"Roy Lewallen" wrote in message
...
Trying to phase two antennas that close together at that frequency range
will be an educational experience at best, but more likely just an
exercise in frustration unless you have much more patience than average.
Such an array will be hyper-sensitive to everything. You might be able to
fleetingly see a null after a lot of tweaking, but I seriously doubt
you'll even get that. A tiny change in frequency, wiggling of the whips,
or even movement in the vicinity of the whips will have a profound effect
on any null you might see.

If a null from a small antenna is what you want, you'd have much better
luck with a carefully constructed and balanced ("shielded") loop.

Roy Lewallen, W7EL

Found my copy of Joe Carr's Practical Antenna Handbook, and re-read the
section on phasing verticle antennas. I believe you. Back to square one,
which was the thought that a loop was probably my best bet (I had come to
that conclusion a while back, but forgot why.)

Did try a shielded loop once upon a time, but didn't feel it gave me
anything to look forward to. Guess I'll dig it out and try it again. Will
try shielding it with copper "tape" and see what that buys me. I did try a
piece of coax wound in a triple-turn loop to give me 2.5 or 3 uH with which
to tune, with the shield cut away to expose the center conductor for a
couple inches, but didn't feel this offered anything either. Not sure what
I'll do. Poke around and try different things until I find something that
works better than the rest. Any ideas? I'm all ears. I tried the whips
because I had them on hand, and they were easy to install. Seems I read
somewhere that contrary to conventional wisdom, the shield on a shielded
loop doesn't actually shield at all, but becomes the antenna element.
Anyone know anything about that line of thought? I obviously know nothing,
and am trying to learn. Just don't know where to focus my energies.

Thanks,

Dave

Dave wrote:
. . .
. . .Seems I read
somewhere that contrary to conventional wisdom, the shield on a shielded
loop doesn't actually shield at all, but becomes the antenna element.
Anyone know anything about that line of thought? I obviously know nothing,
and am trying to learn. Just don't know where to focus my energies.

That's been discussed on this newsgroup a number of times. You should be
able to find the relevant threads via groups.google.com.

Yes, the "shield" doesn't shield the antenna -- in fact, the outside of
the "shield" *is* the antenna. What it does is aid in balancing the
antenna, reducing common mode pickup which can reduce the null depth.
"Conventional wisdom" that holds otherwise isn't wisdom at all, but a
lack of understanding of some basic electromagnetic principles.

There's undoubtedly a massive amount of information easily available on
the web regarding building and using small loop antennas. All you have
to do is ignore the ubiquitous "conventional wisdom" explanations of how
a "shielded" loop operates.

Roy Lewallen, W7EL

"Dave" wrote in
:


"Roy Lewallen" wrote in message
...
Trying to phase two antennas that close together at that frequency
range will be an educational experience at best, but more likely just
an exercise in frustration unless you have much more patience than
average. Such an array will be hyper-sensitive to everything. You
might be able to fleetingly see a null after a lot of tweaking, but I
seriously doubt you'll even get that. A tiny change in frequency,
wiggling of the whips, or even movement in the vicinity of the whips
will have a profound effect on any null you might see.

If a null from a small antenna is what you want, you'd have much
better luck with a carefully constructed and balanced ("shielded")
loop.

Roy Lewallen, W7EL

Found my copy of Joe Carr's Practical Antenna Handbook, and re-read
the section on phasing verticle antennas. I believe you. Back to
square one, which was the thought that a loop was probably my best bet
(I had come to that conclusion a while back, but forgot why.)

Did try a shielded loop once upon a time, but didn't feel it gave me
anything to look forward to. Guess I'll dig it out and try it again.
Will try shielding it with copper "tape" and see what that buys me. I
did try a piece of coax wound in a triple-turn loop to give me 2.5 or
3 uH with which to tune, with the shield cut away to expose the center
conductor for a couple inches, but didn't feel this offered anything
either. Not sure what I'll do. Poke around and try different things
until I find something that works better than the rest. Any ideas?
I'm all ears. I tried the whips because I had them on hand, and they
were easy to install. Seems I read somewhere that contrary to
conventional wisdom, the shield on a shielded loop doesn't actually
shield at all, but becomes the antenna element. Anyone know anything
about that line of thought? I obviously know nothing, and am trying
to learn. Just don't know where to focus my energies.

