Antenna for cordless phone
in [Design]
|
From: Paul Keinanen on 18 May 2010 03:17 On Mon, 17 May 2010 14:33:44 -0400, "tm" <noone(a)msc.com> wrote: > >"D Yuniskis" <not.going.to.be(a)seen.com> wrote in message >news:hss1ak$m7j$2(a)speranza.aioe.org... >> Hi TOm, >> >> tm wrote: >>> Move the base unit to as high a position as possible, maybe into your >>> attic if you have one. Good suggestion. The losses for a TwistedPair (TP) cables is generally lower than the losses for VHF/UHF signals for short distances. >> >> No attics here. :-/ I was hoping to run *an* antenna >> (on a length of coax) from the base up to a "high(er) spot". >> Nervous about the roof due to lightning, etc. > >Maybe you could put the base unit in a weather proof container on the >roof? At least as a test. > >The mere fact of getting the antenna outside should be a help. You >need to watch running coax as it will have a loss at 900 MHz. Use as >large a cable as you can find connectors for and keep the run short, >say 10 feet or so. RG-213 is a reasonable cable for such low frequencies. >The antenna you linked to will have some gain and that will help. Most likely, you do not want antenna directivity ("gain"), if the other stations are at different directions.
From: John on 18 May 2010 09:43 On Mon, 17 May 2010 13:43:44 -0700 (PDT), mpm <mpmillard(a)aol.com> wrote: >On May 17, 11:52�am, John <Y...(a)you.com> wrote: >> On Sun, 16 May 2010 10:28:24 -0700, D Yuniskis >> >> >> >> >> >> <not.going.to...(a)seen.com> wrote: >> >Hi, >> >> >Sometimes (rarely), on my "evening sabbatical", I carry >> >a cordless phone (NOT a cell phone) with me. �This has >> >sufficient range to cover almost the entire "development" >> >(e.g., I can get about half a mile, as the crow flies). >> >> >*But*, there is one section (0.52 miles? �:> ) where I >> >lose reception. >> >> >I've toyed with the idea of adding an external antenna to >> >the base unit (which currently just sits on a countertop) >> >to try to improve on that. >> >> >I rescued a "dual band" antenna kit (AllTel) for a cell phone. >> >But, I suspect these operate on a different frequency than >> >my "cordless" (902-928MHz)? �(sorry, I know *nothing* about >> >cell phones -- thankfully! �:> ) >> >> Contrary to the popular believe antennae do not increase the >> transmitting power. They change the transmitting power from some >> directions into other directions. >> You probably are not interested in sending signal to the moon so >> rather then wasting that signal change it to the horizontal plane. >> First you must you must establish the horizontal area that you want to >> cover and if your transmitter is at the end of the terrain you may >> design a small Yagi like the type used to receive TV. >> You can design an antenna that will give you a pattern like a fig. of >> an heart, a figure of eight or a very directional antenna. The >> directionality will depend on the number of elements. >> Ideally you build 2 antennae of the same type and use one for one unit >> and the other for the other unit. >> Coupling to the base unit is another problem. Not easy. >> Describe, please the area you want to cover if you want to make a >> project out of it. I can help. >> >> John- Hide quoted text - You seem to be obsessed with the legality of installing a little antenna that radiates less than 1 W . If the law hasn't change we are allowed to transmit using any frequency , provide the power is less than a certain value. If you interfere with any service and some one complains, you may be asked to change the operating conditions. Don I repeat my last suggestion The best is probably a vertical whip like the one you show, designed to operating at your frequency. The standard impedance of an antennae designed to be connected to a cable have usually an operating impedance of 50 Ohms at that frequency. Make the cable (the one recommended by the antenna manufacturer) as short as possible and if practical move the main unit closer to the antenna. You may find a reasonable improvement just by moving the antenna out of the building Regards John >> >> - Show quoted text - > >Here in the US, it's "antenna" and "antennas". >You'll find antennae on bugs and cockroaches. :) > >Sorry, that's just a pet peeve. Telecom attorneys make the same >mistake all the time! > >Also, if in the US, FCC rules prohibit you from monkeying around with >the antennas. >Legally speaking, if in the US, you'll just have to live with it, or >select an alternate technology / device. > >-mpm
