Ponder This wrote in
news


Just cusrious...

What happens if you pipe the output of one radio in to 2 different
amplifiers, and then take the output of the two amps and send them to
two identical vertical antennas spaced a half wave apart and with
equal length feedlines from the amplifiers.

Will the output of the two amplifiers add together in directions where
the signal is in phase, or will it act like two different signals and
interfere with each other?

-Curious


Why would you do that? It's the same as just splitting a single output
from the radio. Depending on spacing and phase you can get of variety of
different radiation patterns. You don't need to split it between two
amps.

I split the output from my radio, lag one 90 degrees, put one in one yagi,
put one in another yagi and get circular polarization.


sc

Depends--, if in phase, Both INPUT, and OUTPUT,
would add (double power, if SAME power on both,
Also would add, if 180 degrees OUT of Phase, both
Input, and Output. And this would be the same as
with Push-Pull amp (both input, and output). but
if In Phase, on input, and OUT of Phase, on
Output,or vice versa, theoretically, would result
in 0 Output. And, if in different phases, probably
would make a great interference source!!!
(distortion, intermods, harmonics, oddball mixes,
ect!) Jim NN7K


Slow Code wrote:
Ponder This wrote in
news


Just cusrious...

What happens if you pipe the output of one radio in to 2 different
amplifiers, and then take the output of the two amps and send them to
two identical vertical antennas spaced a half wave apart and with
equal length feedlines from the amplifiers.

Will the output of the two amplifiers add together in directions where
the signal is in phase, or will it act like two different signals and
interfere with each other?

-Curious

What happens if you pipe the output of one radio in to 2 different
amplifiers, and then take the output of the two amps and send them to
two identical vertical antennas spaced a half wave apart and with
equal length feedlines from the amplifiers.

Will the output of the two amplifiers add together in directions where
the signal is in phase, or will it act like two different signals and
interfere with each other?

-Curious


I would assume the following: If you use a splitter with an equal
length of coax to the two amps, you would be able to get 100 watts out
from the radio to be 50 watts into each amp. I would suspect that you
would have double the power out to the antenna assuming you used the
same length of coax from the amps to the antenna.

Of course, you have to deal with impedance problems with the splitting
of the coax, for example, two 50 ohm cables would result in 25 ohms to
the amps. Not good. then the two 50 ohm outputs from the amps would
result in 100 ohms to the antenna, not good again....


--
73 for now
Buck
N4PGW

Curious wrote:
"Will the output of two amplifiers add together in directions where the
signal is in phase, or will it act like two different signals and
therefore interfere with each other?"

For stereo?

The signals are coherent from two amplifiers or from one.

Two close antennas fed the same signal in the same phase generally add
broadside to the plane containing the antennas and cancel at right
angles to the lobes containing the added signals.

See page 91 of Kraus` 3rd efition of "Antennas" for: "Two Isotropic
Point Sources of the Same Amplitude and Phase."

Another example is the pair af CB antennas used by truckers, one on
either side of the truck cab, to reinforce the signal fore and aft of
the truck.

The 1/2-wave dipole is another example. Its two elements have the same
cuerrent amplitude and direction. Its lobes are broadside and its nulls
are at right angles off the tips of the elements.

Best regards, Richard Harrison, KB5WZI

Richard Harrison wrote:
Two close antennas fed the same signal in the same phase generally add
broadside to the plane containing the antennas and cancel at right
angles to the lobes containing the added signals.

One thought of interest is that the phasing for a phased
antenna system might be done at the input of one of the
amps, rather than having to manage high power. But I
wonder if two separate amps could maintain coherency
under all conditions of supply voltage, temperature,
humidity, etc.
--
73, Cecil http://www.qsl.net/w5dxp

Cecil, W5DXP wrote:
"I wonder if two separate amps could maintain coherency under all
conditions of supply voltage, temperature, humidity, etc."

If reasonable control applies, it works.

I built a rat-race, hybrid-ring, diplexer to parallel two identical
shortwave broadcast transmitters. They were fed from the same RF
oscillator and from the same audio source. Both were adjusted for nearly
100% modulation. The pair produced nearly 100 KW, fully modulated into
the same antenna. It worked fine. No jerking around and little
unbalanced energy dissipated into the dummy load. This was no sweat for
the antennas which worked with our 100 KW transmitters every day. This
is what you need to do when frequency shortages become acute.

The votages in the transmitters were regulated by Sola transformers
which had been shipped to us as 60 Hz transformers but reresonated on
site for 50 Hz which was our European supply frequency.

Best regards, Richard Harrison, KB5WZI

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.

--
Yuri Blanarovich, K3BU, VE3BMV

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.


Well, the expert, or should I say, the new GURU, has spoken. He seems
to know all about this complex subject.

I know I will never try this again, as my previous efforts, which seemed
to work, could not possibly have done so. Obviously Wilkenson hybrids
are useless, likewise any ring hybrids, and all other methods of
splitting/combining a transmitter feed.

Sorry guys, they won't work. Yuri said so.

tom
K0TAR

On Wed, 24 May 2006 15:59:28 -0400, "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.


OK, this brings up another thought... Would the transmitted signal
from antenna a, being close to b, cause b to have a high swr and vica
versa?


--
73 for now
Buck
N4PGW

OK, this brings up another thought... Would the transmitted signal
from antenna a, being close to b, cause b to have a high swr and vica
versa?
________

Yes. Depending on the single-radiator pattern shapes and installation
geometry, mutual coupling between two adjacent antennas of the same
polarization, and cut for the same frequency can be -10 dB or less. An
"apparent reflected power" of -10 dBc = 1.92 SWR to each tx, plus
whatever SWR each antenna system has to the tx hardwired to it.

This performance may be OK for amateur radio, but not for broadcast
stations. To avoid this situation, broadcast system designs using
several r-f amplifiers combine the amplifier outputs to drive the
antenna system from a single set of terminals.

The antenna system design itself provides omnidirectional or
directional coverage in the horizontal plane as needed, but it is
always fed from a single set of terminals.