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Another page from the same site about ganging antennas and the indoor two antenna trick which is of limited value because there are no analog channels to see ghosts on to adjust the positions, this makes it more of a haphazard set and see procedure.
The point about unilluminated elements being vampiric and sucking more signal than they would have contributed. should be considered carefully. It's one reason I think parabolics out perform large phased arrays of similar size.
i also believe vertical stacks are more likely to acquire a good lock on strong channels NOT in its beam.
Finally we should include Stagger stacking for an extreme F/B ratio.
Horizontal stacking narrows the pattern left and right while vertical stacks flatten the pattern up and down but don't reduce the beamwidth.
 

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Discussion Starter · #4 ·
I'm thinking about replacing my slightly damaged 8bay of unknown brand with a pair of Stellar labs 8bays vertically stacked. Question is what can I expect to gain? Attached is my Rabbit ears report. Currently I can get 20,22,29 & 40 24X7 13 usually after dark, as well as 23. For some reason I don't get anything on 44 and I hope the Stellar labs 2476 VHF Hi will get me 11 & 13 24X7. Could I possibly get Ch 27,39 & 21 with the stacked 8 bays? I'm having trouble de ciphering the signal strength chart in the report. Stacking should give 3DB gain over a single but surely that is more than 1 S unit of signal power.

 

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Discussion Starter · #5 ·
Copying this over from eham Where I asked a question about UHF stacking distance. First chance I get I'm going to measure an 8bay center to center and see what frequency optimum translates to using this formula.

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A non-modeling method commonly used for VHF and UHF stacking is to divide 57 by the 3 dB beamwidth of one antenna in the stacking plane, in degrees. The result is the recommended spacing in wavelengths from center to center of the antennas. This technique is commonly called D-opt (optimum distance stacking).

It is a simplification of the formula:

D = λ / (2sin(B/2)) [meters]

If your objective is something other than maximum plane gain then most other techniques are purely experimental.

- Glenn W9IQ "
 

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Copying this over from eham Where I asked a question about UHF stacking distance. First chance I get I'm going to measure an 8bay center to center and see what frequency optimum translates to using this formula.

"
A non-modeling method commonly used for VHF and UHF stacking is to divide 57 by the 3 dB beamwidth of one antenna in the stacking plane, in degrees. The result is the recommended spacing in wavelengths from center to center of the antennas. This technique is commonly called D-opt (optimum distance stacking).

It is a simplification of the formula:

D = λ / (2sin(B/2)) [meters]

If your objective is something other than maximum plane gain then most other techniques are purely experimental.

- Glenn W9IQ "
Did you ever do this? Just wondering I have two Winegard HD8800's I would like to stack.
 

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Discussion Starter · #7 ·
Did you ever do this? Just wondering I have two Winegard HD8800's I would like to stack.
Not yet, I did reconfigure one of my 8 bays vertical and vary the distance between the two 4 bay panels taking signal readings across the spectrum. I don't have that data in front of me but it was basically a tradeoff so the spacing will be custom so you get max gain on the channel you desire. Hopefully I will bw dopoping my 8 bay soon and adding the 2nd one. I have a 4 way combiner. I plan on making my patch cables and testing on the ground with a local station before I put it back up
 

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Not yet, I did reconfigure one of my 8 bays vertical and vary the distance between the two 4 bay panels taking signal readings across the spectrum. I don't have that data in front of me but it was basically a tradeoff so the spacing will be custom so you get max gain on the channel you desire. Hopefully I will bw dopoping my 8 bay soon and adding the 2nd one. I have a 4 way combiner. I plan on making my patch cables and testing on the ground with a local station before I put it back up
What about making a nearly loss less harness from 300 ohm Twin lead ?
12080
 

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Discussion Starter · #9 ·
I have seen that before and thought about employing that method. In my case I would have to eliminate the integrated 4:1 balun for each set of 4 bays and create a direct point where I could connect the twin lead. Others on the site have mentioned that there may be phasing issues that would need to be sorted. When I drop my tower I'll do a temporary mount with both antennas and play with the spacing a little and add them 4 bays at a time to track my added gain with each new set of 4 bays. Once I have it sorted I'll eep my fingers crossed that it will act the same way at 90' that it does at 25'
 

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I'm interested to see if there really is a phasing issue if you use the exact same length 300 ohm coax and encase it somehow to keep the water off of it you stand a pretty good chance of it being in phase right away.

