What happens if you pipe the output of one radio in to 2 amps?
 

Cecil Moore wrote:
Pot - Kettle, Kettle - Pot. Here's one of your rantings.

W8JI wrote:
I feel sorry for anyone who has to deal with you on a daily basis.
No wonder your wife split.

Your technical content is noted.
73, Cecil http://www.qsl.net/w5dxp

You're absolutely right Cecil.

There is no reason for anyone, including me, to personally attack
others or to rant and rave like a lunatic.

It absolutely ruins techincal forums when people get too personal, no
matter who does it. I think that is a major reason why this newsgroup
fell from being very popular to barely used.

73 Tom

What happens if you pipe the output of one radio in to 2 amps?
 

wrote:

Cecil Moore wrote:
Pot - Kettle, Kettle - Pot.

You're absolutely right Cecil.

Someone needs to tell W8JI that there's a nice person
forging postings from his ISP address. :-)
--
73, Cecil, W5DXP

What happens if you pipe the output of one radio in to 2 amps?
 

I'm gonna be like Brer Rabbit and say nuffin.

What happens if you pipe the output of one radio in to 2 amps?
 

So stick to technical questions and answers, keep comments about someone's
wife, license class, foaming, etc. to yourself. You start the crap and then
scream when "favor" is returned. Just go back and look who initiates that,
instead of answers to questions in question.

Bada BUm

wrote in message
oups.com...

Cecil Moore wrote:
Pot - Kettle, Kettle - Pot. Here's one of your rantings.

W8JI wrote:
I feel sorry for anyone who has to deal with you on a daily basis.
No wonder your wife split.

Your technical content is noted.
73, Cecil http://www.qsl.net/w5dxp

You're absolutely right Cecil.

There is no reason for anyone, including me, to personally attack
others or to rant and rave like a lunatic.

It absolutely ruins techincal forums when people get too personal, no
matter who does it. I think that is a major reason why this newsgroup
fell from being very popular to barely used.

73 Tom

What happens if you pipe the output of one radio in to 2 amps?
 

.. .
Yuri Blanarovich wrote:

There is another potential problem if feeding two amps to two antennas
that are reasonably close: RF from one antenna is induced into the
other
antenna, gets fed into the amp and causes some interference (mixing ?)
that shows up as a raspy signal.
Tried it, and heard it on another station attempting the same setup.
It seems that it would be easier to control the phasing at the input of
the PAs, but the above effect messes it up, unless antennas are widely
separated and they do not "feed" each other setup.
So, it appears that it is better to use one bigger amp and use proper
phasing to feed the two or more antennas.


I hope I did not cut incorrectly in the complex post...

The effect is that the *impedance* looking into each antenna will change due
to the mutual coupling of the two antennas. You can also think of it as
each antenna is not just staring into open space, but you can consider the
field of the other antenna to be changing the space around the first antenna
(and visa versa). It is also not umlike simply putting a reflecting plane or
other paracitic elements neat a driven element - the feed point impedance
changes. This power, being from the same transmitter, is coherent (phase
locked) and therefore changes the current that flows which manifests itself
as an impedance change. Given the current from the feed line voltage and
then the superposition of the current induced from the other antenna, you
get a new current that flows (aparently from the feed line voltage) and
therefore it appears as a different impedance (from the feed line's
perspective). I hope one of these analogies works for you.
This can indeed cause amplifiers to do funny things if they can't handle the
resulting SWR. If you correctly match to the new impedances, there should
be no problems, just the new antenna radiation pattern.

Side bar:
For some situations, the resistive part of this new impedance can even go
negative. This means that this antenna is absorbing power, not radiating
it. This can happen in phased, directive arrays used in broadcast. A
friend of mine described such a situation that vexed him for a while until
he improved his calculations to be more general to be applicable to this
situation (to get the correct result).
Don't ask me how to match to a negative resistance. All I know is that
given some certain directional pattern that is desired, this happens and
with the proper math you can design a matching network that works and
restores order to the universe and keeps the big bang happy (:-)

73, Steve, K9DCI

What happens if you pipe the output of one radio in to 2 amps?
 

Steve N. wrote:
. . .

Side bar:
For some situations, the resistive part of this new impedance can even go
negative. This means that this antenna is absorbing power, not radiating
it. This can happen in phased, directive arrays used in broadcast. A
friend of mine described such a situation that vexed him for a while until
he improved his calculations to be more general to be applicable to this
situation (to get the correct result).
Don't ask me how to match to a negative resistance. All I know is that
given some certain directional pattern that is desired, this happens and
with the proper math you can design a matching network that works and
restores order to the universe and keeps the big bang happy (:-)

Negative feedpoint resistances in phased arrays have of course been
known for a very long time. One of the example files (4Square.EZ) which
comes with EZNEC shows an element with a slightly negative feedpoint
resistance. The accompanying "antenna notes" file includes a brief
explanation of the phenomenon.

You can't "match to" a negative resistance, because matching
requirements are determined by the load, not source, impedance, and an
element with a negative resistance is a source rather than a load. But
there's no necessity to match individual elements and, in fact,
attempting to do so complicates the problem of achieving the desired
element current ratios. One thing you can count on, though -- the
resistance of the whole array will be positive. And that's what needs
matching.

Roy Lewallen, W7EL

What happens if you pipe the output of one radio in to 2 amps?
 

