Re: Tie phone lines
- From: Don Bowey <dbowey@xxxxxxxxxxx>
- Date: Sat, 03 May 2008 09:54:48 -0700
On 5/3/08 9:24 AM, in article 481c91e1$0$11598$607ed4bc@xxxxxx, "ScadaEng"
<scadaeng@xxxxxxxxxxxxx> wrote:
"Martin Griffith" <mart_in_medina@xxxxxxxx> wrote in message
news:n12p14hflr96vjcig6o0v316uashkt88vg@xxxxxxxxxx
On Sat, 3 May 2008 11:31:13 -0400, in sci.electronics.design
"ScadaEng" <scadaeng@xxxxxxxxxxxxx> wrote:
I have aproject that needs to "tie" a VOIP modem phone line to a localRewire the transformers as a hybrid
pots
line. The device works in most locations as designed, but not all. In one
particular area the lines are poor, with low gain. Because of this the
DTMF
signals do not get to the device. I am using two 600:600 ohm transformers
to
connect the two lines now. The primary of T1 goes to L1 through a
non-polarized 10µf series cap. T1 secondary connects to T2 secondary. and
T2
secondary is connected to L2 through another 10µf (np) cap. This is a
simplified explanation, I have line protection as well as two girator
circuits to sieze the line at the proper impedance. The problem is the
losses in this circuit. I'm loosing around 3 dbm through both transformers
plus the losses accross each cap adds to the problem. I'm wondering if I
can
tie the lines after a bridge rectifier by tieing the bridge negatives and
coupling the positives with my 10µf cap? I know that different line
impedances will play into this, but i'm hopping that won't be an issue.
The
VOIP modem being isolated should not create any common ground problems I
would think. Any thoughts?
http://www.lundahl.se/pdfs/datash/6702.pdf
martin
Thanks Martin,
I did do a circuit with LTSpice using two hybrids and two amplifiers (to
compensate for inductive losses). Problem with that is the receive to
transmit isolation (and vice vers) changes quite a bit with frequency.
Because of the nature of the transformer hybrids they allow for a bit of
feedback (sidetone) which is unwanted for my application. I tried making a
hybrid electronically, using two op amps and the existing two transformers,
however I encountered similar results to the passive transformer hybrid
circuit. I'm basically looking for an easier solution, design time is short.
Thanks for your input.
Did you achieve a balanced condition it the two hybrids? Unless something
is incorrect they should achieve, perhaps, 18 dB of balance across the
voice-band. What did you use as a balance network? How much gain did you
insert in each path?
.
- Follow-Ups:
- Re: Tie phone lines
- From: ScadaEng
- Re: Tie phone lines
- References:
- Tie phone lines
- From: ScadaEng
- Re: Tie phone lines
- From: Martin Griffith
- Re: Tie phone lines
- From: ScadaEng
- Tie phone lines
- Prev by Date: Re: OT Dual core CPUs versus faster single core CPUs?
- Next by Date: Re: Tie phone lines
- Previous by thread: Re: Tie phone lines
- Next by thread: Re: Tie phone lines
- Index(es):
Relevant Pages
|