I made a perfecly workable little DF once on a ferrite rod, wound with a
few turns. Worked like gangbusters on the local 2 and 6mhz stuff that I
was trying to locate.



--
Dave Oldridge+
ICQ 1800667

"Dave" wrote in
:

....
were easy to install. Seems I read somewhere that contrary to
conventional wisdom, the shield on a shielded loop doesn't actually
shield at all, but becomes the antenna element. Anyone know anything
about that line of thought? I obviously know nothing, and am trying
to learn. Just don't know where to focus my energies.

I have written a simple explanation on the operation of the so called
'shielded loop' at http://www.vk1od.net/shieldedloop/index.htm .

You may find the article of interest.

If you read and understand the content of the article, you will see the
pitfalls in using tape to 'shield' a loop.

Owen

On 20 Sep, 22:39, Roy Lewallen wrote:
Trying to phase two antennas that close together at that frequency range
will be an educational experience at best, but more likely just an
exercise in frustration unless you have much more patience than average.
Such an array will be hyper-sensitive to everything. You might be able
to fleetingly see a null after a lot of tweaking, but I seriously doubt
you'll even get that. A tiny change in frequency, wiggling of the whips,
or even movement in the vicinity of the whips will have a profound
effect on any null you might see.

If a null from a small antenna is what you want, you'd have much better
luck with a carefully constructed and balanced ("shielded") loop.

Roy Lewallen, W7EL

Let me clarify some of the remarks made. A efficient antenna is when
the wire is
one wave length long and fed at its extremities. This can be
circumvented on a loop
by winding the 1WL wire on a non conductive hoolah loop both in a
clock wise and counterclockwise
in a overlapping method ( insulated magnet wire preffered )
such that the windings inductance balance to zero for a resistive
impedance
at the feed point The windings may have to be stretched some what to
balance outany stray capacitance added
or a broadcast type variable capacitor can be added if one is lazy.
The bandwidth is broad enough on most bands with a resistive impedance
of around 50 odd ohms.
If one deviates much from the desired frequencylength one will see a
resistive impedance
in the single digits so take care with the wave length measurements
This loop design based on Gaussian laws provides a broad bandwidth
with smaller physical size
compared to the standard magnetic loop design together with extra
gain. And yes one does not
need that expensive high voltage variable capacitor required for
movement around the band as required with presently known loop
designs.
By the way the element can be jumpered for use on other bands!
Have fun
Art KB9MZ
PS I have written a somewhat amaterish thesis on Gaussian antennas
for which I have applied for a patents, I am sure that a scan of past
posts on the subject will reveal the URL which I have not put in my
memory box.
Amateurs have not used this new design method as they are happy with
existing
arrays knowing that all is already known about antennas and all later
designs
must be fraudulent
Art KB9MZ....xg

"art" wrote in message
ps.com...
On 20 Sep, 22:39, Roy Lewallen wrote:
Trying to phase two antennas that close together at that frequency range
will be an educational experience at best, but more likely just an
exercise in frustration unless you have much more patience than average.
Such an array will be hyper-sensitive to everything. You might be able
to fleetingly see a null after a lot of tweaking, but I seriously doubt
you'll even get that. A tiny change in frequency, wiggling of the whips,
or even movement in the vicinity of the whips will have a profound
effect on any null you might see.

If a null from a small antenna is what you want, you'd have much better
luck with a carefully constructed and balanced ("shielded") loop.

