Measuring Splitter/combiners

[MavamQ]

I think I have found a good place to ask my questions. I want to test several TV splitter/combiners. Mostly to measure their losses.
I have a NanoVNA and I have a nano spectrum analyzer and signal generator.
I'm mostly concerned about Losses when combining two antenna signals, theoretically you should get 3db gain, but some have
an actual loss when adding signals and others have 2 to 2.5db gain. Anyway that what I want to measure.
Any thought about how to measure 75Ω equipment with a 50Ω Nano?

 

[KevinC]

Not answering your question, but if you’re trying to combine 2 antennas to one radio a splitter isn’t going to work for that.

 

[cavmedic]

talking all passive devices here, 2 way splitter is -3.5 db per leg . Balanced 3 way is -5.5 per leg, an un-balanaced 3 way will be -3.5 one leg and -7.5 the other two legs and a 4 way is 7-9 db loss per leg..
If you wanna play with the nano, inject a level and read it at the output ports. The difference between 50 and 75 ohm will not be noticeable..

results will vary based on the cheapness of the splitter. The above were losses from CommScope splitters used by the industry providers, not Captain Radio Shack , Larry Lowes, or Jonny Home Depot

 

[prcguy]

TV type splitters can vary in loss, some are real Wilkinson dividers and some are transformer based which have more loss. But what do you expect for a $.75 part that gets jacked up to a ridicouls price of $5 to $7?

Anyway, when combining two identical narrow band TV antennas at the right spacing in phase with exact length cables you can get close to 3dB gain with a good quality splitter if that's what the OP is doing. Combining two antennas in phase actually gets you 6dB improvement but you loose at least 3dB of that in the combiner. If combining two random antennas with non critical lengths of coax you will get a good 3dB or more loss through the splitter and usually less.

 

[MavamQ]

Not answering your question, but if you’re trying to combine 2 antennas to one radio a splitter isn’t going to work for that.

If you think that is true, I would need you to give me reasons why. And I'm actually looking at combining two antennas to a TV. Theoretically you get 3db gain, but, depending on the combiner, the losses range from 0.5db to to much to be useful. But, I'll listen to your reasoning.

 

[MavamQ]

talking all passive devices here, 2 way splitter is -3.5 db per leg . Balanced 3 way is -5.5 per leg, an un-balanaced 3 way will be -3.5 one leg and -7.5 the other two legs and a 4 way is 7-9 db loss per leg..
If you wanna play with the nano, inject a level and read it at the output ports. The difference between 50 and 75 ohm will not be noticeable..

results will vary based on the cheapness of the splitter. The above were losses from CommScope splitters used by the industry providers, not Captain Radio Shack , Larry Lowes, or Jonny Home Depot

Your numbers are when used as a splitter, I want to use them as a combiner. What is the loss from the theoretical 3db gain?

 

[MavamQ]

TV type splitters can vary in loss, some are real Wilkinson dividers and some are transformer based which have more loss. But what do you expect for a $.75 part that gets jacked up to a ridicouls price of $5 to $7?

Anyway, when combining two identical narrow band TV antennas at the right spacing in phase with exact length cables you can get close to 3dB gain with a good quality splitter if that's what the OP is doing. Combining two antennas in phase actually gets you 6dB improvement but you loose at least 3dB of that in the combiner. If combining two random antennas with non critical lengths of coax you will get a good 3dB or more loss through the splitter and usually less.

No, the theoretical gain when adding two antennas in phase is 3db, then you have combiner losses, of 0.2db to way to much. When splitting a signal yes, you lose 3db because you have half the power going to each outlet, when combining signal you double the power or and have 3db gain. Mini circuits have splitter/combiners that have 0.2db insertion loss, meaning you would have 2.8db gain when adding two in phase signals. If you think it is 6db you are thing voltage gain not power gain.

 

[dlwtrunked]

Your numbers are what used as a splitter, I want to use them as a combiner. What is the loss from the theoretical 3db gain?

