4nec2 hidden variables.
Helmut Wabnig
got into the editor, which was difficult enough.
The optimizer says: no variables selected
but there are none to select.
Empty list field.
Oh, how I hate this.
Praise Bill Gates for his user-friendly WINDOWS
and to hell with all amateur softwares.
Nowhere in the helps and getting started they explain that.
I do not want to learn from examples, I rather work from the
basics upwards. Would anyone learn math from a calculus
formula without knowing the arabic numbers first?
Am in a baad mood tooday.
w.
Richard Clark
-.dotat> wrote:
>Am trying to run an optimization on my 3 element yagi which I finally
>got into the editor, which was difficult enough.
>The optimizer says: no variables selected
>but there are none to select.
>Empty list field.
I have no experience with 4nec2 to speak of, but what it sounds like
is for an optimizer to work, you must first describe (name as a
variable) what characteristic you would like to vary until the
optimizer achieved an optimal result.
One guess for a three element yagi, I would suspect you would name
three variables, the elements, changing each by by an incremental
length (another variable) at a fixed frequency (another variable) for
maximum gain (another variable) in a particular direction (another
variable). Having said that little at seven variables (some fixed in
value), it is quite a page full of algebra stated in a formulaic way
for the optimizer (However, I fully expect that would be in a table
description, not a literal formula).
Having said even that little, it lends a peek into the number of all
the combinations and permutations of design this leads to. Each
variable taken individually against all the possible others - and then
repeated for the others in turn - leads to what mathematicians call
Combinatorial Explosion (you don't have enough time to wait for the
best solution). This is where constraints are added to the algebra,
and you offer "close enough" as one of them to limit testing.
>Nowhere in the helps and getting started they explain that.
>I do not want to learn from examples, I rather work from the
>basics upwards. Would anyone learn math from a calculus
>formula without knowing the arabic numbers first?
Proving the validity of numbers consumed a volume of proofs back when
Whitehead and Russell wrote "Principia Mathematica." It was logically
dead on arrival BEFORE it was published - and yet it was the best
description of simple math known. Calculus was simpler as it is
principally symbol dominated.
73's
Richard Clark, KB7QHC
Richard Clark
>>formula without knowing the arabic numbers first?
>
>Proving the validity of numbers consumed a volume of proofs back when
>Whitehead and Russell wrote "Principia Mathematica."
"From this proposition it will follow,
when arithmetical addition has been defined, that
1+1=2."
Volume I, 1st edition, page 379
Jeff Liebermann
-.dotat> wrote:
>Am trying to run an optimization on my 3 element yagi which I finally
>got into the editor, which was difficult enough.
>The optimizer says: no variables selected
>but there are none to select.
>Empty list field.
Are you using symbols, or did you hard code all the dimentions in ft
or meters? The optimizer won't work without using symbols.
4NEC2 forums. Where to ask such questions:
<http://fornectoo.freeforums.org>
>Oh, how I hate this.
If it were easy, it would not be fun.
One must suffer before enlightenment.
>Praise Bill Gates for his user-friendly WINDOWS
>and to hell with all amateur softwares.
If you were around in the bad old days of computing, you might be
praising Bill Gates for saving us from the evils of big computer
companies. There was a time when you had to buy pre-formatted
floppies to work in DEC PC's, and when every machine had a different
floppy disk format. Anyway, your frustration with not reading the
manual and learning to use 4NEC2 has nothing to do with Windoze or
Bill Gates.
>Nowhere in the helps and getting started they explain that.
True. Found with Google in a few minutes:
4NEC2 tutorial including optimizer and evolver:
<http://heplx3.phsx.ku.edu/~dzb/antcal/nec-files/_GetStarted.txt>
See section 5.
Video of optimizer (25 min):
<http://www.youtube.com/watch?v=kYy6Yur127A>
>I do not want to learn from examples,
Then you will fail or at least be more frustrated. Hacking your own
path throught the wilderness is far more work than following in
someone elses footsteps.
>I rather work from the
>basics upwards. Would anyone learn math from a calculus
>formula without knowing the arabic numbers first?
Most certainly possible. There are numerous tools the devices that I
use with only a minimal understanding for how they work. For example,
there are many drivers on the road that could not even begin to
explain how a gasoline engine works. (Hint: Carnot heat engine). I
suspect that such basic knowledge would not improve their driving
ability.
>Am in a baad mood tooday.
Have a better day.
--
Jeff Liebermann je...@cruzio.com
150 Felker St #D http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann AE6KS 831-336-2558
Helmut Wabnig
wrote:
>..........
I am making progress, though.
Got the optimizer running and edited a few of the example files
to have the variables selection available.
Works.
Now I watch the optimizer quickly de-optimizing the antennas
until they radiate into the wrong direction or get stuck in a
circular radiation diagram. In one case the optimizer bent
and rotated the dipoles around, I bet no specialist can do what I can.
Real fun, that is :-)
>
>Video of optimizer (25 min):
><http://www.youtube.com/watch?v=kYy6Yur127A>
>
Yeah, thats good. Sitting back and watch.
Thanks for the idea of watching the Youtube demos.
Better than endless trial-and-error.
My goal is to find out what makes a direction finding antenna
different from a gain optimized antenna.
F/B ratio is all that matters for ARDF, for example.
Gain is secondary and side-lobes should be absent.
I must get that NEC working by all means.
Regards,
w.
Jeff Liebermann
-.dotat> wrote:
>My goal is to find out what makes a direction finding antenna
>different from a gain optimized antenna.
That's easy (having helped design 2 commercial direction finders). Low
side lobes and good front to back. Gain is well down the list of
requirements. Side lobes will drive any direction finding scheme
towards insane results by generating false peaks in the direction. The
ability to recognize these is a function of how much time you want to
put into the software. Reflections will also cause problems, but more
so with side lobes.
To prove a point, I once threw together a rotating antenna direction
finder using a low gain directional antenna (but with low side lobes,
and no rear lobe). Due to the low gain, the -3dB beam width was a
rather wide 60 degrees. I rotated the antenna slowly, and the
computah made lots of signal level measurements. The result was that
I could determine the direction within about +/-2degrees. Of course a
higher gain antenna would resolve the signal direction much better,
and could probably be rotated faster, but all would be much larger.
However, there's a problem. High gain antennas tend to have boresight
errors. Small asymmetries, such as mountings, gamma matches, and
baluns, will have an effect.
>F/B ratio is all that matters for ARDF, for example.
F/B could be considered a side lobe at 180 degrees. Like other side
lobes, it needs to be minimized.
>Gain is secondary and side-lobes should be absent.
Absent is difficult. Minimized might be a better goal. With a log
amp driving the signal level measuring device, three orders of
magnitude should be sufficient.
>I must get that NEC working by all means.
Slow down. Such things take time.
What manner of direction finder are you building and what frequency?
Doppler? Rotating antenna? Phasing? Time difference of arrival?
Homer? Adcock? Ouija board?
Helmut Wabnig
wrote:
>
>>Am in a baad mood tooday.
>
>Have a better day.
Sorry, bad mood again.
Watched the tutorials on Youtube.
Remarkably he starts loading an antenna and then deleting the elements
to get a blank builder screen.
The 4nec2 cannot start with a "new" file, it must load something from
before. Only then I may select NEW. This is a bug.
I copied the moves from the tutorial on my NEW antenna,
and I cannot place a source on the dipole. Does not work.
No error message, nothing.
So I will load some old antenna, delete everything and try again
as shown in the tutorial.
Within 5 minutes of work I have a list of 5 errors,
program errors, repectively bugs, mis-leading the user.
Can't type as fast as the bugs occur, I just described only one.
Of course I have no right to complain because it's free.
Yeah.
w.
