We have been using the RB751 for a little while and it has been working out great. For some of our particular applications we need to mount the RB751 inside a sealed metal enclosure. For this application we have been using the external antenna port on the RB751 to connect to an antenna that is mounted outside the enclosure.
When the RB951 came out I was excited by the increased processing power, and ordered a few to do testing with. When they came I realized that I had overlooked that this model no longer has the external antenna connection like the RB751.
Upon finding this out I opened the case to see if I could figure anything out. Here is what I am thinking.
Looking at the PCB you can see that there are two unpopulated places where antenna connectors could possibly be installed (Figure 1). On the left side of the board (Chain 0) the connector header is labeled as J700 and J701, and on the right side (Chain 1) it is labeled as J702 and J703. Looking at the footprint it appears as if that area could accept two different styles of antenna connectors, which would explain why there are two part designators at each location.
If you pop the RF covers off the board you can see the Transmitter IC and the L-Band switch (Figure 2) which I believe is the following part (http://www.cel.com/pdf/datasheets/UPG2009TB.pdf)
On the input side of the L-Band switch you can the trace coming from the internal antenna connected to the input pin of the switch via an 0402 sized capacitor (Figure 3). You can also see the trace that comes from the unused antenna connector that ends right next to the input pin of the switch. It appears to me that the board is designed such that the input capacitor could be installed one of two different ways. The way it ships from the Factory it is installed connecting the internal antenna to the switch, but I’m wondering if the capacitor could be de-soldered and installed so that it connects to the trace that leads to the empty antenna connector. Once doing that it would be easy to solder the appropriate antenna connector (possibly this one: http://www.molex.com/molex/products/datasheet.jsp?part=active/0734152061_RF_COAX_CONNECTORS.xml) to the empty location on the board.
Has anyone tried this yet? Can anyone from Mikrotik confirm what I am thinking here? Any insight on this would be greatly appreciated.
That looks exactly like what I want to do. I might test it out sometime this week, although I’ll need to order some SMD MMCX connectors before I can really test it out. I’ll be sure to keep everyone updated as soon as I get the parts.
Unfortunately that model is too large for our current application. The RB751 that we currently use goes into an embedded design. We take it out of the plastic housing and mount it along with a few other circuit boards and components inside a metal chassis. The RB951 is great because it has the exact same footprint and hole pattern as the RB751. If I can figure out the antenna problem then I think we will be good to go.
Hey everyone, a quick update: I ordered the connectors and got them soldered on. It was tricky to do so since the center pin of the antenna connector is not accessible with a soldering iron. You really need a hot air rework station to solder the connector on properly. The main problem that has me stuck right now is that I ran into an issue when trying to solder the dc blocking capacitor on to the secondary antenna trace. While positioning the capacitor for soldering is slipped out of my tweezers and flew across the room never to be found again. I’m stuck now since I don’t know the proper value of that capacitor. My best guess is something in the low pF range. 10-100 pF. The type is most likely an RF/Microwave type MLCC 0402 case size with a C0G dielectric. something similar to this: http://www.mouser.com/ProductDetail/Kemet/CBR04C470F3GAC/?qs=zoGAYOF739DLIaI35UpDNw%3d%3d
I am wondering if anyone from Mikrotik might be able to tell me the value of this capacitor so that I can buy some spares.
Great! Thanks for your help! Now I can order some more of the capacitors and get the board up and running. Just to satisfy my curiosity, what did you use to measure such a small capacitance? My initial thought was to solder a large value resistor (10 M) to the cap and use a signal generator and a scope and the measure the time constant. However, the caps are so tiny and fragile that I broke the second one trying to measure it.
Why did you cut the transmitter cover.
I can see you have soldered two mmcx connectors to the board, but did you add another thing to the board? Where is it?
Long time no post, but the external antenna modification has been working very well for us. We bought the SMD MMCX connectors to install on the empty pads on the board. We have reflowing them with solder paste and a hot air gun. The only difficulty is desoldering the tiny 0402 capacitor from the board and then re-installing it on the other position without damaging or losing it. It makes it difficult to solder since it is directly underneath the edge of the RF can, so there is not a good way to get an iron and tweezers in there.
I’m wondering if, anyone has been able to accurately measure the value of the output capacitor, on the RF switch. I know that the datasheet for the RF switch shows a 56 pF cap on the example circuit, however this is just an example and not necessarily what is used on this board.
I would really like to order some spare capacitors to do this mod on other RB951 modules. I’m wondering if anyone at Mikrotik and tell me what the value of this capacitor is. I currently do not have the equipment to accurately measure the value of this component.
Hi dudes! Maybe this will help:
weblance.com.ua/192-mikrotik-rb951ui-2hnd-rb951g-2hnd-podklyuchenie-vneshney-antenny.html
russian lang, but it because russians very often do hacks )))