I have not seen that you understand phasing the signals is required. There is no theoretical 3 dB gain unless the signals are properly phased and note that is frequency and location of antennas dependent. If you do not understand and account for that, do not say "theoretical" because you have not accounted for necessary considerations. Replies have told you why.

 

[KevinC]

If you think that is true, I would need you to give me reasons why. And I'm actually looking at combining two antennas to a TV. Theoretically you get 3db gain, but, depending on the combiner, the losses range from 0.5db to to much to be useful. But, I'll listen to your reasoning.

Other explained it. But what you need is a phasing harness, lots of math and precise cable lengths required. Random parts will give random results and less that stellar performance.

 

[MavamQ]

I have not seen that you understand phasing the signals is required. There is no theoretical 3 dB gain unless the signals are properly phased and note that is frequency and location of antennas dependent. If you do not understand and account for that, do not say "theoretical" because you have not accounted for necessary considerations. Replies have told you why.

Absolutely, the signals must be in phase. I did say in phase in post #7.

 

[MavamQ]

Other explained it. But what you need is a phasing harness, lots of math and precise cable lengths required. Random parts will give random results and less that stellar performance.

Cable length doesn't matter as long as the cables are equal length and also the antennas have to be in the same alignment, i.e. same distance from transmitter.

 

[dlwtrunked]

Absolutely, the signals must be in phase. I did say in phase in post #7.

Your post appeared while I was typing and I only saw it after posting.

 

[prcguy]

No, the theoretical gain when adding two antennas in phase is 3db, then you have combiner losses, of 0.2db to way to much. When splitting a signal yes, you lose 3db because you have half the power going to each outlet, when combining signal you double the power or and have 3db gain. Mini circuits have splitter/combiners that have 0.2db insertion loss, meaning you would have 2.8db gain when adding two in phase signals. If you think it is 6db you are thing voltage gain not power gain.

The theoretical gain of combining any two signals in phase is 6dB but you have to deal with the loss of the combiner or in this case a splitter used backwards. You take a theoretical 3dB hit right out the gate from the combiner then the additional component/circuit loss can be a fraction of a dB for a good combiner to a couple dB for a lousy TV splitter. The end result is a maximum of 3dB realized gain from combining the two in phase signals from an antenna or any other source using a "lossless" splitter but they all have some loss so your net gain will be a little less than 3dB.

That's how its taught from an engineering perspective and not from a discussion on the CB. And part of my job for 18yrs was combining high power microwave transmitters optimizing wide band Ku TWTAs up to 750w each and in one case pairs of 3kW C-band Klystron amps to get 6kW for destructive testing. I'm intimately familiar with combining techniques, phase and loss in the process and was responsible for training others to properly phase combine high power microwave systems so I might ask what your combining experience is?

You can probably get close to the theoretical 3dB gain using a pair of narrow band single channel antennas but not with a wide band TV antenna because the preferred distance between the two antennas being combined will only be correct over a narrow frequency range.

Does the OP plan on combining single channel TV antennas or wide band?

 

[MavamQ]

Sorry but you are just wrong about the theoretical 6db gain when adding in phase signals, it is 3db. Why would it be 6db? when talking theoretic without losses of in phase signals., say you have two 1 watt signal and you add them, you get 2 watts, double the power, not 6 watts 4 times the power. There are Combiners with as low as 0.2db loss, look at some of Minicircuit splitter/combiners, and don't look at them as slitters where they say 3.2db loss or, if you do, you need to subtract the 3db loss because you are sending 1/2 the power to one outlet and 1/2 the power to the other plus 0.2db loss. look at insertion loss, you will find as low as 0.2db.

 

[MavamQ]

Your post appeared while I was typing and I only saw it after posting.

No problem, it is an important point, I should have added it in my first post. Sometimes you just assume others know and don't mention things. I should have said that, this is not the first time I had to go back and make that clear.

