In message , Ralph
Mowery writes

wrote in message
...
Dear John,

Stacking 2 HD6065P antennas in the same direction for gain you would mount
them 72" apart vertically from boom to boom. The phasing line will be 52"
long each +/- 1/8" of each other in length. The phasing lines will feed a
CC-7870 coupler to combine the signals. Your single output is now you
signal.

Cordially,
Hans Rabong
Tech. Service Manager.
Winegard Company

Unless I am missing something, seems like a waste of antenna and money.

I looked for the coupler and found this:

"You have the CC-7870 hooked up properly. However this coupler is just like
a 2-way splitter hooked up in reverse; in that it will reduce the signal
from each antenna by about 30%. "

If it is just a 2 way splitter in reverse, there is usually a 3 db loss and
all you get with 2 antennas is a gain of 3 db, so you gain nothing over a
single antenna with this coupler.

To get close to 3 db of gain you need to have a combiner of near zero loss.
This is often done by using an odd number of wavelenghts of feedline of a
differant impedance and hooking them in parallel to keep the impedance the
same. I doubt it would work very well over the while FM band,but may for a
small portion of it.

I don't know how big the antenna is, but you would be beter off with a
single larger antenna, or possiably an amplifier.
Maybe an even beter feedline.

Strange as it may seem, if you use (for example) a TV 2-way '3dB'
splitter to combine two identical in-phase signals, you DON'T lose 3dB.
Apart from the unavoidable slight inherent losses of the two
transformers the circuit uses (a total of around 0.5dB at low VHF,
increasing to 1dB at high UHF), the splitter is lossless. Ignoring the
transformer loss, the 3dB loss occurs simply because the power at each
output port is half of that at the input. You haven't actually lost
anything.

If the splitter is now turned around to become a combiner, it doesn't
suddenly become more lossy. If you again ignore the transformer losses,
the two identical in-phase signals you feed into the 'output' ports are
added, and the result is a signal 3dB higher.

An interesting experiment would be to cascade two splitters - the first
used as a splitter, and the second used to combine the two split signals
(via identical lengths of coax). The loss (because of the transformers)
should be only 1dB (low VHF) to around 2dB (high UHF), and not 7 to 8dB.
--
Ian

"Ian Jackson" wrote in message

Strange as it may seem, if you use (for example) a TV 2-way '3dB' splitter
to combine two identical in-phase signals, you DON'T lose 3dB. Apart from
the unavoidable slight inherent losses of the two transformers the circuit
uses (a total of around 0.5dB at low VHF, increasing to 1dB at high UHF),
the splitter is lossless. Ignoring the transformer loss, the 3dB loss
occurs simply because the power at each output port is half of that at the
input. You haven't actually lost anything.

If the splitter is now turned around to become a combiner, it doesn't
suddenly become more lossy. If you again ignore the transformer losses,
the two identical in-phase signals you feed into the 'output' ports are
added, and the result is a signal 3dB higher.


Jeff found a url with the specs for the combiner.
http://www.solidsignal.com/pview.asp?p=cc7870&d=winegard-cc-7870-2-way-tv-antenna-joiner-coupler-(cc7870)

It says 3.5 db of loss. I assume they use the simple resistor network
instead of transformers. If so, then the net results not counting feedline
loss would be a minus .5 db.

That combiner does not seem to be made to add signals from idinitical
antennas for more gain, but just to let you use one feedling for several
differant antennas such as putting a FM antenna up and a TV antenna up, or a
seperate UHF and VHF antenna up and using one feedline to the receiver.

I have one for designed for my ham transceivers,and have measured less
than .5 db of loss, but that is for differant frequency ranges and not to
combind two antennas on the same band.


Even if he does get the maximum of 3 db of gain, will that acutally get him
anywhere ? Will that be enough gain for the FM broadcast band to be
noticiable ?



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In message , Ralph
Mowery writes

"Ian Jackson" wrote in message

Strange as it may seem, if you use (for example) a TV 2-way '3dB' splitter
to combine two identical in-phase signals, you DON'T lose 3dB. Apart from
the unavoidable slight inherent losses of the two transformers the circuit
uses (a total of around 0.5dB at low VHF, increasing to 1dB at high UHF),
the splitter is lossless. Ignoring the transformer loss, the 3dB loss
occurs simply because the power at each output port is half of that at the
input. You haven't actually lost anything.

If the splitter is now turned around to become a combiner, it doesn't
suddenly become more lossy. If you again ignore the transformer losses,
the two identical in-phase signals you feed into the 'output' ports are
added, and the result is a signal 3dB higher.


Jeff found a url with the specs for the combiner.
http://www.solidsignal.com/pview.asp...cc-7870-2-way-
tv-antenna-joiner-coupler-(cc7870)

$18.99? They're having a laff! $5 max.

It says 3.5 db of loss. I assume they use the simple resistor network
instead of transformers. If so, then the net results not counting feedline
loss would be a minus .5 db.

