Is there a measurement I can do

ParrotHead · EVDO Newbie Joined: 21 Mar 2008 Posts: 5 Location: Denver

with a multimeter on a Wilson cellular antenna to verify it hasn't failed? I have an SWR meter but it's for 2-meter HAM - if I recall from years ago, SWR meters are made for specific bandwidths. Or is there an SWR meter for cellular, reasonably priced say from Radio shack? Thanks for your comments.

n6gn · Posted: Sat Mar 22, 2008 2:55 pm Post subject:

You can *try* measuring continuity between center and pin of the connector on a low resistance range. If it is a high resistance you can then try shorting the antenna to the ground at it's base. If the ohm meter indicates continuity after making this connection, it's likely that everything is still connected, connectors OK etc.
However, if the initial connection is a short it doesn't prove anything one way or the other, as an antenna can be constructed to be low resistance at DC.
The above measurement can give confidence that it's good but doesn't easily indicate whether it is bad.

SWR bridges for the UHF range are generally hard to find and most commonly a device called a 'directional coupler' is used in conjunction with a power meter or spectrum analyzer in order to determine the VSWR or reflected power of an antenna. A vector network analyzer is another piece of equipment which has directional devices built-in which can also make such a measurement.

I suspect that if you have a failure, it is likely that it can be seen with a DC measurement but in order to interperet the data you really need to know how the antenna *should* look and that may not be easy to know.

n6gn

ParrotHead · EVDO Newbie Joined: 21 Mar 2008 Posts: 5 Location: Denver

Ohmeter says resistance is infinity. Specs on this model antenna say 50 ohms impedance. Maybe I don't understand where that's measured as I expected to see something around 50Ω measured between the pin & ground. Or maybe I found the problem - an open? I'm getting around -110dbm per the Sprint connection tool, with just the adapter plugged in - same as if the antenna is also connected to the adapter. Remove the adapter so it enables the internal antenna & the connection tool pretty consistently reports -84dbm. I'm thinking either the antenna is shot or there's an open in the circuit board on the lead-in from the external antenna - that is, if there can be an open while still detecting the adapter is attached in order to disconnect the internal antenna.

Let me see if I have this right. It's OK to ground the base of the antenna? Also, does the antenna being positioned slightly differently make any difference? IOW, if I have someone watch the gain on the computer while I move the antenna around on it's mount, should I expect that to have any effect?

n6gn · Posted: Sat Mar 22, 2008 6:10 pm Post subject:

50 ohms is it's impedance (approximately) at the operating frequencies. At DC it is most likely either zero or open. That's what your multimeter will measure. To measure RF impedance you need a vector network analyzer.

To see if the connections from the connector to antenna are OK, set up so that you are measuring (the infinity) at the connector. Now use a separate clip lead or hookup wire to short the antenna to its base. See if that causes the ohmeter to indicate near-zero. If so, the connector, cable and connections are almost certainly OK. If not, there might be a problem withing connector,cable or antenna but there's no proof unless we know more about how the antenna was designed.

n6gn

ParrotHead · EVDO Newbie Joined: 21 Mar 2008 Posts: 5 Location: Denver

OK, jumpered the bare metal of the antenna right below the coil to the ground plane radials and got continuity at the plug. So the cable & adapter and connections are good. I'm thinking the problem is more likely in the external antenna circuit on the 595U card now. Next step, replace the card. At least we're still inside the 30 day trial for the card. Thanks for your help.

n6gn · Posted: Sun Mar 23, 2008 9:41 pm Post subject:

ParrotHead · EVDO Newbie Joined: 21 Mar 2008 Posts: 5 Location: Denver

Final result: Examined the connectors closely with a loupe. The center wire of the 595U connector is broken off and stuck alongside the center connector on the end of the adapter. I recall when I examined them earlier to determine compatibility of the original adapter (595) & why it didn't fit, that the center pin on the 595U card was not exactly in the center. Apparently subsequently the 595U adapter was inserted while the center pin was misaligned, which then got alongside the tubular center connector of the adapter, jammed and then ripped out when they were pulled apart. FYI, if one hasn't seen this center wire and the tiny metal tube it fits into - they are so small as to be invisible to my old eyes, without magnification. Eg. my normal 2X readers aren't strong enough to see them, I need a 10X loupe to see them clearly.

Both the 595U and the adapter need replacement. Going forward, it will be necessary to examine the connectors each time before making the connection, to be sure the center pin is centered.

It is not clear to me why plugging in the adapter disconnects the internal antenna. I know some devices have a seperate switch that detects when a plug is inserted. I'm thinking of such switches used with earphone plugs.

n6gn · Posted: Mon Mar 24, 2008 11:35 am Post subject: