___Original Message_________________________________________
From: Sal
Date: Wed, 26 Oct 2011 Time: 19:51:49

http://homepage.ntlworld.com/wadei/aim4170.htm

Say, after following the link, above, I just took a look at that AIM4170 web
site and it looks like it's more trouble to get it up and running than most
things.


Sal

I assume you are talking about the AIM Forum, he

http://aim4150.proboards.com/index.cgi?board=analyzer

Yes, there are many questions about AIM4170 operation there, but look
closely at the dates of the messages. Most of them are now very old. The
software has settled down very nicely now, and the instrument is indeed
very easy to set up and use.

To find out all the information you need, download the latest version of
the software (currently in AIM_846.zip), from he

http://www.w5big.com/prog_update.htm

The download contains the AIM software (which you can run in demo mode
without the AIM hardware), plus the manual.

--
73
Ian, G3NRW

The AIM4170 Antenna Analyzer:
http://homepage.ntlworld.com/wadei/aim4170.htm

"Sal" wrote in :

....

Say, after following the link, above, I just took a look at that
AIM4170 web site and it looks like it's more trouble to get it up and
running than most things. A lot of the steps are left to the
imagination ... or they assume a whole lot about what potential buyers
already know.

Sal, I bought an AimUHF, and it worked fine out of the box.

I suspect that the problem that most hams encounter with analysers and
VNAs is that the knowledge of basic complex numbers, AC circuit theory,
transmission lines, and antenna systems does not 'come in the box'.

If acquiring such a thing is the stimulus for expanding knowledge on
those topics using the box as a learning aid, that is great. But to
many, they are safer to just treat it as a VSWR measuring device.

I am staggered by the popular advice offered to newbies who ask 'why is
my VSWR high' on eHam and QRZ to borrow an analyser. The advice appears
to offered mainly by people who don't understand the instruments, and
possibly have never used them effectively.

A classic example is the advice to connect the instrument at the shack
end and tune for resonance, for as everyone knows, "an antenna just
ain't gonna work any good unless it is resonate (sic)".

The getting of knowledge just isn't a priority in a world of instant
gratification.

Owen

Jim Lux wrote in news:j846r5$7h3$1
@news.jpl.nasa.gov:

There's a goodly bit of empiricism in trap design.

And a goodly bit of misinformation in some of the traditional ham sources.

I have had an interest in the so called coax traps, and just in the last
week or so, make some headway with some good measurments of the underlying
inductor formed by the coil of coax shield. There were some surprises. For
those interested, see http://www.vk1od.net/antenna/coaxtrap/index.htm .

Short of performing Medhurst style measurements on a range of inductors,
there is no way to be sure that the effects observe apply generally, or
what a more general model might be.

Owen

very interesting
thanks a lot

On 10/26/2011 12:37 AM, Owen Duffy wrote:
Jim wrote in news:j846r5$7h3$1
@news.jpl.nasa.gov:

There's a goodly bit of empiricism in trap design.

And a goodly bit of misinformation in some of the traditional ham sources.

I have had an interest in the so called coax traps, and just in the last
week or so, make some headway with some good measurments of the underlying
inductor formed by the coil of coax shield. There were some surprises. For
those interested, see http://www.vk1od.net/antenna/coaxtrap/index.htm .

Short of performing Medhurst style measurements on a range of inductors,
there is no way to be sure that the effects observe apply generally, or
what a more general model might be.


There is a fair amount of literature on L and C (and loss) for shielded
inductors, which is what a lot of traps look like.. the ones which use
the C to the surrounding tube, anyway, like in the 4,5,6-BTV. Some
papers have generic cookbook-ey design equations which might be useful
(although I don't have any citations off the top of my head).

For a bare coil of the appropriate L/D ratio, Medhurst will get you in
the right starting place.

The problem would be things like manufacturing variability, if you're
copying (or writing instructions) one-off design. Stuff like 'how thick
is the enamel/polyurethane/PVC insulation'.

