Looking for Nor UHF Dummy load connector

[Hicham M]

Hello,

I'm trying to test a GSM module with a dummy load

I found 2 dummy load with different connector type : N and UHF, my GSM has a SMB Coaxial connector, here as the links with photos

for dummy load with N connector
**broken link removed**

for dummy load with UHF connector
**broken link removed**

and for the GSm SMB Coaxial connector
http://uk.farnell.com/amphenol/fa1-ncrp-pcb-10/plug-fakra-c-r-a-pcb/dp/1718673


I'm trying to find the connector /adapter that i can use betweenthe the SMB Coaxial connector and N or UHF connector, can anyone help me choosing the right one ?

I also have the antenna with the right connector that fits the SGM connector, Can I cut the antenna and add an adapter so i can connect it with the dummy load ? cause I should use the dummy load with a short coaxial cable.

 

[FvM]

Non of the said dummy loads is specified for GSM frequencies, just read the catalog data.

A GSM module has maximum 2 W pulse power with respective duty cycle and can be well used with a standard 1 or 2W SMA terminator or attenuator. No need for higher power dummy loads.


In any case, you can use two coaxial connectors and a piece of 50 ohms cable. SMB to SMA adaptors should be available, too.

 

[Hicham M]

Non of the said dummy loads is specified for GSM frequencies, just read the catalog data.

A GSM module has maximum 2 W pulse power with respective duty cycle and can be well used with a standard 1 or 2W SMA terminator or attenuator. No need for higher power dummy loads.


In any case, you can use two coaxial connectors and a piece of 50 ohms cable. SMB to SMA adaptors should be available, too.

Thank you for the clarification, I noticed that the dummy load goes up to 500Mhz yet the 0.5W SMA attenuator goes even higher up to 6GB and i only need 1.9Ghz .

The module is a Telit HE863 that has GSM/GPRS/EDGE communication. and i want to cut the network using what people suggested a dummy load. Would SMA attenuator do the same job ? from it's name i believe it does attenuate the signal !

 

[FvM]

Depends on what you want to achieve. Often you'll want to monitor the transmitter output signal with a spectrum analyzer or power meter. Then an attenuator will be used instead of a termination.

A GSM module terminated without antenna connection won't register to the network and not activate the transmitter, unless it's provided with a special test mode (and you know how to control it).

 

[Hicham M]

Depends on what you want to achieve. Often you'll want to monitor the transmitter output signal with a spectrum analyzer or power meter. Then an attenuator will be used instead of a termination.

A GSM module terminated without antenna connection won't register to the network and not activate the transmitter, unless it's provided with a special test mode (and you know how to control it).

The module i'm using can connect and register to a network and send data to a server without an antenna, the idea here is to simulate a total absence of network. and i can monitor that in debugging mode through a microcontrolleur to PC (things i'm good at ).

So far the easier way simulate an absence of network is bu using the famous dummy load. would that work ?

 

[FvM]

"register to a network and send data to a server without an antenna" can mean a lot. Either the open connector is still working as an antenna, or it's RF leakage of the module ("cabinet radiation"). A dummy load is not necessary suffcient to block the unwanted residual transmission, but I would try it. Just a cheap 2 GHz SMA termination and an SMA to SMB adaptor.

Otherwise shielding of the RF module might be necessary, or you are making your tests at a place with less GSM field strength, e.g. a cellar. That's working for me, also without a dummy load.

 

[Hicham M]

"register to a network and send data to a server without an antenna" can mean a lot. Either the open connector is still working as an antenna, or it's RF leakage of the module ("cabinet radiation"). A dummy load is not necessary suffcient to block the unwanted residual transmission, but I would try it. Just a cheap 2 GHz SMA termination and an SMA to SMB adaptor.

Otherwise shielding of the RF module might be necessary, or you are making your tests at a place with less GSM field strength, e.g. a cellar. That's working for me, also without a dummy load.

I think I will go for SMA terminator, this way i'll be sure that there i block everything.

i'm thinking to get a shielded box, as a last solution (too expensive), and going to a place where there is not GSM is little bit tricky where i work

Thank you for the advice, i'll let you know how things goes once i get the SMA terminator

Thank u again

 

[Hicham M]

"register to a network and send data to a server without an antenna" can mean a lot. Either the open connector is still working as an antenna, or it's RF leakage of the module ("cabinet radiation"). A dummy load is not necessary suffcient to block the unwanted residual transmission, but I would try it. Just a cheap 2 GHz SMA termination and an SMA to SMB adaptor.

Otherwise shielding of the RF module might be necessary, or you are making your tests at a place with less GSM field strength, e.g. a cellar. That's working for me, also without a dummy load.

I finally got the SMA Terminator and the SMA to SMB adaptor, I attached them to the module but unfortunately it didn't block the network.
yet when i request signal quality the bit error changed to 99 and the rssi didn't change (between 11 to 15 )

here is the meanings of each value
<rssi>- received signal strength indication
0 - (-113) dBm or less
1 - (-111) dBm
2..30 - (-109)dBm..(-53)dBm / 2 dBm per step
31 - (-51)dBm or greater
99 - not known or not detectable
<ber>- bit error rate (in percent)
0 - less than 0.2%
1 - 0.2% to 0.4%
2 - 0.4% to 0.8%
3 - 0.8% to 1.6%
4 - 1.6% to 3.2%
5 - 3.2% to 6.4%
6 - 6.4% to 12.8%
7 - more than 12.8%
99 - not known or not detectable

I also notice that the SMA terminator that i have a power of 1W and my device goes up to 2w, is this why the SMA terminator couldn't block the network ?


Any ideas guys ?

 

[FvM]

I also notice that the SMA terminator that i have a power of 1W and my device goes up to 2w, is this why the SMA terminator couldn't block the network ?

Absolutely not. GSM devices don't start to send before the receive a base station signal. And 2 W is peak power, average power is much lower.

The problem is obviously that your module to SMB attachment, or the module itself has insufficient shielding. A shielded test box seems to be necessary. There's a certain chance that external shielding and/or a RF absorber arround the antenna interface might help.