[BC] Xmitters at aol.com

[RichardBJohnson@comcast.net]

The telco 111-C "repeat coils" are available on the surplus market. They are probably the finest audio-frequency transformers --ever. They have four shielded coils and the core is a toriod made of mu-metal strip. Very impressive for something designed in the 1920s. The companion shunt equalizers are also available although I don't remember the number. They consist of a tapped inductor and tapped series resistors. Basically, you shunt-out
the low frequencies the same amount as the high frequencies have been shunted-out by the line capacitance. A one-mile long physical pair, with no side-legs or stubs can be equalized to over 100 kHz, so equalizing it to 15 kHz is a no-brainer. You won't need any amplification, the line-loss after equalization will be less than 10 dB.

You connect your  station's audio feed at the studio to the outgoing 111-C "coil" primary. You make the primary by connecting any two coils in series. You connect the other two series-connected coils to the phone line. At the transmitter, you connect another "coil" the same way. On the telco side, you connect will your shunt equalizer but don't connect it yet. Since you probably don't have a helper at the studio, you go to the studio and send 15 kHz. You go back to the transmitter and measure the signal, it will probably be about 9 dB below  what you are sending from the studio. Write this down! Then you go back to the studio and send the exact same level at 100 Hz. Then you go to the transmitter and connect the equalizer. You leave the resistor in its default (mid) position, and you adjust the taps on the inductor to reduce the 100 Hz level to the level of the 15 kHz tone previously measured and written down. You should be able to get it within 1 dB.

The result will be an equalized "program channel A," in telco lingo. For a mile-long line, you will certainly
have it equalized well enough for AM, perhaps even FM. In a previous life I was able to equalize stereo pairs to 15 kHz, although I needed a Langevin  EQ-257-A  equalizer. It had a multi-turn wirewound potentiometer in series with
the inductor.
  
--
Cheers,
Richard B. Johnson
Read about my book
http://www.AbominableFirebug.com


 -------------- Original message ----------------------
From: RLO2L at aol.com
>  
> In a message dated 4/6/2007 1:29:50 A.M. Central Daylight Time,  
> Xmitters at aol.com writes:
> 
> Hello:
> 
> I have one of those rare situations where I actually have  access to telco 
> copper from my studio over to my STL center/backup  satellite RO, a mile and 
> a 
> half away. Who makes program quality repeat  coils and program equalizers 
> anymor
> e? 
> Tell Labs still  around?
> 
> 
> 
> Jeff:
>  
> Sorry, hit wrong button.
>  
> I can get you commercial coils from a number of the manufacturers. If you  
> don't mind paying the cost, Jensen Transformers make some of the best these  
> days.
>  
>  
>  
> Russel L.  O'Toole, P.C.
> R&M Consulting
> 
> 31 Ponderosa  Drive
> Romeoville, Illinois 60446
> 815-372-1990 voice
> 630-699-2965  cell
> 815-886-9232 fax
> KD5OAE General
> 
> 
> 
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