 

[prcguy]

Sorry but you are just wrong about the theoretical 6db gain when adding in phase signals, it is 3db. Why would it be 6db? when talking theoretic without losses of in phase signals., say you have two 1 watt signal and you add them, you get 2 watts, double the power, not 6 watts 4 times the power. There are Combiners with as low as 0.2db loss, look at some of Minicircuit splitter/combiners, and don't look at them as slitters where they say 3.2db loss or, if you do, you need to subtract the 3db loss because you are sending 1/2 the power to one outlet and 1/2 the power to the other plus 0.2db loss. look at insertion loss, you will find as low as 0.2db.

The loss through a splitter or combiner is 3dB at best so how do you get 3dB GAIN from combining two identical signals via a device that has a fixed 3dB loss in both directions? The act of combing two in phase signals is actually 6dB and you loose 3dB of that in the process of combining that's how.

That's what is taught in school so please explain to me how you get the 3dB gain from sticking two signals into a device that has 3dB loss other than its actually a 6dB increase leaving you with 3dB gain after combiner loss. If you can't explain that you might go back to school and learn it.

 

[MavamQ]

The loss through a splitter or combiner is 3dB at best

Not true the loss through a splitter is 3db at best. When combining signals the add to double the power, at best.

so how do you get 3dB GAIN from combining two identical signals via a device that has a fixed 3dB loss in both directions?

A good combiner doesn't have 3db loss. This probably won't convince you, because you have to interpret it properly.
If you look at the spec's at the top it says insertion loss 0.3db typ. that is if used as a combiner, however you do have to add the insertion loss to the signal at each output, then if you look at the chart which is showing use as a splitter, Say at 90MHz, the signal at one output is 3.21db loss. 3db from splitting 0.21db from insertion loss.

The act of combing two in phase signals is actually 6dB and you loose 3dB of that in the process of combining that's how.

That's what is taught in school so please explain to me how you get the 3dB gain from sticking two signals into a device that has 3dB loss other than its actually a 6dB increase leaving you with 3dB gain after combiner loss. If you can't explain that you might go back to school and learn it.

Again how do you get 4 times the power when adding two signals, it is only 2 time the power, not 4 times.

 

[MavamQ]

Can we first agree that if you add 1watt to 1watt we get 2 watts? Theoretical.

 

[MavamQ]

Here is an array calculator, if you put 2 antennas it is 3.01 db gain, if you put 4 it is 6.02db gain.

Array Gain Calculator

The Array Gain Calculator is designed to help in calculating the gain of an antenna array, which is the increase in signal strength.

calculatorshub.net

 

[prcguy]

Not true the loss through a splitter is 3db at best. When combining signals the add to double the power, at best.

A good combiner doesn't have 3db loss. This probably won't convince you, because you have to interpret it properly.
If you look at the spec's at the top it says insertion loss 0.3db typ. that is if used as a combiner, however you do have to add the insertion loss to the signal at each output, then if you look at the chart which is showing use as a splitter, Say at 90MHz, the signal at one output is 3.21db loss. 3db from splitting 0.21db from insertion loss.

Again how do you get 4 times the power when adding two signals, it is only 2 time the power, not 4 times.

When you see combiner loss stated less than 3dB like .2dB or some other very low number, that is in addition to the theoretical 3dB and that will be stated somewhere in the technical data. MiniCircuits and others do that and when you look around you will find that statement. A two way combiner has 3dB loss plus a little more like that .3dB and in both directions. Its impossible to have less no matter if its a Wilkinson or coax phasing harness or 3dB hybrid, they all have a minimum of 3dB loss.

If you have any combiners like this please measure them and you will see they have 3dB + loss. Its impossible not to. In fact pick a two way RF combiner that says its less than 3dB loss. We will measure it. If its got less than 3dB loss I'll give you $1000 cash. Will you do the same if it measures less than 3dB like only .3dB?