Re: Tie phone lines


"ScadaEng" <scadaeng@xxxxxxxxxxxxx> wrote in message
news:481e5564$0$25057$607ed4bc@xxxxxxxxx

"Don Bowey" <dbowey@xxxxxxxxxxx> wrote in message
news:C4439786.B80AC%dbowey@xxxxxxxxxxxxxx
On 5/4/08 12:23 PM, in article 481e0d32$0$25025$607ed4bc@xxxxxx,
"ScadaEng"
<scadaeng@xxxxxxxxxxxxx> wrote:


"Don Bowey" <dbowey@xxxxxxxxxxx> wrote in message
news:C4434471.B803A%dbowey@xxxxxxxxxxxxxx
On 5/3/08 2:46 PM, in article 481cdd5a$0$15204$607ed4bc@xxxxxx,
"ScadaEng"
<scadaeng@xxxxxxxxxxxxx> wrote:


"Don Bowey" <dbowey@xxxxxxxxxxx> wrote in message
news:C441F543.B7F50%dbowey@xxxxxxxxxxxxxx
On 5/3/08 10:17 AM, in article 481c9e25$0$25033$607ed4bc@xxxxxx,
"ScadaEng"
<scadaeng@xxxxxxxxxxxxx> wrote:


"Don Bowey" <dbowey@xxxxxxxxxxx> wrote in message
news:C441E3C3.B7F37%dbowey@xxxxxxxxxxxxxx
On 5/3/08 8:31 AM, in article 481c8569$0$15204$607ed4bc@xxxxxx,
"ScadaEng"
<scadaeng@xxxxxxxxxxxxx> wrote:

Do the transformers have a split primary and/or secondary?

Both Pri & Sec are center tapped, but not seperated.

Do you have a diagram you can post, and provide a link to it? I'm
not
familiar with the Girator and what they do. What do you mean "they
seize
the line at the proper impedance?" Depending on how it is
connected,
it
could introduce additional losses. They may also mess up the
impedance.

The girator circuit allows me to couple the line at a desired dc
load
without affecting the impeadance,
I believe I set that around 20ma. It offers a high impeadance to the
line
to
allow the ac component to pass. Therefore the impeadance is
the series cap and transf primary (close to 600?). The transf cannot
connect
to the line directly
being it is of the "dry" type, and would saturate by any line
current.

I have never uploaded a schematic to the news group. Do I send it
here?
I
created it in "Eagle" (.sch). Are there
file size limitations?



You can put it on alt.binaries.schematics.electronic as a message
attachment, or post it on a web page somewhere and post the link
here.

I suggest you take a screen-shot of the schematic (.jpg for example)
and
post it rather than the .sch file. I can open about 200 file types
and
.sch
isn't among them.

Thanks

I found a circuit on line that is equivilant to a telco 22 repeater.
This
fits my needs exactly!
It uses a readily available hybrid transformer, TM-028 available from
mouser.
Thanks to all for your replys!



The type 22 will allow you to insert gain in both directions, but what
is
your intention for passing DC supervisory signals between the POTS and
VOIP
interfaces?

Good question! I thought I would insert an opto isolator (led-to NPN)
led in
series with
the "dummy line" resistor (which I will use a pot - for line imp
matching).
That way I can
monitor line current for the hang up "wink" pulse. That will work on the
VOIP end, but
another problem is the POTS line. Where I'm using it, they don't use
"wink"
pulse for hang up.
I think I'm going to look for 20 seconds of silence, then hang up.

Anyway, the repeater offers new chalanges. I think I will need two
independent bi polar
DC supplies to individually power each op amp. Otherwise I will ground
out
the hybrid!
Maybe I can steal power from each line, I'll have to chew on that.
It's not the easy solution I was hoping for, but it's the best I have so
far.

Steve...




It sounds like you are going to use the Lundahl transformers or an
equivalent. It looks good.

If this is a "for sale" product in the US or it will be put in service
commercially, you should look at CFR 47, Part 68 or the appropriate ANSI
Standard for the Telco interface you are meeting. You may need to
Register
the equipment.

I'm cruising the internet for info about the VOIP station interface. I'm
still in the dark, but did find some high-level insight about what's
going
on. If you're interested:

http://www.atis.org/TOPSC/WebsiteDocuments/voip/VOIP%20fact%20***.pdf

Good luck


The unit will not be used in the US, although I did stick closely to the
guidelines.. It is a one - off, I have no plans to market it.


The 3-4 db loss in my present transformer design is not a problem here in
the US, the problem was with a
country with a poor phone system. It's not like the US, you can't tell them
they have poor gain, line imbalance, etc...
If the phone works (can talk) they don't want to know about it.

I have no imeadiate plans to market the device, but I might be talked into
selling my plans
to someone who wants to venture further.

Steve...


.

Quantcast