From: mpm on 18 May 2010 18:40 On May 18, 8:43 am, John <Y...(a)you.com> wrote: > On Mon, 17 May 2010 13:43:44 -0700 (PDT), mpm <mpmill...(a)aol.com> > wrote: > > > > > > >On May 17, 11:52 am, John <Y...(a)you.com> wrote: > >> On Sun, 16 May 2010 10:28:24 -0700, D Yuniskis > > >> <not.going.to...(a)seen.com> wrote: > >> >Hi, > > >> >Sometimes (rarely), on my "evening sabbatical", I carry > >> >a cordless phone (NOT a cell phone) with me. This has > >> >sufficient range to cover almost the entire "development" > >> >(e.g., I can get about half a mile, as the crow flies). > > >> >*But*, there is one section (0.52 miles? :> ) where I > >> >lose reception. > > >> >I've toyed with the idea of adding an external antenna to > >> >the base unit (which currently just sits on a countertop) > >> >to try to improve on that. > > >> >I rescued a "dual band" antenna kit (AllTel) for a cell phone. > >> >But, I suspect these operate on a different frequency than > >> >my "cordless" (902-928MHz)? (sorry, I know *nothing* about > >> >cell phones -- thankfully! :> ) > > >> Contrary to the popular believe antennae do not increase the > >> transmitting power. They change the transmitting power from some > >> directions into other directions. > >> You probably are not interested in sending signal to the moon so > >> rather then wasting that signal change it to the horizontal plane. > >> First you must you must establish the horizontal area that you want to > >> cover and if your transmitter is at the end of the terrain you may > >> design a small Yagi like the type used to receive TV. > >> You can design an antenna that will give you a pattern like a fig. of > >> an heart, a figure of eight or a very directional antenna. The > >> directionality will depend on the number of elements. > >> Ideally you build 2 antennae of the same type and use one for one unit > >> and the other for the other unit. > >> Coupling to the base unit is another problem. Not easy. > >> Describe, please the area you want to cover if you want to make a > >> project out of it. I can help. > > >> John- Hide quoted text - > > You seem to be obsessed with the legality of installing a little > antenna that radiates less than 1 W . If the law hasn't change we are > allowed to transmit using any frequency , provide the power is less > than a certain value. If you interfere with any service and some one > complains, you may be asked to change the operating conditions. > > Don > I repeat my last suggestion > The best is probably a vertical whip like the one you show, designed > to operating at your frequency. > The standard impedance of an antennae designed to be connected to a > cable have usually an operating impedance of 50 Ohms at that > frequency. > Make the cable (the one recommended by the antenna manufacturer) as > short as possible and if practical move the main unit closer to the > antenna. > You may find a reasonable improvement just by moving the antenna out > of the building > Regards > > John > > > > > > >> - Show quoted text - > > >Here in the US, it's "antenna" and "antennas". > >You'll find antennae on bugs and cockroaches. :) > > >Sorry, that's just a pet peeve. Telecom attorneys make the same > >mistake all the time! > > >Also, if in the US, FCC rules prohibit you from monkeying around with > >the antennas. > >Legally speaking, if in the US, you'll just have to live with it, or > >select an alternate technology / device. > > >-mpm- Hide quoted text - > > - Show quoted text -- Hide quoted text - > > - Show quoted text - Not obsessed. Just alerting the OP to federal law. :) If he chooses to break the law, those same laws provide for fines and arrest of the equipment (in rem arrest), and the FCC can also refer cases to the Justice Department for further prosecution. Monetary fines for something like this can range from a few thousand, to ten thousand dollars or more. See generally, FCC Rules 47CFR1.80 Those are the facts. Now, does the FCC catch a lot of folks hacking illegal antennas into their cordless phones? No. But you might be suprised at just how many violations are issued each year by the FCC's Enforcement Division. I have personally been on a couple equipment witch hunts (for interference) with the Miami and Denver field agents. The outcomes are rarely pretty in the cases which I'm typically involved in (the high profile ones). The average homeowner can expect a Citation (no money fine) for a first offense, but things can get nasty if they're uncorporative, etc..., or if the Agent (for whatever reason) feels justified in pursing the matter more aggressively. Plus, in my former career (a post you may have missed?) it should be painfully obvious why I recoil when I hear that people want to hack into their consumer electonics. You would not believe the headaches this can cause for licensed radio services!! But to your facts, For most unlicened devices like cordless phone and the like, they'll be registered under Part-15 rules. (47CFR15) Those rules will provide field strength limits (not transmitter power output restrictions). Therefore, antennas matter greatly! The allowable field varies by frequency, according to a chart in FCC Rules part 15.209 Before leaving this topic, you should be aware that just because you might feel Part-15 devices are low power, that DOES NOT mean they are incapable of causing harmful interference. Far from it. For example, did you know a typical CDMA or GSM cell