In doing some study of active receiving antennas I see in a couple of
white papers on the subject that the author determined he needed a
specific phase shift between one or more of the elements and the
combiner, such as 110 degrees, so he proceeded to cut a specific
length of coax determined by it's velocity factor X the desired
fraction of a wave...
This is one of those things that you always accept at face value in a
published work, but this time my doubting side kicked in... We know
that simply inserting a nominal electrical length of coax - such as 90
deg or 180 deg - into phased transmit arrays does not work as planned
most of the time due to mutual coupling... I have read the
contributions of Roy and Al Christman, et. al. on this not
intimating that I understand it...
Anyway, in shortened, loaded, active amplifier, receiving arrays can
one simply insert a nominal number of electrical degrees of phasing
line as the mathematical model calls for, or is their more to it...
Hoping that Roy, AL, or Walt, or others will chime in here...

denny / k8do

On Tue, 13 Nov 2007 18:44:51 -0000, Denny wrote:

Anyway, in shortened, loaded, active amplifier, receiving arrays can
one simply insert a nominal number of electrical degrees of phasing
line as the mathematical model calls for, or is their more to it...
Hoping that Roy, AL, or Walt, or others will chime in here...

Hi Denny,

The free version of EZNEC comes with a file (foursquare) that does
this. Why not check it out with variations in that design to see what
happens?

73's
Richard Clark, KB7QHC

Denny wrote:
Anyway, in shortened, loaded, active amplifier, receiving arrays can
one simply insert a nominal number of electrical degrees of phasing
line as the mathematical model calls for, or is their more to it...
Hoping that Roy, AL, or Walt, or others will chime in here...

Roy has a SIMPFEED program available from eznec.com that
will tell one if what one is trying to do is possible
and then perform the calculations. I tried the early
version on phased verticals on 75m in AZ and it worked
very well. I could throw a coaxial switch and switch the
beaming function toward CA or TX.

Also, using EZNEC to estimate the feedpoint impedances,
one can always use a Smith Chart to solve the feedline
phasing problems the old-fashioned way. (Years ago, while
using Microsmith, I stumbled upon a method of obtaining
a free lossless phase shift.)
--
73, Cecil http://www.w5dxp.com

OK, well I have had EL and EZ from the early days to the current Eznec
+ v5 and I use it often.. (about as well as a cow tap dances)

And I have read the stuff I mentioned - and in particular, Tom submits
that a shortened, heavily top hatted, heavily R loaded, 20 foot
vertical element on 160, is free of major impedence shifts in the
presence of other objects/ antennas... So, one is free to infer that
perhaps one could simply insert a calculated length of coax between
two array elements to get a desired phase shift without calculating
for mutual coupling?

The impetus for this line of thought is this morning I was having
problems working VK land on 160 as the DX was only about Q3 at best
moments and Q0 at others... So, not hearing well I hesitated at the
critical moment of turn over and W1MK stomped on me...
I have a 4 Square active receive array but that lobe favors JA over VK
and I don't have a Beverage pointed in VK direction having gotten rid
of most of them after getting the active array...
Anyway, I am tinkering with a 4el endfire-broadside 70 x 270 spacing
receive array and the best pattern is with 135 degree phase shift
between the endfire elements - which is what prompted my question as I
know that if they were full size transmitting elements I cannot
blithely just insert a calculated 135 E degrees of coax and get the
wanted phasing...

Looks like I will have to put up a pair and custom engineer the
phasing line...
denny / k8do

I'm glad my harping on this topic (mostly via Chapter 8 in the _ARRL
Antenna Book_) is having an effect, and that some folks are catching on.

The receiving antenna trick is to begin with elements that are either
very short or very lossy or both. This reduces the effect of mutual
coupling to a negligible value, so all elements will have the same
source impedance. Then the transmission lines are all terminated in
their characteristic impedances at the receiver end. This is the
condition under which the delay in the lines equals their electrical
lengths. Under those conditions, the scheme works nicely.

Roy Lewallen, W7EL

Denny wrote:
In doing some study of active receiving antennas I see in a couple of
white papers on the subject that the author determined he needed a
specific phase shift between one or more of the elements and the
combiner, such as 110 degrees, so he proceeded to cut a specific
length of coax determined by it's velocity factor X the desired
fraction of a wave...
This is one of those things that you always accept at face value in a
published work, but this time my doubting side kicked in... We know
that simply inserting a nominal electrical length of coax - such as 90
deg or 180 deg - into phased transmit arrays does not work as planned
most of the time due to mutual coupling... I have read the
contributions of Roy and Al Christman, et. al. on this not
intimating that I understand it...
Anyway, in shortened, loaded, active amplifier, receiving arrays can
one simply insert a nominal number of electrical degrees of phasing
line as the mathematical model calls for, or is their more to it...
Hoping that Roy, AL, or Walt, or others will chime in here...

denny / k8do

On 13 Nov, 15:23, Roy Lewallen wrote:
I'm glad my harping on this topic (mostly via Chapter 8 in the _ARRL
Antenna Book_) is having an effect, and that some folks are catching on.

