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So, I overhauled my phone network this weekend. most is good, one issue.

Started by RB, February 26, 2018, 11:27:24 AM

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RB

I spent a great deal of the weekend overhauling my phone network.
I now have cat5 cables in all but one room, I cant reach that far into the corner.
The switchboard has 8 rj12 sockets on the back, with 4 wire patch cables in between the board, and the wall
which has also an 8 port plate.
Each cable supports l1, l2, Batt + and -.
I did this because I have been buying tons of batteries, and holders.
So, I decided to run the batt power from my switchboard out to each phone.
began testing, and noticed a very loud hiss in the extensions.
and a low buzz in the receivers when the phone was on hook.
I used a power supply that was layin around, I guess it is not filtered much.
That will be replaced with a more suitable supply when I find one.
Any suggestions on a well filtered supply at about 5volts, and a couple amps?
Any reason why this would not work?
I figured it was a good replacement for all those batts I have been buyin???

AE_Collector

Panasonic PBX?

Most of your phones are "Local Battery"...Magneto Sets?

You are using the Panasonic's Data Pair to power each phone?

I don't use a Panasonic so,have no idea what the data pairs power is like.

Just trying to clarify how you've set it up. Any pictures?

Terry

RB

Hi Terry
No pbx, currently stand alone. Hope to add one tho.
I posted pics of my switchboard here when I built it. not sure post title.
My board in its current configuration, is completely passive.
supporting my local batt phones.
I added a 5 volt pwr supply to get rid of the batts.
the wiring is
pin 2=5v
pin 3=l1
pin 4=l2
pin 5=5v gnd
all phones are wired to accept this config.

dsk

Local battery telephones are: Local Battery telephones and some of them has the battery (transmitter) circuit isolated from the line, but most has some kind of connection, with a common battery, that makes the risk of noise and other kinds of trouble possible. The voltage of those circuits are low, 1.5- 4.5 depending on what you have connected, voltage drop may also be an issue here.

Ill try to make a sketch.

dsk

RB

yup, definitely a drop in voltage from 5.1 on hook, to 3.2 off hook.
need a bigger supply, and one with a good filter.
I know some have common connections and produce some noise, hoping to get around that as much as possible.

dsk

I just picked 2 random magneto wiring diagrams from net, a WE 317 and a South African phone.
The last one will have little or no problems, but looking at the WE and the phones connected trough the board, the DC + (yellow) will be fed to the transformer (induction coil) from both sides. This may be interesting, and probably noisy.

If we somewhere in the system switches the line terminals (here in the switchboard) The battery + will again make problems in the  WE, some current will travel trough the transmitter, receiver and back, some trough transmitter and coil as intended.

I have not been looking at how a ring-off current will go.


dsk

RB

Thank you for that info DSK!
These look like sidetone phones. I have some of both ST, and AST
I wonder if the anti sidetone models with 4 wire hook switch would act the same?
or would fair better?

dsk

As far as I understand almost every local battery telephone will get issues with a common battery feed. In addition to all this mentioned the parallel coupling of the transmitter circuit without a a filtering of signals traveling in those wires may also cause problems.  I am sorry but Local battery telephones are designed to have their own local battery, and not a common one.

You are not the first to do this, and getting unexpected results!

Some intercom systems from the early times used a choke in each telephone, and was extremely sensitive for switching wires.

dsk

AE_Collector

We used inductors at work when feeding talk battery to manual intercom circuits to keep everything separated properly. Not certain if that would solve this problem as well?

Terry

dsk

Quote from: AE_Collector on February 26, 2018, 03:54:14 PM
We used inductors at work when feeding talk battery to manual intercom circuits to keep everything separated properly. Not certain if that would solve this problem as well?

Terry

That is what i called chokes.  (my English 8)   )


dsk

AE_Collector

I've heard that term as well.

Condensers, Capacitors. Cycles per Second, Hertz. .....

Terry

RB

no surprise. :(
seems most goes that way for me.
Anyone got a schematic of a choke install?

dsk

I have a set up here, you may try it out.

All capacitors are 2.2 uF 200V 

The chokes are ideally coils with great impedance, but you may use resistors to save money.

I guess resistors of 330 ohms will do the job pretty well, You have to adjust the voltage to get a suitable current  18-35 milli-amps in off hook state. 

I guess an old power-supply from a laptop will do the job.   I f that 18-22V  are to little you may change one or both resistors to a smaller value, but not less than 220 ohms.  The  capacitor across will flatten the DC  In off hook state this should be not to far from the voltage the specified on the telephone.

You will need one setup like this for each phone, you may put it where it fits best in the circuit between the exchange and the phone.


dsk

RB

Thank you. I will give it a try soon.
need a quieter power supply too.