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Need to directly connect two phones via 1 pair

Hi All

I have a situation where I have Location A and Location B. Both locations are outside and are about 500m away from each other.

We have a requirement to have a phone at each location which is connected directly to the other location via a dedicated Pair.

Previously we had old phones with big batteries which would last 6 months or so but these phones are broken now.

Can anybody reccommend a replacement for us? I have scoured the web and connot find anything suitable. They will be outside but will be protected and dont need to nescessarily have number pads or anything. All we want is to pick up the phones at either side and be able to talk to the other side.

Any reccommendations/ideas greatly apreciated.

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darran_d
Asked:
darran_d
3 Solutions
 
cybervzhn_techCommented:
I would search for sound powered phones.  Sound powered telephones are used in commercial or industrial applications.  They are typically used in emergencies or when no power is available in commercial locations.  Some examples are:

ships/naval vessels, airports, fire and police rescue crews, public utilities, schools, vaults, refrigeration plants, civil defense, bridge installations, ski slopes, oil fields, parks and forest, railroads, salvage yards, sporting arenas, shipyards, diving projects, mines, and geophysical operations where power is not available.

Typically the range is over 1 mile.

The cheapest solution is easily military surplus or used commercial equipment.

If you can find some in military surplus or online, a US military TA-1 field phone is voice powered and has a max range of 3.7 miles.  It has a hand powered crank to ring the phone on the other end of the 2 wires.  Models still used sometimes by the US military are TA-312 and TA-838 analog field phones.

Some more recent manufacturers or suppliers of battery/sound powered commercial phones:

Dynalec Corporation - Sodus, NY
Sound Powered Communications Corp. - Trenton, NJ
Comtrol Corp. - Irwin, PA
Telcoa Corp. - Meriden, CT

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Tiras25Commented:
A couple of tin cans and 500m of string.  Of course, if dedicated pair wiring is required use that instead of string.

The issue..... is signaling. Directly connecting to telephone instruments with the correct voltage is simple.

Signaling when someone want to communicate via the line is another matter. Signaling presents another matter, as this is where complications will arise due to the design of modern telephones.

If you're going to need a walkie talkie or intercom to signal the request to use the phone, it's easier to use the intercom instead of the phone.

Why don't you post a bit about how this line is envisioned by you the staff. How do you envision this working, and perhaps I can then provide you with recommendations regarding signaling
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cybervzhn_techCommented:
The solution I mention does include signaling and doesn't require the wires to be powered, just like darran_d mentioned, a dedicated pair of wires.

Sound powered phones are not like regular telephones.  
http://en.wikipedia.org/wiki/Sound-powered_telephone

Regular telephones require -48 volts of DC for audio and up to 90 volts of 20 Hz AC superimposed for ring voltage.  Sound powered phones and closed loop intercoms operate on different principles.  Read the prior post again, the US Military TA-1 field phone has a max distance of 3.7 Miles using nothing other than two wires, 2 phones, and your voice (well, and your thumb to press the lever to alert the person on the other end to pick up).  If the person on the other end misses the call there is a visual indicator that a call was missed so they know to return the call.

That easily covers 500m with no batteries to worry about.  Many of the sound powered phones have a lever or hand crank for signaling or ring voltage.  The bonus is that the military phones work with regular phone lines as well as just two unpowered wires.

I saw the older surplus military phone TA-1 on ebay for $21 USD.  The newer ones cost more but have the same capabilities plus more and do have batteries but don't need them for 500m.  They still cost less than the commercial battery or voice powered versions and will last forever.

Just my .02...
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kode99Commented:
I think the voice powered phones are really good option.

You could also use a line simulator device,  here's an example

http://www.vikingelectronics.com/products/view_product.php?pid=38

With a unit like this you can connect two standard phones at distances up to a couple of miles.  It basically looks like an active phone line and can use any standard phone.  When the phone is picked up it automatically rings the other connected phone.

The Viking unit I linked is around $120 cost.  Obviously it does require power but only for the unit and it could go anywhere along the lines.  So if you have power anywhere it could be installed at that point on the line.  If not a car battery would give you quite a bit of talk time.  The maximum draw is 600 ma,  not sure what the actual and standby draw is (somebody seems to have borrowed my unit) but if this is a potential direction I can find out.

Viking also have door phones ranging in the $150-$300 range which are line powered and pretty durable.  Though any phone that works with the line voltage would do.  Not sure what the 'standard' is in your area.



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darran_dAuthor Commented:
Thanks for the replies everyone.

I contacted a few companies about the sound powered phones but they have come back to me and said that they wont be suitable.

Im not sure where I am going to go with this to be honest.
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darran_dAuthor Commented:
Not sure how am I going to get this working but I'll keep looking
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