tune it up. So I just
guesstimated, and tuned the match for max signal, noise, etc..I don't
know how well it came out as far as the match, but the antenna worked
great.
A simple fast way to design an NBS yagi for any freq, is to use the
eznec demo. It has a NBS yagi as a demo, and it can be easily scaled
for any freq. MK

Okay, but aren't these models only sufficiently accurate if you use the
dimensions in the models to build an actual yagi, if the boom is non
conducting? Is it not true that if the boom is conducting you cannot rely on
the model dimensions?

Richard wrote:

A simple fast way to design an NBS yagi for any freq, is to use the
eznec demo. It has a NBS yagi as a demo, and it can be easily scaled
for any freq. MK

Okay, but aren't these models only sufficiently accurate if you use the
dimensions in the models to build an actual yagi, if the boom is non
conducting?

I don't worry about the boom. It's effect on the antenna is small. All
my booms normally are metal.
Is it not true that if the boom is conducting you cannot rely on
the model dimensions?

I don't think it is to any great degree worth losing sleep over. I built
the eznec NBS yagi for 6m, and used those dimensions, using my own
construction techniques, and it came out nearly perfect as per the
model, and modeled results. To me, you are taking a simple task, and
overly complicating things by insisting on utter perfection in element
diameters, boom, element mounting, etc. For a VHF receive 3-4 el yagi,
it's just not *that* critical. When I built a marine yagi, I paid little
attention to exact element dia, mounting , boom, etc. I used coathanger
wire welded directly to the copper tube boom. I didn't try to optimise
the lengths, etc. In fact, this was waaaay before I'd ever seen a
modeling program. It still worked just fine.
MK

--
http://web.wt.net/~nm5k

"Mark Keith" wrote in message ...
Richard wrote:

A simple fast way to design an NBS yagi for any freq, is to use the
eznec demo. It has a NBS yagi as a demo, and it can be easily scaled
for any freq. MK

Okay, but aren't these models only sufficiently accurate if you use the
dimensions in the models to build an actual yagi, if the boom is non
conducting?

I don't worry about the boom. It's effect on the antenna is small. All
my booms normally are metal.
Is it not true that if the boom is conducting you cannot rely on
the model dimensions?

I don't think it is to any great degree worth losing sleep over. I built
the eznec NBS yagi for 6m, and used those dimensions, using my own
construction techniques, and it came out nearly perfect as per the
model, and modeled results. To me, you are taking a simple task, and
overly complicating things by insisting on utter perfection in element
diameters, boom, element mounting, etc. For a VHF receive 3-4 el yagi,
it's just not *that* critical. When I built a marine yagi, I paid little
attention to exact element dia, mounting , boom, etc. I used coathanger
wire welded directly to the copper tube boom. I didn't try to optimise
the lengths, etc. In fact, this was waaaay before I'd ever seen a
modeling program. It still worked just fine.
MK

--
http://web.wt.net/~nm5k

What has happenned is that I, who know little of the art, am relying on
whoever condescends to make a comment. And comments so far have tended to
highlight how unsatisfactory it is taking a model and bulding a yagi on the
dimensions. There seems to have been a desire to point out to me how
impossible a task it is to build a decent antenna unless one factors in
alteration of boom size and element diameters. Technically these comments
are correct, you cannot expect to get the same antenna performance if these
things are ignored and I feel I've been concentrating on these details for
fear of not doing enough. But on the other hand, will the difference on
receive amount to much whether elements are insulted from a boom or not .
Probably not eh.