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This is great. I met briefly with a company developing software radio products that led me to believe such devices are illegal or require special licensing. I

This is great. I met briefly with a company developing software radio products that led me to believe such devices are illegal or require special licensing. Is my impression wrong or has this changed recently? Second, can this do GSM, receive at least? Frequency band works, but maybe it doesn't have the bandwidth?

benjamincburns 13y ago
It's been a while since I've looked into this, but last I knew it was legal to listen to any band you want, but illegal to transmit on any band for which you don't posses the required license, if any. Then there's all kinds of rules about transmit power. For instance, last I knew you could transmit unlicensed on the public FM and AM radio bands so long as you're under some minimal threshold - I think it was 1W.
- VLM 13y ago
  "I think it was 1W." LOL no, you know .gov they make it as complicated as possible. If I recall the AM is DC input power limited and the FM limits are some weird field strength which is non-trivial to measure. Google for 47 CFR 15 and you're looking for part C 15.221 and .239 probably. You can read this stuff for free at gpo.gov. There are about a zillion other part 15 bands you can legally operate under if you're willing to bother figuring out how. If you're smart enough to figure out how to legally operate part 15, you're certainly smart enough to get a license to operate part 97, which doesn't have even a fraction of those goofy restrictions and is the original techie social network.
yyao 13y ago
The question of receiving signals is more a philosophical one of ethics. The question of broadcasting signals is one governed by law. In North America, you can't broadcast on a part of the spectrum that you don't have a licence for. Wifi devices, 900MHz phones and CB radios and such operate in a frequency band which has special provisions for such use. I looked at their product specification and there isn't any mention of phase noise of the local oscillator. It turns out that a critical requirement for tuning into GSM signals is the phase noise or jitter of the local oscillator. Chances are, they are using a pretty good cystal, but probably not good enough for a GSM base station. There is a good reason why GSM base stations all run off rubidium standards. In fact, you can grab 10MHz rubidium standards for a very (relatively) cheap price off eBay. They are all from decommissioned cell towers. There is a possibility that you can still tune into a GSM signal with a substandard local oscillator. However, this behaviour would be intermittent.

benjamincburns 13y ago

It's been a while since I've looked into this, but last I knew it was legal to listen to any band you want, but illegal to transmit on any band for which you don't posses the required license, if any. Then there's all kinds of rules about transmit power. For instance, last I knew you could transmit unlicensed on the public FM and AM radio bands so long as you're under some minimal threshold - I think it was 1W.

VLM 13y ago
"I think it was 1W." LOL no, you know .gov they make it as complicated as possible. If I recall the AM is DC input power limited and the FM limits are some weird field strength which is non-trivial to measure. Google for 47 CFR 15 and you're looking for part C 15.221 and .239 probably. You can read this stuff for free at gpo.gov. There are about a zillion other part 15 bands you can legally operate under if you're willing to bother figuring out how. If you're smart enough to figure out how to legally operate part 15, you're certainly smart enough to get a license to operate part 97, which doesn't have even a fraction of those goofy restrictions and is the original techie social network.

yyao 13y ago

The question of receiving signals is more a philosophical one of ethics. The question of broadcasting signals is one governed by law. In North America, you can't broadcast on a part of the spectrum that you don't have a licence for. Wifi devices, 900MHz phones and CB radios and such operate in a frequency band which has special provisions for such use. I looked at their product specification and there isn't any mention of phase noise of the local oscillator. It turns out that a critical requirement for tuning into GSM signals is the phase noise or jitter of the local oscillator. Chances are, they are using a pretty good cystal, but probably not good enough for a GSM base station. There is a good reason why GSM base stations all run off rubidium standards. In fact, you can grab 10MHz rubidium standards for a very (relatively) cheap price off eBay. They are all from decommissioned cell towers. There is a possibility that you can still tune into a GSM signal with a substandard local oscillator. However, this behaviour would be intermittent.