phone (operating at its lower power output of ~ -50dBm) actually radiates LESS power than the maximum permissible under Part-15 Rules for unlicensed devices? In other words, something that's unlicensed (and lower power) actually puts out MORE power than your cell phone -- which is very much a licensed service (FCC Part 22, 24 or 27) And note also that Part-15 Low Power does not restrict operation in the Cellular / PCS bands. Think about that next time you drop a call. It may just be your neighbor hacked in an antenna on his cordless phone (or garage door opener, or blender, or TV or god knows what!) This is one of hundreds of examples I could give to you. So yeah, you might say I'm "obsessed" -- but I am absolutely correct, and this history books are filled with examples of horrendous interference cause by well-intentioned folks just like the OP.!! Specific to this exact situation, here is the precise rule the OP would be violating: Sec. 15.203 Antenna requirement. 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. The use of a permanently attached antenna or of an antenna that uses a unique coupling to the intentional radiator shall be considered sufficient to comply with the provisions of this section. The manufacturer may design the unit so that a broken antenna can be replaced by the user, but the use of a standard antenna jack or electrical connector is prohibited. This requirement does not apply to carrier current devices or to devices operated under the provisions of Sec. 15.211, Sec. 15.213, Sec. 15.217, Sec. 15.219, or Sec. 15.221. Further, this requirement does not apply to intentional radiators that must be professionally installed, such as perimeter protection systems and some field disturbance sensors, or to other intentional radiators which, in accordance with Sec. 15.31(d), must be measured at the installation site. However, the installer shall be responsible for ensuring that the proper antenna is employed so that the limits in this part are not exceeded. Enjoy. -mpm
From: D Yuniskis on 18 May 2010 19:05 Hi John, John wrote: [attributions elided] >>>> Sometimes (rarely), on my "evening sabbatical", I carry >>>> a cordless phone (NOT a cell phone) with me. This has >>>> sufficient range to cover almost the entire "development" >>>> (e.g., I can get about half a mile, as the crow flies). >>>> >>>> I rescued a "dual band" antenna kit (AllTel) for a cell phone. >>>> But, I suspect these operate on a different frequency than >>>> my "cordless" (902-928MHz)? (sorry, I know *nothing* about >>>> cell phones -- thankfully! :> ) >> >>> Coupling to the base unit is another problem. Not easy. >>> Describe, please the area you want to cover if you want to make a >>> project out of it. I can help. >> The neighborhood is roughly: >> >> (view in fixed width font) >> >> +-----+ >> | | >> | | >> | | >> | | >> | | >> | | >> | +------------+ >> | | >> | X | >> | | >> +------------------+ >> >> This is *roughly* to scale. The "base" is located at X. >> The area is residential in nature so there are houses >> filling the region. The top of the illustration is >> at a higher elevation than the bottom -- maybe 60 ft? >> >> There are no commercial establishments in the area. >> Most of the construction is masonary. No dense >> foliage. >> >> The problem area (reception) is at the upper left (and >> the bottom right) -- no doubt as there are the most >> "obstructions" along the sight line. >> >> I'll drag out a GPS and get some actual measurements, >> if necessary. I've not done an exhaustive survey >> of where things work/don't work. Though I have found >> the upper left corner to be a problem area as I am >> often passing through there when I lose signal. >> >> The antenna that I was *questioning* will (physically) >> mate to a Linksys wireless router (though not intended >> to do so, "just coincidence" -- sorry, I don't deal with >> RF stuff so i can't tell you what sort of connectors >> they are -- I don't think they will mate with the >> base unit on the phone :<) >> >> This is similar to what the manufacturer suggests for >> an external antenna: >> >> http://www.sn900.com/graphic/extant20.jpg >> >> Any pointers appreciated! (RF is BFM!) > > Don > Since you are interested on increasing the signal at 2 areas that are > at opposite sides but not in line, a directional antenna is not a > solution. Understood. I believe you can get more *gain* from a directional antenna? > The best is probably a vertical whip like the one you show, designed > to operating at your frequency. OK, ejicate me on antenna geometries. What *physical* characteristics of an antenna correspond to "whatever" electrical characteristics? E.g., what difference (?) do the little radial spikes make to the antenna's behavior? Why the little coil instead of just lengthening the antenna? etc. (sorry, my "pure EE" coursework is *so* far behind me that I have forgotten more of it than I ever *knew*!) For example, the "dual band cell