RF Combiner

[electroRF]

Hi,
I'm interested in the following RF Dual-Band Combiner:
https://www.electro-tech-online.com/custompdfs/2013/01/78210800.pdf

It has the following design:


I don't manage to understand what is the DC/AISG part, and what is the other parallel part.

Could you please help me figure out this issue?

Thank you very much!

 

[unclejed613]

quite often, antenna preamps are "phantom" powered through the coax cable. the bandpass filters in the combiner/splitter needs to be bypassed in some way that doesn't interfere with the filters, but still be able to pass DC to the device being powered. the bypass device is likely to be an inductor of large enough value that it doesn't pass RF outside the passband of the filter.

 

[JimB]

What unclejed said.

Also have a look here:
https://www.electro-tech-online.com/custompdfs/2013/01/793301.pdf

and here
https://www.electro-tech-online.com/custompdfs/2013/01/793304.pdf

to get a bit more insight into the "phantom power" idea.

JimB

 

[dr pepper]

Those modules are available with dc feedthrough on one the other or both i/p's, so you need to consider that in your application, if 2 units were connected that both wanted to phantom power the incomming cable then there could be contention with a combiner with dc feedthrough on both.

 

[electroRF]

Hi,
Thank you very much dear fellows

My application passes cellular RF signal through this combiner, so I assume that no DC should reach the combiner, is it correct to assume so?

If my application is all about cellular, it means that I'll need to use an external DC blocker on each port?

Thank you!

 

[electroRF]

Hi,
I'd appreciate help mates

 

[JimB]

If we knew what you were really trying to do it would help.
JimB

 

[electroRF]

hi,
thanks Jim.

This is my purpose:



The Blue modules are the RF Dual-Band Combiners.

I wanna use a MIMO Antenna and separate the LTE Band7 from the UMTS Band1 & GSM-1800

My question is, would these combiners filter these bands as my purpose?
The DC/AISG parts confuse me.

Thank you.

 

[JimB]

I cannot comment on a MIMO antenna as I have no knowledge/experience in that area.

However if the MIMO antenna is completely passive (ie has no built-in amplifier) then you do not need the DC/AISG parts.

JimB

 

[electroRF]

Hi Jim, thanks again!

Could you expalin what the DC/AISG parts do?

The RF Combiner I'd like to purchase has them built-in in either one of the ports or in two of the ports:


So I can't avoid them.

 

[electroRF]

Perhaps anyone would know

 

[JimB]

Could you expalin what the DC/AISG parts do?

I thought that had been explained in posts 2, 3, and 4 of this thread.

To recap, it is a means of feeding DC power to an active device at the antenna, eg a pre-amplifier.

JimB

 

[electroRF]

Oh I see,
I actually did not manage to understand this.

This is the antenna btw.

In my application, the antenna is connected to port 3.
Ports 1,2 will be connected to a cellular mobile phone.

The cellular mobile phone is not supposed to pass any DC power into the RF Combiner.

So, if I got you right, it means that the DC/AISG part is not needed, right?

Thank you Jim

 

[unclejed613]

that won't be a very good antenna for 1.8Ghz, as it's a 2.4Ghz antenna. i would guess that the SWR of that antenna at 1.8Ghz would be much higher than 3:1, if it's higher than 3:1, you lose all of the gain the antenna provides and then some... an antenna is usually a narrow bandwidth device, and outside of that bandwidth they don't perform well at all. there are antenna designs that perform relatively well over wide bandwidths, such as discone or biconicals, but they have very little gain at all, as they are basically wideband dipoles.

 

[electroRF]

Hi,
Thanks a alot Jed!

I already checked it, and I get a very good signal of WB @ 2100MHz - therefore I assume that I can use this antenna at this frequency band as well.
When you meant that it doesn't perform well at this frequency band, you meant the signal strength reception? (so if strength is ok, I assume it can be used well there).

Regarding the DC/AISG module, this antenna does not need any DC signal, is it correct?

 

[smethbet]

there are antenna designs that perform relatively well over wide bandwidths**broken link removed**

 

[electroRF]

Thanks

My main concern is, regarding the DC/AISG module.
This antenna does not need any DC signal, is it correct?

 

[unclejed613]

if you don't have anything connected that is at a DC potential, you don't have to worry about it. in your diagram you showed a device connected that was operating at 1800Mhz, are you actually trying to connect one? if so it won't perform well on that antenna. 2200Mhz may be ok, but not 1800Mhz.

 

[electroRF]

Hi Jed,
What do you mean by - it won't perform well?

Currently, when I use just the antenna (2.3-2.7GHz), with no filters, and connect to it a GSM mobile phone, then the mobile phone manages to communicate with the network on the 1800MHz band.

However, there might be things / problems which I didn't notice yet (for example, i did not check the quality of the voice call audio).

Therefore, could you expalin 'not perform well'?
Do you mean just reception strength, or something else?

Thanks a lot

 

[kubeek]

I think he meant that 2.3-2.GHz antenna will have very little gain at 1.8GHz asi it is outside the band it is designed for.