"Steve N." wrote in message
...
.. .
Yuri Blanarovich wrote:

There is another potential problem if feeding two amps to two antennas
that are reasonably close: RF from one antenna is induced into the
other
antenna, gets fed into the amp and causes some interference (mixing ?)
that shows up as a raspy signal.
Tried it, and heard it on another station attempting the same setup.
It seems that it would be easier to control the phasing at the input
of
the PAs, but the above effect messes it up, unless antennas are widely
separated and they do not "feed" each other setup.
So, it appears that it is better to use one bigger amp and use proper
phasing to feed the two or more antennas.


I hope I did not cut incorrectly in the complex post...

The effect is that the *impedance* looking into each antenna will change
due
to the mutual coupling of the two antennas. You can also think of it as
each antenna is not just staring into open space, but you can consider the
field of the other antenna to be changing the space around the first
antenna
(and visa versa). It is also not umlike simply putting a reflecting plane
or
other paracitic elements neat a driven element - the feed point impedance
changes. This power, being from the same transmitter, is coherent (phase
locked) and therefore changes the current that flows which manifests
itself
as an impedance change. Given the current from the feed line voltage and
then the superposition of the current induced from the other antenna, you
get a new current that flows (aparently from the feed line voltage) and
therefore it appears as a different impedance (from the feed line's
perspective). I hope one of these analogies works for you.
This can indeed cause amplifiers to do funny things if they can't handle
the
resulting SWR. If you correctly match to the new impedances, there should
be no problems, just the new antenna radiation pattern.


That could be a challenging task, if one wanted to have switchable or
tunable phasing. Some fancy detection and adjustments needed!?

Side bar:
For some situations, the resistive part of this new impedance can even go
negative. This means that this antenna is absorbing power, not radiating
it. This can happen in phased, directive arrays used in broadcast. A
friend of mine described such a situation that vexed him for a while until
he improved his calculations to be more general to be applicable to this
situation (to get the correct result).
Don't ask me how to match to a negative resistance. All I know is that
given some certain directional pattern that is desired, this happens and
with the proper math you can design a matching network that works and
restores order to the universe and keeps the big bang happy (:-)

73, Steve, K9DCI


Hi Steve,

That makes sense (and subject for scientwists to argue "it can't be" :-)

I was considering two scenarios for contesting.
One, mainly for expeditioning case, use two smaller amps (transportation
limitations) and low power (continuous) phasing network between the exciter
and two amps feeding two antennas.
Two, feeding two amps and two antenna systems firing in different directions
(offset stacks).
I tried the crude application of it, and was "bugged" that my CW tone or SSB
modulation was raspy. I knew that rig was OK, firing one leg was no problem
and had to conclude that the problem had to be mutual coupling, feedback and
"beating" back in the amp circuits. I did not pursue the rectification of
the problem, considered it too complicated for what I wanted to do. Learned
it to be a no-no trying to feed phased arrays with individual amplifiers, at
the same frequency.
Feeding antennas that are widely separated with no mutual coupling, firing
in different directions, should not be a problem, as long as there is no
significant signal being induced into the other system.
We will play with some outrageous combinations of about 40 rhombics and
other antennas, capable of being fed by 16 transmitters from the new Tesla
RC QTH of old AT&T Ocean Gate NJ site (makes old W6AM site look like
kindergarten :-). Antenna matrix (wall unit) switch that does the selection
is a piece of art in itself. We have to get rid of pigeons and "paintings"
they left and get the site operational by the fall contest season.

--
73, Yuri Blanarovich, K3BU, VE3BMV

What happens if you pipe the output of one radio in to 2 amps?
 

Yuri, K3BU wrote:
"Learned it to be a no-no trying to feed phased arrays with individual
amplifiers, at the same frequency."

I`m not sure separate amplifiers have anything to do with distortion
because I`ve seen distortion at certain azimuths from arrays driven by
a single amplifier.

Drive around a broadcast array with sharp nulls while listening. You
will notice severe distortion at the edges of sharp nulls. I always
attributed this to phase out of the carrier frequency at an azumuth
where the sidebands aren`t completely nulled out, and this produces the
overmodulation and distortion. It`s only a speculation to explain the
cause of an observed effect.

Best regards, Richard Harrison, KB5WZI

What happens if you pipe the output of one radio in to 2 amps?
 

"Roy Lewallen" wrote in message
...
Steve N. wrote:
. . .
Side bar:
For some situations, the resistive part of this new impedance can even
go
negative. ...

Negative feedpoint resistances in phased arrays have of course been
known for a very long time.

Roy,
I didn't mean to imply it wasn't known previously, only wanted to give a
real life example (as a preemptive attempt at heading off a potential "but
that's all theory" response -- perhaps a little gun-shy on this news group
(:-)). I also have no direct knowledge of this type of the network design,
but it has to be designed and the antenna with the neg real part is part of
the system that gets hooked to the network.


You can't "match to" a negative resistance, because matching
requirements are determined by the load, not source, impedance,

OOPS ! I *know* what you mean, but it takes knowledte of both ends -
We, me included, can eaily forget that we have an arbitrarily defined (50
ohm) system that we easily take for granted. ya gotta know you're in a 50
ohm (or whatever) system to "do" the match.

73, Steve, K9DCI

What happens if you pipe the output of one radio in to 2 amps?
 

"Reg Edwards" wrote in message
...


I'm gonna be like Brer Rabbit and say nuffin.



But you just did!

sorry, couldn't resist.
I wasn't gonna say anything, until I just thought of that:

73, Steve, K9DCI