With my Winegard HD 8800s I first plan to use the stock Baluns and combine them with a Holland splitter in reverse. If that works out I'll move on to the phasing harness.
 

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What about making a nearly loss less harness from 300 ohm Twin lead ?
you have mixed phases, some of your array elements run in opposite phase
all 4 elements should be excited in-phase
if all lines have same length, all dipole terminals from the same side should be connected together


12090


if you swap polarity, far field of such array split in 2 halves (deep null and 2 side lobes)
 

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Stacking-Ganging 4 300ohm Antennas with Twinlead_2.jpg


At first, I couldn't make sense of Ken Nist's diagram when I mentally connected 2 and 3 in series (600 ohms), then 1 and 4 in series (600 ohms), and then both in parallel (300 ohms). But, when I connected 1 and 2 in parallel (150 ohms), then 3 and 4 in parallel (150 ohms), and then both in series (300 ohms), it made more sense. I hope Ken Nist got it right.
 

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There is no "series" in connecting transmission lines (waveguides) because when you change distance between conductors (waveguide cross-section) by a tiny fraction - it become non-homogeneous and acts as impedance transformer. If you further increase distance by more than tiny fraction - you completely brake transmission line and make radiating monopole/coil (dipole whiskers)

Waveguides are always technically connected in parallel (T-junction), no matter if you twist/flip them or not.
T-junction always decrease impedance N times (for N lines). To transform this impedance you need impedance matching transformer of any kind.
Twisting/flipping or non-equal lengths are just phasing techniques for T-joints.
By twisting you can rotate phase exactly 180 degree (if length is kept constant) at all frequencies.
 

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There is no "series" in connecting transmission lines (waveguides) because when you change distance between conductors (waveguide cross-section) by a tiny fraction - it become non-homogeneous and acts as impedance transformer. If you further increase distance by more than tiny fraction - you completely brake transmission line and make radiating monopole/coil (dipole whiskers)
If what you say is true, then Ken Nist's diagram is wrong and his idea will not work.

I have no way to prove if it will work other than trying it myself.

If I wanted to combine two 8-bay antennas, I would probably transform each 4-bay section to 75 ohms with a 4:1 balun and combine the four 75 ohm lines with a power divider or coax harness. A 4-way splitter in reverse would also work.
stacking with power splitters
T-junction always decrease impedance N times (for N lines). To transform this impedance you need impedance matching transformer of any kind.
Twisting/flipping or non-equal lengths are just phasing techniques for T-joints.
By twisting you can rotate phase exactly 180 degree (if length is kept constant) at all frequencies.
That alternative would also work. Combine the four coax lines in parallel and transform the low impedance to 75 ohms with an L-network.

This is the way Ken actually did it:
A 16-Bay UHF Antenna
A 16-Bay UHF Antenna

16-bay Antenna by Ken Nist_1.jpg


It looks like he used two baluns, one from each 8-bay stock wire harness.

16-bay Antenna by Ken Nist_3.jpg
 

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This page:
has following statement: "The “two in series, two in parallel” connection maintains 300 ohms. "

This statement is fully obsolete. Series junction of transmission lines do not exist.

Author of this statement, probably assumed, that T-joint of out-of-phase signal is "series junction" which add voltages (hence increase impedance).

T-junction follow superposition rules, which are described good in 1st paragraph.
According to this superposition rules, if two out-of-phase (opposite phase) signals come to T-joint, 100% reflection occurs (zero energy is dissipated on load after T-junction).

Thats why from forward direction such phased antenna array will have deep null (theoretically infinite supression).
But when incoming wave come from different azimuth, out-of-phase (180 degree) lag is not mantained any more on T-junction termninals and it work good.
Radiation pattern of such stack has 2 strong side lobes and deep null.

Stacking of any arrays have 3 possible approaches:
1) Star topology
2) Tree leaf topology
3) bus topology

To stack 4 antennas one possible solution is 4 equal length transmission lines (no matter twin lead or coax) coming to T-joint (N=4). That's "star" topology.