A typical TV 2-way equal splitter has 3dB splitting loss (because it
splits the signal in two), plus a little loss in the two ferrite-cored
RF transformers inside. The spec is usually something like 3.5dB at
50MHz, increasing to 4 or 4.5dB at 900MHz.

A resistive 2-way star or delta splitter/combiner has a loss of 6dB (3
due to the splitting, and 3 in the resistors), However, whereas the 3dB
transformer splitter theoretically has infinite isolation between the
outputs (when the input is terminated) - and in practice it is 25 to
40dB - the 6dB resistive splitter/combiner has only 6dB (essentially,
all three ports are interchangeable).

That combiner does not seem to be made to add signals from idinitical
antennas for more gain, but just to let you use one feedling for several
differant antennas such as putting a FM antenna up and a TV antenna up, or a
seperate UHF and VHF antenna up and using one feedline to the receiver.

It is extremely bad practice to use a wideband combiner to connect two
antennas pointing in different directions. For analogue signals, that's
a sure recipe for multipath and ghosting - and it can't be good for
digitals either. The combiner needs to be filtered (eg a diplexer), so
that one antenna provides signals (on the appropriate frequencies) from
one direction, and the other antenna provides signals (on the
appropriate frequencies) from the other direction.

I have one for designed for my ham transceivers,and have measured less
than .5 db of loss, but that is for differant frequency ranges and not to
combind two antennas on the same band.

That sounds like a diplexer (frequency selective), and not a wideband
splitter/combiner. These can indeed be low loss, as they consist of
frequency-selective (or lowpass-highpass) filters connected to a common
port, and there is no need for wideband combining/splitting.

Even if he does get the maximum of 3 db of gain, will that acutally get him
anywhere ? Will that be enough gain for the FM broadcast band to be
noticiable ?

Well, every little helps!


--
Ian

"Ian Jackson" wrote in message
Strange as it may seem, if you use (for example) a TV 2-way '3dB'
splitter to combine two identical in-phase signals, you DON'T lose 3dB.
Apart from the unavoidable slight inherent losses of the two transformers
the circuit uses (a total of around 0.5dB at low VHF, increasing to 1dB at
high UHF), the splitter is lossless. Ignoring the transformer loss, the
3dB loss occurs simply because the power at each output port is half of
that at the input. You haven't actually lost anything.

If the splitter is now turned around to become a combiner, it doesn't
suddenly become more lossy. If you again ignore the transformer losses,
the two identical in-phase signals you feed into the 'output' ports are
added, and the result is a signal 3dB higher.



I don't have a TV splitter/combiner to play with. I do have a MiniCircuits
combiner I have been playing with.
http://www.minicircuits.com/pdfs/ZFSC-2-2.pdf

I am not sure what is in the combiner but it must be transformers of some
type as the resistance of the ports are near zero ohms.

Their specs is for a 3 db loss and then an aditional loss of about .2 to
1.2 depending on the frequecy. Are you sure that is not the case where you
are saying you do not loose the 3 db ? That is the ratings is for the extra
..5 or so not counting the already 3 db of loss.

Maybe you can tell me if I am playing with the wrong type of combiner.. Here
are some results of my tests. using a HP 8924C service monitor and another
signal generator.


With one input port of the combiner having a signal and the other port
terminated with a 50 ohm load (the nominal impedance of all devices) there
is a 3 db loss (small values not being included) not the low values you
mention to the output port. When I hook up the other signal generator, I
get from almost a total of 0 db to 6 db of loss. I asume the spectrum
analizer going from 0 to 6 db is the phasing of the two generators.



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In message , Ralph
Mowery writes

"Ian Jackson" wrote in message
Strange as it may seem, if you use (for example) a TV 2-way '3dB'
splitter to combine two identical in-phase signals, you DON'T lose 3dB.
Apart from the unavoidable slight inherent losses of the two transformers
the circuit uses (a total of around 0.5dB at low VHF, increasing to 1dB at
high UHF), the splitter is lossless. Ignoring the transformer loss, the
3dB loss occurs simply because the power at each output port is half of
that at the input. You haven't actually lost anything.

If the splitter is now turned around to become a combiner, it doesn't
suddenly become more lossy. If you again ignore the transformer losses,
the two identical in-phase signals you feed into the 'output' ports are
added, and the result is a signal 3dB higher.



I don't have a TV splitter/combiner to play with. I do have a MiniCircuits
combiner I have been playing with.
http://www.minicircuits.com/pdfs/ZFSC-2-2.pdf

The spec says "• low insertion loss, 0.4 dB typ."
This is the real loss - the loss that will make the splitter get warm
when you feed a signal into it.

I am not sure what is in the combiner but it must be transformers of some
type as the resistance of the ports are near zero ohms.

