Hello,
I'd like to directly cable a handset to a nanoBTS and thought I could:
- put attenuators on the nanoBTS TX and RX ports - connect the other side of each attenuator to a resistive splitter/combiner that has 6dB loss - connect the combiner common port to the MS
Does this sound sensible and if so what size of attenuators might I want assuming MS and BTS were each set at 6dBm? I've seen figures for receiver sensitivity, but wasn't sure as to a "good" RF level to use with direct cabling!
I also have 10/20 dB directional couplers and circulators if they might find use in a better configuration.
Regards,
Andrew
Phew ! why do you need to do this at all ?
To avoid RF emission ? even using this method you will still leak out enough RF which you can easily use the MS over the air.
On Thu, Oct 25, 2012 at 11:21 PM, Andrew Back andrew@carrierdetect.comwrote:
Hello,
I'd like to directly cable a handset to a nanoBTS and thought I could:
- put attenuators on the nanoBTS TX and RX ports
- connect the other side of each attenuator to a resistive
splitter/combiner that has 6dB loss
- connect the combiner common port to the MS
Does this sound sensible and if so what size of attenuators might I want assuming MS and BTS were each set at 6dBm? I've seen figures for receiver sensitivity, but wasn't sure as to a "good" RF level to use with direct cabling!
I also have 10/20 dB directional couplers and circulators if they might find use in a better configuration.
Regards,
Andrew
-- Andrew Back http://carrierdetect.com
On 25 October 2012 19:01, Nik Pakar nikpakar@gmail.com wrote:
Phew ! why do you need to do this at all ?
Since the only BTS hardware I currently have access to is 1900MHz and thus cannot be licensed in the UK.
To avoid RF emission ? even using this method you will still leak out enough RF which you can easily use the MS over the air.
I see, but this would almost suggest that you need a development licence just to tune a bench signal generator to a frequency in spectrum such as used by GSM ...
Regards,
Andrew
Ok. understand your issue. But trying to do what you suggest wont help that much.
I think using maximum attenuation on BTS (3dBm power with 20dB attenuation) and also forcing MS to use lowest power, you will have lab coverage without interfering external world. It will hardly go out if your lab is a concrete or brick building.
On Thu, Oct 25, 2012 at 11:39 PM, Andrew Back andrew@carrierdetect.comwrote:
On 25 October 2012 19:01, Nik Pakar nikpakar@gmail.com wrote:
Phew ! why do you need to do this at all ?
Since the only BTS hardware I currently have access to is 1900MHz and thus cannot be licensed in the UK.
To avoid RF emission ? even using this method you will still leak out
enough
RF which you can easily use the MS over the air.
I see, but this would almost suggest that you need a development licence just to tune a bench signal generator to a frequency in spectrum such as used by GSM ...
Regards,
Andrew
-- Andrew Back http://carrierdetect.com
Does this sound sensible and if so what size of attenuators might I want assuming MS and BTS were each set at 6dBm? I've seen figures for receiver sensitivity, but wasn't sure as to a "good" RF level to use with direct cabling!
I also have 10/20 dB directional couplers and circulators if they might find use in a better configuration.
Yes it sounds perfectly good. Make sure you connect attenuators as close to the BTS and MS as possible to avoid as much leak as possible.
You should target something like - 60 dBm at the RX. So something like 90 dB attenuation or so. Make sure to use semi rigid cable because at that level of attenuation the cable leaks are non negligible :)
Cheers,
Sylvain
On 25 October 2012 19:47, Sylvain Munaut 246tnt@gmail.com wrote:
Does this sound sensible and if so what size of attenuators might I want assuming MS and BTS were each set at 6dBm? I've seen figures for receiver sensitivity, but wasn't sure as to a "good" RF level to use with direct cabling!
I also have 10/20 dB directional couplers and circulators if they might find use in a better configuration.
Yes it sounds perfectly good. Make sure you connect attenuators as close to the BTS and MS as possible to avoid as much leak as possible.
That is good to hear.
You should target something like - 60 dBm at the RX. So something like 90 dB attenuation or so.
Wouldn't 90 dB attenuation for -60 dBm at RX suggest a TX power of 30 dBm = 1 watt? Seems high and was thinking of closer 6 dBm at TX. But if I know to aim for -60 dBm at receive ...
Make sure to use semi rigid cable because at that level of attenuation the cable leaks are non negligible :)
Good advice, thanks!
Cheers,
Andrew
My BTS has a min xmit power of -1dbm. I couldn't find specs on max rcv input power for my particular device, but similar devices have specs in the -20 to -25dbm range. My test set is adjustable from -104 to -25. No need to attenuate all the way to -60. But if you can find specs for your receiver, it's better to use them than info from some guy on the Internet.
I've done this. My employer likes me to stay legal, so I looked up the FCC rules about unlicensed operation (I'm in the US), did the calculations, and determined that I could in fact keep the leakage below limits, and the input power to the HS and BTS receivers within proper range. I'm using the BTS at minimum power of course. I use a Minicircuits ZAPD-20-S+ power splitter, which has 30db isolation between the two ports, and a single 30db attenuator on the HS side. With my equipment I need a minimum of 24db attenuation between each transmitter and the opposite receiver. I did not check the leakage as I don't have a calibrated field strength meter but according to specs it should be ok. I've got the numbers if you're interested.
-
Andrew Back -
Jim Rees -
Nik Pakar -
Sylvain Munaut