Star topology has couple drawbacks:
1) with higher frequencies (microwave) it's getting harder and harder to mantain equal length in T-joint.
2) total transmission lines length (and associated losses) is overkill
3) impedance transformers with high trans ratio are hard to manufacture, you have to deal with insanely low impedances. High tr ratio also mean less bandwidth. Lambda/4 transformer 1:4 has less BW than 1:2 transformer. With high-power (TX) applications big ratios mean big reactances, big currents or voltages (high risk of failures).

With N=4 and UHF frequencies, star is fine, but if N>4 or f>1 GHz, star is not good choice.

Tree topology (2:1, 2:1, 2:1...) doesn't have this drawbacks. But number of bridges/couplers increase.
for N=4 you need 3 spliiters with "1:2" ratio.

Bus topology is not practical, as it require directional couplers with desired amount of energy to be "sucked" from main bus. That is extremely hard for R&D and production. The only benefit is single transmission line (minumum possible total length)

Tree topology is very often used in ham applications (Yagi arrays), in patch antennas (printed) and professional high-power applications, because it perfectly work with Wilkinson power divider (1:1 impedance ratio), which has some benefits over Lambda/4 transformer + T-junction.

Star topology with coax and N=4 is very easy (up to 1 GHz).
But I cannot imagine how to do N=4 with Zo=300 Ohm twinlead.

How geometrically 4 open (non shielded) lines can come in 1 point?
 

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Star topology with coax and N=4 is very easy (up to 1 GHz).
But I cannot imagine how to do N=4 with Zo=300 Ohm twinlead.

How geometrically 4 open (non shielded) lines can come in 1 point?
Four 300 ohm lines in parallel (X configuration geometrically) gives 75 ohms. Use 1:1 balun.

But it would be difficult because the 300 ohm twinlead would have to be supported on plastic insulators to keep it away from metal and to keep it from flapping in the wind. Also, the SWR would change when the twinlead gets wet.

Using coax would be easier.
 

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If what you say is true, then Ken Nist's diagram is wrong and his idea will not work.

I have no way to prove if it will work other than trying it myself.

If I wanted to combine two 8-bay antennas, I would probably transform each 4-bay section to 75 ohms with a 4:1 balun and combine the four 75 ohm lines with a power divider or coax harness. A 4-way splitter in reverse would also work.
stacking with power splitters

That alternative would also work. Combine the four coax lines in parallel and transform the low impedance to 75 ohms with an L-network.

This is the way Ken actually did it:
A 16-Bay UHF Antenna
A 16-Bay UHF Antenna

View attachment 12094

It looks like he used two baluns, one from each 8-bay stock wire harness.

View attachment 12096
I'm hoping to get to this project sooner than later with my Winegard HD 8800s. Right now it looks like I can encase twin lead in some PVC tubing to keep it dry and stable in the Wind.

There's also some theory about twisting the twin lead. Each exact length of twin lead needs to be Twisted the same amount. Or is that just Overkill?

Of course first of all, I think I'm going to stack the two with the stock baluns with a simple splitter in reverse. Is there a minimum length of coax before the splitter? I can make my own coax leads right down to the millimeter.

When I do use the twin lead, how important is the twisting? Also, if everything is going to be in parallel like I believe it's supposed to be I just take all four of my my left side terminals, connect them with the left side of my coax lead which I will Mark with a paint pen. And of course all the right side go with the right side solder them together to a balun. Will I need a special balun or used one of the ones that came with the two HD 8800s?
12101


12102



12103


12104


12105


I'm hoping to get somewhere with this project this weekend.
 

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300 ohm twinlead is not meant to be twisted. Should be laid out straight, gentle bends where required, neat and tidy.
 

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Is there a technical reason for twisting 300 ohm cable? Also the issue that water affects the cable? Really you have a down lead from the antenna to the entry point into the building. There is no issue of water accumalating on the wire. So how does rain affect the performance? When I was a kid growing up, all we had was 300 ohm cable. Don't remember any issues with it. We had stand off supports for the cable and all was good.
 
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