Roy Lewallen, W7EL

Let me clarify some of the remarks made. A efficient antenna is when
the wire is
one wave length long and fed at its extremities. This can be
circumvented on a loop
by winding the 1WL wire on a non conductive hoolah loop both in a
clock wise and counterclockwise
in a overlapping method ( insulated magnet wire preffered )
such that the windings inductance balance to zero for a resistive
impedance
at the feed point The windings may have to be stretched some what to
balance outany stray capacitance added
or a broadcast type variable capacitor can be added if one is lazy.
The bandwidth is broad enough on most bands with a resistive impedance
of around 50 odd ohms.
If one deviates much from the desired frequencylength one will see a
resistive impedance
in the single digits so take care with the wave length measurements
This loop design based on Gaussian laws provides a broad bandwidth
with smaller physical size
compared to the standard magnetic loop design together with extra
gain. And yes one does not
need that expensive high voltage variable capacitor required for
movement around the band as required with presently known loop
designs.
By the way the element can be jumpered for use on other bands!
Have fun
Art KB9MZ
PS I have written a somewhat amaterish thesis on Gaussian antennas
for which I have applied for a patents, I am sure that a scan of past
posts on the subject will reveal the URL which I have not put in my
memory box.
Amateurs have not used this new design method as they are happy with
existing
arrays knowing that all is already known about antennas and all later
designs
must be fraudulent
Art KB9MZ....xg


Thanks, Art (and others). I'll do a few searches on Google, and see what I
can come up with.

Much appreciated.

Dave

On 20 Sep, 22:39, Roy Lewallen wrote:
Trying to phase two antennas that close together at that frequency range
will be an educational experience at best, but more likely just an
exercise in frustration unless you have much more patience than average.
Such an array will be hyper-sensitive to everything. You might be able
to fleetingly see a null after a lot of tweaking, but I seriously doubt
you'll even get that. A tiny change in frequency, wiggling of the whips,
or even movement in the vicinity of the whips will have a profound
effect on any null you might see.

If a null from a small antenna is what you want, you'd have much better
luck with a carefully constructed and balanced ("shielded") loop.

Roy Lewallen, W7EL

If it was just for receiving I would make two antennas in coil fashion
as shown every where
on the net, connect them together with a half wave length coax and try
stretch them apart as much as room suplies and then roll the excess
phasing coax up. The cb's have the super scanner antenna that partialy
follows this principle using 1 wave length antennas with the
connecting coax folded and pushed inside the connecting aluminum
channel. Using a rolled antenna tesla style with them being physically
close together would be an interesting experiment. Look up in the net
home made radios for the station tuning method and also you might want
to choose different methods to connect them starting with a wire
connecting the two wound antennas at the top and feeding th bottom!
( that method by the way requires the two antennas to be wound
inopposite directions) I imagine you could get a null just like
turning an inside tv antenna because these stations in this
frequencyare high power as can be seen when a rogue station opens up
ontop of the station that you are listenning to and want to null out
of the picture.
Have fun
Art KB9MZ

"Roy Lewallen" wrote in message
...
Trying to phase two antennas that close together at that frequency range
will be an educational experience at best, but more likely just an
exercise in frustration unless you have much more patience than average.
Such an array will be hyper-sensitive to everything. You might be able to
fleetingly see a null after a lot of tweaking, but I seriously doubt
you'll even get that. A tiny change in frequency, wiggling of the whips,
or even movement in the vicinity of the whips will have a profound effect
on any null you might see.

If a null from a small antenna is what you want, you'd have much better
luck with a carefully constructed and balanced ("shielded") loop.

Roy Lewallen, W7EL

Quck question, Roy,

Would it matter if I "separated" the whips electrically with, say, 55 feet
of coax? (That's approx the length I get for RG-174 coax, which is
something like 1/8" in diameter, with a velocity vactor of .66 and working
with 9 MHz.) Just a thought, but I don't know whether it has any merit or
not. And I am thinking I could adjust that "length" with an RLC circuit
through which I sort of "tune" it. What say you? Is this line of thought
worth persuing? Or would wiggling he whips still throw everything off?

