[BC] Xmitters at aol.com

[Dana Puopolo]

You can use ONE winding to source 300 ohms. Put a 300 ohm resistor across the
ubused winding.

-D


------ Original Message ------
Received: Tue, 10 Apr 2007 09:05:25 AM EDT
From: RichardBJohnson at comcast.net
To: "Broadcasters' Mailing List" <broadcast at radiolists.net>,
broadcast at radiolists.netCc: K7qa at aol.com
Subject: Re: [BC] Xmitters at aol.com


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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