Helmut Wabnig
Now I watched the tutorial again and again
http://www.youtube.com/watch?v=3AqMq0J3WBc
and after 14:11 he adds a voltage source.
He does a horizontal movement with the cursor on the dipole wire
and only then the 4nec2 will place the voltage source on the dipole.
He does not mention that or explain that move.
This stupid bug -and a program bug that is, and a large one-
this stupid bug has cost me 2 hours of struggling.
Ready for the next bug.
w.
Helmut Wabnig
-.dotat> wrote:
>.........
>This stupid bug -and a program bug that is, and a large one-
>this stupid bug has cost me 2 hours of struggling.
>
>Ready for the next bug.
>
Want one?
4nec2 from time to time destroys it's saved antenna files.
Just lost another 2 hours of work.
Now I understand why it's free.
Can't charge money for bugs.
w.
Jeff Liebermann
-.dotat> wrote:
>On Sat, 13 Aug 2011 14:15:22 -0700, Jeff Liebermann <je...@cruzio.com>
>wrote:
>Sorry, bad mood again.
Like I said. One must suffer before enlightenment.
>Watched the tutorials on Youtube.
>Remarkably he starts loading an antenna and then deleting the elements
>to get a blank builder screen.
>The 4nec2 cannot start with a "new" file, it must load something from
>before. Only then I may select NEW. This is a bug.
Well, there is no "new" button or choice under "File". Ask Arie Voors
for the feature. It seems easy enough to add to the program.
>I copied the moves from the tutorial on my NEW antenna,
>and I cannot place a source on the dipole. Does not work.
>No error message, nothing.
>So I will load some old antenna, delete everything and try again
>as shown in the tutorial.
Well, I've never had that problem because I don't try to "paint" the
antenna using the isometric or 3D views. It's not accurate enough
unless you snap to a grid. I create the antenna either externally,
with a text editor, or using the spreadsheet style editor. I import
that into 4NEC2 and make any necessary changes (and fix any screwups).
For geometric shapes, I use the external shape generator, which will
do surfaces, parabolic dishes, etc. 4NEC2 is not a drawing program.
>Within 5 minutes of work I have a list of 5 errors,
>program errors, repectively bugs, mis-leading the user.
Impressive. You might want to search the 4NEC2 forums to see if any
of them have been previously reported.
<http://fornectoo.freeforums.org>
Note that there is a section specifically for requesting new features.
>Can't type as fast as the bugs occur, I just described only one.
>Of course I have no right to complain because it's free.
In my limited experience, people complain more about free software
than paid software. That's usually because the author(s) encourage
feedback in order to improve their product.
>Yeah.
Thanks for ignoring my questions.
Jeff Liebermann
-.dotat> wrote:
>Want one?
Not really, since I can't do anything to fix the alleged problem.
>4nec2 from time to time destroys it's saved antenna files.
>Just lost another 2 hours of work.
Nobody does backups until after they have lost data. I've been using
4NEC2 for at least 7 years and have never lost a file. Well, I have
accidentally overwritten a file, but that was my fault. When I tinker
with antennas, I save multiple versions of the same design with the
version number appended as in file001.nec. This way, if I make a
horrible mistake, I can go back to a previous version and try again.
>Now I understand why it's free.
>Can't charge money for bugs.
Well, that why we have alternatives to 4NEC2 and why I don't charge
for my free advice:
<http://www.smeter.net/antennas/mmana.php>
<http://www.eznec.com>
<http://www.nittany-scientific.com>
<http://www.hamradiosecrets.com/antenna-design-software.html>
<http://www.si-list.net/swindex.html> (old but still useful)
Helmut Wabnig
wrote:
>On Sun, 14 Aug 2011 23:27:33 +0200, Helmut Wabnig <hwabnig@.- ---
>-.dotat> wrote:
>
>>Want one?
>
>Not really, since I can't do anything to fix the alleged problem.
>
>>4nec2 from time to time destroys it's saved antenna files.
>>Just lost another 2 hours of work.
>
>Nobody does backups until after they have lost data. I've been using
>4NEC2 for at least 7 years and have never lost a file. Well, I have
>accidentally overwritten a file, but that was my fault. When I tinker
>with antennas, I save multiple versions of the same design with the
>version number appended as in file001.nec. This way, if I make a
>horrible mistake, I can go back to a previous version and try again.
>
>>Now I understand why it's free.
>>Can't charge money for bugs.
>
>Well, that why we have alternatives to 4NEC2 and why I don't charge
>for my free advice:
><http://www.smeter.net/antennas/mmana.php>
><http://www.eznec.com>
><http://www.nittany-scientific.com>
><http://www.hamradiosecrets.com/antenna-design-software.html>
><http://www.si-list.net/swindex.html> (old but still useful)
###########"Backup, you say it". ###########
When optimizing for F/B also 4nec2 results in a too short driven
element, same as YAGICAD, they obviously use the same formula,
(a long two-liner) from literature.
I actually built antennas following that prescription,
and they do not work without additional corrections,
e.g. a very long hair-pin match.
Imagine a 3 element 2 meter yagi,
|
| |
| | |
| | |
| | |
| | |
| | |
| |
|
Something is wrong here with the capacitive driven element.
Now I am having a hard time, because I want to find out in
what differs a gain optimized vs a F/B optimized antenna
and it is questionable whether that can be done with software.
Have not tried other programs yet.
http://imageshack.us/photo/my-images/837/snc14096a.jpg/
The Front to Back ratio is very frequency dependent
http://imageshack.us/photo/my-images/220/fbratio.jpg/
(Without the hair pin match)
http://img5.imageshack.us/img5/3479/snc14112hairpin.jpg
Therefore I put the driver on a slider
http://img841.imageshack.us/img841/8530/snc14097small.jpg
which allows to adjust the working frequency of the antenna
over a >10 MHz range on 2 meters. Adjust for minimum reception
from the back and the antenna is optimized for that frequency.
Now I want to collect a list of recipes which allow to build the
antenna without having to tweak it on the antenna analyzer.
A similar design once was offered by DIAMOND MAY1000
http://www.rfparts.com/diamond/MAY1000.html
Look at the frequency chart
http://www.rfparts.com/diamond/pdfdocs/MAY1000%20Adj%20Chart.pdf
With that antenna one could adjust the element lengths *and*
the distance between the elements, which is crucial for the F/B ratio.
A Yagi with fixed element positions can only be used for 1 frequency
(within a very small range) and therefore may be impractical
in many situations. The CEBIK tape measure antenna with their
water-pipe construction could be easily modified with a moveable
center element.
http://www.g6hoq.com/documents/2m%20tape%20measure%20yagi%20instructions.pdf
Above line as shortlink: http://tinyurl.com/3m5p5nq
w.
Jeff
Helmut,
your ranting and raving about 4Nec2 seem entirely unfair, the 'bugs'
that you complain do not seem to be bugs at all, just the way the
program works; which is not to your liking.
Placing sources requires that you click whilst away from the wire and
then drag the source onto the wire. This is not a bug, just the way that
the author chose to do it.
In many years of using 4Nec2 I have never had it loose a file, so I can
only assume that there is some sort of problem at your end.
Yes, it would be nice to have a 'New' button, but again not a bug, just
the way that the program works. If this minor inconvenience pains you
that much ask the author to add one.
Regarding optimization the phrase 'garbage in garbage out' springs to
mind. Optimizers are just that, optimizers, they WILL NOT take a rubbish
design and turn it into the perfect antenna.
Optimizers rely on finding minima (or maxima) in the set of parameters
that you supply, so unless you are close to a good design it is very
likely that they will 'get stuck' in a local minima and then home in on
something other than an optimum design. So you have to have a good
design to start with and also not try to optimize to a set of
unrealistic goals. This applies TO ALL optimizers not just 4Nec2.
