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The Wrong Adapter
could fry your transmitter



Running your Handheld as a Mobile
Simple enough. Use an adapter that mates to the connector on your antenna. But now you find you can't hit the local repeaters. It must be a bad antenna, right?
Not necessarily.
Last week I connected my TD-9800 to my mobile antenna and realized that...
All Adapters are not Universal
The three connectors below all serve the same purpose, and that's to connect a handheld with an SMA-F to a BNC fitting. But not all connectors are compatible with all radios.

The critical concern is that center pin goes far enough into the radio's connector to make a positive contact.
The example below shows a TD-9800 / TR-7400 antenna. Nothing appears out of the ordinary, so let's try our three adapters.
The gold adapter only screws on by only one thread due to the ridge around the antenna connector. The antenna screwing below that ridge helps with the IP67 waterproof rating, but also prevent the adapter from screwing in.
The black connector below fits nicely below the ridge and the seats tightly against the locking ring, but yet still does not make the proper connection.
The two piece adapter works perfectly and makes a flawless connection. Is it waterproof? Probably not, but inside your car I would hope it wouldn't need to be.
Here's why
Fitting flush against the nut isn't the solution if the center pin doesn't make contact. The reason the first two do not fit is the recessed area around to the threads and the center pin on the antenna connector is below the top of the threads. This prevents the center pin from inserting completely.
Although the radio shown above is a TID TD9800 DMR, many other radios fall into the same category.
Never assume a good connection. Always verify with a wattmeter or SWR bridge that the connection is 100% solid. A bad connection to the antenna will damage the radio transmitter.
If this article saves one radio, it was worth my time to create it.

John 'Miklor'  K3NXU


Connector Link