Sort of like the measurements of Z and loss for zipcord. The dielectric
properties aren't controlled in manufacturing, so what you measure on
brand X, 16 Feb 2001 may have little or no relation to what you measure
on brand X, 20 Oct 2010 vintage.

Jim Lux wrote in
:

On 10/26/2011 12:37 AM, Owen Duffy wrote:
Jim wrote in news:j846r5$7h3$1
@news.jpl.nasa.gov:

There's a goodly bit of empiricism in trap design.

And a goodly bit of misinformation in some of the traditional ham
sources.

I have had an interest in the so called coax traps, and just in the
last week or so, make some headway with some good measurments of the
underlying inductor formed by the coil of coax shield. There were
some surprises. For those interested, see
http://www.vk1od.net/antenna/coaxtrap/index.htm .

Short of performing Medhurst style measurements on a range of
inductors, there is no way to be sure that the effects observe apply
generally, or what a more general model might be.


There is a fair amount of literature on L and C (and loss) for
shielded inductors, which is what a lot of traps look like.. the ones
which use the C to the surrounding tube, anyway, like in the
4,5,6-BTV. Some papers have generic cookbook-ey design equations
which might be useful (although I don't have any citations off the top
of my head).

For a bare coil of the appropriate L/D ratio, Medhurst will get you in
the right starting place.

The problem would be things like manufacturing variability, if you're
copying (or writing instructions) one-off design. Stuff like 'how
thick is the enamel/polyurethane/PVC insulation'.

Sort of like the measurements of Z and loss for zipcord. The
dielectric properties aren't controlled in manufacturing, so what you
measure on brand X, 16 Feb 2001 may have little or no relation to what
you measure on brand X, 20 Oct 2010 vintage.

All noted.

Many readers will recall my interest over more than a decade in
predicting the effective RF resistance of the outside surface of a
braided coax shield, especially when it forms a solenoid... as in the
coax traps.

The last round of measurements by VK2KRB were most interesting, because
they strongly suggested that Q was not proportional to root of f as
Medhurst and predecessors observed for round copper wire (and of course,
R was higher than for an equivalent sized round copper conductor).

Jim, interesting that you mention ZIP cord. I have seen a number of
articles recently discussing the TL characteristics of ZIP cord, and
again many readers will recall Jack Smith's measurements published here
about 10 years ago.

I recently put a new TL calculator up, it uses input parameters of Ro,
vf, k1, k2 to solve problems similarly to the older TLLC. It is at
http://www.vk1od.net/calc/tl/atllc.htm . I wrote an article with some
examples of using it at http://www.vk1od.net/calc/tl/atllcEx.htm .
Example 2 plots Jack's data on ZIP attenuation from back then. A
stunning set of measurements, and statistically tighter than I have seen
from any one else. Nevertheless, I see a wavelike shape to the error
between actual and the model, a growing sinusoid that prompts the
question of why, was it some common mode effect and radiation.

Owen

On 10/20/2011 09:19 AM, béo-master wrote:
HI,

I picked up two coils that could be a trap for the CWA-840 COMET
antenna. (They have two stickers "CL-840").
The manual of the CWA-840 says : 40/80m dipole.

I found amazing that there isn't any capacitor in // of these coils...
These coils measure 76uH.
Could someone tell me how they works ?
In the manual of the CWA-840, each leg of the 7MHz section, is
11.1meters in lenght , wich, it seems to me, that it is rather longer
that 1/4 wave. (10.1m).
Why ?

Thanks a lot for your answers

CWA-840:

-----[ ]-------------ooo--//--
2.3m coil 11.1m balun

This is not a trap antenna:

1)- At 40 meters the coil works like a medium impedance insulator,76uH
represents 5300 ohms.

2)- At 80 meters, the antenna works like a vertical mobile antenna, the
coil resonates with the 2.3m section.

I made several of these antennas years ago, and the 40 meter section is
always longer than in a simple 40 meter dipole.
--
Alejandro Lieber LU1FCR
Rosario Argentina

Real-Time F2-Layer Critical Frequency Map foF2:
http://1fcr.com.ar