Regards
Jeff
Owen Duffy
result of your own ignorance of modelling, NEC and 4NEC2.
Helmut, your vitrolic rant doesn't strike a chord with me.
Right now, Arie has some personal issues that we would all rather not have
in our lives, and yet he is finding time for some problem resolution.
Arie, I dips me lid (that means "hats off" in Oz).
Owen
Helmut Wabnig
>Placing sources requires that you click whilst away from the wire and
>then drag the source onto the wire. This is not a bug, just the way that
>the author chose to do it.
Show me the place in the manual or help where that is described.
Normally we do drag and drop, but here we must drag, drop & move.
Made me crazy, but no longer now since I know it,
and I will keep it a secret and not tell anyone.
>
>In many years of using 4Nec2 I have never had it loose a file, so I can
>only assume that there is some sort of problem at your end.
>
Of course, it's free, so it must be my fault.
From the little programming I did, I know it's 99% user interface
and 1% programming the more interesting part.
>Yes, it would be nice to have a 'New' button, but again not a bug, just
>the way that the program works. If this minor inconvenience pains you
>that much ask the author to add one.
>
No, no, it's free.
>Regarding optimization the phrase 'garbage in garbage out' springs to
>mind. Optimizers are just that, optimizers, they WILL NOT take a rubbish
>design and turn it into the perfect antenna.
>
>Optimizers rely on finding minima (or maxima) in the set of parameters
>that you supply, so unless you are close to a good design it is very
>likely that they will 'get stuck' in a local minima and then home in on
>something other than an optimum design. So you have to have a good
>design to start with and also not try to optimize to a set of
>unrealistic goals. This applies TO ALL optimizers not just 4Nec2.
>
>Regards
>Jeff
You are right, that's how it is.
w.
Jeff
> On Mon, 15 Aug 2011 09:59:00 +0100, Jeff<je...@jsystems.com> wrote:
>
>
>> Placing sources requires that you click whilst away from the wire and
>> then drag the source onto the wire. This is not a bug, just the way that
>> the author chose to do it.
>
>
> Show me the place in the manual or help where that is described.
> Made me crazy, but no longer now since I know it,
> and I will keep it a secret and not tell anyone.
Firstly it is not 'drag, drop& move'; it is click, drag & drop! Try
reading the Help a little more closely, you will find that it says:
"The next thing to do is add a voltage-source. While still in Add-mode,
click the 'Source button' (right of the 'Wire button'). Next click and
hold down your left mouse-button somewhere in the picture-box. At the
current mouse-pointer position a new source-object is displayed. Drag
the source-object to the middle of the second wire, just between the two
lower wires-ends of the feedline and release the mouse-button. When
properly positioned a new source is now added."
>>
>> In many years of using 4Nec2 I have never had it loose a file, so I can
>> only assume that there is some sort of problem at your end.
>>
> Of course, it's free, so it must be my fault.
> From the little programming I did, I know it's 99% user interface
> and 1% programming the more interesting part.
No one else reports this problem so draw your own conclusions!!! The
fact that it is free has no bearing on it.
>
>> Yes, it would be nice to have a 'New' button, but again not a bug, just
>> the way that the program works. If this minor inconvenience pains you
>> that much ask the author to add one.
>>
>
> No, no, it's free.
Have you contacted the author and asked for this feature? No? I thought
not. Again the fact that it is free has no bearing.
>
>> Regarding optimization the phrase 'garbage in garbage out' springs to
>> mind. Optimizers are just that, optimizers, they WILL NOT take a rubbish
>> design and turn it into the perfect antenna.
>>
>> Optimizers rely on finding minima (or maxima) in the set of parameters
>> that you supply, so unless you are close to a good design it is very
>> likely that they will 'get stuck' in a local minima and then home in on
>> something other than an optimum design. So you have to have a good
>> design to start with and also not try to optimize to a set of
>> unrealistic goals. This applies TO ALL optimizers not just 4Nec2.
>>
>> Regards
>> Jeff
>
> You are right, that's how it is.
Yes that is the way it is with ALL optimizers, not just 4nec2; gigo.
No one is forcing you to use 4nec2, however, no one else seems to be
having the problems that you claim are 'bugs', perhaps you should have
more patience, read the help more closely, and not be so quick to criticize.
Jeff
Helmut Wabnig
>On 15/08/2011 13:50, Helmut Wabnig wrote:
>> On Mon, 15 Aug 2011 09:59:00 +0100, Jeff<je...@jsystems.com> wrote:
>>
>>
>>> Placing sources requires that you click whilst away from the wire and
>>> then drag the source onto the wire. This is not a bug, just the way that
>>> the author chose to do it.
>>
>>
>> Show me the place in the manual or help where that is described.
>> Normally we do drag and drop, but here we must .
>> Made me crazy, but no longer now since I know it,
>> and I will keep it a secret and not tell anyone.
>
>
>Firstly it is not 'drag, drop& move'; it is click, drag & drop! Try
>reading the Help a little more closely, you will find that it says:
>
>"The next thing to do is add a voltage-source. While still in Add-mode,
>click the 'Source button' (right of the 'Wire button'). Next click and
>hold down your left mouse-button somewhere in the picture-box. At the
>current mouse-pointer position a new source-object is displayed. Drag
>the source-object to the middle of the second wire, just between the two
>lower wires-ends of the feedline and release the mouse-button. When
>properly positioned a new source is now added."
>
It does not work as described, period.
w.
Helmut Wabnig
>On 15/08/2011 13:50, Helmut Wabnig wrote:
>> On Mon, 15 Aug 2011 09:59:00 +0100, Jeff<je...@jsystems.com> wrote:
>>
>>
>>> Placing sources requires that you click whilst away from the wire and
>>> then drag the source onto the wire. This is not a bug, just the way that
>>> the author chose to do it.
>>
>>
>> Show me the place in the manual or help where that is described.
>> Normally we do drag and drop, but here we must .
>> Made me crazy, but no longer now since I know it,
>> and I will keep it a secret and not tell anyone.
>
>
>Firstly it is not 'drag, drop& move'; it is click, drag & drop! Try
>reading the Help a little more closely, you will find that it says:
>
>"The next thing to do is add a voltage-source. While still in Add-mode,
>click the 'Source button' (right of the 'Wire button'). Next click and
>hold down your left mouse-button somewhere in the picture-box. At the
>current mouse-pointer position a new source-object is displayed. Drag
>the source-object to the middle of the second wire, just between the two
>lower wires-ends of the feedline and release the mouse-button. When
>properly positioned a new source is now added."
>
It does not work as described, when inserting a source on a dipole
wire in the center segment, one of the first things to do in Example1.
w.
Jeff
>> Firstly it is not 'drag, drop& move'; it is click, drag& drop! Try
>> reading the Help a little more closely, you will find that it says:
>>
>> "The next thing to do is add a voltage-source. While still in Add-mode,
>> click the 'Source button' (right of the 'Wire button'). Next click and
>> hold down your left mouse-button somewhere in the picture-box. At the
>> current mouse-pointer position a new source-object is displayed. Drag
>> the source-object to the middle of the second wire, just between the two
>> lower wires-ends of the feedline and release the mouse-button. When
>> properly positioned a new source is now added."
>>
> It does not work as described, when inserting a source on a dipole
> wire in the center segment, one of the first things to do in Example1.
>
>
> w.
Utter Rubbish!!! It works EXACTLY as described!!!
Hold down the left mouse button, drag the source to the segment where
you wish it to be, release the button - exactly as described!!!
