Ok, I was going overboard but basically when you take into account the power output of a cell phone you find that its direct talk range will be much less than a cheap dollar store radio.

Does anyone know the FCC regulations on the max power output of a cell phone? Didn't mobile units (i.e. the old car mounted cell phones) have a higher power output and handheld cell phones?

I'm just asking since the assumption that has developed on this thread is that DirectTalk is broadcast at the usual cellular output. I have no idea, but it's possible that DirectTalk mode is higher power.

Someone with more knowledge, please correct me, but I recall reading that because of Nextel's origins as a mobile radio company (like taxi fleet dispatching) rather than a true telecom/cellular company, it's transmission system and iDen technology is actually more like mobile radio with cellular-like call handling than it is a true cellular service, like Sprint or Verizon. Maybe different FCC regs apply to Nextel phones?

That said, Nextel's claim of "up to six miles" seems satisfactory for short range use, especially compared to the "up to two miles" of FRS.

If I remember correctly, the earliest cell phones were closer to 3-5 watts. Current ones are somewhere between roughly .25 - .5 watts. The FCC generally limits SAR, rather than transmission power, because different frequencies are absorbed differently by the body. Perhaps cell phones have special rules but I would have no idea about that.

You can contrast that with handheld ham radios ("Handi-Talkies"), which can go up to 10 watts, but I wouldn't transmit at 10 watts next to my head unless my brain was feeling cold and needed some toasting.

By the way, it's not uncommon to hit repeaters that are several miles away on .5 watts VHF with a ham radio. (Note I didn't say it's reliable.) Of course, this is apples and oranges to what you're talking about because I'm referring to an analog FM transmission and you've said the Nextel is digital.

Thanks, Fitzoid.

Yeah, it's unclear what Nextel means by "digital". However, the press release also mentions "15 privacy codes," which sounds like CTCSS to me. I would think that if the transmissions were digitally encoded, something like "privacy codes" wouldn't be necessary.

Another part of phone power is size/sexiness. Small phones = small batteries = less power. In general, this works well. You simply add more towers so, on average, you are closer to a tower.

In order to make cell phones cheaper, the receivers are generally half-deaf. Cell towers throw out around 100 times the power of the cell phones themselves. So, while this works well for normal phone calls, it hurts cell-to-cell calls.

There other thing, as I've learned from other FRS/GMRS forums, is that output power is much less important than antenna height. Given that, is would not surprise me that relatively low power cell phones communicate fairly well with cell towers, which are typically positioned at strategic high-point towers in the area. Radio-to-radio reception would be MUCH MUCH worse unless the users are in line-of-sight, such as one of them on a high building or on top of a hill. In an urban area you'll be lucky to get more than a couple of blocks distance.

Heavy duty radio users (GMRS and hams) focus very heavily on antenna height, placement, and design as a first priority for direct transmission (not bouncing the signal). The power is secondary.

Yes, exactly right. Antennas and receiver sensitivity can make all the difference. There's a whole subgroup of hams who do QRP, which is low power, long distance communication, e.g., a thousand miles on a fraction of a watt, but those guys have some fancy radios... <img src="/images/graemlins/grin.gif" alt="" />

Yup. And the members of this forum can really appreciate the fancy case of THIS RADIO.

Nice. If I remember correctly from an old thread I just read a little while ago, if you ground that Altoids tin properly, you've just shielded that puppy from electromagnetic pulse as well! Sweet... <img src="/images/graemlins/smile.gif" alt="" />

If you're going to work CW, you can get by with an even simpler radio. That's a veritable ultra high tech beast compared to the ancient homebrew stuff people used to build.

Arney, that has ICs, so it should be toasted by an EMP. You'll have to move back to vacuum tubes to get something pulse-proof. That would be one hell of a cool Altoids tin, with tubes poking out the top. <img src="/images/graemlins/smile.gif" alt="" />