[Imported] Antennas for bench test use (900 MHz & 450 MHz)


[Imported] Antennas for bench test use (900 MHz & 450 MHz)

>>Message imported from previous forum - Category:Trio Data Radios<<
User: joelw, originally posted: 2018-10-16 21:39:37 Id:33
This is a re-posting from the obsoleted (October 2018) "Schneider Electric Telemetry & SCADA" forum.


Quite commonly you might want to test your radios on the bench before taking them to the field. You don't really want to connect up the big yagi and omni antennas you'll be using, so how do you get some simple antennas to make things work just for now?_**


At 900 MHz it's helpful that the channels are shared by everybody. There are no license holders to possibly interfere with! All you need to do is find or make simple whip antennas and you'll be in good shape.

Note: You'll want to set your transmit power as low as possible, to avoid having the radios "shout" at each other. Radios a foot or two apart on the bench can be deafened by the normal transmit power levels used out in the field.

Control Microsystems does have some whip antennas with TNC connectors which will work for the KR900 and JR900 radios. These are part number 297001. If there are none available (they're special order), if you need antennas with SMA connectors for the KP or KI radios, or if you want to buy them more locally, you can talk to Hutton, Talley or Tessco who can supply them.

One popular model of antenna is the Radiall-Larsen dipole whip. For the TNC connector you'll want the SPDA17918, or for the SMA connector it will be the SPDA24918.

If you're in a hurry and can't wait for antennas to be delivered, you can make your own from some solid conductor insulated wire. (eg 20-22 gage) Cut a piece of wire about 7.5 cm long (3 inches) then strip about 0.5 cm of insulation from one end. (0.2")

If the wire is thick enough you can push it directly into the center pin socket in the RF connector. If it's loose then just double the tip of the wire back on itself.

Make sure while you're inserting the antenna that you don't short circuit the center pin to the shield or you might damage the radio!! Control Microsystems is NOT responsible for any damage caused this way.

In the 400-500 MHz licensed bands, you can buy pre-built whips as well, but they may come with TNC or other connectors. If so you'll also need to buy adapters to go to N. (eg TNC female to N male)

Or you can make your own whip antennas just like at 900 MHz. The center pin of an N connector is a bit bigger so you might need thicker wire. As the frequency is lower you'll need longer pieces of wire.

In the licensed band you might be programming your radio for anywhere between 400 and 500 MHz, so it's harder to give exact instructions for all frequencies. But here are two examples that will be about right in most cases.

Cut the following amount of insulated solid conductor wire. Strip about 0.5 cm or 0.2" and double it back to make it fat enough to stay in the center hole.

415 MHz -17 cm (6.7")
460 MHz - 16 cm (6.3")

One issue when running bench tests using licensed radios is that you may not yet own any frequencies to use for your tests. Even if you do, is the system currently in use? If so you may interfere with it when you run your tests! Or the legitimate user may interfere with YOU!

So when doing testing of licensed radios, to avoid interference issues, we recommend either of two solutions.

1) Buy dummy loads for all radios. (eg Bird 2-T-MN 2 watt) The radios will only let out a very small amount of RF though, so you'll need to stack them literally one on top of another.

2) Buy 20 dB or greater attenuators for all radios (eg Bird 5-A-MFN-20) and run as little power as possible. (eg 15 dBm) Put whip antennas on the attenuators. Now you can place them around the room. They'll still talk fine but will have much fewer problems.