Jeff
Jim Lux
Then when you set up your optimization criteria in 4nec2, weight the F/B
or F/R with 100% and the others with zero (although sometimes, you may
want to weight forward gain at 10%, just to keep it from driving to zero
gain)
Jim Lux
Does your model have symbols defined (using the 4nec2 specific SY card?)
That's what it uses to populate the list.
Which editor are you using? If you already have a NEC input deck, it's
easiest to use the non-graphical editor.
What are you optimizing for.
Sure, you can whine about wanting better help files, but face it, Arie
is providing the product for free. If you are already proficient in
NEC, the help provided is fairly useful. If you are learning if from
scratch, yep, it's a pain.
Jim Lux
>
>
> When optimizing for F/B also 4nec2 results in a too short driven
> element, same as YAGICAD, they obviously use the same formula,
> (a long two-liner) from literature.
Unlikely...
4nec2 is just driving the finite element NEC engine underneath. YagiCad
uses analytical approximations.
NEC is *very* sensitive to segmentation, spacing, and wire diameters,
etc. particularly when close together or angled. The NEC4 engine is
quite a bit better, but you're probably using the default free NEC2 engine.
To effectively use this kind of thing, you need to be pretty aware of
the limitations and peculiarities of the underlying FEM codes. While I
wouldn't expect someone to have read the theory manual for NEC2, you
might want to check out some of L.B.Cebik's writeups on using MoM codes,
or the stuff in the ARRL Antenna Compendium from time to time.
> I actually built antennas following that prescription,
> and they do not work without additional corrections,
> e.g. a very long hair-pin match.
>
>
>
> Imagine a 3 element 2 meter yagi,
>
> |
> | |
> | | |
> | | |
> | | |
> | | |
> | | |
> | |
> |
>
> Something is wrong here with the capacitive driven element.
Depends on what you were optimizing for.
If all you said was "drive F/B to maximum", then it won't try to get you
a decent match, all it will do is drive to having element currents that
optimize for F/B, which will almost certainly have an evil feedpoint
impedance.
> Now I am having a hard time, because I want to find out in
> what differs a gain optimized vs a F/B optimized antenna
> and it is questionable whether that can be done with software.
> Have not tried other programs yet.
What I do is not try to use the optimizer to design the whole antenna
including matching network. I optimize the basic element design first
(without matching network). Then I add the matching network, hold the
element spacing and length constant, and let that optimize. Then I go
back and allow element length to change, but hold matching network
dimensions/component values (I tend to use lumped element matching
networks) fixed.
It's an iterative thing because it's tough to specify an appropriate
optimization cost function with a simple interface. What you really
want is something like "optimize F/B, but keep the feedpoint impedance
>20 ohms and <100 reactive ohms"
>
> A Yagi with fixed element positions can only be used for 1 frequency
> (within a very small range) and therefore may be impractical
> in many situations. The CEBIK tape measure antenna with their
> water-pipe construction could be easily modified with a moveable
> center element.
this is just not true (otherwise the SteppIR wouldn't work.. it has
fixed element spacing and works over a huge (>1 octave) frequency range)
with fairly good performance.
One can also do similar with fixed spacing, and fixed length, and
reactive loading of the elements at the centers.
Jeff Liebermann
-.dotat> wrote:
>http://imageshack.us/photo/my-images/837/snc14096a.jpg/
Cute cat. However the antenna seems a bit odd. The high carbon steel
tape measure elements are not the best for RF conductivity. Good
enough for receive, but I would check for RF heating in transmit.
The tape measure is also not a circular rod element. You probably
modeled it using a circular cross section. That's probably a good
first try, but if you want accuracy, the actual element cross section
will be needed. That's what I had to do with this stamped sheet metal
antenna:
<http://802.11junk.com/jeffl/antennas/mfj1800/>
>(Without the hair pin match)
>http://img5.imageshack.us/img5/3479/snc14112hairpin.jpg
>Therefore I put the driver on a slider
>http://img841.imageshack.us/img841/8530/snc14097small.jpg
I presume the hairpin match goes between the wing nuts. Looking at
the photo of the hairpin, it seems small for matching a simple 2m
yagi. It's also a good idea to add a balun and to ground the center
of the hairpin match to the center boom.
<http://vk1od.net/antenna/misc/BetaMatch.htm>
Helmut Wabnig
Activate the source & add button, then click on the middle segment
and expect the source symbol to appear there.
It appears but vanishes in an instant leaving a highlighted segment.
If the sideways motion is not performed, you do not get it.
You have to pull it and that is counterintuitive.
The above description may be correct in that you have to pull
the object. After having worked with dozens of CAD programs
I did not expect such a trap.
Many users claim similar difficulties, the internet is full of them.
Honestly, who reads all the help files, hundreds of pages?
I know there are people who think every bug is a feature.
Those people do not live from their own work,
somebody else must pay for their living.
It took me 3 days to learn 4nec2 because of a long list of "features"
including data loss and program crashes. "Notify the author"
it suddenly says. The user sits there "What did I do wrong?"
which is a nagging question actually when the fault lies elsewhere.
All that counts is WALL CLOCK TIME.
But it's free.
w.
Jeff
>>
>>
>> Utter Rubbish!!! It works EXACTLY as described!!!
>>
>> Hold down the left mouse button, drag the source to the segment where
>> you wish it to be, release the button - exactly as described!!!
>>
> and expect the source symbol to appear there.
> It appears but vanishes in an instant leaving a highlighted segment.
> If the sideways motion is not performed, you do not get it.
> You have to pull it and that is counterintuitive.
> The above description may be correct in that you have to pull
> the object. After having worked with dozens of CAD programs
> I did not expect such a trap.
> Many users claim similar difficulties, the internet is full of them.
> Honestly, who reads all the help files, hundreds of pages?
>
>
> I know there are people who think every bug is a feature.
> Those people do not live from their own work,
> somebody else must pay for their living.
Well if you don't actually follow the instructions on the Help then what
can you expect! Don't blame the program and then say the Help is wrong
or not there! RTFM.
"click and hold down your left mouse-button somewhere in the
picture-box" then "Drag the source-object to the middle of the second wire".
Jeff
Helmut Wabnig
wrote:
>.............
>
>>
>> A Yagi with fixed element positions can only be used for 1 frequency
>> (within a very small range) and therefore may be impractical
>> in many situations. The CEBIK tape measure antenna with their
>> water-pipe construction could be easily modified with a moveable
>> center element.
>
>this is just not true (otherwise the SteppIR wouldn't work.. it has
>fixed element spacing and works over a huge (>1 octave) frequency range)
>with fairly good performance.
>
>One can also do similar with fixed spacing, and fixed length, and
>reactive loading of the elements at the centers.
>
>
In theory ( from the simulations) the Yagi is rather narrowband.
Especially the F/B ratio is very frequency dependend.
The SteppIr does vary the elements, if I understand it correctly?
For practical reasons they do not change element positions on
the boom but sufficiently adapt to each frequency band.
For the same practical reasons I do it the other way round,
move the driver element in the 3 element yagi, and leave
everything else as is. This is intended for mobile direction finding.
Based on the Cebik pages and improved by making it tuneable
by moving the driver along the boom.
There is a story behind.
ARDF is a sporting endeavour, where people run around in
a restricted area searching for a defined signal, or several
foxes, as they are called. The antennas are optimized for the
fox frequencies. That's child play compared to real world.
One night I got a phone call from a desperate guy in Bosnia.
They had held a model flight competition there, class F1C,
and his model airplane flew ten kilometers away.
They put crash transmitters on the models and they
range in frequency from 140 to 160 Mhz without any approved
frequency raster, just what they can get and not to disturb
the neighbour model transmitter. So they need equipment for
a 20 MHz range. Most of them use amateur radio handhelds.
The transmitters weigh about 5 grams.