And I do seem to have a fair abount of patience with this sort of thing.
Been working on the current project for about 2 years, had it working on and
off, taking it apart occasionally to implement some new retrofit or
engineering change. I am on disability, and have nothing but time on my
hands.

Thanks for any feedback...

Dave

"Dave" wrote in message
...

"Roy Lewallen" wrote in message
...
Trying to phase two antennas that close together at that frequency range
will be an educational experience at best, but more likely just an
exercise in frustration unless you have much more patience than average.
Such an array will be hyper-sensitive to everything. You might be able to
fleetingly see a null after a lot of tweaking, but I seriously doubt
you'll even get that. A tiny change in frequency, wiggling of the whips,
or even movement in the vicinity of the whips will have a profound effect
on any null you might see.

If a null from a small antenna is what you want, you'd have much better
luck with a carefully constructed and balanced ("shielded") loop.

Roy Lewallen, W7EL

Quck question, Roy,

Would it matter if I "separated" the whips electrically with, say, 55 feet
of coax? (That's approx the length I get for RG-174 coax, which is
something like 1/8" in diameter, with a velocity vactor of .66 and working
with 9 MHz.) Just a thought, but I don't know whether it has any merit or
not. And I am thinking I could adjust that "length" with an RLC circuit
through which I sort of "tune" it. What say you? Is this line of thought
worth persuing? Or would wiggling he whips still throw everything off?

And I do seem to have a fair abount of patience with this sort of thing.
Been working on the current project for about 2 years, had it working on
and off, taking it apart occasionally to implement some new retrofit or
engineering change. I am on disability, and have nothing but time on my
hands.

Thanks for any feedback...

Dave



Forgot to mention one thing. Don't know if I said this before or not, but
this is of course for receive only. No transmitting with such a cob job...

Thanks,

Dave

Dave wrote:

Quck question, Roy,

Would it matter if I "separated" the whips electrically with, say, 55 feet
of coax? (That's approx the length I get for RG-174 coax, which is
something like 1/8" in diameter, with a velocity vactor of .66 and working
with 9 MHz.) Just a thought, but I don't know whether it has any merit or
not. And I am thinking I could adjust that "length" with an RLC circuit
through which I sort of "tune" it. What say you? Is this line of thought
worth persuing? Or would wiggling he whips still throw everything off?

And I do seem to have a fair abount of patience with this sort of thing.
Been working on the current project for about 2 years, had it working on and
off, taking it apart occasionally to implement some new retrofit or
engineering change. I am on disability, and have nothing but time on my
hands.

Thanks for any feedback...

You can answer most of your questions by modeling it with EZNEC. The
free demo program available from http://eznec.com is perfectly adequate
for the job. After going through the "Test Drive" tutorial in the
manual, I suggest that you take a look at the d_Cardioid.ez example file
to see how you can model an array with an ideal feed system. What you
should do is model your array in a similar manner, with two perfect
current sources. With the sources equal in magnitude and 180 degrees out
of phase, you'll get a bidirectional pattern, and it won't be sensitive
to frequency or element spacing. But then see what happens when you
change the phase and/or magnitude of one of the sources just slightly,
to simulate what any real phasing network would do. What happens to the
pattern? Look at the feedpoint impedances at various frequencies, and
see if you can figure out how you'll make a network to deliver the
correctly phased currents into those impedances. Another thing you can
do is try phasing them for a unidirectional pattern by giving the
sources a relative phase angle of 180 degrees minus the electrical
spacing of the elements (which of course will be different at each
frequency). You can get a nice looking pattern, but you'll find it
extremely sensitive to frequency and element spacing.

EZNEC will give you the opportunity to turn some of that available time
into an educational experience. I guarantee you'll learn a lot in the
process. If you want to learn even more about phased arrays, see Chapter
8 of the _ARRL Antenna Book_. The phased array section was completely
rewritten and updated for the latest (21st) edition.

Roy Lewallen, W7EL