SWR Help – Mobile 2 Meter

[Jamey Finchum]

Ok, I need some help. I’ve installed a 2m/70cm mobile antenna on my car for my Icom IC-7100. The reading on the antenna analyzer reads a maximum of 1:1.2 SWR across the band.

Once the antenna is plugged into the radio I get a very high SWR reading on the radio. I’m stumped as to what it could be.

Any thoughts?

73,

Jamey, AC1DC

[Hamilton]

Hello Jamey,

There are two differences in the measurements.

The one that I would track first is power. The analyzer is <10mW, the 7100 is watts. If there is a near short such as a stray ground braid wire or a insulator O ring that is off center it may cause a problem at higher power.

Try reducing the 7100’s power and remeasure. At minimum power the SWR reading may be off a little, that isn’t important for the test.

The second item is the 7100 is grounded to the vehicle, I doubt the analyzer was. The antenna and cable as a system may be 1.2:1 but once the cable end is grounded at the radio it may be different.

Try touching the connector at the analyzer to ground and observe the SWR. If it changes significantly you found the problem.

I can think of a couple of other possible causes but they are a stretch.

Let me know how it goes.

[Author]

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