The Yugoslavian Balkan war was just over, where the killed 200000
people by shooting and cutting throats, and the mine fields were
still active and most of them still are today. They put fences around
and automatic siren warnings. That desperate guy's model airplane
was in or near such an area and night doomed. He has searched
for the whole day , was exhausted and could not locate it.
"Signals from everywhere and from all directions", he said.
That model was his only one for the competition and very expensive,
they cost a few thousand dollars.
"Signals from everywhere and from all directions."
That is a very interesting statement. Did you ever experience such
a situation? I had to place foxes and go after them to find out what
the problem was which the guy described. I expected an easy job,
because I am such an old fart in radio engineering. It was late summer
and corn standing two meters high, railway routes nearby,
high voltage lines criscrossing the landscape, buildings, hills,
mountains, fences, and now imagine it's getting dark and you are
in a foreign country where you never had been before,
between lakes, rivers, wet ditches and waste water canals.
I never knew that 2 or 3 meter high corn fields act as an antenna
array. The power lines and railways are wave ducts of extraordinary
quality, every metal fence collects and reflects and adds to the
reflections from the rocky mountains. Electromagnetic interference
overlays the fox signal until you only hear noise and crackles.
There you go. I hope the reader can imagine what is the difference
to a well planned amateur sport radio fox hunting event.
Quickly I recognized that a fixed-frequency ARDF antenna is
not suited for the task and one must be able to tune the F/B ratio
for the different frequencies the transmitters use, in combination
with a conventional attenuator. If your antenna receives from the
back, you will hear "signals from all directions".
w.
Helmut Wabnig
>
>Well if you don't actually follow the instructions on the Help then what
>can you expect! Don't blame the program and then say the Help is wrong
>or not there! RTFM.
>
>"click and hold down your left mouse-button somewhere in the
>picture-box" then "Drag the source-object to the middle of the second wire".
>
>Jeff
Of course you are right,
but there are thousands of (unread) help pages left.
Should I read them all?
On YOUTUBE another (not me) user said, he falls asleep
after 4 pages of help text ( the getting started stuff).
I printed the "getting started" but fell asleep after page 3.
w.
Helmut Wabnig
wrote:
>On Mon, 15 Aug 2011 08:53:35 +0200, Helmut Wabnig <hwabnig@.- ---
>-.dotat> wrote:
>
>>http://imageshack.us/photo/my-images/837/snc14096a.jpg/
>
>Cute cat. However the antenna seems a bit odd. The high carbon steel
>tape measure elements are not the best for RF conductivity. Good
>enough for receive, but I would check for RF heating in transmit.
>
>The tape measure is also not a circular rod element. You probably
>modeled it using a circular cross section. That's probably a good
>first try, but if you want accuracy, the actual element cross section
>will be needed. That's what I had to do with this stamped sheet metal
>antenna:
><http://802.11junk.com/jeffl/antennas/mfj1800/>
>
>>(Without the hair pin match)
>>http://img5.imageshack.us/img5/3479/snc14112hairpin.jpg
>>Therefore I put the driver on a slider
>>http://img841.imageshack.us/img841/8530/snc14097small.jpg
>
>I presume the hairpin match goes between the wing nuts. Looking at
>the photo of the hairpin, it seems small for matching a simple 2m
>yagi. It's also a good idea to add a balun and to ground the center
>of the hairpin match to the center boom.
><http://vk1od.net/antenna/misc/BetaMatch.htm>
Thank you for the links, appreciate your help.
I fear that in the end I will have to cut and tweak using the
antenna analyzer, and with the time perhaps find
"tape measure correction factors".
Want to keep the design as simple as possible,
and hope it works without a balun or additional tricks.
Am not yet sure if it will work that way, or not.
w.
Jeff
Well since the instructions on how to add a source are on page one, it
would appear that you went to sleep earlier than you thought!!
Just because a program does not work the way that YOU expect, or perhaps
would like, does not warrant the out and out rant that you started this
thread with.
All of the information on how to run the program was actually there if
you had bothered to read it rather than wasting time complaining about
nothing.
Jeff
Jeff Liebermann
-.dotat> wrote:
>Thank you for the links, appreciate your help.
Y'er welcome. However, I still don't have a clue what you're trying
to accomplish. If you want super front to back ratio for a direction
finding antenna, you need a wall, not a phased single wire reflector
as in a yagi. Something like a dish or a panel reflector will work,
but is probably not practical. As you discovered, the position of the
reflector is very critical for maintaining the best F/B ratio. It's
also very sensitive to frequency. You might be able to make it work
with a flimsy tape measure, but it probably won't be very stable in
the field.
Permit me to offer another idea. Instead of direction finding by the
peak signal, do it with a null. Two identical dipoles, a T connector,
and some coax, are all that are required. Space them about 1/4
wavelength apart. Insert a 3/4 wave coax phasing section between the
two dipoles. Signals from the front antenna will cancel when they
reach the 2nd antenna yielding a cardioid pattern. It will be just as
critical and sensitive to frequency and position as your yagi, but
methinks will work better. I've obtained 50dB deep nulls with this
method. The good news is that you really only need one adjustment on
the antenna, which is the relative distance between dipoles, which is
easily accomplished by sliding the antenna on the boom. The
adjustment range is limited, so an assortment of coax phasing lengths
will also be needed. Adjusting the antenna for best null at a
specific frequency, prior to transmitter hunting, is a necessary
complication.
I also use this method on my home base station to null out a rather
strong repeater, so I can talk to a distant repeater on the same
frequency. I've also built one using 4 identical rubber ducky
antennas for 2meters. It sorta worked but I could only get a 10dB
deep null.
Both EZNEC and 4NEC have HF examples of this type of antenna.
cardioid.ez and \models\HFvertical\cardioid.nec
>I fear that in the end I will have to cut and tweak using the
>antenna analyzer, and with the time perhaps find
>"tape measure correction factors".
More bad news. You really do have to TEST your creations to see if
the simulations and models are correct. I tend to make far too many
simplifying assumptions in my models, which show up as errors in the
actual construction.
>Want to keep the design as simple as possible,
Simple is good. Crude is not. Recognizing the difference is
difficult.
>and hope it works without a balun or additional tricks.
>Am not yet sure if it will work that way, or not.
It won't work well without a balun. The coax will radiate, giving
unpredictable directional indications. You can minimize the effects
with ferrite beads, a sleeve balun, or with just a coax loop.
Jeff Liebermann
-.dotat> wrote:
>The SteppIr does vary the elements, if I understand it correctly?
>For practical reasons they do not change element positions on
> the boom but sufficiently adapt to each frequency band.
Perhaps reading the Steppir patent might be illuminating:
<http://www.google.com/patents?id=rw6xAAAAEBAJ>
Note that the elements do not change position, only their length.
Jim Lux
> On Tue, 16 Aug 2011 11:21:20 +0200, Helmut Wabnig<hwabnig@.- ---
> -.dotat> wrote:
>
>> Thank you for the links, appreciate your help.
>
> Y'er welcome. However, I still don't have a clue what you're trying
> to accomplish. If you want super front to back ratio for a direction
> finding antenna, you need a wall, not a phased single wire reflector
> as in a yagi. Something like a dish or a panel reflector will work,
> but is probably not practical. As you discovered, the position of the
> reflector is very critical for maintaining the best F/B ratio. It's
> also very sensitive to frequency. You might be able to make it work
> with a flimsy tape measure, but it probably won't be very stable in
> the field.
>
> Permit me to offer another idea. Instead of direction finding by the
> peak signal, do it with a null.
Exactly.. you can get very sharp nulls pretty easily. For simple
antennas, there's usually an ambiguity, but you can resolve that by
other means.
Jim Lux
Should you read them?
