power splitter/combiner maximum power question - Page 1
Forum section: electronics / rf-microwave

author: CopperCone
author_rank: Super Contributor
timestamp: September 21, 2017, 12:02:15 am
content: https://www.minicircuits.com/pdfs/ZN8PD-272SMP+.pdfIt says 10W as splitter and 6W as a combiner of non-coherent signals (page 2).What exactly does non-coherent signals mean? I thought you were supposed to use phase matched signals in a combiner, so they are coherent.Does this mean that, so long your signals are in phase, you can transmit 10 watts through it, but if they are out of phase, you can lose as much as 6watts in the combiner without damage (making the output power 4 watts?), meaning you have two 5 watt signals that are out of phase enough to cause 6 watts of losses?Does this mean you can use an equation involving phase shift between the two signals to calculate the dissipation in the combiner based on their power (and keep it under 6 watts, while subtracting the dissipated power from the total allowed transmit power?)So, if your phase error is enough to cause 1 watt of loss, and your output is 9 watts, you are ok?

author: Rory
author_rank: Frequent Contributor
timestamp: September 21, 2017, 01:01:00 am
content: Mini-circuits has a wealth of application notes that are very useful to understand the theory of their products.Here's their index.https://www.minicircuits.com/applications/application_notes.htmlIt might be a good idea for you to read this, it's about power splitters:https://www.minicircuits.com/app/AN10-006.pdf

author: CopperCone
author_rank: Super Contributor
timestamp: September 21, 2017, 02:05:05 am
content: Ok, I read that before. It does not answer (or I cannot find the answer) if you can just use the rating given for splitting if its summing coherent signals or how to derate for mismatch. They have two different ratings. And the app note does not have any formulas.In a power combiner application, the power loss across the internal resistor must also be considered in addition to the transformer core effects. For example, in a 2 way power combiner, the internal resistor must be able to dissipate half the power applied to each port. The specifications for the internal load dissipation rating for each power combiner N way group is givenon the individual specification pages.This is unclear to me. It says nothing about coherence. The datasheet gives a rating specifically for non-coherent signals. What about coherent signals? I assume it has relevance because its specifically stated, otherwise imo it would just say "splitting max power: xxx combing max power: yyy" I think there should be a formula as coherance is a analog phenomena, you cannot simply declare two things coherant or noncoherant (I guess you can, if they are at different frequencies), but I am only interested in phase difference.

author: David Hess
author_rank: Super Contributor
timestamp: September 21, 2017, 06:09:46 pm
content: Figure 4 in the application note shows the problem.When used as a splitter, all of the outputs are in phase and the current through the balancing resistor is zero so power is limited by loss and saturation in the transformers. When used as a combiner with non-coherent signals, current through the balancing resistor creates additional loss. If the combined signals were identical and in phase, then the higher power limit would apply.

author: CopperCone
author_rank: Super Contributor
timestamp: September 21, 2017, 09:45:05 pm
content: Does this penalty begin to apply if the phases are correct, but the amplitudes are different (say 3dBm difference)?

author: David Hess
author_rank: Super Contributor
timestamp: September 21, 2017, 10:56:50 pm
content: Quote from: CopperCone on September 21, 2017, 09:45:05 pmI think their specification assumes worst case.

author: CopperCone
author_rank: Super Contributor
timestamp: September 22, 2017, 09:31:01 am
content: I wonder if I can modify it to put a thermocouple against that crux resistor.

author: 4CX35000
author_rank: Regular Contributor
timestamp: September 24, 2017, 07:33:30 am
content: I suppose it is a mix of Mini-Circuits have explained this poorly and/or assume the reader automatically knows what is being referred to. Whatever the case, I suspect what is meant for example. If the combiner is used with 2 x 5 watt amplifiers to gain 10 watts total output and one amplifier failed. At this stage you have a non-coherent system and the balance load becomes part of the circuit to maintain the 50 ohms input/output impedance and the power is then dissipated as heat. The upper limit of power the balance load resistor handle is provided in the data.

author: Antonio84e
author_rank: Contributor
timestamp: September 24, 2017, 04:10:18 pm
content: Following the comment by David Hess which I think is correct,If you use it as a splitter and only apply a signal to the input port. Assuming all output ports are terminated, then the max input power specified is 10W.If you are going to use it as a combiner, and you are going to inject multiple signals, then it is important to know if the signals are going to be coherent or not. (Again, please terminate any ports that are not used). Worst case scenario for the balance resistors is that you apply pairs of signals of same power and out of phase by 180 degrees in which case, all the power will be dissipated by the internal loads (which is what limits the max input power when used as a combiner for non-coherent signals).I would not suggest modifying the component as this will void the warranty.

author: CopperCone
author_rank: Super Contributor
timestamp: September 25, 2017, 02:05:32 am
content: what can liquid nitrogen or helium do for me in this case? (cheaper then buying the fucking rated coupler

author: T3sl4co1l
author_rank: Super Contributor
timestamp: September 25, 2017, 05:30:23 am
content: Quote from: CopperCone on September 21, 2017, 09:45:05 pmYes, mismatch is mismatch.To find out how much, draw the equivalent circuit (N ports, a transformer(/s) and termination resistor(s)) and do an AC steady state analysis.Tim

author: David Hess
author_rank: Super Contributor
timestamp: September 25, 2017, 05:39:20 pm
content: Quote from: Antonio84e on September 24, 2017, 04:10:18 pmThis is the part which confused me but I suspect it is because of the typical applications. I think there is an assumption that coherent signals will all be in-phase which obviously applies to splitting but may also apply to combining. If the combined coherent signals were 180 degrees out of phase, then this would represent a worst case for resistor power dissipation and the rated power would be even lower. No such specification is given because there is no typical application which does this.

author: Antonio84e
author_rank: Contributor
timestamp: September 27, 2017, 08:36:19 pm
content: For non coherent signals, the max power per port is 6W. This will contemplate the worst case scenario of having the input signals out of phase by 180 degrees which is indeed the worst case scenario. In this case, all power is absorbed by the internal loads.

author: David Hess
author_rank: Super Contributor
timestamp: September 27, 2017, 09:08:55 pm
content: Quote from: Antonio84e on September 27, 2017, 08:36:19 pmIs that how Mini-Circuits defines it? If that is the case, then a truly non-coherent signal should have a slightly higher power limit. I would like to think that the Mini-Circuits specification really is the worst case but I am not inclined to take it for granted. It seems ambiguous to me.I would normally consider signals 180 degrees out of phase to still be coherent because I am used to dealing with them that way in both the RF and digital realms but that obviously cannot be part of the coherent specification Mini-circuits gives for the reason we both gave; cancellation is going to be completely absorbed by the resistors.

author: Antonio84e
author_rank: Contributor
timestamp: September 27, 2017, 10:01:18 pm
content: to be sure, I would advise to get in touch with the closest Mini-Circuits rep for confirmation.