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oxxyfx

Dummy Load

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Hello,

I would like to do some testing for range and the RSSI signal level with the 10mW, 100mW and 500mW Airwave transmitter modules, however I am not sure what to connect instead of the antenna not to burn down the transmitter.

I need to operate it few (5-10) minutes at the time without the antenna attached. However I have to connect something there wich will not behave like an aerial but it will hold the place of this so the unit does not burn down...

Any suggestions would be much appreciated.

Thx, Ox.

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if only you have filled out your location ?

we could find out the postage for sending a dummyload.

you must use a real 50 Ohm resistor special made for this frequency band,

and that can handle the 500mW max tx power you have.

I have several on stock, they are mounted inside make SMA plug,

and works up to 5Ghz and handle 1W.

it is IMPOSSIBLE to make one yourself for 2.4GHz,

but for 100Mhz or below it is easy, normal resistors can be used at low frequencys.

Also you need to know this:

when attaching a dummy load to the transmitter, the power say 500mW is not blown away as radio waved into the air, but wasted as heat,

with this SMA connector mounted directly on the transmitter,

now ALL power input = heat loss.

not as with antenna: powerinput - tx power = heat loss.

so it will get hotter, so check for air cooling if it is the 500mW or more modules you want to test for a long time..

another thing:

with a dummyload attached you will still have a range of a few meter,

you will see strange things: for example can a 10mW module have longer range than a 500mW module,

WHY ?? if it is more poorly shilded, or the supply lines or video input lines are not extra carefully shilded, they will work as antennas, giving you funny results.

The dummy loads I have are prof types, 10$ each + postage.

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Thank you Thomas. I am in Canada.

I figured you can explain this to me, but I didn't wanted to bother you with an E-mail, however I will send you now one with my address, shipping details and payment options.

I believe the board is properly shielded since you looked over the design and kind of approved it back in March.

I am planning to experiment with a 3 receiver diversity system, so I will need to move the transmitter around to see if it is properly switching, that's why I need the dummy load.

I have the 10, 100 and 500mW Airwave modules installed in the same PCB design -how lucky Airwave did not change the size and pin settings from 10 to 100 or 500.

I will E-mail you shortly with the address and payment options.

Thanks, Ox.

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Hello,

I would like to do some testing for range and the RSSI signal level with the 10mW, 100mW and 500mW Airwave transmitter modules, however I am not sure what to connect instead of the antenna not to burn down the transmitter.

I need to operate it few (5-10) minutes at the time without the antenna attached. However I have to connect something there wich will not behave like an aerial but it will hold the place of this so the unit does not burn down...

Any suggestions would be much appreciated.

Thx, Ox.

Just use a 5W CARBON NOT WIREWOUND resistor. Solder your connecting leads close to the body of the resistor and cut off the excess leads. Do make the connections as short as possible to minimize the inductive tuning that excess lead length will cause.

This will give you plenty of headroom for a 500mw, 600mw or 1W xmitter.

The value of the resistor should be the output impedance of the transmitter antenna. ~50ohm. Use a .5 or 1% tolerance component and you are good to go. IF it is a RESISTIVE load the output freq makes no difference as it is neutral.

Cost other than your time to assemble.....and not counting a matching SMA connector probably around 50 cents.

Curt

Edited by IndiQa

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Just use a 5W CARBON NOT WIREWOUND resistor.

I have tried this in the past with little luck. It may be good enough to do the testing required as no measurments are to be taken but Im sure it will be a poor match. At 2.4Ghz things become critical and it would not be any good for testing co-ax leads for example.

Terry

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I have tried this in the past with little luck. It may be good enough to do the testing required as no measurments are to be taken but Im sure it will be a poor match. At 2.4Ghz things become critical and it would not be any good for testing co-ax leads for example.

Terry

No he asked about an antenna dummy load. This is for testing an xmittr without effectively broadcasting a signal.

There is no "measurement" inherent in a SIMPLE dummy load. It is only a load to absorb rf. With a purely carbon resistive element i.e. No inductive component as in a wirewound unit, and using connections as short as possible to eliminate as much lead inductance the load will work fine. The "things" will be so small that they can be overlooked.

For testing a length of coax.

1. Why add a loss to the system with a hunk of lead in. And it will be a loss.

2. Any mismatch caused by the coax under test AND the insertion losses of whatever test gear is being used will greatly affect the ultimate signal matching results substantially more than any small inherent defects in the properly constructed dummy load.

I have a DL here which I use to check and maintain my xmittrs it will handle up to a KW.

If I had an SMA on the front of it instead of the 259 I could check the output of a 1w 2.4 unit with no problem....but WHY?

C.

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