Depends on if you want to make use of the program or not. for ANY
modeling program (and any drafting program, as well) there's a fairly
big first step in the learning curve.
And, because 4nec2 isn't a "drafting" or "drawing" program, it's UI
doesn't follow the more common conventions. It's designed to make
entering antennas easy for some subset of people. 4nec2 started with
just using notepad to edit the NEC input deck and a formatted editor to
edit cards.
Folks who start with EZNEC often find using raw NEC decks difficult,
because they're used to the tabular model entry of EZNEC.
Folks who start with Visio, pre version 5, find modern versions of Visio
a pain, because the UI changed to conform to PowerPoint.
Autocad is certainly not "intuitive" unless you've been using it a while.
For what it's worth, the 4nec2 help files are a whole lot better than
the documentation for NEC itself.
Beyond the details of entering the geometry and simulation conditions
(which are idiosyncratic for ALL antenna modeling programs.. no two are
alike, nor are the input file formats directly compatible, for the most
part)
There's a fair amount of "art" in effectively using the programs and
understanding the limitations inherent in the modeling technique being
used (method of moments on wires for NEC). It's not just a matter of
creating a bazillion segments and letting your processor grind away,
because there's all sorts of subtle numerical precision issues.
4nec2 (and EZNEC) both provide some amount of help in keeping you away
from egregious model errors (segment lengths that are unreasonable
relative to wavelength and/or wire diameter).
There's also well known techniques for modeling flat surfaces with
meshes that provide results that match actual measurement, even if the
model doesn't "look" quite right if you render it.
NEC is very much a power tool like a chainsaw.. you can do things that
you couldn't do with hand tools, but you can also do things that you
don't really want. It takes some practice and background knowledge to
use it effectively.
The value of purpose built modeling tools like AO is that they have a
very constrained model space tuned to a particular application, so the
program can
a) have a simple model entry (e.g. you can only do Yagi-Uda)
b) have a sophisticated objective function for optimization
NEC is a lot harder: you can enter any geometry from a simple wire to an
entire battleship with 100s of antennas.
Richard Clark
-.dotat> wrote:
>"Signals from everywhere and from all directions."
Hi Helmut,
The signal is too STRONG. I'm surprised you have not recognized this
common fox hunting problem.
There needs to be an attenuator between the antenna and the receiver.
73's
Richard Clark, KB7QHC
Jeff Liebermann
wrote:
With the cardioid pattern, there's no ambiguity. With a deep null,
and a non-reflective environment, it's easy to use. However,
reflections off buildings and hills are a problem. The antenna is
roughly an omnidirectional antenna, and reflections will appear to
fill in the deep null. Not much can be done about that except to move
and try a different location. My favored method is by using a map.
Find a position, determine a bearing, and draw a line of position on
the map. Then, find a different location, and do it again. Repeat as
often as practical generating as many LOP's as possible. Some of the
LOP's will be totally insane, but a majority should cross at one point
on the map. (This has been automated in software, but a map is good
enough).
In 1976, I helped design the AN/SRD-21 homer DF, which DOES have a 180
degree ambiguity.
<http://802.11junk.com/jeffl/AN-SRD-21/>
If the homing receiver works in the same manner as described in the
above manual (PIN antenna switch, synchronous demodulator, charge
pump, and zero center meter), resolving the ambiguity is easy. Just
rotate the homing antenna to the right. If the zero center meter
indicates that you should turn back to the left, then you have the
correct direction. If it indicates that you should continue to turn
to the right, then you have the wrong direction.
This has nothing to do with the topic at hand, but I thought it might
be of interest. Some of my ancient comments on Doppler direction
finding:
<http://www.qsl.net/n9zia/doppler_notes1.txt>
<http://www.qsl.net/n9zia/doppler_notes2.txt>
Dave Platt
Jeff Liebermann <je...@cruzio.com> wrote:
>With the cardioid pattern, there's no ambiguity. With a deep null,
>and a non-reflective environment, it's easy to use. However,
>reflections off buildings and hills are a problem. The antenna is
>roughly an omnidirectional antenna, and reflections will appear to
>fill in the deep null. Not much can be done about that except to move
>and try a different location. My favored method is by using a map.
>Find a position, determine a bearing, and draw a line of position on
>the map. Then, find a different location, and do it again. Repeat as
>often as practical generating as many LOP's as possible.
I have seen recommendations that one do this by proceeding in a
straight line, taking bearings at positions of around 1/4 wavelength
or so. The effects of multipath will tend to cause the measured
bearing to wobble back and forth across an arc (as you go down the
line) and the true bearing will tend to be close to the center of that
arc.
I haven't tried this approach myself... but it might combine well with
your "take readings from lots of different locations" approach, by
helping cancel out some of the effects of multipath.
--
Dave Platt <dpl...@radagast.org> AE6EO
Friends of Jade Warrior home page: http://www.radagast.org/jade-warrior
I do _not_ wish to receive unsolicited commercial email, and I will
boycott any company which has the gall to send me such ads!
Jim Lux
> In article<39ol4714lqqgjv8b0...@4ax.com>,
> Jeff Liebermann<je...@cruzio.com> wrote:
>
>> With the cardioid pattern, there's no ambiguity. With a deep null,
>> and a non-reflective environment, it's easy to use. However,
>> reflections off buildings and hills are a problem. The antenna is
>> roughly an omnidirectional antenna, and reflections will appear to
>> fill in the deep null. Not much can be done about that except to move
>> and try a different location. My favored method is by using a map.
>> Find a position, determine a bearing, and draw a line of position on
>> the map. Then, find a different location, and do it again. Repeat as
>> often as practical generating as many LOP's as possible.
>
> I have seen recommendations that one do this by proceeding in a
> straight line, taking bearings at positions of around 1/4 wavelength
> or so. The effects of multipath will tend to cause the measured
> bearing to wobble back and forth across an arc (as you go down the
> line) and the true bearing will tend to be close to the center of that
> arc.
>
> I haven't tried this approach myself... but it might combine well with
> your "take readings from lots of different locations" approach, by
> helping cancel out some of the effects of multipath.
>
There's a photograph of this technique on a field with little flags at
different distances all oscillating around a single line illustrating it
in some ARRL publication (probably an antenna compendium, but maybe the
handbook or antenna book).
Jeff Liebermann
wrote:
>On 8/16/2011 3:16 PM, Dave Platt wrote:
I think the photo was on interferometry for direction finding, where
they were trying to plot the wavefront pattern. I recall the photo,
but I couldn't find it in the ARRL Antenna Handbook (19th edition).
However, the handbook does have a full chapter on direction finding
(Ch 14) which includes the cardioid antenna.
The purpose of me using multiple bearings is simply to eliminate the
effects of reflections. It's not totally foolproof, but better than
chasing a single bearing.
There are better ways, but they're usually not very portable. A
rotating antenna direction finder can easily distinguish between the
incident signal from a reflection. Such direction finders display
something like the antenna pattern on a polar display. The incident
signal is very steady and does not move in azimuth. Reflections
jitter dramatically in both amplitude and azimuth. They also tend to
appear and disappear rapidly and erratically.
Rotating antenna DF antennas:
<http://www.rockwellcollins.com/sitecore/content/Data/Products/EW_and_Intelligence/SIGINT/ANT-1040A_Airborne_Spinning_DF_Antenna.aspx>
<http://www.rockwellcollins.com/sitecore/content/Data/Products/EW_and_Intelligence/SIGINT/ANT-1040_Spinning_DF_Antenna.aspx>
20 in diameter, 25 in high, 50 lbs.
Another method that I've used is to generate a narrow "beam" using two
identical yagi antennas that share a common reflector. The antennas
are oriented about 20 degrees apart with the reflector at the vertex.
