Outdoor antennas for cordless phones?

Question

hi i have heard some cordless phones reaching a whopping 5 miles. is there instructions on how to build your own long range cordless phone perhaps building an antenna to place on the outside of your home? how would you connect it to your existing phone? i've read 900mhz is the best but i think i'll try it on my old 5.8ghz phone i have; any ideas on how to go about doing it yourself?

Answer 1

First, I must mention the link that another answerer has posted referring to a site that sells "long range cordless phones" is selling equipment that are ILLEGAL to use, especially in developed countries that easily have the means to fine you $10,000 and/or throw you in jail for 6 months.  They operate on 230-450 MHz, 135-137.5 MHz, 235-237.5 MHz which are allocated to civilian and MILITARY aircraft, ham radio, public safety such as POLICE, amongst other things all of which your phone calls would be interfering with.  

As for the original question, adding an external antenna to a 900MHz phone is also illegal in the US.  47 CFR Section 15.243 (d) of the FCC rules state, "Any antenna

that may be used with the device shall be permanently attached thereto and shall not be readily modifiable

by the user."  This applies to licence free 900MHz phones.  Being that ham radio is the primary user of the frequencies allocated to 900MHz phones it is not much of a surprise.  In addition, unlicenced 900MHz devices must accept all interference from licenced users and must also cease operation if interference is experienced by licenced users of those frequencies, external antenna or not.  

Furthermore, section 15.203 states, "An intentional radiator shall be designed to ensure that no antenna other than that furnished by the responsible party shall be used with the device."  Unlicenced 2.4GHz and 5.8GHz devices are allowed directional fixed point to point antennas like used in wireless lan but a cordless handset is hardly fixed.  It looks like PCS rules apply to DECT handsets since it's in the same band and none of the special supplements for DECT cordless phones in subpart D mention anything about an antenna so we might see DECT phones with external antennas in the future; who knows.  

That being said... aside from the legal implications it would be difficult to set up an external antenna on a 5.8GHz phone.  Coax has a hard time carrying high frequencies.  RG-6A (similar to your standard cable TV cable) has a loss of 14.6dB at a length of only 50 feet at 5.8GHz!  What does that mean?  If you were to transmit 100 watts into that cable, only 3 watts would be supplied to the antenna at the other end.  You'd lose 97% of the signal, receive and transmit.  2.4GHz?  8.35dB loss at 50 feet for over 85% loss of signal.  900MHz is 4.66dB for 66% loss at 50 feet.  Using some super awesome cable (like LMR-600) you could get that down to 25%.  Fact of the matter is, unless you are looking for coverage in one direction, you're going to have a hard time finding an antenna with enough gain to overcome the loss garnered from a coax run.  You'd be better off putting the base in a waterproof tupperware container on top of your roof or a mast and running the power and telephone cables back inside.  You could charge your handset with extra charging cradles.  Put the base on a UPS so that you don't have to reassociate the base and handset when the power goes out.  Then, if you live in the middle of nowhere (meaning no one else around using the same frequencies and no electrical noise, intermod interference, etc), on top of a hill with no trees or other obstructions you MIGHT get your whopping 5 miles.