The receiving antenna trick is to begin with elements that are either
very short or very lossy or both. This reduces the effect of mutual
coupling to a negligible value, so all elements will have the same
source impedance. Then the transmission lines are all terminated in
their characteristic impedances at the receiver end. This is the
condition under which the delay in the lines equals their electrical
lengths. Under those conditions, the scheme works nicely.

Roy Lewallen, W7EL



Denny wrote:
In doing some study of active receiving antennas I see in a couple of
white papers on the subject that the author determined he needed a
specific phase shift between one or more of the elements and the
combiner, such as 110 degrees, so he proceeded to cut a specific
length of coax determined by it's velocity factor X the desired
fraction of a wave...
This is one of those things that you always accept at face value in a
published work, but this time my doubting side kicked in... We know
that simply inserting a nominal electrical length of coax - such as 90
deg or 180 deg - into phased transmit arrays does not work as planned
most of the time due to mutual coupling... I have read the
contributions of Roy and Al Christman, et. al. on this not
intimating that I understand it...
Anyway, in shortened, loaded, active amplifier, receiving arrays can
one simply insert a nominal number of electrical degrees of phasing
line as the mathematical model calls for, or is their more to it...
Hoping that Roy, AL, or Walt, or others will chime in here...

denny / k8do- Hide quoted text -

- Show quoted text -

By Golly. Well done. You should get a gold medal from your peers
namely George W Bush.
You and you alone was the first to point this out to the scientific
community.
You take credit for harping on it in a published book knowing if it is
in
a book it then qualifies as being right.
What ever did the radio community do in those
case before you were born or came along? You should undoubtedly get a
medal for harping in leau of saying "I don't understand" or you
can't
use mechanical laws when the subject is electricity" plus some of
those things you have stated that Cecil could remind you of.
Yes, the credit is yours and you get the gold medal and a fireside
chat with your equal and possibly a mentor George WWWWWWWW BUSH.
YEA....

On Tue, 13 Nov 2007 16:07:49 -0800, art wrote:

get a gold medal
get a medal
get the gold medal

:-)

Denny wrote:
In doing some study of active receiving antennas I see in a couple of
white papers on the subject that the author determined he needed a
specific phase shift between one or more of the elements and the
combiner, such as 110 degrees, so he proceeded to cut a specific
length of coax determined by it's velocity factor X the desired
fraction of a wave...
This is one of those things that you always accept at face value in a
published work, but this time my doubting side kicked in... We know
that simply inserting a nominal electrical length of coax - such as 90
deg or 180 deg - into phased transmit arrays does not work as planned
most of the time due to mutual coupling... I have read the
contributions of Roy and Al Christman, et. al. on this not
intimating that I understand it...
Anyway, in shortened, loaded, active amplifier, receiving arrays can
one simply insert a nominal number of electrical degrees of phasing
line as the mathematical model calls for, or is their more to it...


Assuming the amplifier has an output impedance that matches that of the
transmission line (75 ohms might be convenient in this application..
inexpensive low loss cable tv coax), you're right. Just lash that coax
in there.

Don't forget you also have to deal with loss/amplitude.


Hoping that Roy, AL, or Walt, or others will chime in here...

denny / k8do

Roy Lewallen wrote:
I'm glad my harping on this topic (mostly via Chapter 8 in the _ARRL
Antenna Book_) is having an effect, and that some folks are catching on.

The receiving antenna trick is to begin with elements that are either
very short or very lossy or both. This reduces the effect of mutual
coupling to a negligible value, so all elements will have the same
source impedance. Then the transmission lines are all terminated in
their characteristic impedances at the receiver end. This is the
condition under which the delay in the lines equals their electrical
lengths. Under those conditions, the scheme works nicely.

Or, as the OP mentioned, if you have an *active* array, with buffer
amplifiers at the elements, the amplifier provides the needed impedance
characteristics.

On Wed, 14 Nov 2007 08:51:10 -0800, Jim Lux wrote:
Roy Lewallen wrote:
I'm glad my harping on this topic (mostly via Chapter 8 in the _ARRL
Antenna Book_) is having an effect, and that some folks are catching on.

The receiving antenna trick is to begin with elements that are either
very short or very lossy or both. This reduces the effect of mutual
coupling to a negligible value, so all elements will have the same
source impedance. Then the transmission lines are all terminated in
their characteristic impedances at the receiver end. This is the
condition under which the delay in the lines equals their electrical
lengths. Under those conditions, the scheme works nicely.

Or, as the OP mentioned, if you have an *active* array, with buffer
amplifiers at the elements, the amplifier provides the needed impedance
characteristics.

If you're speaking of phasing together two or more *active* antennas,
you'd best employ identical brand and models of the devices. Elsewise,
knowing the phase change _through_ the active antennas would be a crap
shoot.

Jonesy
--
Marvin L Jones | jonz | W3DHJ | linux
38.24N 104.55W | @ config.com | Jonesy | OS/2
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