A near perfect audible square wave drives two identical PIN diode
switches on the driven elements. While the antenna may have a -3dB
beamwidth of perhaps 10 degrees, the LOP of equal antenna signal
levels is extremely sharp, and often less than 0.5 degrees. A
synchronous demodulator, charge pump, differential amp, and zero
center meter complete the systems. You can also do it by ear by
listening to the null at the switching frequency. If the antennas and
PIN diode switches are perfectly symmetical, all boresight error
cancel. I originally contrived the system by reading about the Lorenz
beam bombing system used by the German's during WWII, but later
discovered that others had anticipated the idea.
Jim Lux
> On Tue, 16 Aug 2011 17:13:15 -0700, Jim Lux<james...@jpl.nasa.gov>
> wrote:
> I think the photo was on interferometry for direction finding, where
> they were trying to plot the wavefront pattern. I recall the photo,
> but I couldn't find it in the ARRL Antenna Handbook (19th edition).
> However, the handbook does have a full chapter on direction finding
> (Ch 14) which includes the cardioid antenna.
Could be..
>
> The purpose of me using multiple bearings is simply to eliminate the
> effects of reflections. It's not totally foolproof, but better than
> chasing a single bearing.
>
> There are better ways, but they're usually not very portable. A
> rotating antenna direction finder can easily distinguish between the
> incident signal from a reflection. Such direction finders display
> something like the antenna pattern on a polar display. The incident
> signal is very steady and does not move in azimuth. Reflections
> jitter dramatically in both amplitude and azimuth. They also tend to
> appear and disappear rapidly and erratically.
>
<snip>
>
> Another method that I've used is to generate a narrow "beam" using two
> identical yagi antennas that share a common reflector. <snip>
>
A popular scheme from WJ 30 years ago (at the advent of digital signal
processing) used 3 antennas in a triangle, and basically did
interferometry. Sampling the data and using an FFT lets you do a wide
band at one time (which is handy if you want to DF frequency hopping
radios, which became very popular in the 80s)
NM5K
> A popular scheme from WJ 30 years ago (at the advent of digital signal
> processing) used 3 antennas in a triangle, and basically did
> interferometry. Sampling the data and using an FFT lets you do a wide
> band at one time (which is handy if you want to DF frequency hopping
> radios, which became very popular in the 80s)
>
As far as VHF, I know a couple here in town I've seen using arrays
for direction finding. But they used four verticals in a square.
It worked quite well. We had one guy that kept jamming one of the
repeaters, and the user of said array was easily capable of tracking
him down to a shopping center parking lot where the guy was sitting
in his car. I suspect the expression on the jammers face when the
tracker tapped on his window was priceless. :)
The device in the car used an array of LED's in a cross configuration
if I remember right.
He had the antenna array on the back of his truck. I don't recall the
element spacing.
Dave Platt
>for direction finding. But they used four verticals in a square.
>It worked quite well. We had one guy that kept jamming one of the
>repeaters, and the user of said array was easily capable of tracking
>him down to a shopping center parking lot where the guy was sitting
>in his car. I suspect the expression on the jammers face when the
>tracker tapped on his window was priceless. :)
>The device in the car used an array of LED's in a cross configuration
>if I remember right.
>He had the antenna array on the back of his truck. I don't recall the
>element spacing.
Likely a Doppler direction-finder, possibly a Ramsey DDF-1 or one of
the others of that sort.
They aren't perfect... definitely subject to errors due to multipath,
and they works best when looking for a relatively clean, non-modulated
carrier. Fun, though... I've used mine on several occasions to locate
sources of QRM or jamming.
I've seen similar 4-vertical arrays on the roofs of some police cars
in my area. I infer that they're used to track down cars which have
had their Lojack locators triggered, after a car theft.
Jim Lux
> I've seen similar 4-vertical arrays on the roofs of some police cars
> in my area. I infer that they're used to track down cars which have
> had their Lojack locators triggered, after a car theft.
>
You are correct with respect to LoJack, which radiates in the high VHF
band. They do pseudo-doppler direction finding. I don't know how
fashionable LoJack is these days... the sophisticated thieves know how
to jam it. The widespread deployment of in-car GPS/cell (On-Star, etc)
covers a lot of the other cases. Face it, most car thieves aren't all
that smart.
Jeff Liebermann
wrote:
>Likely a Doppler direction-finder, possibly a Ramsey DDF-1 or one of
>the others of that sort.
Agreed. There are various commerical implimentations. Basically, the
diameter of the "circle" of antennas controls the deviation of the
doppler signal heard on the receiver. The bigger the diameter, that
better the signal to noise ratio. Typical is about 1/2 wave diameter.
Smaller diameters will work, but require narrower digital filters
which slow down aquisition.
>They aren't perfect... definitely subject to errors due to multipath,
>and they works best when looking for a relatively clean, non-modulated
>carrier.
Plenty more wrong with doppler DF. They don't like horizontally
polarized signals. Reflections cause false readings. Forward
alignment (0 degree heading) varies somewhat with frequency. Switching
PIN diodes in the antenna cause interpolation errors every 90 degrees.
Multiple transmitters on the same frequency result in erronious
readings. Antenna tilt causes big errors. Reflections off building
and in particular, the ground ahead of the antenna, causes errors.
There are fixes and work around for most of these, but I haven't seen
any on ham quality dopplers. Some of my ancient comments on the
topic:
<http://www.qsl.net/n9zia/doppler_notes1.txt>
<http://www.qsl.net/n9zia/doppler_notes2.txt>
>Fun, though... I've used mine on several occasions to locate
>sources of QRM or jamming.
Ummm.... How did you get it to produce a usable bearing if there were
two transmitters on the air at the same time? I can see if it you
waited until the jammer was the only carrier, but few jammers allow
that to happen. Mostly we use doppler for the traditional stuck
transmitter.
Mini-rant: Why do almost ALL commerical radios have tx timeout
timers, while almost ALL ham radios don't have this feature?
>I've seen similar 4-vertical arrays on the roofs of some police cars
>in my area. I infer that they're used to track down cars which have
>had their Lojack locators triggered, after a car theft.
That's LoJack. I rode around in test vehicle with one trying to make
sense of the indication. In an urban jungle, it's very difficult to
get a decent bearing due to all the building reflections. I suggested
we try an elevated freeway, and the bearings improved. Works much
better in the suburbs.
Sal
"Jeff Liebermann" <je...@cruzio.com> wrote in message
news:t06t479a3mevj1im3...@4ax.com...
< snip >
> Mini-rant: Why do almost ALL commerical radios have tx timeout
> timers, while almost ALL ham radios don't have this feature?
Is it because we're all known to be gasbags?
Timeout? Why the very *impudence* of that radio!!!
All kidding aside, we had a major repeater outage in San Diego some years
ago. A 50w mobile, in the middle of a hotel parking lot, was on the air for
hours, holdng the repeater. The T-hunters who found the car ID'ed the owner
by his callsign plate and contacted him in the hotel. It was the old
microphone-between-the-seat-cushions trick. Timeout would have helped that
day.
"Sal"
Jeff Liebermann
>
>"Jeff Liebermann" <je...@cruzio.com> wrote in message
>news:t06t479a3mevj1im3...@4ax.com...
>
>< snip >
>
>> Mini-rant: Why do almost ALL commerical radios have tx timeout
>> timers, while almost ALL ham radios don't have this feature?
>
>Is it because we're all known to be gasbags?
Yes. That's also why many Japanese ham radios are severely lacking in
microphone gain. I guess they assume that all Americans are always
yelling.
>Timeout? Why the very *impudence* of that radio!!!
Ok, bad choice of a name for the timer. Perhaps "anti-ratchet mouth"
or "monolog restrictor" might be better.
