[BC] Xmitters at aol.com

[RichardBJohnson@comcast.net]

The impedance of various telephone cables is well documented. 16-gauge spiral-four toll entrance cable is 540 ohms -j460, 22 AWG emergency cable is 464 ohms -j449, paper insulated (inter-city toll cable) is 910 ohms for 26 AWG, 22 AWG is 756 ohms, 19 AWG is 453 ohms, 16 AWG  is 320. All from Page 823, Wire Transmission, Reference Data for Radio Engineers, fourth edition. Nothing is close to 150 ohms. It is well known that the series 500 "standard black telephone" was called the "500" because its hybrid (anti sidetone network) was designed
for 500 ohms. Historically, the telephone lines have been called "500 ohm" circuits.

Also, there are no 300-ohm windings on a 111-C. The transformer consists of four identical windings that are electrostatically shielded so they can be connected in any manner. The usual (read correct) connection is for two windings to be series-connected for the output, and two windings to be series-connected for the output.

See http://www.oldradio.com/current/111c.html , It shows the two usual methods of connection. Note that both the line-side and the drop side can be connected either in series or parallel. Don't be fooled by the "typical use" note. It's for "short" i.e., unequalized circuits.

I would guess that your response was either a test to see if I was still awake, or not very well thought out!

--
Cheers,
Richard B. Johnson
Read about my book
http://www.AbominableFirebug.com


 -------------- Original message ----------------------
From: K7qa at aol.com
>  
> In a message dated 4/9/2007 6:41:47 AM Pacific Daylight Time,  
> RichardBJohnson at comcast.net writes:
> 
> The  circuit feeding the telco pair should not be connected as 150 ohms  
> unless
> there has been a problem obtaining the required frequency response.  
> 
> 
> Most standard balanced telco multiconductor trunk lines used for many years  
> had an internal surge impedance of 135 to 150 ohms at audio frequencies. The  
> 111C had individual 300 ohm windings for a good reason.  Connect the  111C 
> transformer split windings in parallel to achieve 150 ohms on the line side  and 
> in series for the 600 ohm equipment side. 
>  
> tm
> 
> 
> 
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