The usual basic circuit is:
Input port to ground - a 2:1 impedance ratio step-down ferrite-cored
autotransformer T1 to ground.
T1 tap is connected to the centre tap of a second 1:1 ratio
ferrite-cored autotransformer T2.
Each end of T2 of connected to each output port.
A 100* ohm resistor R is connected between the ends of T2 (ie between
the output ports).
*R is 2 x Zo, so for a 75 ohm system, it will be 150 ohms. Note the
purpose of T2 and R is to provide isolation between the outputs (for
signals coming back into the output ports).

Their specs is for a 3 db loss and then an aditional loss of about .2 to
1.2 depending on the frequecy. Are you sure that is not the case where you
are saying you do not loose the 3 db ? That is the ratings is for the extra
.5 or so not counting the already 3 db of loss.

For forward-going signals, T2 and R play no part in the operation of
the circuit. The signal current from T1 tap enters T2 at its centre tap,
splits, and flows outwards in opposite directions to the ends of T2. The
magnetic flux created by the currents cancels out, so T2 presents no
impedance whatsoever. In effect, it isn't there, and the two outputs are
connected in parallel. The impedance presented to the centre tap of T1
is therefore 25 ohms, which is exactly what T1 is there for - to match
the 50 ohm input to 25 ohms of the two (effectively) parallel outputs.

So you see that apart from the unavoidable losses in the transformers
and in the copper wire, there are no losses in this circuit. However,
because the power emerging from each output is half the power of the
input, the loss measures 3dB (plus a bit). If you can devise a passive
2-way equal splitter with less than 3dB loss, you will make a fortune!

Maybe you can tell me if I am playing with the wrong type of combiner.. Here
are some results of my tests. using a HP 8924C service monitor and another
signal generator.

Theoretically, this type of circuit has no loss (whether used as a
splitter of an in-phase combiner). It's only the 'extra' losses that
will give you trouble. The same is true of any other type of combiner,
so which one you use may depend on which will have the least extra loss.
If you don't need high (or any) isolation between the 'output' ports
('input' if a combiner), you might do better with one of the
transmission line alternatives.

With one input port of the combiner having a signal and the other port
terminated with a 50 ohm load (the nominal impedance of all devices) there
is a 3 db loss (small values not being included) not the low values you
mention to the output port. When I hook up the other signal generator, I
get from almost a total of 0 db to 6 db of loss. I asume the spectrum
analizer going from 0 to 6 db is the phasing of the two generators.

Not quite sure what you're doing here. However, for this circuit to act
as a lossless combiner, it relies on there being no voltage across the
resistor R. This means that the two input signals must in phase and of
equal amplitude.

Typical measurements for this sort of device would be (with all three
ports correctly terminated):
In to Out: 3.5dB
Out to Out: 30dB
With one Out unterminated (o/c or s/c):
In to Out: 3.5 to 4dB
With In unterminated (o/c or s/c):
Out to Out: 7dB
--
Ian

"Ian Jackson" The usual basic
circuit is:
Input port to ground - a 2:1 impedance ratio step-down ferrite-cored
autotransformer T1 to ground.
T1 tap is connected to the centre tap of a second 1:1 ratio ferrite-cored
autotransformer T2.
Each end of T2 of connected to each output port.
A 100* ohm resistor R is connected between the ends of T2 (ie between the
output ports).
*R is 2 x Zo, so for a 75 ohm system, it will be 150 ohms. Note the
purpose of T2 and R is to provide isolation between the outputs (for
signals coming back into the output ports).

Now we are getting somewhere. The circuit you describe is differant from
any that I have seen in my very short search for combiners. With nothing
but transformers in the circuit I can see where the losses would only be
part of a DB or so. Much differant than the combiners that I saw using
either resistors or combinations of resistors and a single core
'transformer'.




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In message , Ralph
Mowery writes

"Ian Jackson" The usual basic
circuit is:
Input port to ground - a 2:1 impedance ratio step-down ferrite-cored
autotransformer T1 to ground.
T1 tap is connected to the centre tap of a second 1:1 ratio ferrite-cored
autotransformer T2.
Each end of T2 of connected to each output port.
A 100* ohm resistor R is connected between the ends of T2 (ie between the
output ports).
*R is 2 x Zo, so for a 75 ohm system, it will be 150 ohms. Note the
purpose of T2 and R is to provide isolation between the outputs (for
signals coming back into the output ports).

Now we are getting somewhere. The circuit you describe is differant from
any that I have seen in my very short search for combiners. With nothing
but transformers in the circuit I can see where the losses would only be
part of a DB or so. Much differant than the combiners that I saw using
either resistors or combinations of resistors and a single core
'transformer'.

This circuit is used in 1001 makes of wideband FM/TV splitters
(typically 5 to 900+MHz) and even in satellite IF splitters up to
2100MHz. It is also widely used for combining signals on different
frequencies (where the loss is indeed 3-plus-some dB). However, while it
CAN be used for combining co-phased antennas, it's more usual to use
transmission lines (as have been described). Note that the small
ferrite-cored transformers are completely suitable for putting any real
RF power into, but transmission lines don't have this problem.
--
Ian