phone" antenna that I have looks similar to the one I referenced (URL) above. But, *without* the radial spokes and *with* a cylindrical "blob" up near the top of the whip. (I assume the grey/aluminum stuff beneath the "spokes" is part of a mast assembly and not germane to the actual antenna's design?) From what I've stumbled across, the "dual bands" are somewhere in the high 800's and again in the 1900MHz region. Is this governed solely by the physical geometry of the antenna? I.e., if I "snip a bit off", can something that works in the "high 800's" be coerced to perform adequately in the "low 900's" band? Or, are other magic incantations required? (If push comes to shove, i can live *without* the added coverage area for my cordless phone -- or buy the *right* antenna. Instead, I am trying to learn something, here... E.g., I will eventually like to get rid of this and add broader area coverage for my wifi... learn now, do later!) > The standard impedance of an antennae designed to be connected to a > cable have usually an operating impedance of 50 Ohms at that > frequency. This is important because the impedance changes with the > frequency and for optimum power transfer the antenna, the cable and > the output stage of your transmitter must be of similar impedance at > that operating frequency. Yes. Match the output impedance of the source to the load. *That* much I remember! :> > The cable usually sold for TV is 75 Ohms and you want 50 Ohms if the > antenna was design for that impedance at your operating frequency. I can get damn near any cable I might need. The "dual band" antenna has a length of (where's my magnifying glass?) coax -- seems to be labeled "NFC 200 COAXIAL CABLE" but that is pure speculation as only the bottom 50% of the print is legible (small diameter cable so the printwheel probably didn't maintain contact with it). E.g., I know I have RG6, 9, 58, 59 out in the garage. Probably some other scraps, too. > One of the bands used on Cell phones is on the 900 MH band make sure > the one you get is for that band and not for the 1800 band. The antenna is "dual band". It is intended for a cell phone. My problem is my *cordless* phone (NOT a cell phone) operates 900+ (I think 906-926 or something like that... I think I posted it here somewhere) so I am questioning "how close is close enough"? > Propagation of UHF and higher frequencies usually required line of > site but are easly reflected by the obstacles they can't penetrate. > Installing the antenna outside as high as possible is essential for a > reliable link. I think that is the problem. Consider the diagram, again. A line from the X to the upper left corner passes through lots of "stuff" (houses). And, since it is uphill, I may even be in the shadow of the *ground* between that corner and the base (i.e., the ground may not be monotonic increase in elevation) > The solution to your problem adopted by a communication company, would > be what I have suggested and if that would' work they would install > repeaters. Repeaters are not an option. :> I guess I should: - drag the base up to the roof some evening (go snow blind up there during the day!). I already have a phone line up there (<grin> Though I didn't expect to use it thusly!) - figure out *where* (exactly) the dead spots are If the dead spots remain (or, don't significantly improve), then there's no practical solution. return (0). - repeat this with the base back inside to have limits on the types of performance I can expect -- best + worst. - then experiment with different antenna types and see how close to "best" and "worst" I end up? - then, see how far *into* the house i can pull the antenna while still maintaining the coverage. (ideally, I would like to locate it "in* the ceiling so it isn't exposed to weather and is less of a lightning bug) Is there any harm in trying the "cell phone" antenna? Thx, --don
From: D Yuniskis on 18 May 2010 19:09
Hi Joerg, Joerg wrote: >> I'll drag out a GPS and get some actual measurements, >> if necessary. I've not done an exhaustive survey >> of where things work/don't work. Though I have found >> the upper left corner to be a problem area as I am >> often passing through there when I lose signal. >> >> The antenna that I was *questioning* will (physically) >> mate to a Linksys wireless router (though not intended >> to do so, "just coincidence" -- sorry, I don't deal with >> RF stuff so i can't tell you what sort of connectors >> they are -- I don't think they will mate with the >> base unit on the phone :<) > > Cordless phone on a Linksys router? > > <scratching head> No, I was trying to describe the type of connector on the antenna that I am "questioning" -- without KNOWING the proper names for the various RF plumbing! :> I figured most folks have seen a linksys router (with removable antennae) so could relate to that example. The phone's base unit is something like a "reverse TNC" (??) so I can't mate the antenna to the base unit "as is". |