>All kidding aside, we had a major repeater outage in San Diego some years
>ago. A 50w mobile, in the middle of a hotel parking lot, was on the air for
>hours, holdng the repeater. The T-hunters who found the car ID'ed the owner
>by his callsign plate and contacted him in the hotel. It was the old
>microphone-between-the-seat-cushions trick. Timeout would have helped that
>day.
Yep. It's all too common. My guess is one every month or so.
Unfortunately, I managed to jam the microphone under the debris pile
that usually clutters the passenger seat, jamming the local repeater.
I was easily identified by the classical music in the background since
nobody else around listens to classical music. What's really
irritating are the number of packet radios that end up on repeater
frequencies. Usually, we can decode the call sign and contact the
culprit. Occasionally, there's no call sign as the owner is trying to
setup his TNC. There's also the stuck transmitter on commercial and
public safety frequencies. Those are fun and gets us plenty of points
from the various agencies. Extra credit to the local comm shop that
likes to defeat the timeout timer, for no obvious reason.
My favorite stuck transmitter was on marine channel 16. There was a
very strong carrier on Ch 16, that could be heard all over Monterey
Bay. Everyone dug out their DF hardware and the searching began.
Strong signal, no modulation, 100% duty cycle. This should be easy.
Right...
After 5 days of bad guesses and dead ends, the culprit turned out to
be a marine base station on Fremont Pk (3,000ft). It was rarely used
and was only functional in order to maintain the license. Something
went wrong with the DC wireline control system (with no timer) which
stuck it on the air. Why so difficult? The strong signal created a
wide assortment of reflections. Everyone had trouble separating the
strong reflections from the incident signal with the Doppler DF boxes.
I was using my rotating antenna kludge, but stupidly used a 5 element
yagi tuned to 146Mhz. At 156.8Mhz, I later discovered that it had
almost as much gain towards the back of the antenna as it did in the
forward direction.
Incidentally, there's another difference between ham and commercial
mobiles. Commercial mobiles have a PL hang up function, where the
receiver is in PL decode when the mic is hung in the hanger, and goes
to carrier squelch when removed. Many ham mobiles seem to be missing
this useful feature.
dave
>
> Incidentally, there's another difference between ham and commercial
> mobiles. Commercial mobiles have a PL hang up function, where the
> receiver is in PL decode when the mic is hung in the hanger, and goes
> to carrier squelch when removed. Many ham mobiles seem to be missing
> this useful feature.
>
>
This is so the commercial operator listen to the whole channel (and not
just his company's CTCSS filtered traffic) prior to transmitting. A
typical ham channel is continuously monitored and everyone has the
same CTCSS tone.
Dave Platt
Jeff Liebermann <je...@cruzio.com> wrote:
>>Fun, though... I've used mine on several occasions to locate
>>sources of QRM or jamming.
>
>Ummm.... How did you get it to produce a usable bearing if there were
>two transmitters on the air at the same time? I can see if it you
>waited until the jammer was the only carrier, but few jammers allow
>that to happen. Mostly we use doppler for the traditional stuck
>transmitter.
A lot of the jamming in question is jamming of repeaters, so you are
DF'ing on the repeater's input frequency.
If you have a rough idea where the jammer is operating, you can often
get a Doppler detector (e.g. on a car) into that area and get a decent
signal from it when he's jamming... but be far enough away from the
person being jammed that you don't hear any of his signal (although
the repeater does).
A Dopper rig on the roof of a car has a far smaller line-of-sight
radius than a repeater receiver mounted up on a high building or
hilltop.
Jeff Liebermann
Sure, but we have several other distant repeaters on the same channels
I like to monitor. I also hear plenty of RF leaks and odd sources of
RF as I drive around. So, I turn on the PL decode. With a ham radio,
I just pickup the mic, the receiver stays in PL decode, and proceed to
talk. With the Maxtrac I currently use in the car, as soon as I
pickup the mic, I hear all the junk, which helps to make sure I'm not
causing a problem by talking over other users on the distant
repeaters. (We have somewhat overlapping coverage areas). Also, when
in PL decode, there's about a 600msec delay before the rx squelch
opens, which obliterates the first two syllables.
Rob
> TNC. There's also the stuck transmitter on commercial and
> public safety frequencies. Those are fun and gets us plenty of points
> from the various agencies. Extra credit to the local comm shop that
> likes to defeat the timeout timer, for no obvious reason.
It does not seem the public safety radio devices always had this
timeout timer either.
Before the public safety services here switched to a digital system,
they used NBFM equipment from companies like Motorola, and it was very
common to hear stuck transmitters that blocked an entire repeater channel.
(which often consists of multiple receivers and transmitters over a city area)
Police used mobile transceivers in the cars on VHF and portables on UHF
so it usually was possible to alert the users on the other channel and
hope the stuck PTT key was found that way, but on major events like
queen's day it often happened that the portables channel was jammed for
half an hour or so before the culprit was found.
Of course the equipment was aging by that time, it probably was from
the eighties. Now they are all on TETRA and AFAIK that system allows
the operator to just tune out stuck transmitters or devices that fell
into wrong hands.
Jeff Liebermann
>Jeff Liebermann <je...@cruzio.com> wrote:
>> TNC. There's also the stuck transmitter on commercial and
>> public safety frequencies. Those are fun and gets us plenty of points
>> from the various agencies. Extra credit to the local comm shop that
>> likes to defeat the timeout timer, for no obvious reason.
>
>It does not seem the public safety radio devices always had this
>timeout timer either.
Methinks that just about every radio, by Motorola and Kenwood have a
transmit timeout timer.
<http://802.11junk.com/jeffl/pics/drivel/slides/too-many-radios.html>
The dip switch programmable radios (SP10) do not have a timer, but
literally every radio that requires a computah to setup has a timer.
Note that I was talking about mobile radios all of which are
programmable, not handhelds.
>Before the public safety services here switched to a digital system,
>they used NBFM equipment from companies like Motorola, and it was very
>common to hear stuck transmitters that blocked an entire repeater channel.
>(which often consists of multiple receivers and transmitters over a city area)
That's a programming issue. The timer is off by default and must be
enabled and set for a specific number of seconds. 60 seconds is the
typical timeout.
Digital radio comes in many flavors. One of the big advantages of
digital is that the repeater and channel can handle more than one
transmission at a time (either by TDM or FDM). Therefore a stuck
digital transmitter does not timeout or disable the repeater. In
addition, many such radios are full duplex, which allows the
dispatcher or comm shop to remotely disable the transmitter and yell
at the user. Whether the PSAP is setup and trained to do this is
debatable.
>Police used mobile transceivers in the cars on VHF and portables on UHF
>so it usually was possible to alert the users on the other channel and
>hope the stuck PTT key was found that way, but on major events like
>queen's day it often happened that the portables channel was jammed for
>half an hour or so before the culprit was found.
Yep. Simply identifying the stuck transmitter is often insufficient.
I've heard stuck transmitters in vehicles rolling down the freeway for
an hour with a stuck transmitter. It was obvious who it was but
nothing short of an RF seeking missile was going to get their
attention. In one case, someone noticed that they were listening to
specific local radio station. The dispatcher called the radio station
and had them make a special announcement to the driver to unstick the
transmitter. It worked, instantly.
>Of course the equipment was aging by that time, it probably was from
>the eighties. Now they are all on TETRA and AFAIK that system allows
>the operator to just tune out stuck transmitters or devices that fell
>into wrong hands.
Yep. Nice feature. In the US, the high end radios are P25. Various
other narrow band solutions exist, most of which have remote
programming and remote deactivation. Despite all the government
programs intended to provide interoperability, the manufacturers (and
the FCC) have gone out of their way to introduce proprietary
enhancements and introduce intentional incompatibility.